U.S. patent application number 10/521024 was filed with the patent office on 2006-07-13 for bed occupant monitoring system.
This patent application is currently assigned to Tactex Controls Inc. Invention is credited to D. Robert Inkster, DavidM Lokhorst.
Application Number | 20060152378 10/521024 |
Document ID | / |
Family ID | 30005554 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060152378 |
Kind Code |
A1 |
Lokhorst; DavidM ; et
al. |
July 13, 2006 |
Bed occupant monitoring system
Abstract
The invention provides a bed occupant monitoring system
comprising a pressure sensitive member attached to a support member
for supporting a bed occupant, the pressure sensitive member
comprising a plurality of pressure sensors. Each of the pressure
sensors is configured to provide a reflected wave energy pressure
signal by reflecting incident wave energy with an intensity which
varies with a pressure applied to the sensor. A pair of fibres are
coupled to each pressure sensor, each pair of fibres comprising an
input fibre and an output fibre. The fibres are coupled to
interface electronics comprising a wave energy source coupled to
the input fibre of each of the pairs of fibres for providing the
applied light energy, and, a wave energy detector coupled to the
output fibre of each of the pairs of fibres for converting the
scattered light energy into an electrical signal.
Inventors: |
Lokhorst; DavidM; (Victoria,
CA) ; Inkster; D. Robert; (Victoria, AU) |
Correspondence
Address: |
OYEN, WIGGS, GREEN & MUTALA LLP;480 - THE STATION
601 WEST CORDOVA STREET
VANCOUVER
BC
V6B 1G1
CA
|
Assignee: |
Tactex Controls Inc
Victoria
CA
V9A 3K5
|
Family ID: |
30005554 |
Appl. No.: |
10/521024 |
Filed: |
July 17, 2003 |
PCT Filed: |
July 17, 2003 |
PCT NO: |
PCT/CA03/01081 |
371 Date: |
August 3, 2005 |
Current U.S.
Class: |
340/666 |
Current CPC
Class: |
G08B 21/22 20130101;
G08B 21/0446 20130101; A61B 5/6892 20130101; A61B 2562/0247
20130101; A61B 5/11 20130101; A61B 2562/0233 20130101; A61B 5/447
20130101; G08B 21/0461 20130101; A61B 2562/223 20130101; A61B
5/7239 20130101; A61B 2562/046 20130101; A61B 5/113 20130101; A61B
5/0205 20130101; A61B 5/1102 20130101; G08B 21/0453 20130101 |
Class at
Publication: |
340/666 |
International
Class: |
G08B 21/00 20060101
G08B021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 17, 2002 |
CA |
2393880 |
Claims
1. A bed occupant monitoring system comprising: (a) a pressure
sensitive member coupled to a support member for supporting a bed
occupant, the pressure sensitive member comprising a plurality of
pressure sensors, each of the pressure sensors configured to
provide an optical pressure signal having an intensity which varies
with a pressure applied thereto; (b) at least one wave energy
source coupled to the plurality of pressure sensors for providing
wave energy to the plurality of pressure sensors; and, (c) at least
one wave energy detector coupled to the plurality of pressure
sensors for converting the optical pressure signals into electrical
pressure signals.
2. A bed occupant monitoring system according to claim 1 comprising
interface electronics with threshold circuitry for comparing the
electrical pressure signals to a predetermined threshold.
3. A bed occupant monitoring system according to claim 2 wherein
the threshold circuitry comprises a threshold comparer for
determining if the electrical pressure signals are below the
predetermined threshold.
4. A bed occupant monitoring system according to claim 3 wherein
the threshold circuitry further comprises a threshold crossing
detector configured to reset a timer when the electrical pressure
signals cross the predetermined threshold.
5. A bed occupant monitoring system according to claim 4 further
comprising an alarm signal generator coupled to the timer and the
threshold comparer by means of an AND gate, the alarm signal
generator configured to generate an alarm signal if the timer is
not reset for a predetermined time period and the electrical
pressure signals are below the predetermined threshold.
6. A bed occupant monitoring system according to claim 1 comprising
a signal concentrator connected to receive a plurality of the
electrical pressure signals and to output a combined signal
indicative of a property of said plurality of the electrical
pressure signals.
7. A bed occupant monitoring system according to claim 1 comprising
a signal concentrator connected to receive a plurality of the
optical pressure signals and to output a combined optical signal
indicative of a property of said plurality of the optical pressure
signals to the at least one wave energy detector.
8. A bed occupant monitoring system according to claim 1 wherein
the pressure sensitive member comprises a top foam layer and a
bottom foam layer, and wherein each pressure sensor comprises a
pair of optical fibres having ends between the top foam layer and
the bottom foam layer, each pair of optical fibres comprising an
input fibre coupled to the wave energy source and an output fibre
coupled to the wave energy detector.
9. A bed occupant monitoring system according to claim 1 wherein
the pressure sensitive member is constructed from a compressible
material, and wherein each pressure sensor comprises a pair of
optical fibres having ends within the compressible material, each
pair of optical fibres comprising an input fibre coupled to the
wave energy source and an output fibre coupled to the wave energy
detector.
10. A bed occupant monitoring system according to claim 9 wherein
the support member is constructed from a compressible material
having an elastic modulus which is substantially the same as an
elastic modulus of the compressible material of the pressure
sensitive member.
11. A bed occupant monitoring system according to claim 1 wherein
the pressure sensitive member comprises an area of a mattress
constructed from a compressible material, and wherein each pressure
sensor comprises a pair of optical fibres having ends within the
compressible material, each pair of optical fibres comprising an
input fibre coupled to the wave energy source and an output fibre
coupled to the wave energy detector.
12. A bed occupant monitoring system according to claim 1 wherein
each of the pressure sensors is responsive to pressure in a range
of 1 to 15 mmHg.
13. A bed occupant monitoring system according to claim 1 wherein
the wave energy source is coupled to the plurality of pressure
sensors by means of optical fibres.
14. A bed occupant monitoring system according to claim 1 wherein
the wave energy detector is coupled to the plurality of pressure
sensors by means of optical fibres.
15. A bed occupant monitoring system according to claim 1
comprising an indicator device.
16. A bed occupant monitoring system according to claim 1 wherein
the wave energy detector comprises a photodetector.
17. A bed occupant monitoring system according to claim 16 wherein
the photodetector comprises an array of photo-diodes, and wherein
each of the photo-diodes is coupled to one of the plurality of
pressure sensors by means of an optical fibre.
18. A bed occupant monitoring system according to claim 1 wherein
the support member comprises a mattress, and the pressure sensitive
member is positioned atop the mattress.
19. A bed occupant monitoring system according to claim 1 wherein
the support member comprises a mattress, and the pressure sensitive
member is positioned below the mattress.
20. A bed occupant monitoring system according to claim 1 wherein
the support member comprises a mattress, and the pressure sensitive
member is positioned within a cavity in the mattress.
21. A bed occupant monitoring system according to claim 1 wherein
the support member comprises a mattress, and the pressure sensitive
member is positioned in a recess near a top of the mattress, such
that a top surface of the pressure sensitive member is flush with a
top surface of the mattress.
22. A bed occupant monitoring system according to claim 1 wherein
the support member comprises a mattress, and the pressure sensitive
member is positioned in a recess near a bottom of the mattress,
such that a bottom surface of the pressure sensitive member is
flush with a bottom surface of the mattress.
23. A bed occupant monitoring system according to claim 1 wherein
the plurality of pressure sensors are arranged in an array across a
width of the support member, comprising signal processing means for
determining a position of the occupant on the support member.
24. A bed occupant monitoring system according to claim 23 wherein
the plurality of pressure sensors are arranged into a central group
and two side groups, with the side groups positioned adjacent to
edges of the support member and the central group positioned
therebetween, and wherein the signal processing means are
configured to calculate a total applied pressure for each
group.
25. A bed occupant monitoring system according to claim 1 further
comprising an opaque covering material for shielding the pressure
sensors from ambient light.
26. A bed occupant monitoring system according to claim 8 further
comprising a protective sheath covering the optical fibres between
the pressure sensitive member and the interface electronics.
27. A method of monitoring a bed occupant occupying a bed with a
pressure sensitive member coupled thereto, the pressure sensitive
member comprising a plurality of pressure sensors, each of the
pressure sensors configured to provide a reflected wave energy
pressure signal by reflecting incident wave energy with an
intensity which varies with a pressure applied thereto, the method
comprising: (a) applying wave energy to the pressure sensors; and,
(b) measuring pressure signals received from the pressure sensitive
member.
28. A method according to claim 27 comprising processing the
measured pressure signals by taking a sum of a time derivative of
the absolute values of the pressure signals.
29. A method according to claim 27 comprising processing the
measured pressure signals by taking a sum of a time derivative of
the pressure signals.
30. A method according to claim 27 comprising processing the
measured pressure signals by taking a sum of a time derivative of
the squared pressure signals.
31. A method according to claim 27 comprising comparing the
measured pressure signals to a predetermined threshold.
32. A method according to claim 31 comprising generating an alarm
signal if the measured pressure signals remain below the
predetermined threshold for a predetermined time period.
33. A method according to claim 32 wherein the predetermined
threshold and predetermined time period is set in relation to an
expected heat beat pressure signal.
34. A method according to claim 32 wherein the predetermined
threshold is set in relation to an expected pulmonary pressure
signal.
35. A method according to claim 32 wherein the predetermined
threshold is set in relation to an expected bodily movement
pressure signal.
36. A method according to claim 27 comprising computing a heart
rate of the bed occupant from the measured pressure signals.
37. A method according to claim 27 comprising computing a
respiration rate of the bed occupant from the measured pressure
signals.
38. A bed occupant monitoring system comprising: (a) a pressure
sensitive member coupled to a support member for supporting a bed
occupant, the pressure sensitive member comprising a plurality of
pressure sensors; (b) interface electronics coupled to the pressure
sensors for producing at least one pressure signal; and, (c)
threshold circuitry for comparing the pressure signals to a
predetermined threshold.
39. (canceled)
40. (canceled)
Description
TECHNICAL FIELD
[0001] This invention relates to monitoring the health and/or
activity of a person occupying a bed. This invention provides a
novel system comprising a pressure sensitive member coupled to
interface electronics.
BACKGROUND
[0002] It is known to use sensors coupled to a mattress for
monitoring a bed occupant. For example, Triplett et al. (U.S. Pat.
No. 4,175,263) disclose a pressure sensing mechanism for placement
on a hospital bed. The pressure sensing mechanism comprises a first
pressure sensing pad for sensing a patient's weight when the
patient is near the centre of the bed, and a second pressure
sensing pad for sensing the patient's weight when the patient is
near the edges of the bed. An alarm may be triggered when the
patient moves to a location near the edge of the bed.
[0003] Tucknott et al. (U.S. Pat. No. 4,633,237) disclose a patient
bed alarm system comprising a matrix of sensors woven into a mat
for placement on a bed. The matrix of sensors is coupled to a micro
computer for calculating the position of a patient in the bed. An
alarm may be triggered when the patient is about to leave the
bed.
[0004] Alihanka et al. (U.S. Pat. No. 4,320,766) disclose a
capacitive motion sensor placed under a mattress or the like for
monitoring the movements of a person.
[0005] McMahon et al. (U.S. Pat. No. 5,435,317) disclose a device
for detecting a respiratory dysfunction of a person located in a
bed. The device comprises a detection unit which is provided under
the mattress of the bed, and a stimulation unit, which acts, in
response to a signal from the detection unit, to impart a rocking
motion to the bed. The detection unit is embodied as a pad-like
device provided under the mattress.
[0006] Bellin et al. (U.S. Pat. No. 5,558,996) disclose a patient
monitoring device wherein sensors are located in a bed sheet with
which a subject comes in contact. One sensor produces a signal
corresponding to respiratory induced, pulmonary motion, and
myocardial pumping sounds. A second sensor produces a signal
corresponding to changes in body position. A processor amplifies
and filters the induced signals resulting in resolved output highly
correlated to respiration rate, heart beat rate, and changes in
body position.
[0007] Reimer et al. (U.S. Pat. No. 5,917,180) disclose a pressure
sensor which relies on detecting multiply scattered light within an
optical cavity. Changes in the volume of the cavity are sensed by
the change in sampled light intensity. Pressure sensitive mats with
a high density of sensors are assembled using optical fiber
technology.
[0008] Musick (U.S. Pat. No. 5,844,488) discloses a narrow,
pressure-sensitive sensor pad for installation on top of and across
the width of a mattress proximate the midsection of a reclining
patient. The pad has both central and edge switching areas. The
central pressure sensitive switch indicates the presence of a
patient in the center of the bed. When a patient moves toward
either edge of the bed, an edge switch is activated which generates
an early warning signal indicating to attending personnel that a
patient has moved from the center of the bed to an edge and may be
attempting to exit the bed unattended.
[0009] Hammett (U.S. Pat. No. 5,144,284) discloses a bed covering
device adapted to cover a mattress. The device has compliant flat
pressure sensitive means disposed its lower surface for detecting
compressive force exerted by a person, and electrical connector
means emergent from the pressure sensitive means and configured to
connect in modular fashion with a monitoring device and alarm.
[0010] Rudeke (PCT publication No. WO9010281A1) discloses a bed
alarm intended for use with patients in hospitals and like
establishments for indicating when a patient leaves his or her bed.
The alarm includes a pressure sensor which functions to detect
whether a patient is lying in bed or not and which is intended to
be positioned in the bed and preferably between the bed-bottom and
the mattress.
[0011] Rincoe et al. (U.S. Pat. No. 5,993,400) and Scott (U.S. Pat.
No. 6,067,019) disclose devices that utilize arrangements of
sensors to detect the impending egress of a bed occupant. Joseph et
al. (U.S. Pat. No. 5,410,297) disclose a weight-sensitive
capacitive sensor for tracking the position of an occupant. Dixon
et al. (U.S. Pat. No. 6,208,250) disclose a system comprising two
sensors and a processor used to determine the location of a patient
on a bed.
[0012] Rosenthal (U.S. Pat. No. 3,961,201) discloses a switch
located between a mattress and a bedframe that is used to detect
when a patient moves close to the edge of a bed. Feldl (U.S. Pat.
No. 4,020,482) discloses an air bladder below a mattress that
signals egress of a patient when air pressure in the bladder falls
below a threshold. Nicholas (U.S. Pat. No. 4,381,434) discloses a
device including a spring-loaded plate with a limit switch, all
mounted below a mattress.
[0013] Despite the volume of existing patent literature, there are
significant shortcomings in the known devices. For many devices,
reliable operation requires installation on top of the mattress.
This has two major shortcomings: firstly, the devices are often
stiff (i.e. resistant to flexing) and hard, thereby causing
discomfort to the bed occupant. In some applications (for example,
monitoring of demented occupants) this can cause physical and
psychological irritation to the bed occupant. Secondly, because the
devices are on top of the mattress, they rapidly suffer material
fatigue and fail under normal use.
SUMMARY OF INVENTION
[0014] One embodiment of the invention provides a bed occupant
monitoring system comprising a pressure sensitive member coupled to
a support member for supporting a bed occupant, the pressure
sensitive member comprising a plurality of pressure sensors. Each
of the pressure sensors is configured to provide an optical
pressure signal having an intensity which varies with a pressure
applied thereto. The monitoring system also includes at least one
wave energy source coupled to the plurality of pressure sensors for
providing wave energy to the sensors, and, at least one wave energy
detector coupled to the plurality of pressure sensors for
converting the optical pressure signals into electrical pressure
signals.
[0015] The wave energy source may coupled to the plurality of
pressure sensors by means of optical fibres, and the wave energy
detector may also coupled to the plurality of pressure sensors by
means of optical fibres. An indicator device may be coupled to the
interface electronics.
[0016] The wave energy detector may comprise a photodetector. The
photodetector may comprise an array of photo-diodes, and each of
the photo-diodes may be coupled to one of the plurality of pressure
sensors by means of an optical fibre.
[0017] The interface electronics may further comprise threshold
circuitry for comparing the electrical pressure signals to a
predetermined threshold. The threshold circuitry may comprise a
threshold comparer for determining if the electrical pressure
signals are below the predetermined threshold. The threshold
circuitry may further comprise a threshold crossing detector
configured to reset a timer when the electrical pressure signals
cross the predetermined threshold. The system may further comprise
an alarm signal generator coupled to the timer and the threshold
comparer by means of an AND gate, the alarm signal generator
configured to generate an alarm signal if the timer is not reset
for a predetermined time period and the electrical pressure signals
are below the predetermined threshold.
[0018] The pressure sensitive member may comprise a top foam layer
and a bottom foam layer, and each pressure sensor may be formed by
securing a pair of optical fibres between the top foam layer and
the bottom foam layer, the pair of optical fibres comprising an
input fibre coupled to the wave energy source and an output fibre
coupled to the wave energy detector.
[0019] The pressure sensitive member may comprise an area of a
mattress constructed from a compressible material, and each
pressure sensor may be formed by securing a pair of optical fibres
between the top foam layer and the bottom foam layer, the pair of
optical fibres comprising an input fibre coupled to the wave energy
source and an output fibre coupled to the wave energy detector.
[0020] Each of the pressure sensors may be responsive to pressure
in a range of 1 to 15 mmHg.
[0021] The support member may comprise a mattress, and the pressure
sensitive member may be positioned atop the mattress, below the
mattress, within a cavity in the mattress, in a recess near a top
of the mattress, such that a top surface of the pressure sensitive
member is flush with a top surface of the mattress, or in a recess
near a bottom of the mattress, such that a bottom surface of the
pressure sensitive member is flush with a bottom surface of the
mattress.
[0022] The plurality of pressure sensors may be arranged in an
array across a width of the support member, and the interface
electronics may comprise signal processing means for determining a
position of the occupant on the support member. The plurality of
pressure sensors may be arranged into a central group and two side
groups, with the side groups positioned adjacent to edges of the
support member and the central group positioned therebetween, and
the signal processing means are configured to calculate a total
applied pressure for each group.
[0023] The monitoring system may further comprise an opaque
covering material for shielding the pressure sensors from ambient
light.
[0024] The monitoring system may further comprise a protective
sheath covering the optical fibres between the pressure sensitive
member and the interface electronics.
[0025] Another embodiment of the invention provides a method of
monitoring a bed occupant occupying a bed with a pressure sensitive
member coupled thereto, the pressure sensitive member comprising a
plurality of pressure sensors, each of the pressure sensors
configured to provide a reflected wave energy pressure signal by
reflecting incident wave energy with an intensity which varies with
a pressure applied thereto. The method comprises applying wave
energy to the pressure sensors, and, measuring pressure signals
received from the pressure sensitive member.
[0026] The method may comprise processing the measured pressure
signals by taking a sum of a time derivative of the absolute values
of the pressure signals, taking a sum of a time derivative of the
pressure signals, or taking a sum of a time derivative of the
squared pressure signals.
[0027] The method may comprise comparing the measured pressure
signals to a predetermined threshold. The method may comprise
generating an alarm signal if the measured pressure signals remain
below the predetermined threshold for a predetermined time period.
The predetermined threshold and predetermined time period may be
set in relation to an expected heat beat pressure signal, an
expected pulmonary pressure signal, or an expected bodily movement
pressure signal.
[0028] The method may comprise computing a heart rate of the bed
occupant from the measured pressure signals, and/or computing a
respiration rate of the bed occupant from the measured pressure
signals.
[0029] Another embodiment of the invention provides a bed occupant
monitoring system comprising a pressure sensitive member coupled to
a support member for supporting a bed occupant, the pressure
sensitive member comprising a plurality of pressure sensors,
interface electronics coupled to the pressure sensors for producing
at least one pressure signal; and, threshold circuitry for
comparing the pressure signals to a predetermined threshold.
BRIEF DESCRIPTION OF DRAWINGS
[0030] In drawings which illustrate non-limiting embodiments of the
invention:
[0031] FIG. 1 illustrates schematically an occupant lying in a bed
equipped with a monitoring system according to one embodiment of
the invention;
[0032] FIG. 2 illustrates schematically interface electronics
according to an embodiment of the invention;
[0033] FIG. 3 is a block diagram of some circuit elements of
interface electronics according to another embodiment of the
invention;
[0034] FIG. 4 graphically depicts externally applied pressure over
time for an example situation of a patient occupying a bed equipped
with a monitoring system according to the invention;
[0035] FIG. 5 is a flowchart illustrating a method of monitoring a
bed occupant according to one embodiment of the invention;
[0036] FIG. 6 shows a pressure sensitive member and interface
electronics according to one embodiment of the invention;
[0037] FIG. 7(a) shows a top view of a portion of the pressure
sensitive member of FIG. 2, with the top layer removed;
[0038] FIG. 7(b) is a cross-sectional view of the portion of the
pressure sensitive member of FIG. 3(a), with the top layer
present;
[0039] FIG. 8 is a sectional view of a portion of a mattress with a
pair of fibres inserted therein according to another embodiment of
the invention;
[0040] FIG. 9(a) illustrates an embodiment of the invention wherein
the pressure sensitive member is coupled to the top of a support
member;
[0041] FIG. 9(b) illustrates an alternative embodiment of the
invention wherein the pressure sensitive member is coupled within a
recess in a top surface of the support member;
[0042] FIG. 9(c) illustrates an alternative embodiment of the
invention wherein the pressure sensitive member is coupled within a
cavity within the support member;
[0043] FIG. 9(d) illustrates an alternative embodiment of the
invention wherein the pressure sensitive member is coupled within a
recess in a bottom surface of the support member;
[0044] FIG. 9(e) illustrates an alternative embodiment of the
invention wherein the pressure sensitive member is coupled to the
bottom of the support member; and,
[0045] FIG. 10 illustrates an alternative embodiment of the
invention wherein pressure sensors are arranged into three groups
within the pressure sensitive member.
DESCRIPTION
[0046] Throughout the following description specific details are
set forth in order to provide a more thorough understanding of the
invention. However, the invention may be practiced without these
particulars. In other instances, well known elements have not been
shown or described in detail to avoid unnecessarily obscuring the
present invention. Accordingly, the specification and drawings are
to be regarded in an illustrative, rather than a restrictive,
sense.
[0047] The invention provides apparatus and methods for monitoring
a bed occupant, such as a patient, lying in a bed. Apparatus
according to the invention can facilitate monitoring of the bed
occupant's presence, heart rate, respiration, and/or movement. The
apparatus comprises a pressure sensitive member in the bed coupled
to interface electronics. The pressure sensitive member preferably
comprises an array of pressure sensors which produce signals
representative of the pressures applied to the sensors.
[0048] FIG. 1 is a schematic view of a bed occupant monitoring
system 7 according to one embodiment of the invention. A bed
occupant 6 lies upon a bed which includes a mattress or other
support member 4. Monitoring system 7 includes a pressure sensitive
member 1 on support member 4. Pressure sensitive member 1 is
coupled to interface electronics 2 by signal carriers 8. Signal
carriers 8 may comprise optical fibres, wires or other signal
carriers capable of carrying signals from pressure sensors 5 in
pressure sensitive members 1 to interface electronics 2.
[0049] Interface electronics 2 may be housed in a single enclosure
as illustrated in FIG. 1, or they may be housed in more than one
enclosure connected by signal means (not shown). The signal means
may comprise any suitable signal carriers, for example, one or more
wires, optical signal carriers, wireless connections, or the like.
Optionally, interface electronics 2 comprises an indicator device
3. Indicator device 3 may comprise an visible or audible alarm, a
data display system, an attendant call system, a data logging
system, or the like.
[0050] Pressure sensitive member 1 comprises a plurality of
pressure sensors 5. Each pressure sensor 5 measures the bearing
pressure applied by occupant 6 in proximity thereto. A change in
the bearing pressure results in a change in the output of pressure
sensor 5. Pressure sensors 5 are preferably responsive to pressures
in the range of 1 to 15 mmHg. Pressure sensors 5 preferably
comprise pressure sensors which produce optical output signals.
Most preferably the pressure sensors are optical sensors which do
not require any electrical or electronic devices to be at the
location of the sensor. The term "optical", as used herein, is to
be understood to refer to electromagnetic wave energy of any
wavelength, and not only to those wavelengths which correspond to
the visible spectrum. Optical pressure sensors are advantageous
because they allow monitoring of occupant 6 without the need for
electrical devices in the bed, which may be hazardous.
[0051] Pressure sensors 5 may be constructed in accordance with
U.S. Pat. No. 5,917,180 to Reimer et al., which is hereby
incorporated by reference. Such sensors are available under the
brand name Kinotex.TM. from Tactex Contols Inc. of Victoria,
British Columbia, Canada. Such sensors are particularly
advantageous for bed occupant monitoring as they exhibit a high
level of sensitivity to minor pressure variations over a wide range
of pressure levels. Conventional pressure sensors with comparable
sensitivity typically will be unable to sense minor pressure
variations at elevated pressure levels, such as when a person is
lying or sitting upon them.
[0052] In certain specific embodiments of the invention, each
pressure sensor 5 is configured to reflect incident wave energy
received from interface electronics 2 with an intensity which
varies with a pressure applied to pressure sensor 5. In such
embodiments, signal carriers 8 comprise a plurality of pairs of
fibres, with one pair coupled to each pressure sensor 5. Each
pressure sensor is coupled to interface electronics 2 by an input
fibre 15 (see FIG. 2), which provides incident wave energy, and an
output fibre 14 (see FIG. 2), which transmits reflected wave energy
to interface electronics 2.
[0053] As described in Reimer et al., Kinotex 1 pressure sensors
utilize an optical-to-electronic interface. The
optical-to-electronic interface comprises one or more wave energy
sources, typically light transmitters (such as one or more
light-emitting-diodes) and one or more wave energy detectors,
typically photodetectors (such as one or more photo-diodes or
photo-transistors). Interface electronics 2 includes the optical-to
electronic interface.
[0054] In one embodiment of this invention, the
optical-to-electronic interface comprises one light emitter and one
photodetector, and the interface electronics comprise analog and/or
digital circuit elements configured to provide an output signal
representative of the total pressure applied to pressure sensitive
member 1. In another embodiment, the optical-to-electronic
interface comprises at least one light emitter and more than one
photodetector, and the signal conditioning electronics comprise
analog and/or digital circuit elements configured to provide
multiple output signals representative of the pressures applied to
different regions of the pressure sensitive member, as discussed
below with reference to FIG. 10.
[0055] In another embodiment of the invention, the interface
electronics are configured to measure signals from each of the
pressure sensors individually. Alternatively (or additionally)
further circuit elements may be included to extract other
information from the signals, such as the time-derivative (i.e.
time rate of change) of the signal or a high-pass filter or a
low-pass filter or a notch filter or any combination of the
foregoing. Each of these provides valuable information regarding
the condition of the bed occupant.
[0056] Although it is possible in principle to implement the
invention using entirely analog electronics, it is preferable to
use a combination of analog, optical and digital electronics. The
signal processing function of interface electronics 2 may be
provided in hardware, in software, or in a combination of hardware
and software. Standard signal processing techniques may be used to
increase the signal to noise ratio of such signals and to extract
desired information from the signals.
[0057] As an example of a preferred embodiment, a simplified
schematic illustration of interface electronics 2 is shown in FIG.
2. A microprocessor 32 is coupled to two LED drive circuits 31 that
provide current to two LEDs 30. LEDs 30 provide illumination for
pressure sensors 5. Although two LEDs 30 and LED drive circuits 31
are shown in FIG. 2 for ease of illustration, it is to be
understood that any number of LEDs 30 and drive circuits 31 are
possible. An input fibre 15 provides light energy from LEDs 30 to
each of pressure sensors 5 (not shown in FIG. 2). An output fibre
14 returns light from each pressure sensor 5 (not shown in FIG. 2)
to photodetector 33. Photodetector 33 preferably comprises an array
of photo-diodes, with each receiving fibre 14 being associated with
a specific photo-diode.
[0058] Microprocessor 32 provides control signals 38 that cause
photodetector 33 to output an analog signal 39 corresponding to the
light intensities received from pressure sensors 5. In the
illustrated embodiment, control signals 38 are used to coordinate
the signals being sent from the individual elements of
photodetector 33 to microprocessor 32 when photodetector 33
comprises an array of photo-diodes or other sensors. Alternatively,
photodetector 33 could be configured to provide a separate analog
signal 39 to microprocessor 32 from each element of photodetector
33. In the further alternative, monitoring system 7 could include a
signal concentrator (not shown) which combines signals from two or
more pressure sensors 5 and provides microprocessor 32 with a
signal indicating a property of the combined signals, for example a
signal containing information about an average pressure exerted on
the two or more pressure sensors 5. The signals may be combined
optically, for example by detecting light from multiple pressure
sensors 5 at a single light detector, or may be combined
electronically after having been detected.
[0059] Optionally, analog signal 39 may be amplified, filtered, or
otherwise conditioned by analog circuitry 34. Analog signal 39 is
then converted into digital form by Analog-to-Digital converter 35,
and the sampled signal is read by micro-processor 32.
Microprocessor 32 implements any necessary signal processing, as
described below, and produces output signals 40 via appropriate
driver circuitry 36. Driver circuitry 36 may optionally comprise
well known electronic interfaces such as RS-232, RS-485, Ethernet,
Universal Serial Bus, or the like, or a digitally controlled
driver. Output signal 40 may be passed to an indicator device 3
(not shown in FIG. 2), a remote monitoring station, an automated
alarm system, or the like.
[0060] Monitoring system 7 may be used to monitor various
indications of health of bed occupant 6, including the pulmonary
and/or heart activity of bed occupant 6. Referring again to FIG. 2,
interface electronics 2 may produce an output signal 40
representative of any of the following parameters: the sum of the
time derivative of all pressure signals; the sum of the time
derivative of the squared pressure signals; or, the sum of the time
derivative of the absolute values of the pressure signals. Output
signal 40 may comprise a digital, analog or optical signal. The
inventors have found that the pulmonary activity, heart activity,
and bodily movement of the bed occupant can be determined from
these computed parameters.
[0061] FIG. 3 shows one possible arrangement of functional
characteristics of interface electronics 2. Photodetector 33
provides pressure signals to signal processor 42. Signal processor
42 amplifies, takes the time derivative, or otherwise processes the
pressure signals, and passes them to threshold circuitry 44, and
optionally also to indicator device 3. Threshold circuitry 44
preferably comprises threshold comparer 45, threshold crossing
detector 46, and timer 47. Threshold comparer 45 is configured to
produce a signal indicating when the pressure signals indicate a
pressure below a predetermined threshold. Threshold crossing
detector 46 is configured to reset timer 47 when the pressure
signals cross the threshold. Timer 47 is configured to produce a
high output if allowed to run without for a predetermined time
period without being reset. AND gate 48 is configured to trigger
alarm signal generator 49 when it receives high outputs from both
threshold comparer 45 and timer 47. Threshold circuitry 44 may be
configured to monitor a number of different thresholds, as
described below.
[0062] FIG. 4 is a typical graph 50 of the sum of the derivatives
of the absolute value of the pressure signals generated by a bed
occupant lying in a bed equipped with a monitoring system according
to the invention, plotted against time. Graph 50 is an idealized
representation of pressure signals generated by a pressure
sensitive member 1 located on top of support member 4. The
variations in the pressure signals are typically less pronounced
when the signals are generated by a pressure sensitive member 1
located within or below support member 4, and as such it may be
difficult to determine the heart rate of bed occupant 6, although
pulmonary activity and movement may still be detected, as described
below. It is to be understood that a graph of actual pressure
signals may include more noise than illustrated, but the noise may
be minimized by any suitable noise reduction techniques.
[0063] In graph 50, time is indicated from left to right, along
axis 51. Peaks 53 and 54 correspond to inhaling and exhaling
respectively. The smaller more frequent peaks 55 correspond to heat
beats. The large disturbance 56 corresponds to bodily movement (for
example, when the bed occupant shifts his weight). Movement signals
56 are typically on the order of ten times larger than pulmonary
signals 53 and 54, which are in turn typically on the order of ten
times larger than heart beat signals 55. The pressure signals will
only remain constant if the bed occupant's heart stops beating, the
bed occupant leaves the bed, or there is a malfunction. Interface
electronics 2 may be configured to generate an alarm signal if the
pressure signals remain below a heart beat threshold for a
predetermined period of time selected according to an expected
heart beat frequency, or if the pressure signals remain constant
for a predetermined period of time. Further signal processing can
optionally be performed by signal processing means in interface
electronics 2 to measure the precise rate of respiration and/or the
rate of heart beat from the signal shown in FIG. 4. The signal
processing means may comprise microprocessor 32, a digital signal
processor, and/or noise reduction circuitry.
[0064] In one embodiment of the invention, a pulmonary threshold 57
may be set such that if the signal remains below pulmonary
threshold 57 for a predetermined period of time, output signal 40
includes a pulmonary alarm which indicates the suspension of
pulmonary activity. The predetermined amount of time for the
pulmonary alarm may be set according to an expected respiratory
frequency. Pulmonary threshold 57 may be determined adaptively by
microprocessor 32 based on the pattern of measured pressure
signals, or may be preset when monitoring system 7 is manufactured
and calibrated. Optionally, a user interface (not shown) may be
provided to allow pulmonary threshold 57 and the time period for
the pulmonary alarm to be adjusted to allow for differences in
weights and breathing patterns of different bed occupants.
[0065] In another embodiment, a bodily movement threshold 58 can be
set such that if the signal remains below movement threshold 58 for
a predetermined period of time, output signal 40 includes a
pulmonary alarm which indicates the suspension of pulmonary
activity. The predetermined time period for the movement alarm is
set so that the alarm will sound before bed occupant 6 has remained
motionless for so long as to be at risk for bed sores. Movement
threshold 58 may be determined adaptively by microprocessor 32
based on the pattern of measured pressure signals, or may be preset
when monitoring system 7 is manufactured and calibrated.
Optionally, a user interface (not shown) may be provided to allow
movement threshold 58 and the time period for the movement alarm to
be adjusted to allow for differences in weights and movement
patterns of different bed occupants.
[0066] FIG. 5 is a flowchart illustrating a method of monitoring a
bed occupant according to one embodiment of the invention. At block
100, pressure signals are measured by photodetector 33. At block
102, the measured signals are processed by signal processor 42. At
block 104, the signals are compared to a threshold by threshold
comparer 45. If the signals are not below the threshold (block 104
NO output), the method returns to block 100. If the signals are
below the threshold (block 104 YES output), the method continues to
block 106. At block 106, threshold crossing detector 46 determines
whether the signals have just crossed the threshold. If they have
(block 106 YES output), timer 47 is reset at block 108 and the
method returns to block 100. If they have not (block 106 NO output)
the method continues to block 110. At block 110, if timer 47 has
been running for a predetermined period since it was last reset
(block 110 YES output), an alarm signal is generated at block 112.
If not, (block 110 NO output), the method returns to block 100.
[0067] FIGS. 6, 7(a) and 7(b) illustrate a pressure sensitive
member 1 according to one embodiment of the invention. Pressure
sensitive member 1 comprises a plurality of Kinotex.TM. pressure
sensors 5 sandwiched between two layers 9, 10 of a compressible
material. The compressible material may comprise foam, and
preferably comprises a soft polyurethane foam. Preferably, several
bundles of plastic optical fibres 8 deliver and retrieve the light
energy from interface electronics 2 to pressure sensors 5. The
bundles of fibre 8 are preferably gathered and optionally passed
through a protective sleeve 12 that terminates at the interface
electronics 2. The bundles of fibre 8 preferably each comprise a
plurality of fibre pairs 14,15. An area of adhesive 11 is
preferably used to secure each fibre pair 14, 15 to the layers 9,
10 above and below each pressure sensor 5. In embodiments wherein
pressure sensitive member is to be located at the top of or within
support member 4, as shown in FIGS. 9(a)-(c), fibre bundles 8 are
preferably arranged sinusoidally between layers 9, 10 and not
adhered along their length so as to provide some flexibility and
resilience to pressure sensitive member 1. In embodiments wherein
pressure sensitive member 1 is to be located at the bottom of
support member 4, as shown in FIG. 9(d)-(e), fibre bundles 8 may be
adhered along their entire length, as pressure sensitive member 1
will preferably be adjacent to or mounted on a rigid surface.
[0068] Top layer 9 and bottom layer 10 are preferably constructed
from material chosen to be suitable with the specific
characteristics of pressure sensors 5. Materials well suited for
use with Kinotex.TM. pressure sensors are structurally
self-supporting, compressible, at least partially transmissive of
light, and optionally elastically resilient. The inventors have
determined that white or natural-coloured low density polyurethane
foam are suitable materials for use with Kinotex.TM. pressure
sensors. Such foam is available from, among others, Lendell
Manufacturing Inc. of St. Charles, Mich., product code HSS. The
inventors have also determined that most standard bed mattress foam
materials can be used as top layer 9 and/or bottom layer 10. It
will be understood that many different foam materials provide
similar characteristics and the present invention is not limited to
a specific material. A covering material (not shown) which is
opaque at wavelengths used by pressure sensors 5 is preferably
provided to keep ambient light from disturbing the Kinotex.TM.
pressure sensors. The opaque covering material preferably comprises
a two-tone flexible plastic cover that is black on the inside and
white on the outside, which envelops pressure sensitive member
1.
[0069] In an alternative embodiment, pressure sensitive member 1
comprises an area of the mattress in which pressure sensors 5 are
formed. FIG. 8 illustrates a section of mattress 13 with input and
output fibres 15, 14 inserted therein. The compressible material of
mattress 13, in addition to supporting bed occupant 6 (not shown in
FIG. 8), reflects incident wave energy received from input fibre 15
to output fibre 14, and thus forms pressure sensors 5. The FIG. 8
embodiment is particularly advantageous for equipping an existing
bed with a bed occupant monitoring system 7 according to the
invention, as one may do so by simply inserting optical fibres into
the mattress.
[0070] Pressure sensitive member 1 is preferably flexible and soft.
Pressure sensitive member 1 can be placed on a support member 4,
which may comprise a bed mattress, underneath the sheets and
coverings upon which bed occupant 6 lies. The inventors have
determined that, where soft sensors such as Kinotex.TM.-type
sensors are used, pressure sensitive member 1 can be made to be
essentially undetectable to a bed occupant 6. In some embodiments,
the deformable material of sensors 5 has an elastic modulus which
is substantially the same as that of the material surrounding
sensors 5.
[0071] It must be understood that FIG. 1 is a schematic
representation of one possible embodiment of the invention. Many
variations in the physical locations and sizes of the elements are
possible. For example, among other things, the pressure sensitive
member 1 may be located in-between occupant 6 and support member 4,
or it may be embedded in support member 4. Some of the possible
positions for pressure sensitive member 1 are shown in FIGS.
9(a)-(e). FIGS. 9(a) to 9(e) illustrate various embodiments of the
invention with pressure sensitive member 1 placed in different
positions with respect to support member 4. FIG. 9(a) illustrates
an embodiment wherein pressure sensitive member 1 is on top of
support member 4. FIG. 9(b) illustrates an embodiment wherein
pressure sensitive member 1 is placed in a recess 17 near the top
of support member 4 so that the top of member 1 is flush with the
top surface of support member 4. FIG. 9(c) illustrates an
embodiment wherein support member 4 is made of at least two layers
laminated together, between which is sandwiched pressure sensitive
member 1 within a cavity 18. FIG. 9(d) illustrates an embodiment
wherein pressure sensitive member 1 is located in a recess 19 near
the bottom of support member 4 so that the bottom of member 1 is
flush with the bottom surface of support member 4. FIG. 9(e)
illustrates an embodiment wherein pressure sensitive member 1 is
attached to the bottom of support member 4.
[0072] The wide dynamic range of Kinotex.TM.-type sensors permits
such sensors to pick up usable signals even when pressure sensitive
member 1 is located under or within a mattress.
[0073] Although many arrangements of pressure sensors 5 are
possible, pressure sensors 5 may conveniently be arranged in a
rectangular array extending across the width of support member 4.
Pressure sensors 5 may be spaced approximately 2 cm to 10 cm apart.
Depending on the intended application, the array of pressure
sensors 5 may extend the entire length of support member 4 or some
portion of the length. For example, to monitor the bed occupant's
respiration, the inventors have found that a 60-sensor array
approximately 90 cm wide by 30 cm in length is sufficient. A larger
device with correspondingly more sensors may be used for larger
occupants.
[0074] FIG. 10 illustrates a pressure sensitive member 20 according
to an embodiment of the invention wherein pressure sensors 5 are
arranged into three groups 21, 22 and 23. Pressure sensitive member
20 of FIG. 10 is dimensioned so that it spans the width of support
member 4, with side groups 21 and 23 adjacent to the edges of
support member 4. The responses of all of the pressure sensors 5
within the central group 22 are summed by interface electronics 2
by using a single photo-sensor (not shown in FIG. 5) to detect
their light output simultaneously. Pressure applied to any pressure
sensor 5 within central group 22 will result in a change in an
output signal from interface electronics 2 which is representative
of the average pressure on the sensors of central group 22. In a
similar manner, the signals from pressure sensors 5 in side groups
21 and 23 are summed using a second photo-sensor (not shown). This
results in two output signals: one representing the total pressure
applied within central group 22, and another representing the
pressure applied within side groups 21 and 23.
[0075] Interface electronics 2 may also comprise further analog
electronics to compare these signals to produce a third signal that
is derived therefrom. The third signal indicates three possible
states: 1) there is no occupant in the bed (determined by both
first and second signals being below a threshold); 2) the bed
occupant is in the central region (determined by the first signal
being above a first threshold and the second signal being below a
second threshold); 3) the bed occupant is near the edge of the bed
(determined by the second signal being above the second threshold).
Interface electronics can be used to active an audible alarm or an
attendant call system depending on which of the three states is
indicated by the third signal, and on predetermined monitoring
parameters.
[0076] As will be apparent to those skilled in the art in the light
of the foregoing disclosure, many alterations and modifications are
possible in the practice of this invention without departing from
the scope thereof. Accordingly, the scope of the invention is to be
construed in accordance with the substance defined by the following
claims.
* * * * *