Note: Descriptions are shown in the official language in which they were submitted.
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BED OCCUPANT MO1VITORING SYSTEM
Technical Field
[0001] This invention relates to monitoring the health andlor activity of a
person
occupying a bed. This invention provides a novel system comprising a pressure
sensitive member coupled to interface electronics.
Back r~ ound
[0002] It is known to use sensors coupled to a mattress for monitoring a bed
occupant. For example, Triplett et al. (U.S. Patent 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. Patent 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.
2,0 [0004] Alihanka et al. (U.S. Patent 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. Patent 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. Patent 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. Patent 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
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sensitive mats with a high density of sensors are assembled using optical
fiber
technology.
[0008] Musick (U.S. Patent 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. Patent 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
1S configured to connect in modular fashion with a monitoring device and
alarm.
[0010] Rudeke (PCT publication No. W09010281A1) 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. Patent No. 5,993,400) and Scott (U.S. Patent 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. Patent No. 5,410,297)
disclose a weight-sensitive capacitive sensor for tracking the position of an
occupant. Dixon et al. (U.S. Patent 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. Patent 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. Patent 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. Patent 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
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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
2,5 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.
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[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
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
10 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
15 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.
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[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] Figure 1 illustrates schematically an occupant lying in a bed equipped
with a
monitoring system according to one embodiment of the invention;
[0032] Figure 2 illustrates schematically interface electronics according to
an
embodiment of the invention;
[0033] Figure 3 is a block diagram of some circuit elements of interface
electronics
according to another embodiment of the invention;
[0034] Figure 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] Figure 5 is a flowchart illustrating a method of monitoring a bed
occupant
according to one embodiment of the invention;
[0036] Figure 6 shows a pressure sensitive member and interface electronics
according to one embodiment of the invention;
[0037] Figure 7(a) shows a top view of a portion of the pressure sensitive
member
of Figure 2, with the top layer removed;
[0038] Figure 7(b) is a cross-sectional view of the portion of the pressure
sensitive
member of Figure 3(a), with the top layer present;
[0039] Figure 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;
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[0040] Figure 9(a) illustrates an embodiment of the invention wherein the
pressure
sensitive member is coupled to the top of a support member;
[0041] Figure 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] Figure 9(c) illustrates an alternative embodiment of the invention
wherein
the pressure sensitive member is coupled within a cavity within the support
member;
[0043] Figure 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] Figure 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] Figure 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] Figure 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
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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
Figure 1, or they may be housed in more than one enclosure connected by signal
S 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 US Patent
5, 917,180 to Reimer et al. , which is hereby incorporated by reference. Such
sensors are available under the brand name Kinotex'~z 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 Figure 2), which provides incident
wave
energy, and an output fibre 14 (see Figure 2), which transmits reflected wave
energy to interface electronics 2.
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[0053] As described in Reimer et al. , Kinotex'r'"' 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 Figure 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 Figure 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 Figure 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
Figure 2). An output fibre 14 returns light from each pressure sensor 5 (not
shown
in Figure 2) to photodetector 33. Photodetector 33 preferably comprises an
array of
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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 Figure 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 Figure 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.
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[0061] Figure 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
eomparer 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 4~ 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] Figure 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
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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 Figure 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 fox the movement alarm to be adjusted to
allow for
differences in weights and movement patterns of different bed occupants.
[0066] Figure 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 axe 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
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method continues to block 110. At block 110, if timer 47 has been running for
a
predetermined period since it was last reset (block I10 YES output), an alarm
signal is generated at block 112. If not, (block 110 NO output), the method
returns
to block 100.
[0067] Figures 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~'~' 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 Figures 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 Figure 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 I~inotex~"s 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~
pressure
sensors. Such foam is available from, among others, Lendell Manufacturing Inc.
of
St. Charles, Michigan, product code HSS. The inventors have also determined
that
most standard bed mattress foam materials can be used as top layer 9 andlor
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
I~inotex'r"~
pressure sensors. The opaque covering material preferably comprises a two-tone
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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. Figure 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 Figure 8), reflects incident wave energy received from input fibre 15
to
output fibre 14, and thus forms pressure sensors 5. The Figure 8 embodiment is
particularly advantageous for equipping an existing bed with a bed occupant
IO 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.
~5 The inventors have determined that, where soft sensors such as Kinotex ~
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.
20 [007I] It must be understood that Figure 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
25 positions for pressure sensitive member 1 are shown in Figures 9(a)-(e).
Figures
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.
Figure
9(a) illustrates an embodiment wherein pressure sensitive member 1 is on top
of
support member 4. Figure 9(b) illustrates an embodiment wherein pressure
30 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. Figure
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. Figure 9(d) illustrates an embodiment wherein pressure
35 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
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4. Figure 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 ~"' 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 90cm wide by 30cm in length is
sufficient. A larger device with correspondingly more sensors may be used for
larger occupants.
[0074] Figure 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 Figure 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 Figure 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
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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.
