Background of the Invention
This disclosure relates generally to patient monitors and physiological sensors
used for acquiring electrophysiological signals from a subjectlpatient. More
particularly, the disclosure relates to monitoring the degradation of physiological
sensors.
A prerequisite of patient care is that accurate and reliable measurements can
be made from the patient to evaluate the patient's state. Since a patient monitor
connected to a sensor may perform rather complex calculations based on the
physiological signals acquired through the sensor and since the results obtained may
depend on a variety of parameters related to the sensor, it is important that the sensor
fulfills certain quality standards and is thus authorized to be used in the patient monitor
for the measurement in question. The use of aged, damaged or low quality sensors may
lead to inaccurate and/or unreliable results, which may in turn contribute to incorrect
medical decisions and even risk patient safety.
In terms of patient safety, the use of non-authentic, unauthorized and/or
counterfeited sensors is also to be prevented, since the cooperation of such sensors with
the patient monitor is not tested and the sensors therefore involve the same risks as
authentic but aged or low quality sensors.
It is therefore common practice to provide a sensor/monitor system with a
detection mechanism that detects aged and/or unauthorized sensors, or with a
mechanism that tends to improve the performance level of the sensor. The solutions
may be classified into different categories according to the type of data stored in the
sensor and according to the way in which data stored in sensor memory is employed. In
one solution, the content of the sensor memory is used by a monitor algorithm to make
the measurement more accurate. For this, the sensor memory may hold sensor
parameters that are relevant to the measurement or provide different calibration
coefficient sets for different two or more ranges of certain sensor parameters. The
sensor parameters are typically variables that the patient monitor is incapable of
measuring, such as LED wavelengths. The sensor memory may also hold operating
parameters that prevent the use of the sensor outside a safe operating range. A further
solution is to record other information related to the use of the sensor into the sensor
memory, such as maximum usage time, expiration data, or warranty date of the sensor.
This data may then be used to prevent the use of the sensor when the stored limit value
is reached. Instead of measuring cumulated use time, the monitor may also measure the
actual total amount of use. This may be carried out by counting the drive pulses
transmitted to the sensor, for example.
Although current solutions are able to ensure a high quality sensor operation
for the entire life of the sensor, the maximum life time of the sensor is typically
determined on a statistical basis so that the risk of a sensor breakage or wear out during
the pre-set and fixed life time is low enough in order not to risk patient safety. This also
means that the safety margin, i.e. the time between the pre-set maximum life time and
the real life time of the sensor is rather long for the majority of sensors. That is, most
sensors are discarded even if there would be a considerable amount of life time left at
the time of discard. The drawback is emphasized in environments where favorable
conditions and good equipment care prolong the life of the sensor.
Consequently, the requirement of patient safety generally and inevitably
translates into a shortened life time of the sensor, which means that the end user cannot
get a maximal utility out of the sensor.
Brief Description of the Invention
The above-mentioned problem is addressed herein which will be
comprehended from the following specification. In the disclosed solution, history data
of one or more parameters measured from the sensor islare used to evaluate the degree
of degradation of the sensor during the usefbl operating life of the sensor. Based on the
evaluation, an early warning of an imminent breakage or wear out of the sensor may be
given to the end user. Further, the end user can get maximal utility of the sensor
without compromising patient safety, since the remaining life time of the sensor may
now be adjusted according to the actual condition of the sensor. The history data may
comprise, for example, parameter values or statistical variables derived from the
parameter values.
In an embodiment, a method for monitoring degradation of a physiological
sensor comprises collecting history data for at least one sensor feature parameter into a
predetermined memory location, wherein the collected history data is indicative of past
characteristics of a physiological sensor, retrieving the history data from the
predetermined memory location when the physiological sensor is connected to a patient
monitor, wherein the retrieving is performed by the patient monitor, and determining,
based on the history data, a degradation measure for the physiological sensor, wherein
the degradation measure is indicative of a degree of degradation of the physiological
sensor and wherein the determining is carried out in the patient monitor.
In another embodiment, a patient monitor for monitoring a subject comprises
a data retrieval unit configured to retrieve history data of at least one sensor feature
parameter from a predetermined memory location, wherein the history data is indicative
of past characteristics of a physiological sensor connected to the patient monitor, and a
degradation determination unit configured to determine, based on the history data, a
degradation measure for the physiological sensor, wherein the degradation measure is
indicative of a degree of degradation of the physiological sensor connected to the
patient monitor.
In a further embodiment, a physiological sensor attachable to a subject for
acquiring a physiological measurement signal from the subject comprises a sensor
element unit configured to output an electrophysiological signal, a sensor memory
storing history data for at least one sensor feature parameter, wherein the history data is
indicative of past characteristics of a physiological sensor, and a memory access
interface for enabling a patient monitor operably connected to the sensor to retrieve the
history data for determination of a degradation measure for the physiological sensor,
wherein the degradation measure is indicative of degree of degradation of the
physiological sensor.
In a still further embodiment, a patient monitor system for monitoring a
subject comprises a memory storing history data for at least one sensor feature
parameter, wherein the history data is indicative of past characteristics of a
physiological sensor, a data retrieval unit configured to retrieve the history data from
the memory when the physiological sensor is connected to a patient monitor, and a
degradation determination unit configured to determine, based on the history data, a
degradation measure for the physiological sensor, wherein the degradation measure is
indicative of a degree of degradation of the physiological sensor.
In a yet further embodiment, a computer program product for monitoring
degradation of a physiological sensor comprises a first program product portion
configured to retrieve history data of at least one sensor feature parameter from a
predetermined memory location, wherein the history data is indicative of past
characteristics of a physiological sensor connected to the patient monitor, and a second
program product portion configured to determine, based on the history data, a
degradation measure for the physiological sensor, wherein the degradation measure is
indicative of degree of degradation of the physiological sensor.
Various other features, objects, and advantages of the invention will be made
apparent to those skilled in the art from the following detailed description and
accompanying drawings.
Brief Description of the Drawings
FIG. 1 is a block diagram illustrating an embodiment of a patient monitor
system;
FIGS. 2 and 3 illustrate an embodiment of a sensor validation mechanism;
FIG. 4 shows an example of the determination of a measure of sensor
degradation;
FIG. 5 illustrates the determination of one sensor feature parameter;
FIG. 6 illustrates an example of the functional units of the patient monitor in
terms of sensor validation; and
FIG. 7 illustrates another embodiment of the patient monitor system.
Detailed Description of the Invention
FIG. 1 illustrates one embodiment of a sensor and monitor system configured
to detect whether a sensor unit connected to a monitor unit is in order and thus also
acceptable for the measurement to be initiated. The sensor system of FIG. 1 comprises
a monitor unit 100 and a sensor unit 120 attachable to a subject (not shown). The
sensor unit 120 is normally connected to the monitor unit 100 through a cable 130, but
the connection may also be wireless. It is to be noted that the system is here discussed
with respect to one monitor unit 100 and one sensor unit 120 connected to the monitor
unit. However, the entire system typically includes several sensor units 120 and one or
more monitor units 100. The sensors that can be connected to one patient monitor may
be of different types and one sensor may be used in one or more monitors.
The monitor unit 100 may be conceived to comprise three basic elements: a
computerized control and processing unit 101, which may be a microcontroller or a
microprocessor unit; a memory 102 for the control and processing unit; and a user
interface 103, which typically comprises a display 104 and one or more user input
devices 105.
A reception branch 110 of the monitor unit is adapted to receive
electrophysiological signals from the sensor. The reception branch typically comprises
an input amplifier, a filter, and an A/D converter (not shown). The digitized signals
output from the AID converter are supplied to the control and processing unit 101,
which processes the signal data and displays the analysis results on the screen of the
display. For optical sensors, for example, the sensor may further include a transmitter
branch comprising a drive unit 1 1 1 for driving the light sources, such as LEDs, of the
sensor.
The memory of the control and processing unit holds the measurement
algorithm(s) 106 needed to process the data received from the sensor unit.
'IL
The sensor unit of FIG. 1 comprises a sensor element unit 121 and a sensor
memory 122. The sensor element unit may comprise an array of light sources combined
with at least one photo detector or an array of electrodes that may be attached onto the
skin of the subject. The sensor memory 122 may be a generic memory from which the
monitor may read data and into which the monitor may write data through a memory
access interface 123. The sensor memory may thus be a plain (non-volatile) memory
with no customized areaslparts, associated intelligence, or data processing capability.
The memory may be, for example, an EEPROM or an EPROM memory. The memory
holds history data 124 for one or more sensor-specific sensor feature parameters
measured from the sensor. The sensor feature parameter is a parameter which is
indicative of a given feature related to the condition of the sensor, and which may be
used as an evaluation tool for evaluating the degradation of the sensor. As discussed
below, in case of an optical sensor the sensor feature parameter may represent, for
example, the ratio (rCTR) of two current transfer ratios (CTRs) of the sensor. The
history data may include degradation reference data 125 indicative of the condition of
the sensor at one or more earlier time instants, i.e. the reference data defines the
reference condition against which the current condition of the sensor may be compared
to find out the degree of degradation of the sensor. For example, the history data may
indicate the condition of the sensor as it was initially in the manufacturing stage of the
sensor. This verified initial condition may deviate from the desired initial condition of
the sensor.
The sensor memory may further hold sensor life expectancy data 126 that
may be indicative of the remaining life time of the sensor. The life expectancy data may
be updated in the course of time according to the degree of degradation determined for
the sensor.
In addition to the measurement algorithm(s), the memory 102 of the control
and processing unit holds a sensor validation algorithm 107 that is executed by the
control and processing unit when a sensor unit 120 is connected to the monitor unit
100. The validation algorithm is configured to employ the history data 124 to make a
decision on the acceptability of the sensor. For this, the validation algorithm may
calculate a degradation measure indicative of the degree of degradation of the sensor.
The validation algorithm may also be configured to update the history data and the life
expectancy data stored in the sensor. The update may be carried out based on the
degradation measure determined.
In a further embodiment, the sensor system may also comprise a sensor
check device 140, which is a device to which the sensor unit 120 may be connected to
aid the measurement of the sensor feature parameters. For example, the device may be
configured to direct the light beams of a reflectance sensor to the photo detector.
FIG. 2 and 3 illustrate an embodiment of a sensor validation method. FIG. 2
illustrates the steps carried out before the sensor is taken into use, while FIG. 3
illustrates the steps carried out by the control and processing unit 101 of the patient
monitor when a sensor is connected to the monitor. The steps of FIG. 2 may be carried
out in the manufacturing phase of the sensor or in connection with the first use of the
sensor, prior to the actual use of the sensor.
The steps carried out prior to the use of the sensor include the determination
of initial value(s) for one or more sensor feature parameter(s) at step 201. The sensor
feature pararneter(s) serve(s) as indicator(s) of sensor wear. The initial value(s) islare
stored into the sensor memory as reference data for hture evaluation of sensor
degradation (step 202). That is, the initial value(s) define(s) a reference level by which
the sensor degradation may be evaluated. This reference data forms the basis of the
history data stored in the sensor. The sensor-specific reference level may deviate from
the desired initial condition of the sensor, which is normally common for all sensors of
the same type. During subsequent use of the sensor, cf. FIG. 3, the history data is
augmented to enable the patient monitor to evaluate the degree degradation based on
up-to-date history data. That is, the history data may be collected by several different
entities over time.
The steps carried out prior to the commissioning of the sensor may also
include storing sensor life expectancy data in the sensor memory (step 203). The life
expectancy data may be indicative of the remaining life time of the sensor, such as
remaining usage time or number of usage times left. If the sensor leaves the factory
with parameters that are inferior to the desired initial state, but good enough to
guarantee enough operating hours, the initial life expectancy may be accordingly
shorter. During the use of the sensor, the life expectancy data may be updated according
to the determined degree of degradation.
Steps 201 to 203 may be carried out by any suitable measuring device used
in the manufacturing phase of the sensor to monitor the quality of the sensor. This
measuring device may be, for example, a monitor or a device that comprises the
measuring units of a patient monitor, since the patient monitor is configured to
determine the sensor feature parameter in order to find out the degree of degradation.
With reference to FIG. 3, during use the control and processing unit of the
patient monitor constantly monitors whether or not a sensor is connected to the monitor
unit (step 301). Upon detecting that a sensor is connected to the monitor unit (step
30l/yes), the control and processing unit retrieves the history data of the sensor feature
parameter(s) from the sensor memory (step 302). The control and processing unit then
determines (step 303) the sensor feature parameter(s) from the sensor. That is, in step
303 the control and processing unit measures the parameter(s) similarly as the
parameter(s) islare measured in step 201. Based on the current value(s) and the
retrieved history data, the control and processing unit then determines in step 304 a
sensor degradation measure indicative of the degree of degradation of the sensor. Based
on the measure, the control and processing unit may further determine a degradation
status for the sensor (step 305). The degradation measure is typically a number that
indicates how far the current parameter value(s) measured in step 302 islare from the
respective initial value(s) measured in step 201. The degradation status is typically a
plain language status that discloses the current condition of the sensor to the end user.
The degradation status may be, for example, "failed", "in order", or "sensor degrades
after 30 operating hours". That is, the degradation status may indicate the usability
status or the life expectancy of the sensor. For estimating the current life expectancy of
the sensor at step 305, the control and processing unit may retrieve the life expectancy
data from the sensor. It is also possible that both the usability status and the life
expectancy of the sensor are determined.
If the sensor is aged, the degradation status is "failed" and the measurement
is rejected (steps 306 and 307). If the sensor is still usable, the measurement is allowed
(step 308). Further, the history data and the life expectancy data are updated and the
user may be informed of the usability status andfor the remaining life time of the
sensor.
In one embodiment, the sensor is checked only at the beginning of each
measurement session. However, in another embodiment the above operation may
continue as a background process during the actual measurement, thereby to detect if
the sensor degrades during a measurement session. This is illustrated as a dotted arrow
309 in the figure.
In one embodiment, no initial history data, i.e. degradation reference data, is
determined in the manufacturing stage, but the sensor memory is left empty. Instead,
the degradation reference data may be determined and stored when the sensor is used
for the first time. The degradation reference data may also be determined within a
certain longer time period since the first use of the sensor, as an average of several
measurements, for example. In a hrther embodiment, the sensor validation process
may write, at step 307, a reject code into the sensor memory or deletelerase the sensor
memory to ensure that the sensor is removed from use.
In a stripped embodiment, only the degradation measure may be determined
and displayed to the user. The measure may be adjusted to a predetermined scale to be
informative. If the measure reaches a given threshold, the measurement is rejected.
FIG. 4 illustrates an example of the determination of the degradation
measure. It is assumed here that two sensor feature parameters are used. The parameter
values obtained are mapped into a two-dimensional parameter space 41, such as an XY
coordinate system where the x-axis represents the first parameter and the y-axis the
second parameter (or vice versa). The data point defined by the initial values of the two
parameters is denoted with a black dot 42. If the data point obtained in step 304 is
outside an acceptable area 43, the sensor is regarded as "failed" in step 305. In the
opposite case, the life expectancy of the sensor may be defined based on the distance of
the data point from the fixed reference point 42. In the course of time, the data point
obtained for a sensor may move as illustrated by small circles and an arrow.
The sensor feature parameter is typically a parameter that the monitor
determines during normal use of the sensor. Further, the sensor feature parameter is
typically a continuous value parameter. For example, in case of an optical sensor, the
current transfer ratio (CTR) or the ratio of two current transfer ratios (rCTR) may be
used as a sensor feature parameter indicative of sensor wearldegradation. CTR indicates
the ratio of the detector output current to the LED input current for a LEDIdetector pair
when the input current is supplied to the LED and LED light is directly visible to the
detector. Consequently, one or more CTRs or rCTRs may be determined in step 201
and stored in step 202 in the sensor memory. The number of CTRs or rCTRs
determined and stored may depend on the number of wavelengths (LEDs) in the sensor.
The CTR may be measured when the sensor is off the measurement site (finger or ear)
or in sensor calibration mode of the monitor.
Another sensor feature parameter that may be used, provided that the monitor
is equipped with the necessary measurement hardware, is forward voltage (also termed
forward voltage drop), which is the voltage drop across a LED when current is flowing
through the LED. This voltage is indicative of overheating and LED wavelength shift
and thus also of wear of the optical components. In addition, the LED voltage may be
determined as a function of LED current. This ramp may be indicative of increased
resistance in sensor wirings or of bad bonding of the LED on the substrate.
FIG. 5 illustrates one embodiment of the determination of forward voltage.
In this embodiment, different currents are supplied to a LED and the corresponding
voltages are measured. As a result, several data points 50 are obtained. Based on the
data points a straight line 5 1 is fitted through the data points. The voltage value that the
line approaches when current approaches zero then indicates the forward voltage. Thus,
in this embodiment, the monitor is configured to measure the voltage over and the
current through desired LEDs.
A firther possible feature parameter is a temperature difference determined
based on the resistance of a thermistor used in the sensor. That is, the behavior of a
thermistor as part of the thermodynamical system of the sensor can be utilized to
determine sensor degradation. The resistance of the sensor thermistor is measured in an
initial "cool" state and then in a "warm" state after the sensor has been used so that
stable state has been reached. If the sensor or the thermistor is not damaged, the
temperature change, i.e. the temperature difference between "warm" and "cool" states,
of the sensor should be substantially the same as initially measured in the
manufacturing phase or prior to the use of the sensor.
The sensor feature parameter may also be an integer-valued parameter or a
Boolean parameter. An integer-valued parameter may indicate, for example, the
number of faulty probe or intermittent sensor fault messages received in a time
window, if the monitor is provided with sensor diagnostics that monitors faults in
sensor operation.
If only one sensor feature parameter is used, the degradation measure may be
obtained as the difference of the initial and current values of the parameter. However,
history data stored does not necessarily comprise parameter values (provided with time
stamps), but statistical variables derived from historical parameter values, such as mean
values and standard deviation values of the parameter(s) may be stored instead of plain
parameter values. In this case the sensor may be rejected when the mean value of a
parameter or the standard deviation of the parameter reaches a respective limit. The
sensor may also be rejected, if the parameter value distribution exceeds certain
normality limit. For example, the sensor may be rejected when the history parameter
values distribute such that the relative portion of the data points further than one
standard deviation away from the mean is more than 16%. If multiple parameters are
used, the history data stored may cover different time lengths for different parameters.
Since the memory size of a cost-effectively implemented sensor is rather limited,
typically around 1000 bits, the history data stored in the memory may be in compressed
form. In one embodiment, the history data may comprise the following items: initial
value(s) of the sensor feature parameter(s), current value(s) of the sensor feature
parameter(s), mean of all previously measured values, standard deviation of all
previously measured values, and number usage times. The last item enables the update
of the mean and standard deviation based on the newest data.
The history data parameters may also be grouped into sets that reflect the
degradation of a certain element in the sensor. For example, such data sets may be
formed to monitor the degradation of the red LED, infrared LED, or the cable or
connector, separately. For monitoring the red LED life expectancy the history data
parameters may comprise the red LED forward voltage, the red LED CTR and the red
LED internal resistance, which can be determined from the red LED forward voltage
measurement as a linear slope of the current-voltage relationship. On the other hand,
for evaluating the condition of the cable lead and the connection, the monitor may
count the number of short andlor open conditions or the number of "Faulty Probe"
messages in a pre-determined time interval. The sensor may be rejected when one or
more of the sensor elements show an unacceptable condition.
In the above embodiments, the decision on the acceptability is made based
on the history data and the current value(s) of the sensor feature parameter(s). However,
the decision may also be made based on the history data only, especially if the history
data is updated at the end of each measurement session to provide up-to-date history
data for the next measurement session. It is also possible that the control and processing
unit measures the current value(s) conditionally. If the history data indicates that the
sensor is in good condition, the measurement of the current value(s) may be omitted at
the beginning of a measurement session. However, if the history data indicates that the
sensor is near to the end of its life time, the current value(s) may be measured to get a
more accurate view of the current condition of the sensor.
The control and processing unit, which is adapted to execute the sensor
validation algorithm, may thus be seen, in terms of the sensor validation, as an entity of
different operational modules or units, as is illustrated in FIG. 6. A data retrieval unit
61 is configured to retrieve the history data of the sensor feature parameter(s) in
response to the connection of the sensor to the monitor, while a sensor feature
determination unit 62 is configured to measure the current value(s) of the sensor feature
parameter(s) from the connected sensor, thereby to obtain up-to-date data of the
condition of the sensor. As indicated above, the current value(s) may be measured in
different stages of a measurement session. A degradation determination unit 63 is
configured to determine the degradation measure of the sensor.
A decision-making unit 64 is further configured to make decision on the
acceptability of the sensor and thus also on the permission/prohibition of the use of the
sensor. The life expectancy, i.e. the remaining life time, may be determined in unit 63
or in separate unit 65 to which the degradation measure is supplied. The decision on the
acceptability of the sensor may be made based on the degradation measure or based on
the remaining life time. In the stripped embodiment, units 64 and 65 may be omitted.
The update functionality may be regarded as a fbnction of a separate update unit 66,
which is configured to update the history data and possibly also the life expectancy
data.
The unit configured to determine the life expectancy may comprise an
autoregressive model, for example. An effective autoregressive model may be created
by collecting a large data set of the sensor history parameters for hundreds of sensors at
different degradation phases. The autoregressive model is then trained to predict the
expected remaining life time of the sensors using the sensor parameter values as
independent variables in the model. The model may be created for predicting the
remaining life time for a certain sensor component or for the whole sensor.
In the disclosed solution, sensor feature parameter values are used in a novel
manner to increase the life of a sensor without compromising patient safety. The sensor
feature parameter(s) may be parameter(s) that islare measured during normal
measurement mode of the monitor, such as forward voltage discussed in connection
with FIG. 5. In this way, no additional hardware or software is needed in the monitor to
determine the parameter value(s) from the sensor, cf. step 302. Based on the sensor's
degree of degradation, an early warning of an imminent breakage or wear out of the
sensor may be given to the end user. Further, the remaining life time of the sensor may
be adjusted according to the actual condition of the sensor, thereby to obtain maximal
utility. Moreover, the end user may adjust, based on the evaluation feedback, hisher
operating habits so as to extend the life time of the sensor.
In the above embodiments, the necessary information for the sensor
evaluation is in the sensor or in the patient monitor, or distributed between the sensor
and the monitor. However, at least part of the necessary information may also be stored
in an external host memory that may be accessed by several monitors through the
network. As is shown in FIG. 7, the host memory 701 may be in conjunction with a
network element, such as a database server 702, through which the host memory may
be accessed by a plurality of monitor units connected to the same network 703 as the
server. The network may be a local area network, such as a hospital network, a wide
area network, or the Internet, for example. Each monitor unit is provided with a
network interface 704 and a suitable transmission protocol for reading from the host
memory 701. In these embodiments, the sensor memory 122 may include a sensor
identifier 724 that identifies the sensor connected to the patient monitor. Based on the
sensor identifier 724, the patient monitor may retrieve the necessary history data 124
from the host memory 701. The manufacturing process 730 may store the sensor
identifier and the initial reference data in the host memory locally or through the
network, depending on the locations of the host memory and the manufacturing
process. Alternatively, this may be carried out by the patient monitor when the sensor is
used for the first time.
A conventional patient monitor may also be upgraded to enable evaluation of
sensor degradation according to the above mechanism. Such an upgrade may be
implemented, for example, by delivering to the control and processing unit a software
unit that includes the entire software system or desired parts thereof. Consequently, the
sofhvare unit comprises at least a first program product portion configured to retrieve
history data of at least one sensor feature parameter from a predetermined memory
location and a second program product portion configured to determine, based on the
history data, a degradation measure for the physiological sensor. The software unit may
also comprise a third program product portion configured to define at least one current
value respectively for the at least one sensor feature parameter and update the history
data by the at least one current value.
This written description uses examples to disclose the invention, including
the best mode, and also to enable any person skilled in the art to make and use the
invention. The patentable scope of the invention is defined by the claims, and may
include other examples that occur to those skilled in the art. Such other examples are
intended to be within the scope of the claims if they have structural or operational
elements that do not differ from the literal language of the claims, or if they have
structural or operational elements with insubstantial differences from the literal
language of the claims.
List of Reference Numbers
Monitor unit
Control and processing unit
Memory
User interface
Display
Input device
Measurement algorithrn(s)
Sensor validation algorithm
Reception branch
Drive unit
Sensor unit
Sensor element unit
Sensor memory
Sensor memory access interface
History data
Sensor degradation reference data
Sensor life expectancy data
Sensor cable
Sensor check device
Determination of initial value(s)
Storing of sensor degradation reference data
Storing of sensor life expectancy data
Detection of connected sensor
Retrieval of history data
Determination of sensor feature parameter(s)
Determination of sensor degradation measure
Determination of sensor degradation status
Degradation status check
Rejection of sensor/measurement
Allowing of measurement, history data update
Two-dimensional parameter space
Initial data point
Acceptable are in parameter space
Data points
Fitted line
Data retrieval unit
Sensor feature determination unit
Degradation determination unit
Decision-making unit
Life expectancy determination unit
Update unit
Host memory
Database server
Network
Network interface
Sensor identifier
Manufacturing process

1. A method for monitoring degradation of a physiological sensor, the method
comprising:
- collecting (202; 308) history data (124) for at least one sensor feature
parameter into a predetermined memory location (122; 701), wherein the collected
history data is indicative of past characteristics of a physiological sensor (120);
- retrieving (302) the history data from the predetermined memory location
when the physiological sensor is connected to a patient monitor (loo), wherein the
retrieving is performed by the patient monitor; and
- determining (304), based on the history data, a degradation measure for the
physiological sensor, wherein the degradation measure is indicative of a degree of
degradation of the physiological sensor and wherein the determining is carried out in
the patient monitor.
2. The method according to claim 1, further comprising defining (303) at least
one current value respectively for the least one sensor feature parameter and updating
the history data by the at least one current value, wherein the defining and updating are
performed by the patient monitor.
3. The method according to claim 1, wherein the collecting comprises
collecting the history data into the predetermined memory location, in which the
predetermined memory location is in a memory (122) of the physiological sensor (1 20).
4. The method according to claim 1, wherein the collecting comprises
collecting the history data, in which the history data includes sensor degradation
reference data determined prior to use of the physiological sensor.
5. The method according to claim 1, further comprising determining (305) life
expectancy of the physiological sensor and informing a user of the patient monitor of
the life expectancy determined.
6. A patient monitor for monitoring a subject, the patient monitor comprising:
- a data retrieval unit (101; 61) configured to retrieve history data of at least
one sensor feature parameter from a predetermined memory location (122; 701),
wherein the history data is indicative of past characteristics of a physiological sensor
(1 20) connected to the patient monitor (1 00); and
- a degradation determination unit (101; 63) configured to determine, based
on the history data, a degradation measure for the physiological sensor, wherein the
degradation measure is indicative of a degree of degradation of the physiological sensor
connected to the patient monitor.
7. The patient monitor according to claim 6, further comprising
- a sensor feature determination unit (101; 62) configured to define at least
one current value respectively for the at least one sensor feature parameter; and
- an update unit (1 01 ; 66) configured to update the history data by the at least
one current value.
8. The patient monitor according to claim 6, wherein the degradation
determination unit (101 ; 63) is further configured to
- derive a degradation status from the degradation measure, wherein the
degradation status discloses the sensor's condition in plain language; and
- inform a user of the degradation status.
9. The patient monitor according to claim 8, further comprising a decisionmaking
unit (101; 64) configured to decide, based on one of the degradation measure
and the degradation measure, on acceptance of the physiological sensor.
10. The patient monitor according to claim 6, wherein the patient monitor is
further configured to
- determine life expectancy of the physiological sensor based on the
degradation measure; and
- inform a user of the patient monitor of the life expectancy.
1 1. The patient monitor according to claim 10, the patient monitor comprises
a predefined model configured to predict the life expectancy.
12. A physiological sensor attachable to a subject for acquiring a
physiological measurement signal from the subject, the physiological sensor (120)
comprising:
- a sensor element unit (121) configured to output an electrophysiological
signal;
- a sensor memory (122) storing history data for at least one sensor feature
parameter, wherein the history data is indicative of past characteristics of a
physiological sensor; and
- a memory access interface (123) for enabling a patient monitor (100)
operably connected to the sensor to retrieve the history data for determination of a
degradation measure for the physiological sensor, wherein the degradation measure is
indicative of degree of degradation of the physiological sensor.
13. The physiological sensor according to claim 12, wherein the sensor
memory (122) further stores life expectancy data (126) indicative of remaining life time
of the physiological sensor.
14. The physiological sensor according to claim 12, wherein the history data
includes at least one statistical variable derived from previous value distribution of the
at least one sensor feature parameter.
15. A computer program product for monitoring degradation of a
physiological sensor (120) connected to a patient monitor (loo), the computer program
product comprising:
- a first program product portion configured to retrieve history data of at least
one sensor feature parameter from a predetermined memory location (122; 701),
wherein the history data is indicative of past characteristics of a physiological sensor
connected to the patient monitor; and
- a second program product portion configured to determine, based on the
history data, a degradation measure for the physiological sensor, wherein the
degradation measure is indicative of degree of degradation of the physiological sensor
(120).