HEATER PLATE ASSEMBLY IN HUMIDIFIER SYSTEMS FOR MEDICAL USE

FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to respiratory and/or surgical humidifier systems, and respiratory or breathing assistance systems for gases to be supplied to a patient or user.

BACKGROUND

[0002] Respiratory apparatuses are used in various environments, such as hospital, medical facilities, residential care, palliative care or home environments. For a range of respiratory applications, it is beneficial to humidify gases being supplied to a patient or user. These applications include where the gases are for breathing by the patient or user and/or where the gas is being supplied during surgery to the patient or user.

[0003] In the case of breathing gases in a noninvasive mode when the inspired gas passes through the upper airway, such as when gas is delivered to the patient or user via a face or nasal mask, the humidity increases patient or user comfort, improves the patient’s or user’s tolerance to the noninvasive ventilation (NIV), and the humidified gases are less prone to drying out the tissues (for example, the nasal mucosa) of the airway of the patient or user. In the case of surgical gases or an invasive mode when the gases delivered to the patient bypass the upper airway, humidification of the gases has been found to improve patient comfort and provide physiological benefits, such as improved mucus transport, can be necessary for patient or user safety, such as for preventing airway obstruction due to inspissation of airway secretion, disruption of the airway epithelium, and/or for improving post-operative outcomes. In the case of high flow therapy, humidified gases are delivered to the patient or user at high flows through an unsealed interface. The patient or user may be spontaneously breathing or may be apneic, such as under anesthesia. A flow therapy apparatus with a humidifier can be used to deliver high flow gases and the therapy apparatus may control characteristics such as for example gases flow, including flow rate, temperature, pressure, humidity, supplementary gases concentration, and the like. In the case of positive airway pressure therapy (PAP) therapy, a PAP therapy apparatus that includes a blower and a humidifier can be used to provide pressure therapy, for example, continuous positive airway pressure therapy (CPAP), to the user.

SUMMARY

[0004] In a respiratory or surgical humidifier system incorporating a humidifier chamber for humidifying gases for supply to the patient or user, it is important that a certain minimum level of water is maintained in order for the humidifier system to have the ability to supply water vapor to the gases flow so as to humidify the gases. Accordingly, it is important for a healthcare professional administering the humidified gases to a patient or user, or the patients or users themselves in the case of home-based administration, to check the water level and add more water to the humidifier chamber when needed. This task may be overlooked, which can pose danger to the patient or user due to prolonged exposure of the airway to dry gases, cause discomfort to patients or users, and/or result in a break in operation of the humidification of the gases, or, in some cases, damage to the respiratory humidifier system. Lack of water and the chamber being dry, such as due to the chamber being out of water also compromises the therapy as the amount of humidification delivered is reduced.

[0005] Some respiratory humidifier systems can detect a water-out condition and/or output water-out alarms based on the determination of the thermal conductivity of the humidifier chamber. These systems may require inputs from flow and/or temperature sensors in various locations of the device, such as in the humidifier chamber heater plate, the humidifier chamber outlet, and/or the patient or user end of the breathing circuit. As a result, such water-out detection and/or alarm functions cannot be implemented in respiratory humidifier systems that do not incorporate all of these flow and/or temperature sensors.

[0006] The present disclosure provides examples of respiratory or surgical humidifier systems that can detect a water-out condition and/or output humidifier chamber water-out alarms with inputs from a minimal number of sensors, for example, as few as one temperature sensor at or near the heater plate. These water-out detection and/or alarms methods can thus be implemented on more types of humidifying systems, or other breathing assistance devices that may include a humidifier, for example, high flow systems and/or CPAP systems. The water-out detection and/or alarm methods disclosed herein can be based on the determination of the specific heat capacity of the humidifier chamber (including its content, such as water), by application of a supplementary power input waveform (also may be referred to as a supplementary signal or a characteristic energization signal in the disclosure herein), and the determination of the magnitude and/or phase of a heater plate temperature signal and/or the temperature reading from a temperature signal on or adjacent the heater plate, filtered at a predetermined frequency. Applying the supplementary signal can be performed by applying the supplementary signal as the signal to the heater plate (for example, during a standby mode), or injecting the supplementary signal into a heater plate control signal (for example, by summating, modulating, interleaving, cycling, or using any other scheme for sending two signals over the same transmission line, the heater plate control signal with the supplementary signal). This supplementary waveform can be superimposed onto the normal heater plate control signal, such as the normal operating heater plate power signal without biasing the normal control. The supplementary waveform can be periodic or cyclic, and/or have a zero mean. The waveform can ensure normal control is not biased. The frequency of the supplementary signal can be a predetermined frequency. The frequency can be selected to be segregated, in the frequency domain, from the normal control responses. The frequency selected can help to avoid interference with the normal control of the heater plate. In one example, the frequency of the supplementary signal can be higher than (for example, being at least 1.5 times of, or other values disclosed herein) a conventional (such as normal operating for purposes of heating a humidification chamber disposed onto the heater plate) heater plate control signal, which can output a duty cycle and/or the like for heating the heater plate.

[0007] Throughout this disclosure, the specific heat capacity of the humidifier chamber, unless explicitly stated otherwise, refers to the specific heat capacity of the humidifier chamber including its content, such as water.

[0008] In addition to requiring fewer sensors, the water-out detection and/or alarm methods disclosed herein can also have any of the following advantages, and/or other advantages. For example, the water-out detection and/or alarm systems disclosed herein are based on the principle of specific heat capacity and are inherently linked to water volume, which allows the system to be independent of the flow rate of the gases. Being independent of the flow rate can allow the water-out detection and/or alarm methods to be more suitable for low flow noninvasive therapy (for example, non-invasive pediatric therapy flow at less than about 10 L/min) or extremely low flow invasive therapy (for example, invasive neonatal therapy at less than about 5 L/min) than detection methods that are dependent on the flow rate. Being independent of the flow rate can also allow the water-out detection and/or alarm methods to be immune to flow sensor errors or to avoid having to make assumption about the flow rate state of the system. Using specific heat capacity as the parameter to determine water out is also advantageous because the water out/alarm methods described herein can function across various different platforms and/or for various different types of chambers. The described water out methodology is more flexible and more versatile. Further, the currently disclosed water out detection method can determine a water out condition (no water or substantially no water condition) when there is no gases flow- through the humidifier, such as for example during a standby scenario.

[0009] The water-out detection and/or alarm methods disclosed herein can also be independent of or invariant to humidity delivery. As a result, the methods disclosed herein can be more suitable for gases delivery in scenarios leading to lower humidity generation, for example from non-invasive therapy using room air entraining and/or turbine driven flow sources. In these cases, there can be higher incoming humidity (for example, greater than about 10 mg/L), higher incoming gas temperature (for example, greater than about 30 degrees Celsius) and/or higher ambient temperature conditions (for example, greater than about 25 degrees Celsius), which can lead to lower humidity addition requirements and adversely affect previous water out detection methods. Similar water out methods disclosed herein can be also be used in high flow mode or any other operating mode.

[0010] The present disclosure also provides improved heater plate structures that improves thermal coupling of the heater plate and may reduce the heat transfer inefficiencies due to the modelled R and C components of the heater plate. The improved heater plate assembly, specifically, the inclusion of a resilient electrical insulator allows for a smaller supplementary signal for the water-out detection, which returns a return signal with an increased amplitude such that the return signal is of an improved signal to noise ratio. The resilient electrical insulator can be flexible and/or compliant as described below. A compliant material can refer to the ability of a material to be soft, compressible, and/or able to conform to a shape of a surface. For example, compliant material may be able to displace air gaps between the surfaces of other materials that may sandwich the compliant material. Throughout this disclosure, an insulation material may refer to an electrical insulation material, which may also be thermally conductive.

[0011] A controller of the respiratory humidifier systems disclosed herein can apply a supplementary signal to the heater plate control signal, rather than exclusively varying the heater plate power input and waiting for specific responses of the heater plate and/or the humidifier chamber during a water-out event. In some example configurations, the controller may continuously apply the supplementary signal. The controller may continuously and/or intermittently apply the supplementary signal to the heater plate. The controller may measure the response to the supplementary signal. The controller may continuously and/or intermittently sample the response to the supplementary signal. The detection and/or alarm process therefore does not have to depend on complex state transitions (such as transitioning between low flow and high flow states) and/or trigger conditions. The processes described herein can be run continuously without affecting a normal operation in energizing the heater plate, and can thus provide adjustable detection time and thresholds such that it could provide a warning before the humidifier chamber actually runs out of water. The water out detection methods described herein is also advantageous because the method does not require therapy interruption, including interruption of the control of the heater plate to cause the heater to heat up or cool down. The supplementary signal can be at a frequency that is substantially different to the normal operating frequency (that is, the heater plate control operating frequency) and is of a zero mean so there is no net energy introduced into the system. The water out detection methods described herein can have a minimal to no adverse effect on humidity generation or delivery of the humidified gases to the patient or user.

[0012] As will be described in greater detail below, the detection and/or alarm methods can also be noise tolerant as the signal of interest is naturally filtered to the frequency of the supplementary signal, also referred to herein as the applied frequency.

[0013] The detection and/or alarm methods described herein can be incorporated into a variety of respiratory and/or surgical humidifier systems, such as CPAP devices, high flow therapy devices, surgical humidifiers, respiratory humidifiers, infant CPAP, infant high flow, NIV therapy, and the like.

[0014] In some configurations, a multi-layer heater plate assembly for a respiratory humidifier can comprise a top heating plate; a heating element configured to generate heat; and a double insulation arrangement configured to provide electrical insulation between the heating plate and the heating element, the double insulation arrangement comprising two insulation elements, a first insulation element of the two insulation elements having a first flexibility and a second insulation element of the two insulation elements having a second flexibility different from the first flexibility.

[0015] In some configurations, the multi-layer heater plate assembly can be removably coupled together by one or more fasteners.

[0016] In some configurations, the multi-layer heater plate assembly can be formed by bolting a bottom plate to the top heating plate with the heating element and the double insulation arrangement therebetween.

[0017] In some configurations, the top heating plate can comprise a sensor-mounting block configured to receive at least one temperature sensor.

[0018] In some configurations, the sensor-mounting block can be configured to receive two temperature sensors.

[0019] In some configurations, the at least one temperature sensor can comprise a thermistor.

[0020] In some configurations, the safety feature can comprise a thermal cutoff unit.

[0021] In some configurations, the bottom plate can comprise a platform to support the safety feature.

[0022] In some configurations, the safety feature can be secured to the platform by screws.

[0023] In some configurations, the platform can protrude from a remainder of the bottom plate.

[0024] In some configurations, the botom plate can comprise a slot where the safety feature is coupled to the bottom plate to improve isolation of the safety feature from the heating element.

[0025] In some configurations, the botom plate can further comprise a cut-out step along a length of the slot.

[0026] In some configurations, the slot can be L-shaped.

[0027] In some configurations, the slot can terminate at or near a periphery of the heating element.

[0028] In some configurations, the slot can extend radially outwardly past a periphery of the double insulation arrangement.

[0029] In some configurations, the bottom plate can comprise a cut-out step near the sensor-mounting block when the heater plate assembly is assembled.

[0030] In some configurations, one insulation element of the double insulation arrangement can be more flexible or compliant than the other insulation element. In some configurations, the first insulation element can be more flexible than the second insulation element.

[0031] In some configurations, one insulation element of the double electrical insulation arrangement can comprise a compliant insulation material configured to displace air gaps between the top heating plate and the heating element.

[0032] In some configurations, one insulation element of the double electrical insulation arrangement can comprise a flexible insulation material.

[0033] In some configurations, the first insulation element can have a first softness and the second insulation element can have a second softness such that one of the insulation elements is softer than the other element.

[0034] In some configurations, the first insulation element can comprise an elastic material.

[0035] In some configurations, one of the insulation elements can have a Shore 00 hardness scale of 50 to 100.

[0036] In some configurations, one of the insulation elements can have a Shore 00 hardness scale of 80.

[0037] In some configurations, the two insulation elements can comprise at least one inflexible insulation layer.

[0038] In some configurations, the at least one inflexible insulation layer can comprise mica.

[0039] In some configurations, the assembly can comprise a layer of compliant insulation material.

[0040] In some configurations, the multi-layer heater plate assembly can further comprise a further layer of compliant insulation material configured to displace air gaps between components of the heater plate assembly.

[0041] In some configurations, the two insulation elements can comprise two inflexible insulation layers.

[0042] In some configurations, the assembly can comprise two layers of compliant insulation materials.

[0043] In some configurations, the two insulation elements can comprise two layers of the compliant insulation materials configured to displace air gaps between components of the heater plate assembly.

[0044] In some configurations, the compliant insulation material can comprise a thermally conductive but electrically insulating elastomer.

[0045] In some configurations, the compliant insulation material can comprise silicone or silicone compound.

[0046] In some configurations, the compliant insulation material can comprise a fiberglass substrate and a thermally conductive material embedded in the substrate or positioned on the substrate.

[0047] In some configurations, the compliant insulation material can have a breakdown voltage of at least 4000 V AC.

[0048] In some configurations, the compliant insulation material can have a breakdown voltage of at least 6000 V AC.

[0049] In some configurations, the compliant insulation material can have a thermal conductivity of at least 1.8 W/(m.K).

[0050] In some configurations, a multi-layer heater plate assembly for a respiratory humidifier can comprise a top heating plate; a bottom plate; a heating element configured to generate heat, the heating element hound by the top heating plate and the bottom plate; a first elastic insulation material between the top heating plate and the heating element; and a second elastic insulation material between the bottom plate and the heating element; wherein the first and second elastic insulation materials can occupy air gaps between the top heating plate and the heating element and between the botom and the heating element, respectively. The first or second insulation material is an electrical insulation material. In some configurations, the first and second elastic electrical insulation materials can displace air gaps between the top heating plate and the heating element and between the bottom plate and the heating element, respectively.

[0051] In some configurations, the multi-layer heater plate assembly can be removably coupled together by one or more fasteners.

[0052] In some configurations, the multi-layer heater plate assembly can be formed by bolting the bottom plate to the top heating plate with the heating element and the first and second elastic insulation materials therebetween.

[0053] In some configurations, the first elastic insulation material and/or the second elastic insulation material can have a Shore 00 hardness scale of 50 to 100.

[0054] In some configurations, the first elastic insulation material and/or the second elastic insulation material can have a Shore 00 hardness scale of 80.

[0055] In some configurations, the assembly can comprise a double electrical insulation arrangement including two insulation elements.

[0056] In some configurations, the two insulation elements can comprise two inflexible electrical insulation layers.

[0057] In some configurations, the multi-layer heater plate assembly can further comprise an inflexible electrical insulation layer.

[0058] In some configurations, the inflexible electrical insulation layers can comprise mica.

[0059] In some configurations, the two insulation elements can comprise two layers that are separate from each other.

[0060] In some configurations, the first and second elastic electrical insulation materials can comprise two layers that are separate from each other.

[0061] In some configurations, the first and/or second elastic electrical insulation material can comprise a thermally conductive hut electrically insulating elastomer.

[0062] In some configurations, the first and/or second elastic electrical insulation material can comprise silicone or silicone compound.

[0063] In some configurations, the first and/or second elastic electrical insulation material can comprise a fiberglass substrate and a thermally conductive material embedded in the substrate or positioned on the substrate.

[0064] In some configurations, the first and/or second elastic electrical insulation material can have a breakdown voltage of at least 4 000 V AC.

[0065] In some configurations, the first and/or second elastic electrical insulation material can have a breakdown voltage of at least 6000 V AC.

[0066] In some configurations, the first and/or second elastic electrical insulation material can have a thermal conductivity of at least 1.8 W/(m.K).

[0067] In some configurations, the first and/or second elastic electrical insulation materials can comprise a compliant material configured to displace air gaps between components of the multi-layer heater plate assembly.

[0068] In some configurations, the top heating plate can comprise a metal.

[0069] In some configurations, the top heating plate can comprise a cavity on a lower surface and an upper surface exposed to contact a base of a humidifier chamber of the respiratory humidifier.

[0070] In some configurations, the top heating plate can comprise a sensormounting block configured to receive at least one temperature sensor.

[0071] In some configurations, the sensor-mounting block can be configured to receive two temperature sensors.

[0072] In some configurations, the at least one temperature sensor can comprise a thermistor.

[0073] In some configurations, the safety feature can comprise a thermal cutoff unit.

[0074] In some configurations, the bottom plate can comprise a platform to support the safety feature.

[0075] In some configurations, the safety feature can be secured to the platform by screws.

[0076] In some configurations, the platform can protrude from a remainder of the bottom plate.

[0077] In some configurations, the bottom plate can comprise a slot where the safety feature is coupled to the bottom plate to improve isolation of the safety feature from the heating element.

[0078] In some configurations, the bottom plate can further comprise a cut-out step along a length of the slot.

[0079] In some configurations, the slot can be L-shaped.

[0080] In some configurations, the slot can terminate at or near a periphery of the heating element.

[0081] In some configurations, the slot can extend radially outwardly past a periphery of the double insulation arrangement.

[0082] In some configurations, the bottom plate can comprise a cut-out step near the sensor-mounting block when the heater plate assembly is assembled.

[0083] In some configurations, a multi-layer heater plate assembly for a respiratory humidifier can comprise a top heating plate; a heating element configured to generate heat, the heating element located below the top heating plate; and a thermal interface layer between the top heating plate and the heating element, the thermal interface layer comprising a compliant thermal interface material configured to displace air gaps between the top heating plate and the heating element.

[0084] In some configurations, the thermal interface layer can be configured to displace air gaps between the top heating plate and the heating element so as to improve thermal conductivity between the top heating plate and the heating element.

[0085] In some configurations, the multi-layer heater plate assembly can be removably coupled together by one or more fasteners.

[0086] In some configurations, the multi-layer heater plate assembly can comprise a bottom plate, wherein the heating element is bound by the top heating plate and the bottom plate.

[0087] In some configurations, the thermal interface layer can comprise a thickness sufficient for providing electrical insulation.

[0088] In some configurations, the multi-layer heater plate assembly can be formed by bolting a bottom plate to the top heating plate with the heating element and the thermal interface layer therebetween.

[0089] In some configurations, the top heating plate can comprise a sensor-mounting block configured to receive at least one temperature sensor.

[0090] In some configurations, the sensor-mounting block can be configured to receive two temperature sensors.

[0091] In some configurations, the at least one temperature sensor can comprise a thermistor.

[0092] In some configurations, the multi-layer heater plate assembly can further comprise a safety feature coupled to the bottom plate.

[0093] In some configurations, the safety feature can comprise a thermal cutoff unit.

[0094] In some configurations, the bottom plate can comprise a platform to support the safety feature.

[0095] In some configurations, the safety feature can be secured to the platform by screws.

[0096] In some configurations, the platform can protrude from a remainder of the bottom plate.

[0097] In some configurations, the bottom plate can comprise a slot where the safety feature is coupled to the bottom plate to improve isolation of the safety feature from the heating element.

[0098] In some configurations, the bottom plate further can comprise a cut-out step along a length of the slot.

[0099] In some configurations, the slot can be L-shaped.

[0100] In some configurations, the slot can terminate at or near a periphery of the heating element.

[0101] In some configurations, the slot can extend radially outwardly past a periphery of the thermal interface layer.

[0102] In some configurations, the bottom plate can comprise a cut-out step near the sensor-mounting block when the heater plate assembly is assembled.

[0103] In some configurations, the thermal interface layer can have a Shore 00 hardness scale of 50 to 100.

[0104] In some configurations, the thermal interface layer can have a Shore 00 hardness scale of 70 to 90.

[0105] In some configurations, the thermal interface layer can have a Shore 00 hardness scale of 80.

[0106] In some configurations, the thermal interface material can be electrically insulating.

[0107] In some configurations, the multi-layer heater plate assembly can further comprise a second layer of compliant insulation material configured to displace air gaps between components of the multi-layer heater plate assembly.

[0108] In some configurations, the second thermal interface layer can be located between the heating element and the bottom plate.

[0109] In some configurations, the second thermal interface layer can be located between the top heating plate and the bottom plate.

[0110] In some configurations, the multi-layer heater plate assembly can comprise at least one inflexible electrical insulation layer.

[0111] In some configurations, the at least one inflexible electrical insulation layer can be located between the compliant thermal interface layer and the heating element.

[0112] In some configurations, the multi-layer heater plate assembly can comprise at least one inflexible electrical insulation layer between the heating element and the bottom plate.

[0113] In some configurations, the multi-layer heater plate assembly can comprise two inflexible electrical insulation layers between the heating element and the bottom plate. [0114] In some configurations, the at least one inflexible electrical insulation layer can comprise mica.

[0115] In some configurations, the second thermal interface layer can be electrically conducting.

[0116] In some configurations, the compliant thermal interface material can comprise a thermally conductive but electrically insulating elastomer.

[0117] In some configurations, the compliant thermal interface material can comprise silicone or silicone compound.

[0118] In some configurations, the compliant thermal interface material can comprise a fiberglass substrate and a thermally conductive material embedded in the substrate or positioned on the substrate.

[0119] In some configurations, the compliant thermal interface material can have a breakdown voltage of at least 4000 V AC.

[0120] In some configurations, the compliant thermal interface material can have a breakdown voltage of at least 6000 V AC.

[0121] In some configurations, the compliant thermal interface material can have a thermal conductivity of at least 1.8 W/(m.K).

[0122] In some configurations, the compliant thermal interface material can be elastic.

[0123] In some configurations, a multi-layer heater plate assembly for a respiratory humidifier can comprise a top heating plate; a bottom plate; a heating element configured to generate heat, the heating element bound by the top heating plate and the bottom plate; a compliant thermal interface layer between the bottom plate and the top heating plate and configured to displace air gaps between the bottom plate and the top heating plate.

[0124] In some configurations, the multi-layer heater plate assembly can be removably coupled together by one or more fasteners.

[0125] In some configurations, the multi-layer heater plate assembly can be formed by bolting a bottom plate to the top heating plate with the heating element and the double electrical insulation arrangement therebetween.

[0126] In some configurations, the top heating plate can comprise a sensor-mounting block configured to receive at least one temperature sensor.

[0127] In some configurations, the sensor-mounting block can be configured to receive two temperature sensors.

[0128] In some configurations, the at least one temperature sensor can comprise a thermistor.

[0129] In some configurations, the multi-layer heater plate assembly can further comprise a safety feature coupled to the bottom plate.

[0130] In some configurations, the safety feature can comprise a thermal cutoff unit.

[0131] In some configurations, the bottom plate can comprise a platform to support the safety feature.

[0132] In some configurations, the safety feature can be secured to the platform by screws.

[0133] In some configurations, the platform can protrude from a remainder of the bottom plate.

[0134] In some configurations, the bottom plate can comprise a slot where the safety feature is coupled to the bottom plate to improve isolation of the safety feature from the heating element.

[0135] In some configurations, the bottom plate further can comprise a cut-out step along a length of the slot.

[0136] In some configurations, the slot can be L-shaped.

[0137] In some configurations, the slot can terminate at or near a periphery of the heating element.

[0138] In some configurations, the slot can extend radially outwardly past a periphery of the compliant thermal interface layer.

[0139] In some configurations, the bottom plate can comprise a cut-out step near the sensor-mounting block when the heater plate assembly is assembled.

[0140] In some configurations, the compliant thermal interface layer can be configured to displace air gaps between an edge of the bottom plate and the top heating plate. [0141] In some configurations, the compliant thermal interface layer can have a Shore 00 hardness scale of 50 to 100.

[0142] In some configurations, the compliant thermal interface layer can have a Shore 00 hardness scale of 70 to 90.

[0143] In some configurations, the compliant thermal interface layer can have a Shore 00 hardness scale of 80.

[0144] In some configurations, the compliant thermal interface layer can be electrically insulating.

[0145] In some configurations, the multi-layer heater plate assembly can comprise a second thermal interface layer configured to displace air gaps between the top heating plate and the heating element.

[0146] In some configurations, the second thermal interface layer can be electrically conducting.

[0147] In some configurations, the multi-layer heater plate assembly can comprise at least one inflexible electrical insulation layer.

[0148] In some configurations, the at least one inflexible electrical insulation layer can comprise mica.

[0149] In some configurations, the at least one inflexible electrical insulation layer can be located between the compliant thermal interface layer and the heating element.

[0150] In some configurations, the at least one inflexible electrical insulation layer can be located between the heating element and the bottom plate.

[0151] In some configurations, the compliant thermal interface layer can comprise a thermally conductive but electrically insulating elastomer.

[0152] In some configurations, the compliant thermal interface layer can comprise silicone or silicone compound.

[0153] In some configurations, the compliant thermal interface layer can comprise a fiberglass substrate and a thermally conductive material embedded in the substrate or positioned on the substrate.

[0154] In some configurations, the compliant thermal interface layer can have a breakdown voltage of at least 4000 V AC.

[0155] In some configurations, the compliant thermal interface layer can have a breakdown voltage of at least 6000 V AC.

[0156] In some configurations, the compliant thermal interface layer can have a thermal conductivity of at least 1.8 W/(m.K).

[0157] In some configurations, the compliant thermal interface layer can be elastic.

[0158] In some configurations, a multi-layer heater plate assembly for a respiratory humidifier can comprise a top heating plate; a heating element configured to generate heat, the heating element located below the top heating plate; and a thermal interface layer between the top heating plate and the heating element, the thermal interface layer comprising an elastic thermal interface material.

[0159] In some configurations, the multi-layer heater plate assembly can be removably coupled together by one or more fasteners.

[0160] In some configurations, the multi-layer heater plate assembly can be formed by bolting a bottom plate to the top heating plate with the heating element and the first and second elastic electrical insulation materials therebetween.

[0161] In some configurations, the elastic electrical insulation material can have a Shore 00 hardness scale of 50 to 100.

[0162] In some configurations, the elastic electrical insulation material can have a Shore 00 hardness scale of 70 to 90.

[0163] In some configurations, the elastic electrical insulation material can have a Shore 00 hardness scale of 80.

[0164] In some configurations, the multi-layer heater plate assembly can comprise an inflexible electrical insulation layer.

[0165] In some configurations, the inflexible electrical insulation layers can comprise mica.

[0166] In some configurations, the elastic electrical insulation material can comprise a thermally conductive but electrically insulating elastomer.

[0167] In some configurations, the elastic electrical insulation material can comprise silicones or silicone compound.

[0168] In some configurations, the elastic electrical insulation material can comprise a fiberglass substrate and a thermally conductive material embedded in the substrate or positioned on the substrate.

[0169] In some configurations, the elastic electrical insulation material can have a breakdown voltage of at least 4 000 V AC.

[0170] In some configurations, the elastic electrical insulation material can have a breakdown voltage of at least 6000 V AC.

[0171] In some configurations, the elastic electrical insulation material can have a thermal conductivity of at least 1.8 W/(m.K).

[0172] In some configurations, the top heating plate can comprise a metal.

[0173] In some configurations, the top heating plate can comprise a cavity on a lower surface and an upper surface exposed to contact a base of a humidifier chamber of the respiratory humidifier.

[0174] In some configurations, the top heating plate can comprise a sensor-mounting block configured to receive at least one temperature sensor.

[0175] In some configurations, the sensor-mounting block can be configured to receive two temperature sensors.

[0176] In some configurations, the at least one temperature sensor can comprise a thermistor.

[0177] In some configurations, the multi-layer heater plate assembly can further comprise a safety feature coupled to the bottom plate.

[0178] In some configurations, the safety feature can comprise a thermal cutoff unit.

[0179] In some configurations, the bottom plate can comprise a platform to support the safety feature.

[0180] In some configurations, the safety feature can be secured to the platform by screws.

[0181] In some configurations, the platform can protrude from a remainder of the bottom plate.

[0182] In some configurations, the botom plate can comprise a slot where the safety feature is coupled to the bottom plate to improve isolation of the safety feature from the heating element.

[0183] In some configurations, the botom plate can further comprise a cut-out step along a length of the slot.

[0184] In some configurations, the slot can be L-shaped.

[0185] In some configurations, the slot can terminate at or near a periphery of the heating element.

[0186] In some configurations, the slot can extend radially outwardly past a periphery of the first and/or second elastic insulation materials.

[0187] In some configurations, the bottom plate can comprise a cut-out step near the sensor-mounting block when the heater plate assembly is assembled.

[0188] In some configurations, a humidifier system for use in medical procedures can comprise a base unit; and a humidifier chamber receivable onto the base unit, wherein the base unit can comprise any of the multi-layer heater plate assembly examples described above.

[0189] In some configurations, the humidifier chamber can comprise a conductive base, the conductive base urged into contact with the heater plate assembly upon the humidifier chamber being positioned on the base unit.

[0190] In some configurations, the heater plate assembly can heat the humidifier chamber to heat contents of the chamber in order to humidify gases passing through the chamber.

[0191] In some configurations, the system can comprise a tube configured to transport gases from the humidifier chamber to a patient interface.

[0192] In some configurations, a humidifier system for use in medical procedures can comprise a housing configured to receive a humidifier chamber: and a heater plate assembly located at least partially within the housing, the heater plate assembly including: a top heating plate, wherein the top heating plate is configured to contact a base of the humidifier chamber when the humidifier chamber is received by the housing; a thermistor located at or near the top heating plate: a heating element configured to generate heat; and an electrical insulation arrangement between the top heating plate and the heating element, wherein the electrical insulation arrangement can thermally couple the heating element and the top heating plate such that heat generated by a power signal to the heating element is transmitted to the top heating plate.

[0193] In some configurations, the electrical insulation arrangement can improve thermal coupling between the heating element and the top heating plate.

[0194] In some configurations, a humidifier system for use in medical procedures can comprise a housing configured to receive a humidifier chamber; and a heater plate assembly located at least partially within the housing, the heater plate assembly including: a top heating plate, wherein the top heating plate is configured to contact a base of the humidifier chamber when the humidifier chamber is received by the housing; a thermistor located at or near the top heating plate; a heating element configured to generate heat; and an electrical insulation arrangement between the top heating plate and the heating element, wherein the electrical insulation arrangement can thermally couple the heating element and the top heating plate such that heat generated by a power signal to the heating element is transmitted to the top heating plate. In some configurations, the electrical insulation arrangement can improve thermal coupling between the heating element and the top heating plate.

[0195] In some configurations, the electrical insulation arrangement can comprise a flexible or compliant insulation sheet.

[0196] In some configurations, the electrical insulation arrangement can comprise an elastic insulation sheet.

[0197] In some configurations, the electrical insulation arrangement can comprise a compliant insulation sheet configured to displace air gaps between the top heating plate and the heating element.

[0198] In some configurations, the flexible or compliant insulation sheet can improve heat conduction from the heating element to the top heating plate.

[0199] In some configurations, the electrical insulation sheet can improve heat conduction from the heating element to the top heating plate.

[0200] In some configurations, the flexible or compliant insulation sheet can reduce a capacitance of the heater plate assembly such that a thermal conductivity is improved between components of the heater plate assembly.

[0201] In some configurations, the electrical insulation sheet can reduce a capacitance of the heater plate assembly such that a thermal conductivity is improved between components of the heater plate assembly.

[0202] In some configurations, the system can comprise a double electrical insulation arrangement including two insulation elements.

[0203] In some configurations, the two insulation elements can comprise two inflexible insulation layers.

[0204] In some configurations, the two inflexible insulation layers can comprise mica.

[0205] In some configurations, the two insulation elements can comprise two layers that are separate from each other.

[0206] In some configurations, the double electrical insulation arrangement can be located between the electrical insulation arrangement and the heating element,

[0207] In some configurations, the electrical insulation arrangement can comprise a thermally conductive but electrically insulating elastomer.

[0208] In some configurations, the electrical insulation arrangement can comprise silicone or silicone compound.

[0209] In some configurations, the electrical insulation arrangement can comprise a fiberglass substrate and a thermally conductive material embedded in the substrate or positioned on the substrate.

[0210] In some configurations, the electrical insulation arrangement comprises a material having a breakdown voltage of at least 4000 V AC.

[0211] In some configurations, the electrical insulation arrangement can comprise a material having a breakdown voltage of at least 6000 V AC.

[0212] In some configurations, the electrical insulation arrangement can comprise a material having a thermal conductivity of at least 1.8 W/(m.K).

[0213] In some configurations, the insulation arrangement can improve thermal coupling between the heating element and the top heating plate such that a waveform applied to the power signal for detecting low water or water out conditions in the humidifier chamber can be of a reduced power. In some configurations, the insulation arrangement can improve thermal coupling between the heating element and the top heating plate such that a waveform injected into the power signal for detecting low water or water out conditions m the humidifier chamber can be of a reduced power.

[0214] In some configurations, the electrical insulation arrangement can improve thermal coupling between the heating element and the top heating plate such that a temperature reading of the thermistor better corresponds to a temperature of water in the humidifier chamber.

[0215] In some configurations, the heater plate assembly can comprise a bottom plate, the heating element and the electrical insulation arrangement can be bound between the bottom plate and the top heating plate.

[0216] In some configurations, the bottom plate can contact the electrical insulation arrangement.

[0217] In some configurations, the heater plate assembly can comprise a flexible or compliant insulation sheet between the top heating plate and the bottom plate.

[0218] In some configurations, the heater plate assembly can comprise a flexible electrical insulation sheet between the top heating plate and the bottom plate.

[0219] In some configurations, the heater plate assembly can comprise a compliant electrical insulation sheet between the top heating plate and the bottom plate configured to displace air gaps between the top heating plate and the bottom plate.

[0220] In some configurations, the top heating plate can comprise a sensor-mounting block configured to receive at least one temperature sensor.

[0221] In some configurations, the sensor-mounting block can be configured to receive two temperature sensors.

[0222] In some configurations, the temperature sensor can comprise a thermistor.

[0223] In some configurations, the safety feature can comprise a thermal cutoff unit.

[0224] In some configurations, the bottom plate can comprise a platform to support the safety feature.

[0225] In some configurations, the safety feature can be secured to the platform by screws.

[0226] In some configurations, the platform can protrude from a remainder of the bottom plate.

[0227] In some configurations, the bottom plate can comprise a slot where the safety feature is coupled to the bottom plate to improve isolation of the safety feature from the heating element.

[0228] In some configurations, the bottom plate can further comprise a cut-out step along a length of the slot.

[0229] In some configurations, the slot can be L-shaped.

[0230] In some configurations, the slot can terminate at or near a periphery of the heating element.

[0231] In some configurations, the slot can extend radially outwardly past a periphery of the double insulation arrangement.

[0232] In some configurations, the bottom plate can comprise a cut-out step near the sensor-mounting block when the heater plate assembly is assembled.

[0233] In some configurations, a respiratory or surgical humidifier system wath low water and/or water-out detection can include a base unit comprising a heater plate including one or more heating elements and a hardware controller in electronic communication with the one or more heating elements of the heater plate and configured to energize the one or more heating elements of the heater plate. In some configurations, the system can further include a humidifier chamber defining a volume and including a conductive base receivable onto the base unit such that the conductive base contacts the heater plate, the humidifier chamber configured to hold a level of water. In some configurations, the hardware controller can be configured to determine a value from which the specific heat capacity of the humidifier chamber can be inferred and determine a low water or water-out condition based at least in part on the determined value from which the specific heat capacity can be inferred.

[0234] In some configurations, the hardware controller can be configured to determine a specific heat capacity valise of the humidifier chamber and determine a low water or water-out condition based at least in part on the determined specific heat capacity value.

[0235] In some configurations, the hardware controller can determine that a low water or water-out condition is present in response to the determined specific heat capacity value being below a threshold. In some configurations, the hardware controller can determine that a low water or water-out condition is present in response to the determined value from which the specific heat capacity can be inferred being below a threshold.

[0236] In some configurations, the hardware controller can continuously determine the specific heat capacity value. In some configurations, the hardware controller can continuously determine the valise from which the specific heat capacity can be inferred.

[0237] In some configurations, the hardware controller can intermittently determine the specific heat capacity value. In some configurations, the hardware controller can intermittently determine the value from which the specific heat capacity can be inferred.

[0238] In some configurations, the specific heat capacity value can be determined as a numerical score. In some configurations, the value from which the specific heat capacity can be inferred can be a numerical score.

[0239] In some configurations, the system can comprise a temperature sensor coupled to or adjacent the heater plate, wherein the temperature sensor determines a temperature of the heater plate.

[0240] In some configurations, the temperature sensor can comprise a thermistor,

[0241] In some configurations, the temperature sensor can comprise two thermistors, each thermistor acting as a voltage divider.

[0242] In some configurations, the hardware controller can determine a temperature value from voltage readings of the two thermistors.

[0243] In some configurations, the hardware controller can determine the specific heat capacity value based on the temperature readings from the temperature sensor. In some configurations, the hardware controller can determine a value from which the specific heat capacity can be inferred based on the temperature readings from the temperature sensor. [0244] In some configurations, the hardware controller is configured to apply a characteristic energization signal to the one or more heating elements of the heater plate, process a temperature signal from the temperature sensor corresponding to the characteristic energization signal, determine the specific heat capacity valise based on the temperature signal, and output a low water or water-out warning in response to the determined specific heat capacity valise being below a threshold. In some configurations, the hardware controller is configured to determine the value from which the specific heat capacity can be inferred based on the temperature signal, and output a low water or water-oist warning in response to the determined value from which the specific heat capacity can be inferred being below a threshold.

[0245] In some configurations, the hardware controller can be configured to continuously apply the characteristic energization signal. In some configurations, the hardware controller can be configured to intermittently apply the characteristic energization signal.

[0246] In some configurations, the hardware controller can be configured to apply the characteristic energization signal to the heater plate control signal. In some configurations, the characteristic energization signal can be applied by being injected into the heater plate control signal. In some configurations, the hardware controller can be configured to apply the characteristic energization signal to a power control line that provides heater plate control signal.

[0247] In some configurations, the characteristic energization signal can be at a higher frequency than heater plate control signal.

[0248] In some configurations, the hardware controller can pass temperature measurements from the temperature sensor through a filter, such as a bandpass filter or a high pass filter having a filter frequency corresponding to a frequency of the characteristic energization signal such that temperature measurements corresponding to the frequency of the characteristic energization signal can be passed. In some configurations, the filter can be a direct conversion receiver, such as a homodyne, or an infinite impulse response filter.

[0249] In some configurations, the temperature measurements corresponding to the frequency of the characteristic energization signal can be used to determine the specific heat capacity value. In some configurations, the temperature measurements corresponding to the frequency of the characteristic energization signal can be used to determine the value from which the specific heat capacity can be inferred.

[0250] In some configurations, the heater plate can comprise any of the heater plate assembly examples described above.

[0251] In some configurations, the system can include one or more features of the humidifier system described above for use in medical procedures.

[0252] In some configurations, a respiratory or surgical humidifier system with low water and/or water-out detection can include a base unit comprising a heater plate including one or more heating elements, a hardware controller in electronic communication with the one or more heating elements of the heater plate and configured to energize the one or more heating elements of the heater plate, and a temperature sensor coupled to or adjacent the heater plate and configured to generate a signal indicative of a temperature of the heater plate. In some configurations, the system can comprise a humidifier chamber defining a volume and including a conductive base receivable onto the base unit such that the conductive base contacts the heater plate, the humidifier chamber configured to hold a level of water. In some configurations, the hardware controller can be configured to apply a characteristic energization signal to the one or more heating elements of the heater plate, receive a signal indicative of a response to the characteristic energization signal, and determine a low water or water-out condition based on a magnitude and/or phase of the received signal indicative of the response to the energization signal.

[0253] In some configurations, the hardware controller can be configured to apply a characteristic energization signal to the one or more heating elements of the heater plate, receive a signal indicative of a response to the characteristic energization signal, and determine a low water or water-out condition based on a magnitude and/or phase of the received signal indicative of the response to the energization signal.

[0254] In some configurations, the determined magnitude being above a threshold can be indicative of a low water or water-out condition.

[0255] In some configurations, the determined magnitude and/or phase satisfying a threshold can be indicative of a low water or water-out condition.

[0256] In some configurations, the determined magnitude and/or phase being outside or within a predefined region in a two-dimensional representation of magnitude and/or phase can be indicative of a low water or water-out condition.

[0257] In some configurations, the magnitude can be inversely proportional to a specific heat capacity of the humidifier chamber.

[0258] In some configurations, the hardware controller can be configured to apply the characteristic energization signal at a characteristic frequency.

[0259] In some configurations, the characteristic frequency can be higher than a normal operating frequency at which the hardware controller energizes the one or more heating elements of the heater plate. In some configurations, the characteristic frequency can be higher than a heater plate control operating frequency at which the hardware controller energizes the one or more heating elements of the heater plate.

[0260] In some configurations, the characteristic energization signal can be at a frequency that is at least 1.5 times the normal operating frequency. In some configurations, the characteristic energization signal can be at a frequency that is at least 1.5 times the heater plate control operating frequency.

[0261] In some configurations, the hardware controller can comprise a signal generator configured to generate and apply the characteristic energization signal.

[0262] In some configurations, the hardware controller can be configured to apply the characteristic energization signal into the heater plate control signal. In some configurations, the characteristic energization signal can be applied by being injected into the heater plate control signal. In some configurations, the hardw¾re controller can be configured to apply the characteristic energization signal to a power control line that provides heater plate control signal.

[0263] In some configurations, the hardware controller can comprise a filter that filters a signal indicative of the temperature of the heater plate to obtain the signal indicative of the response to the energizati on signal.

[0264] In some configurations, the filter can be a bandpass filter or a high pass filter. In some configurations, the filter can be a direct conversion receiver, such as a homodyne, or an infinite impulse response filter.

[0265] In some configurations, the bandpass filter can filter the signal indicative of the temperature of the heater plate within a band corresponding to a frequency of the characteristic energization signal.

[0266] In some configurations, the magnitude of the signal indicative of the temperature of the heater plate at the frequency of the characteristic energization signal exceeding a threshold can be indicative of a low water or water-out condition.

[0267] In some configurations, the received signal indicative of the temperature of the heater plate can comprise a frequency response of the signal indicative of the temperature of the heater plate, the hardware controller configured to determine a low water or water-out condition based on the frequency response.

[0268] In some configurations, the magnitude of the received signal indicative of the response to the characteristic energization signal can be processed to determine a score, wherein when the score is above a threshold, the score can be indicative of a low water or water-out condition.

[0269] In some configurations, the score can be determined by obtaining squared or root-mean-squared (RMS) temperature values of the received signal indicative of the response to the characteristic energization signal , smoothing the received signal indicative of the response to the characteristic energization signal by passing the received signal through a low-pass filter; and calculating the score.

[0270] In some configurations, the characteristic energization signal can comprise a cubed triangle wave. The wave may be applied by a pulse-width modulation (PWM) module of the hardware controller.

[0271] In some configurations, the characteristic energization signal can be a zero mean signal.

[0272] In some configurations, the heater plate can comprise any of the heater plate assembly and the multi-layer heater plate assembly examples described above.

[0273] In some configurations, the system can include one or more features of the humidifier system described above for use in medical procedures.

[0274] In some configurations, a method of detecting a low water or water-out condition in a humidifier chamber of a respiratory or surgical humidifier system can comprise using a hardware controller in a base unit of the respiratory or surgical humidifier system, determining a specific heat capacity value of the humidifier chamber, the humidifier chamber defining a volume and capable of holding a level of water, wherein the humidifier chamber can include a conductive base receivable onto the base unit such that the conductive base contacts a heater plate of the base unit, the heater plate including one or more heating elements in electronic communication with and configured to be energized by the hardware controller; and determining a low water or water out condition based at least in part on the determined specific heat capacity value.

[0275] In some configurations, a method of detecting a low water or water-out condition in a humidifier chamber of a respiratory or surgical humidifier system can comprise using a hardware controller in a base unit of the respiratory or surgical humidifier system, determining a value from which the specific heat capacity of the humidifier chamber can be inferred, the humidifier chamber defining a volume and capable of holding a level of water, wherein the humidifier chamber can include a conductive base receivable onto the base unit such that the conductive base contacts a heater plate of the base unit, the heater plate including one or more heating elements in electronic communication with and configured to be energized by the hardware controller; and determining a low water or water out condition based at least in part on the determined a value from which the specific heat capacity can be inferred.

[0276] In some configurations, the determined specific heat capacity value being below a threshold can be indicative of a low water or water-out condition. In some configurations, the determined value from which the specific heat capacity can be inferred being below a threshold can be indicative of a low water or water-out condition.

[0277] In some configurations, the method can comprise continuously determining the specific heat capacity value. In some configurations, the method can comprise continuously determining the value from which the specific heat capacity can be inferred.

[0278] In some configurations, the method can comprise intermittently determining the specific heat capacity value. In some configurations, the method can

comprise intermittently determining the value from which the specific heat capacity can be inferred.

[0279] In some configurations, the method can comprise determining the specific heat capacity value as a numerical score. In some configurations, the method can comprise determining the value from which the specific heat capacity can be inferred as a numerical score.

[0280] In some configurations, the respiratory or surgical humidifier system can comprise a temperature sensor coupled to or adjacent the heater plate, the temperature sensor configured to determine a temperature of the heater plate.

[0281] In some configurations, the temperature sensor can comprise a thermistor.

[0282] In some configurations, the temperature sensor can comprise two thermistors, each thermistor acting as a voltage divider.

[0283] In some configurations, the method can comprise converting a temperature value from voltage readings of the two thermistors using an equation.

[0284] In some configurations, the method can comprise determining the specific heat capacity value based on the temperature readings from the temperature sensor. In some configurations, the method can comprise determining the valise from which the specific heat capacity can be inferred based on the temperature readings from the temperature sensor.

[0285] In some configurations, the method can further comprise applying a characteristic energization signal to the one or more heating elements of the heater plate, processing a filtered temperature signal from the temperature sensor corresponding to the characteristic energization signal, determining the specific heat capacity value based on the temperature signal, and outputting a low water or water-out warning in response to the determined specific heat capacity value being below a threshold. In some configurations, the method can further comprise applying a characteristic energization signal to the one or more heating elements of the heater plate, processing a filtered temperature signal from the temperature sensor corresponding to the characteristic energization signal, determining the value from which the specific heat capacity can be inferred based on the temperature signal, and outputting a low water or water-out warning in response to the determined value from which the specific heat capacity can be inferred being below a threshold.

[0286] In some configurations, the method can comprise continuously applying the characteristic energization signal. In some configurations, the method can comprise intermittently applying the characteristic energization signal.

[0287] In some configurations, the method can comprise applying the characteristic energization signal to a power control line that provides heater plate control signal.

[0288] In some configurations, the characteristic energization signal can be applied to the heater plate control signal. In some configurations, the characteristic energization signal can be applied by being injected into the heater plate control signal.

[0289] In some configurations, the characteristic energization signal can be at a higher frequency than heater plate control signal.

[0290] In some configurations, the method can comprise passing temperature measurements from the temperature sensor through a filter such that temperature measurements corresponding to the frequency of the characteristic energization signal are passed. In some configurations, the method can comprise passing temperature measurements from the temperature sensor through a bandpass filter having a filter frequency corresponding to a frequency of the characteristic energization signal the such that temperature measurements corresponding to the frequency of the characteristic energization signal are passed. In some configurations, the filter can be a high pass filter. In some configurations, the filter can be a direct conversion receiver, such as a homodyne, or an infinite impulse response filter.

[0291] In some configurations, the method can comprise using the temperature measurements corresponding to the frequency of the characteristic energization signal to determine the specific heat capacity value. In some configurations, the method can comprise using the temperature measurements corresponding to the frequency of the characteristic energization signal to determine the value from which the specific heat capacity can be inferred.

[0292] In some configurations, the heater plate can comprise any of the heater plate assembly and the multi-layer heater plate assembly examples described above.

[0293] In some configurations, the system can include one or more features of the humidifier system described above for use in medical procedures.

[0294] In some configurations, a non-transitory computer-readable medium having stored thereon computer executable instructions that, when executed on a processing device, can cause the processing device to perform the method.

[0295] In some configurations, a method of detecting a low water or water-out condition in a humidifier chamber of a respiratory or surgical humidifier system can comprise using a hardware controller in a base unit of the respiratory or surgical humidifier system, applying a characteristic energization signal to one or more heating elements of a heater plate in the base unit, the one or more heating elements of the heater plate being in electronic communication with and configured to be energized by the hardware controller, wherein the respiratory or surgical humidifier system can further comprise a humidifier chamber defining a volume and including a conductive base receivable onto the base unit such that the conductive base contacts the heater plate, the humidifier chamber capable of holding a level of water; receiving a signal representative of a response to the characteristic energization signal from a temperature sensor coupled to or adjacent the heater plate; and determining a low water or water out condition based on a magnitude of the received signal indicative of the response to the characteristic energization signal. In some configurations, the method can comprise determining a low water or water out condition based on magnitude and/or phase of the received signal indicative of the response to the characteristic energization signal.

[0296] In some configurations, the magnitude being above a threshold can be indicative of a low water or water-out condition. The magnitude can be inversely proportional to a specific heat capacity of the humidifier chamber.

[0297] In some configurations, the determined magnitude and/or phase satisfying a threshold can be indicative of a low water or water-out condition.

[0298] In some configurations, the determined magnitude and/or phase being outside or within a predetermined region in a two-dimensional representation of magnitude and/or phase can be indicative of a low water or water-out condition.

[0299] In some configurations, the method can comprise applying the characteristic energization signal to a power control line that provides heater plate control signal.

[0300] In some configurations, the characteristic energization signal can he applied to the heater plate control signal. In some configurations, the characteristic energization signal can be applied by being injected into the heater plate control signal.

[0301] In some configurations, the method can comprise continuously applying the characteristic energization signal. In some configurations, the method can comprise intermittently applying the characteristic energization signal.

[0302] In some configurations, the method can comprise applying the characteristic energization signal at a characteristic frequency.

[0303] In some configurations, the characteristic frequency can be higher than a normal operating frequency at which the hardware controller energizes the one or more heating elements of the heater plate. In some configurations, the characteristic frequency can be higher than a heater plate control operating frequency at which the hardware controller energizes the one or more heating elements of the heater plate.

[0304] In some configurations, the characteristic energization signal can be at a frequency that is at least 1.5 times the normal operating frequency. In some configurations, the characteristic energization signal can be at a frequency that is at least 1.5 times the heater plate control operating frequency.

[0305] In some configurations, the hardware controller can comprise a signal generator configured to generate and apply the characteristic energization signal.

[0306] In some configurations, the hardware controller can comprise a filter that filters a signal indicative of the temperature of the heater plate to obtain the signal indicative of the response to the characteristic energization signal.

[0307] In some configurations, the filter can be a bandpass filter. In some configurations, the filter can be a high pass filter. In some configurations, the filter can be a direct conversion receiver, such as a homodyne, or an infinite impulse response filter.

[0308] In some configurations, the bandpass filter can filter the signal indicative of the temperature of the heater plate within a band corresponding to a frequency of the characteristic energization signal.

[0309] In some configurations, the magnitude of the signal indicative of the temperature of the heater plate at the frequency of the characteristic energization signal exceeding a threshold can be indicative of a low water or water-out condition.

[0310] In some configurations, the received signal can comprise a frequency response of a signal indicative of the temperature of the heater plate, the hardware controller configured to determine a low water or water-out condition based on the frequency response.

[0311] In some configurations, the method can comprise processing the magnitude of the received signal indicative of the response to the characteristic energization signal to determine a score, wherein when the score is above a threshold, the score can be indicative of a low water or water-out condition.

[0312] In some configurations, the method can comprise determining the score by obtaining squared or root-mean- squared (RMS) temperature values of the received signal indicative of the response to the characteristic energization; smoothing the received signal indicative of the response to the characteristic energization by passing the received signal through a low-pass filter; and calculating the score.

[0313] In some configurations, the characteristic energization signal can comprise a cubed triangle wave. The wave may be applied by a pulse-width modulation (PWM) module of the hardware controller.

[0314] In some configurations, the characteristic energization signal can be a zero mean signal.

[0315] In some configurations, the heater plate can comprise any of the heater plate assembly and multi-layer heater plate assembly examples described above.

[0316] In some configurations, the system can include one or more features of the humidifier system described above for use m medical procedures.

[0317] In some configurations, a non-transitory computer-readable medium having stored thereon computer executable instructions that, when executed on a processing device, can cause the processing device to perform the method.

BRIEF DESCRIPTION OF THE DRAWINGS

[0318] These and other features, aspects, and advantages of the present disclosure are described with reference to the drawings of certain embodiments, which are intended to schematically illustrate certain embodiments and not to limit the disclosure,

[0319] Figure 1A illustrates schematically an example respiratory humidifier system.

[0320] Figure 1B illustrates schematically an example heater base unit of the respiratory humidifier system of Figure 1A.

[0321] Figure 1C illustrates schematically an example respiratory humidifier system.

[0322] Figure ID illustrates schematically an example heater base unit of the respiratory humidifier system of Figure 1C.

[0323] Figure 1E illustrates schematically a partial view of the heater base unit and an example breathing circuit heating element adapter of Figure 1C.

[0324] Figure 2A illustrates schematically an example respiratory humidifier system with separate blower and heater base units and connected to a nasal mask.

[0325] Figure 2B illustrates schematically the respiratory humidifier system of Figure 2A connected to a nasal cannula,

[0326] Figure 2C illustrates schematically an example respiratory humidifier system with an integrated blower and heater base unit.

[0327] Figure 2D illustrates an example surgical insufflation system,

[0328] Figure 2E illustrates an example high flow therapy system,

[0329] Figures 3A-3B illustrate flow charts of example processes for detecting a low water and/or water-out condition in a humidifier chamber of a respiratory humidifier system.

[0330] Figure 3C illustrates graphs showing an example returned signal prior to and during a water-out condition.

[0331] Figure 3D illustrates example returned signals with and without a water-out condition in the time domain.

[0332] Figure 3E illustrates example returned signals with and without a water-out condition in the frequency domain.

[0333] Figure 3F illustrates example data points representing magnitude and phase of returned signals and an example water-out classification boundary based on the magnitude of the returned signals.

[0334] Figure 3G illustrates example data points representing magnitude and phase of returned signals and an example water-out classification boundary based on the phase of the returned signals.

[0335] Figure 3H illustrates example data points representing magnitude and phase of returned signals and two example water-out classification boundaries based on the magnitude and the phase of the returned signals.

[0336] Figure 4A illustrates a system diagram of an example humidifier system for detecting a low water and/or water-out condition.

[0337] Figure 4B illustrates example heater plate temperatures and output dew points in time domain and frequency domain prior to and during a water-out condition.

[0338] Figure 4C illustrates a graph showing example waveforms of a supplementary signal for applying to (for example, injecting into) a heater plate power signal of a humidifier system.

[0339] Figure 4D illustrates a graph showing harmonics contents of the waveforms in Figure 4B.

[0340] Figure 4E illustrates an example heater plate temperature transfer function of a humidifier system,

[0341] Figure 4F illustrates example waveforms of combined heater plate temperature and power signals, THP’ and PHP’ .

[0342] Figure 4G illustrates an example band filter in the system diagram of Figure 3A.

[0343] Figure 5A illustrates example algorithms for determining a low water and/or water-out condition based on the return signal.

[0344] Figure 5B illustrates example water-out scores and dew points prior to and during a water-out condition.

[0345] Figure 6 illustrates an example leaky detector for determining a magnitude of the return signal.

[0346] Figure 7 illustrates example heater plate temperature signal gain and phase of different chambers and/or at different flow rates.

[0347] Figures 8A and 8B illustrate example circuit models or systems for detecting a low water and/or water-out condition in a humidifier chamber.

[0348] Figure 8C illustrates an example resistor-capacitor (RC) filter formed by the interaction between the resistance and capacitance terms of the system of Figure 8A or 8B.

[0349] Figure 8D illustrates clipping of an example applied (for example, injected) waveform for detecting low water and/or water-out conditions.

[0350] Figure 9 illustrates an exploded view of an example heater plate assembly.

[0351] Figure 9A illustrates an exploded view of another example heater plate assembly.

[0352] Figures 9B and 9C illustrate various perspective views of the example heater plate assembly of Figure 9A without wires for connecting to a power source.

[0353] Figure 9D illustrates a cross-sectional view of the example heater plate assembly of Figures 9B and 9C.

[0354] Figure 9E illustrates a perspective view of a portion of an example heater plate assembly.

[0355] Figure 10 illustrates schematically an example heater plate stacking arrangement.

[0356] Figure 11 illustrates schematically another example heater plate stacking arrangement.

[0357] Figure 12A illustrates an example three-dimensional representation of a top heating plate in the heater plate stacking arrangement of Figure 11.

[0358] Figures 12B-12C illustrate various views of an example three-dimensional representation of a top heating plate in the heater plate stacking arrangement of Figure 11.

[0359] Figures 12D-12E illustrate various views of an example three-dimensional representation of a bottom plate in the heater plate stacking arrangement of Figure 11. [0360] Figure 12F illustrates a bottom view of the top heating plate of Figures

12B-12C.

[0361] Figure 12G illustrates a cross-section of the top heating plate of Figure 12F along axis F-F.

[0362] Figures 12H-12M illustrate side, top, bottom perspectives, top perspective, and bottom views of the top heating plate of Fi gure 12F.

[0363] Figures 12N-12R illustrate top, top perspective, bottom, and side views of a bottom plate configured to be used with the top heating plate of Figure 12L.

[0364] Figures 13A-13D illustrate schematically operation of the thermal interface material.

[0365] Figure 14 illustrates schematically an example heater plate stacking arrangement.

[0366] Figure 15 illustrates schematically an example heater plate stacking arrangement.

[0367] Figures 16A-1638 illustrate schematically first and second side views of an example heating element.

[0368] Figures 17A-E illustrate various views of an example three-dimensional representation of the top heating plate in the heater plate stacking arrangement of Figure 15.

[0369] Figures 18A-F illustrate various views of an example three-dimensional representations of the bottom plate in the heater plate stacking arrangement of Figure 15.

[0370] Figures 19A-19F illustrate various views of another example bottom plate.

[0371] Figure 20A illustrates a bottom view of a heater plate assembly incorporating the example botom plate of Figures 19A-19F.

[0372] Figures 20B-20C illustrate various cross-sectional views of the heater plate assembly of Figure 20A.

[0373] Figures 21A-21F illustrate various views of another example botom plate.

[0374] Figures 22A-22B illustrate various cross-sectional views of a heater plate assembly incorporating the example bottom plate of Figures 21A-21F.

DETAILED DESCRIPTION

[0375] Although certain embodiments and examples are described below, those of skill in the art will appreciate that the disclosure extends beyond the specifically disclosed embodiments and/or uses and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the disclosure herein disclosed should not be limited by any particular embodiments described below. For example, the dimensions provided in the present disclosure are examples and not being limiting.

Example Respiratory Humidifier Systems

[0376] The present disclosure provides examples of a respiratory or surgical humidifier system configured to supply humidified and/or heated gas to a patient or user in multiple modes. The modes can include at least an invasive mode (for example, for patients with bypassed airway or laparoscopic surgery) and a noninvasive mode (for example, for patients or users with breathing masks). Each mode can have individualized humidity output, which can be expressed as dew point output set points. For example, a user can select a set point, which can denote the mode of operation. The non-invasive mode can have set points of 31 degrees, 29 degrees, 27 degrees Celsius, or others. The invasive mode can have set points of 37 degrees Celsius or others. Some respiratory humidifier systems disclosed herein can also include a high flow, unsealed mode or any other modes known to those of skill in the art. The high flow, unsealed mode (herein referred to as Optiflow® mode) is marketed as Optiflow® by Fisher and Paykel Healthcare Limited of Auckland, New Zealand.

[0377] Referring to Figures 1A and 1C, an example respiratory humidifying system 100, 101 can include a heater base unit 102 having a heater plate 120 (see Figures IB and 1D). The heater plate 120 can include one or more heating element(s). The heater base unit 102 can have a housing and a controller (for example, a microprocessor) contained within the housing for controlling the supply of energy to the heating element(s).

[0378] The humidifier heater plate 120 can have a temperature sensor (see temperature sensor 262 in Figure 2A) (for example, a temperature transducer, thermistor, or other types of temperature sensor). Multiple different temperature sensors may also be used. The temperature sensor can measure a temperature of the heater plate 120. The temperature sensor can be in electrical communication with the controller in the heater base unit 102 so that the controller can monitor the temperature of the heater plate 120. Measurements made by the temperature sensor can be used as the input in the low water and/or water-out detection processes that will be described below.

[0379] The temperature sensor can also optionally include two or more thermistors. Each thermistor can act as a voltage divider. An average of the readings from the two thermistors can be used as the input in the low water and/or water-out detection process. Two or more thermistors may also be used for redundancy. Additional thermistors can also be included. The temperature sensor is positioned on an underside surface of the heater plate. The temperature sensors may be preferably placed on a top heating plate of a heater plate assembly. The top heating plate is the plate that is in contact with a humidifier chamber. The heater plate 120 here may refer to the top heating plate that is exposed and is positioned to be contact the base of the humidifier chamber when the humidifier chamber is positioned in an operative position on the heater base. The temperature sensors may be positioned at an edge of the heater plate or substantially in the center of the heater plate. The heating elements used are nichrome wire or other types of heating filaments wrapped around an electrical insulator block or core. The heater plate may include a plurality of electrical insulation layers. The heater plate may include a back plate or bottom plate with the multiple parts being screwed or bolted together. Additional details of examples of a heater plate suitable for implementing the technologies disclosed herein are described below with reference to Figures 8A-18F. Alternatively the heater plate may include a plurality of layers that may be laminated together or may be adhered together to form a unitary heater plate. In a further alternative configuration, the heater plate may be formed on a semiconductor by etching, or deposition, or any suitable arrangement.

[0380] The humidifier chamber 103 can be removably received and retained on the heater base unit 102, such that the humidifier chamber base is positioned in contact with the heater plate 120 in the heater base unit 102. Referring to Figures 1B and 1D, which illustrate examples of the heater base unit 102 of Figures 1A and 1C respectively, the humidifying base 102 can have a collar 124 for engaging with a flange on the humidifier chamber 103, such as shown in Figures 1A and 1C. The collar 124 defines a lip that engages a flange of the humidifier chamber 103 to retain the humidifier chamber 103 in an operative position on the heater base 102. The humidifier chamber 103 can mclude a conductive base. When engaged with the heater base unit 102, the conductive base of the humidifier chamber 103 can be in contact with the heater plate 120, such as an upper surface of a top heating plate of the heater plate 120. Water inside the chamber 103 is heated when a power signal is sent to the heating element to energize the heating element. The chamber 103 can also be connected to a water source 142 (Figure 1C), which can add water to the chamber 103 when the water is low or completely out in the chamber 103. Adding of water can be manually performed or controlled by the controller, such as upon a warning from the system 101 that there may be a low water or water-out condition,

[0381] With continued reference to Figures 1A and 1C, the gases to be humidified can include one or more of air, oxygen, anesthetic, other auxiliary gases, or any mixture of gases. The gases can be supplied to the humidifier chamber 103 through a gases inlet 104, which can be connected to a gas source, such as a ventilator, in the case of CPAP therapy a CPAP blower, or a remote source. For high flow therapy, a blower or further alternatively a wall source with a flow and/or pressure regulator can supply the gases. The humidifier chamber 103 can also include a gases outlet 105, which can connect to a breathing circuit 106. The breathing circuit 106 can convey humidified and heated gases to a patient or user. As shown in Figure 1A, a patient end 107 of the breathing circuit 106 can connect to a patient interface, such as a nasal cannula 113 or a nasal mask 114. The breathing circuit 106 can also connect to other types of patient or user interface, such as a full face mask, an endotracheal tube, or others. The breathing circuit 106 of Figure 1C can also be connected to any suitable patient interface disclosed herein.

[0382] A heating element 110 (such as one or more heater wires) can be provided within the breathing circuit 106. The heating element 110 can help prevent condensation of the humidified gases within the breathing circuit 106. The heating element 110 can also optionally be in electrical communication with the controller in the heater base unit 102. As shown in Figures 1C and 1E, a breathing circuit heating element adaptor cable 128 can have two connectors at two ends of the cable 128 for coupling the heating element 110 to the heater base unit 102 (such as to the controller of the heater base unit 102). The heating element adaptor cable 128 can facilitate an easy connection between the heating element 110 and the heater base unit 102. The heating element 110 is controlled by the control unit, including the controlling of power to the heating element 110 by the control unit. The heating element 110 in the breathing circuit 106 reduces condensation and also ensures the temperature of gases is maintained in a predetermined range. The heating element adaptor cable 128 can also include an ambient temperature sensor 126, which can allow the system 101 to adjust the heating element 110 power to compensate for ambient temperatures or changes in the ambient temperature. A heating element indicator 130 can be embedded into the connector that couples to the heater base unit 102. The heating element indicator 130 can be illuminated when a properly functioning heating element 110 is connected to the heater base unit 102. When the heating element indicator 130 is illuminated, the system 101 can heat the gas inside the breathing circuit 106 via the heating element 110 to minimize condensate in addition to heating the gas passing through the humidifier chamber 103 via the heater plate 120. If the heating element 110 is malfunctioning or not connected, or if the heating element indicator 130 is not illuminated, the system 101 may heat the gas only by heating the water in the chamber 103 via the heater plate 120. Alternatively, the heating element indicator 130 may be illuminated when there is a fault or a disconnection of the adaptor cable 128. The illuminated indicator 130 can act as a visual message or a visual warning. The indicator 130 may not be illuminated if the heating element 110 is functioning correctly.

[0383] The controller of the respiratory humidifier system 100, 101 can control at least the heater plate 120, and preferably or optionally also the heating element 110, without additional sensors (for example, in the humidifier chamber, in the breathing circuit, and/or elsewhere in the system). This can be achieved by estimating the flow rate of gases through the respiratory humidifier system 100, 101 using parameters already available to the controller. For a given respiratory humidifier system, the controller can determine an appropriate level of power to apply to the heater plate 120. Applying power to the heater 120 can generate humidity and heat the gases. The power applied to the heater plate can be at a rate to generate a predetermined amount of humidity. Additionally, the parameters can also optionally be used by the controller to provide a more appropriate level of energization to the heating element 110. As shown in Figures 1C and 1E, the system 101 can also include the

ambient temperature sensor 126. The ambient temperature sensor can be located anywhere that is exposed to the ambient air. For example, the system 101 can include the ambient temperature sensor 126 on the heating element adaptor cable 128.

[0384] As shown in Figure 1E, a front panel of the heater base unit 102 can include a plurality of user controls and indicators, such as a power button 132, a humidity setting push buton 134, and a plurality of (such as three, four, five or more) humidity settings indicators 136 (which can include LED lights) next to the humidity setting push button 134. The locations, shapes, and sizes of the user controls and indicators are not limiting. There can be four levels of humidity settings available which are indicated by the four humidity-setting indicators 136. The four humidity settings may correspond to different types of therapies provided to a patient. For example, the highest amount of humidity can be selected when the humidifier is operating in an invasive therapy mode. The lowest amount of humidity may be applied in a low flow oxygen therapy mode. The amount of humidity can be selected based on therapeutic requirements or therapy type or may be predefined. Alternatively, the humidifier 100, 101 may include a controller that is configured to automatically select the amount of humidity to be delivered based on a therapy mode, the patient, or the type of therapy being applied to the patient. Optionally, the humidifier 100, 101 may include a touch screen that may communicate information to the user. The touch screen may also be configured to receive inputs from the user.

[0385] The humidity level can be adjusted by pressing the humidity settings push button 134, which can also be a momentary push button. The front panel can also include a plurality of alarm indicators 138 (which can include LED lights) to indicate the following non-limiting examples of conditions: “water out” condition (including low water and water-out), heating element adaptor not connected, audible alarm muted, and a “See Manual” indication used to indicate that a fault has occurred within the system 101.

[0386] The system 101 can be suitable for providing respiratory therapy of different purposes, such as for critical care (for example, in the hospital) and home care. The system 101 is suitable for provide invasive, non-mvasive and high flow therapies for both adult and pediatric patients.

[0387] As will be described in detail below, the controller of the respiratory humidifier system 100, 101 can also determine a humidifier chamber low water and/or water-out condition using inputs from the temperature sensor. The controller may not need inputs from additional sensors for water-out detection. Requiring only one sensor reduces costs of the respiratory humidifier system 100, 101 and/or allows the respiratory humidifier system 100, 101 to be simpler and lighter than respiratory humidifier systems having multiple sensors. As will be described below, the system 101 is also configured to improve thermal coupling within the system to enable water-out detection at lower power levels, winch can involve low flow, low humidity, or no chamber scenarios. The described assembly improves the thermal coupling, that is, improves thermal conductivity between the elements of the heater plate assembly components such that the heat generated is transferred to the top heating plate and detected by the thermistors.

WHAT IS CLAIMED IS:

1. A multi-layer heater plate assembly for a respiratory humidifier, the heater plate assembly comprising:

a top heating plate;

a heating element configured to generate heat, the heating element located below the top heating plate; and

a thermal interface layer between the top heating plate and the heating element, the thermal interface layer comprising a compliant thermal interface material configured to displace air gaps between the top heating plate and the heating element.

2. The multi-layer heater plate assembly of Claim 1, wherein the thermal interface layer is configured to displace air gaps between the top heating plate and the heating element so as to improve thermal conductivity between the top heating plate and the heating element.

3. The multi-layer heater plate assembly of Claim 1 or 2, comprising a bottom plate, wherein the heating element is bound by the top heating plate and the bottom plate.

4. The multi-layer heater plate assembly of any of Claims 1-3, wherein the thermal interface layer comprises a thickness sufficient for providing electrical insulation.

5. The multi-layer heater plate assembly of any of Claims 1-4, wherein the multi-layer heater plate assembly is removably coupled together by one or more fasteners.

6. The multi-layer heater plate assembly of any of Claims 1-5, wherein the multi-layer heater plate assembly is formed by bolting a bottom plate to the top heating plate with the heating element and the electrical insulation layer therebetween.

7. The multi-layer heater plate assembly of any of Claims 1-6, wherein the top heating plate comprises a sensor-mounting block configured to receive at least one temperature sensor.

8. The multi-layer heater plate assembly of Claim 7, wherein the sensor-mounting block is configured to receive two temperature sensors.

9. The multi-layer heater plate assembly of Claim 7 or 8, wherein the at least one temperature sensor comprises a thermistor.

10. The multi-layer heater plate assembly of any of Claims 3-10, further comprising a safety feature coupled to the bottom plate.

11. The multi-layer heater plate assembly of Claim 10, wherein the safety feature comprises a thermal cutoff unit.

12. The multi-layer heater plate assembly of Claim 10 or 11, wherein the bottom plate comprises a platform to support the safety feature.

13. The multi-layer heater plate assembly of Claim 12, wherein the safety feature is secured to the platform by screws.

14. The multi-layer heater plate assembly of Claim 12 or 13, wherein the platform protrudes from a remainder of the bottom plate.

15. The multi-layer heater plate assembly of any of Claims 10-14, wherein the bottom plate comprises a slot wherein the safety feature is coupled to the bottom plate to improve isolation of the safety feature from the heating element.

16. The multi-layer heater plate assembly of Claim 15, wherein the bottom plate further comprises a cut-out step along a length of the slot.

17. The multi-layer heater plate assembly of Claim 15 or 16, wherein the slot is L-shaped.

18. The multi-layer heater plate assembly of any of Claims 15-17, wherein the slot terminates at or near a periphery of the heating element.

19. The multi-layer heater plate assembly of any of Claims 15-18, wherein the slot extends radially outwardly past a periphery of the thermal interface layer.

20. The multi-layer heater plate assembly of any of Claims 10-19, wherein the bottom plate comprises a cut-out step near the sensor-mounting block when the heater plate assembly is assembled.

21. The multi-layer heater plate assembly of any of Claims 1-20, wherein the thermal interface layer has a Shore 00 hardness scale of 50 to 100.

22. The multi-layer heater plate assembly of Claim 21, wherein the thermal interface layer has a Shore 00 hardness scale of 80.

23. The multi-layer heater plate assembly of any of Claims 1-22, further comprising at least one inflexible electrical insulation layer.

24. The multi-layer heater plate assembly of Claim 23, wherein the at least one inflexible electrical insulation layer comprises mica.

25. The multi-layer heater plate assembly of any of Claims 1-24, wherein the thermal interface material is electrically insulating.

26. The multi-layer heater plate assembly of any of Claims 1-25, comprising a second thermal interface layer that comprises a compliant thermal interface material configured to displace air gaps between components of the multi-layer heater plate assembly.

27. The multi-layer heater plate assembly of Claim 26, wherein the second thermal interface layer is located between the heating element and the bottom plate.

28. The multi-layer heater plate assembly of Claim 26, wherein the second thermal interface layer is located between the top heating plate and the bottom plate.

29. The multi-layer heater plate assembly of Claim 28, wherein the second thermal interface layer is electrically conducting.

30. The multi-layer heater plate assembly of any of Claims 1-29, wherein the compliant thermal interface material comprises silicone or silicone compound.

31. The multi-layer heater plate assembly of any of Claims 1-30, wherein the compliant thermal interface material comprises a fiberglass substrate and a thermally conductive material embedded in the substrate or positioned on the substrate.

32. The multi-layer heater plate assembly of any of Claims 1-31, wherein the compliant thermal interface material has a breakdown voltage of at least 4000 V AC.

33. The multi-layer heater plate assembly of Claim 32, wherein the compliant thermal interface material has a breakdown voltage of at least 6000 V AC.

34. The multi-layer heater plate assembly of any of Claims 1-33, wherein the compliant thermal interface material has a thermal conductivity of at least 1.8 W/(m.K).

35. The multi-layer heater plate assembly of any of Claims 1-34, wherein the compliant thermal interface material is elastic.

36. A multi-layer heater plate assembly for a respiratory- humidifier, the heater plate assembly comprising:

a top heating plate;

a bottom plate;

a heating element configured to generate heat, the heating element bound by the top heating plate and the bottom plate;

a compliant thermal interface layer between the bottom plate and the top heating plate and configured to displace air gaps between the bottom plate and the top heating plate.

37. The multi-layer heater plate assembly of Claim 36, wherein the multi-layer heater plate assembly is removably coupled together by one or more fasteners.

38. The multi-layer heater plate assembly of Claim 36 or 37, wherein the multi-layer heater plate assembly is formed by bolting the bottom plate to the top heating plate with the heating element and the electrical insulation layer therebetween.

39. The multi-layer heater plate assembly of any of Claims 36-38, wherein the top heating plate comprises a sensor-mounting block configured to receive at least one temperature sensor.

40. The multi-layer heater plate assembly of Claim 39, wherem the sensor-mounting block is configured to receive two temperature sensors.

41. The multi-layer heater plate assembly of Claim 39 or 40, wherein the at least one temperature sensor comprises a thermistor.

42. The multi-layer heater plate assembly of any of Claims 36-41, wherein the compliant thermal interface layer is configured to displace air gaps between an edge of the bottom plate and the top heating plate.

43. The multi-layer heater plate assembly of any of Claims 36-42, wherein the compliant thermal interface layer is electrically insulating.

44. The multi-layer heater plate assembly of any of Claims 36-43, comprising a second thermal interface layer configured to displace air gaps between the top heating plate and the heating element.

45. The multi-layer heater plate assembly of any of Claims 36-44, further comprising at least one inflexible electrical insulation layer.

46. The multi-layer heater plate assembly of Claim 45, wherein the at least one inflexible electrical insulation layer comprises mica.

47. The multi-layer heater plate assembly of Claim 45 or 46, wherein the at least one inflexible electrical insulation layer is located between the compliant thermal interface layer and the heating element.

48. The multi-layer heater plate assembly of any of Claims 45-47, wherein the at least one inflexible electrical insulation layer is located between the heating element and the bottom plate.

49. A humidifier system for use in medical procedures, the system comprising: a base unit; and

a humidifier chamber receivable onto the base unit,

wherein the base unit comprises a multi-layer heater plate assembly according to any of Claims 1-48.

50. The system of Claim 49, wherein the humidifier chamber comprises a conductive base, the conductive base urged into contact with the heater plate assembly upon the humidifier chamber being positioned on the base unit.

51. The system of Claim 49 or 50, wherein the heater plate assembly heats the humidifier chamber to heat contents of the chamber in order to humidify gases passing through the chamber.

52. The system of any of Claims 49-51, further comprising a tube configured to transport gases from the humidifier chamber to a patient interface.

53. A humidifier system for use in medical procedures, the system comprising: a housing configured to receive a humidifier chamber; and

a heater plate assembly located at least partially within the housing, the heater plate assembly comprising:

a top heating plate, wherein the top heating plate is configured to contact a base of the humidifier chamber when the humidifier chamber is received by the housing;

a thermistor located at or near the top heating plate;

a heating element configured to generate heat; and an electrical insulation arrangement between the top heating plate and the heating element,

wherein the electrical insulation arrangement thermally couples the heating element and the top heating plate such that heat generated by a power signal to the heating element is transmitted to the top heating plate, and wherein the electrical insulation arrangement improves thermal coupling between the heating element and the top heating plate.

54. The system of Claim 53, wherein the electrical insulation arrangement comprises a flexible and/or elastic insulation sheet.

55. The system of Claim 53 or 54, wherein the electrical insulation arrangement comprises a compliant insulation sheet configured to displace air gaps between the top heating plate and the heating element.

56. The system of any of Claims 53-55, wherein the electrical insulation sheet improves heat conduction from the heating element to the top heating plate.

57. The system of any of the Claims 53-56, wherein the electrical insulation sheet reduces a capacitance of the heater plate assembly such that a thermal conductivity is improved between components of the heater plate assembly.

58. The system of any of Claims 53-57, further comprising a double electrical insulation arrangement including two insulation elements, wherein the two insulation elements comprises two inflexible insulation layers.

59. The system of Claim 58, wherein the two inflexible insulation layers comprise mica.

60. The system of any of Claims 58-59, wherein the two insulation elements comprise two layers that are separate from each other.

61. The system of any of Claims 58-60, wherein the double electrical insulation arrangement is located between the electrical insulation arrangement and the heating element.

62. The system of any of Claims 53-61, wherein the electrical insulation arrangement composes a thermally conductive but electrically insulating elastomer.

63. The system of any of Claims 53-62, wherein the electrical insulation arrangement comprises silicone or silicone compound.

64. The system of any of Claims 53-63, wherein the electrical insulation arrangement comprises a fiberglass substrate and a thermally conductive material embedded in the substrate or positioned on the substrate.

65. The system of any of Claims 53-64, wherein the electrical insulation arrangement comprises a material having a breakdown voltage of at least 4000 V AC.

66. The system of Claim 65, wherein the electrical insulation arrangement comprises a material having a breakdown voltage of at least 6000 V AC.

67. The system of any of Claims 53-66, wherein the electrical insulation arrangement comprises a material having a thermal conductivity of at least 1.8 W/(m.K).

68. The system of any of Claims 53-67, wherein the electrical insulation arrangement improves thermal coupling between the heating element and the top heating plate such that a waveform applied to the power signal for detecting low water or water out conditions in the humidifier chamber can be of a reduced power.

69. The system of any of Claims 53-68, wherein the electrical insulation arrangement improves thermal coupling between the heating element and the top heating plate such that a temperature reading of the thermistor better corresponds to a temperature of water in the humidifier chamber.

70. The system of any of Claims 53-69, wherein the heater plate assembly comprises a bottom plate, the heating element and the electrical insulation arrangement is bound between the bottom plate and the top heating plate.

71. The system of Claim 70, wherein the bottom plate contacts the electrical insulation arrangement.

72. The system of Claim 70, wherein the heater plate assembly comprises a flexible electrical insulation sheet between the top heating plate and the bottom plate.

73. The system of any of Claims 70-72, wherein the heater plate assembly comprises a compliant electrical insulation sheet between the top heating plate and the bottom plate configured to displace air gaps between the top heating plate and the bottom plate.

74. A respiratory or surgical humidifier system, comprising:

a base unit comprising:

a heater plate including one or more heating elements; and

a hardware controller in electronic communication with the one or more heating elements of the heater plate and configured to energize the one or more heating elements of the heater plate; and

a humidifier chamber defining a volume and including a conductive base receivable onto the base unit such that the conductive base contacts the heater plate, the humidifier chamber configured to hold a level of water,

wherein the hardware controller is configured to determine a value from which the specific heat capacity of the humidifier chamber can be inferred and determine a low water or water-out condition based at leastin part on the determined value from which the specific heat capacity can be inferred.

75. The respiratory or surgical humidifier system of Claim 74, wherein the hardware controller determines that a low water or water-out condition is present in response to the determined value from which the specific heat capacity can be inferred being below a threshold.

76. The respiratory or surgical humidifier system of Claim 74 or 75, wherein the hardware controller continuously determines the value from which the specific heat capacity can be inferred.

77. The respiratory or surgical humidifier system of any of Claims 74-76, wherein the hardware controller intermittently determines the value from which the specific heat capacity can be inferred.

78. The respiratory or surgical humidifier system of any of Claims 74-77, wherein the value from which the specific heat capacity can be inferred is determined as a numerical score.

79. The respiratory or surgical humidifier system of any of Claims 74-78, comprising a temperature sensor coupled to or adjacent the heater plate, wherein the temperature sensor determines a temperature of the heater plate.

80. The respiratory or surgical humidifier system of Claim 79, wherein the temperature sensor comprises a thermistor.

81. The respiratory or surgical humidifier system of Claim 79, wherein the temperature sensor comprises two thermistors, each thermistor acting as a voltage divider.

82. The respiratory or surgical humidifier system of Claim 81, wherein the hardware controller determines a temperature value from voltage readings of the two thermistors.

83. The respiratory or surgical humidifier system of any of Claims 74-82, wherein the hardware controller determines a value from which the specific heat capacity can be inferred based on the temperature readings from the temperature sensor.

84. The respiratory or surgical humidifier system of any of Claims 74-83, wherein the hardware controller is configured to:

apply a characteristic energization signal to the one or more heating elements of the heater plate;

process a temperature signal from the temperature sensor corresponding to the characteristic energization signal;

determine the value from which the specific heat capacity can be inferred based on the temperature signal; and

output a low water or water-out warning in response to the determined value from which the specific heat capacity can be inferred being below a threshold.

85. The respiratory or surgical humidifier system of Claim 84, wherein the hardware controller is configured to continuously and/or intermittently apply the characteristic energization signal.

86. The respiratory or surgical humidifier system of Claim 84 or 85, wherein the hardware controller is configured to apply the characteristic energization signal to a heater plate control signal.

87. The respiratory or surgical humidifier system of Claim 86, wherein the hardware controller is configured to inject the characteristic energization signal into the heater plate control signal.

88. The respiratory or surgical humidifier system of any of Claims 84-87, wherein the characteristic energization signal is at a higher frequency than a heater plate control signal.

89. The respiratory or surgical humidifier system of any of Claims 84-88, wherein the hardware controller passes temperature measurements from the temperature sensor through a bandpass filter having a filter frequency corresponding to a frequency of the characteristic energization signal such that temperature measurements corresponding to the frequency of the characteristic energization signal are passed.

90. The respiratory or surgical humidifier system of Claim 89, wherein the temperature measurements corresponding to the frequency of the characteristic energization signal are used to determine the value from which the specific heat capacity can be inferred.

91. The system of any of Claims 74-90, wherein the heater plate comprises the multi-layer heater plate assembly according to any of Claims 1-48.

92. A respiratory or surgical humidifier system, comprising:

a base unit comprising:

a heater plate including one or more heating elements;

a hardware controller in electronic communication with the one or more heating elements of the heater plate and configured to energize the one or more heating elements of the heater plate; and

a temperature sensor coupled to or adjacent the heater plate and configured to generate a signal indicative of a temperature of the heater plate; and

a humidifier chamber defining a volume and including a conductive base receivable onto the base unit such that the conductive base contacts the heater plate, the humidifier chamber configured to hold a level of water,

wherein the hardware controller is configured to:

apply a characteristic energization signal to the one or more heating elements of the heater plate;

receive a signal indicative of a response to the characteristic energization signal; and

determine a low water or water-out condition based on a magnitude and/or phase of the received signal indicative of the response to the characteristic energization signal.

93. The respiratory or surgical humidifier system of Claim 92, wherein the determined magnitude being above a threshold is indicative of a low water or water-out condition.

94. The respiratory or surgical humidifier system of Claim 92 or 93, wherein the determined magnitude and/or phase satisfying a threshold is indicative of a low water or water-out condition.

95. The respiratory or surgical humidifier system of Claim 94, wherein the determined magnitude and/or phase being outside or within a predefined region in a two-dimensional representation of magnitude and/or phase is indicative of a low water or water-out condition.

96. The respiratory or surgical humidifier system of any of Claims 92-95, wherein the magnitude is inversely proportional to a specific heat capacity of the humidifier chamber.

97. The respiratory or surgical humidifier system of any of Claims 92-96, wherein the hardware controller is configured to apply the characteristic energization signal at a characteristic frequency.

98. The respiratory or surgical humidifier system of Claim 97, wherein the characteristic frequency is higher than a heater plate control operating frequency at which the hardware controller energizes the one or more heating elements of the heater plate.

99. The respiratory or surgical humidifier system of Claim 98, wherein the characteristic energization signal is at a frequency that is at least 1.5 times the heater plate control operating frequency.

100. The respiratory or surgical humidifier system of any of Claims 92-99, wherein the hardware controller comprises a signal generator configured to generate and apply the characteristic energization signal.

101. The respiratory or surgical humidifier system of any of Claims 92-100, wherein the hardware controller is configured to inject the characteristic energization signal into the heater plate control signal.

102. The respiratory or surgical humidifier system of any of Claims 92-101, wherein the hardware controller comprises a filter that filters a signal indicative of the temperature of the heater plate to obtain the signal indicative of the response to the energization signal.

103. The respiratory or surgical humidifier system of Claim 102, wherein the filter is a bandpass filter.

104. The respiratory or surgical humidifier system of Claim 103, wherein the bandpass filter filters the signal indicative of the temperature of the heater plate within a band corresponding to a frequency of the characteristic energization signal.

105. The respiratory or surgical humidifier system of Claim 104, wherein the magnitude of the signal indicative of the temperature of the heater plate at the frequency of the characteristic energization signal exceeding a threshold is indicative of a low writer or water-out condition.

106. The respiratory or surgical humidifier system of Claim 92, wherein the received signal comprises a frequency response of the signal indicative of the temperature of the heater plate, the hardware controller configured to determine a low water or water- out condition based on the frequency response.

107. The respiratory or surgical humidifier system of any of Claims 92-106, wherein the magnitude of the received signal indicative of the response to the characteristic energization signal is processed to determine a score, wherein when the score is above a threshold, the score is indicative of a low water or water-out condition.

108. The system of any of Claims 92-107, wherein the heater plate comprises the multi-layer heater plate assembly according to any of Claims 1-48.

109. A method of detecting a low water or water-out conditionin a humidifier chamber of a respiratory or surgical humidifier system, comprising:

using a hardware controller in a base unit of the respiratory or surgical humidifier system:

determining a value from which the specific heat capacity of the humidifier chamber can be inferred, the humidifier chamber defining a volume and capable of holding a level of water, wherein the humidifier chamber includes a conductive base receivable onto the base unit such that the conductive base contacts a heater plate of the base unit, the heater plate

including one or more heating elements in electronic communication with and configured to be energized by the hardware controller; and

determining a low water or water out condition based at least in part on the determined value from which the specific heat capacity can be inferred.

110. A method of detecting a low water or water-out condition in a humidifier chamber of a respiratory or surgical humidifier system, the method comprising:

using a hardware controller in a base unit of the respiratory or surgical humidifier system:

applying a characteristic energization signal to one or more heating elements of a heater plate in the base unit, the one or more heating elements of the heater plate being in electronic communication with and configured to be energized by the hardware controller, wherein the respiratory or surgical humidifier system further comprises a humidifier chamber defining a volume and including a conductive base receivable onto the base unit such that the conductive base contacts the heater plate, the humidifier chamber capable of holding a level of water;

receiving a signal representative of a response to the characteristic energization signal from a temperature sensor coupled to or adjacent the heater plate; and

determining a low water or water out condition based on a magnitude and/or phase of the received signal indicative of the response to the characteristic energization signal.