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FORCE OPTIMIZATION SURFACE APPARATUS AND METHOD
Background and Summary of the Invention
The present invention relates to controllable surfaces, and particularly
to surfaces for preventing and treating pressure ulcers.
Pressure ulcers in bedridden patients can be caused by excessive forces
between the patient and a surface upon which the patient is resting. It is
known to
provide controllable mattresses that allow for adjusting pressures within a
mattress
surface. For example, it is known to adjust air pressure within multiple
chambers of an
10 air mattress, to reduce interface forces over a given bony protuberance
based on
sensed air pressures within the chambers.
According to the present invention, an interface sensing system
eliminates the need to conduct independent interface force testing for a
patient at each
body and bed position on an ongoing basis. An intelligent control system is
provided
15 for adjusting internal cushion pressures in a mattress surface based on
interface force
measurements.
In the present invention, a method of minimizing a force between a
modifiable support surface and a patient located thereon includes the steps of
establishing an initial recorded force between the patient and the support
surface,
20 performing a first procedure including modifying the support surface in a
first manner
for a predetermined time increment, measuring the current force between the
patient
and the surface, comparing the current force to the recorded force, and
replacing the
recorded force with the current force. The first procedure is repeated so long
as the
current force is less than the recorded force, then a second procedure is
performed
25 including modifying the support surface in a second manner for a
predetermined time
increment, measuring the current force between the patient and the support
surface,
comparing the current force to the recorded force, and replacing the recorded
force
with the current force. The second procedure is repeated so long as the
current force
is less than the recorded force.
30 In the present invention, a support surface apparatus includes at least
one support member for supporting a person, and a force sensor located on the
at least
one support member. The force sensor is configured to measure a force between
the
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person and the at least one support member. The apparatus also includes a
mechanism
configured to adjust a support characteristic of the at least one support
member based
upon the force detected by the force sensor to minimize the force between the
person
and the at least one support member.
In an illustrated embodiment of the present invention, a support surface
apparatus includes at least one air bladder for supporting a person, a force
sensor
located on the at least one air bladder, an air supply coupled to the at least
one air
bladder, and a controller coupled to the force sensor. The force sensor is
configured
to measure a force between the person and the at least one air bladder. The
controller
10 is configured to adjust air pressure within the at least one air bladder
based on the
force detected by the force sensor to minimize the force between the person
and the at
least one bladder.
In addition, sensors contained within the force optimization surface of
the present invention eliminate the need for individual equipment and monitors
for
15 measuring specific patient parameters such as heart rate, temperature, and
respirations.
An apnea monitor is provided to reduce and/or prevent occurrences of episodes
of
apnea. A built-in weight sensor system eliminates the need for external,
cumbersome
scales.
Additional features of the invention will become apparent to those
20 skilled in the art upon consideration of the following detailed description
of illustrated
embodiments exemplifying the best mode of carrying out the invention as
presently
perceived.
Brief Description of the Drawings
25 The detailed description particularly refers to the accompanying figures
in which:
Fig. 1 is a perspective view of a support surface system, lead/tubing
assembly and control interface assembly according to the present invention;
Fig. 2 is a block diagram of a system according to the present invention
30 including a controller, force, weight, heart rate, respiration, bladder
pressure, and
temperature sensors, the controller coupled to mattress control, display/print
output,
vital alert, and apnea oscillator systems;
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Fig. 3 is an exploded view of the support surface system of Fig. 1
showing a bottom cover, foam support layer, air support layer, sensor layer,
fire
barrier, anti-sheer layer, and top cover;
Fig. 4 is a sectional view along line 4-4 of the support surface of Fig. 1;
5 Fig. 5 is a blowup of the cross section of the sensor layer enclosed in
circle 5 in Fig. 4;
Fig. 6 is a flow diagram of the algorithm for a start phase controlling
the inflation of the zones of the air support layer in accordance with the
present
invenrion;
10 Fig. 7 is a flow diagram of an upper level algorithm for. a force
management phase for controlling the inflation of the zones of the air support
layer in
accordance with the present invention;
Fig. 8 is a flow diagram of a lower level algorithm for a force
management phase for controlling the inflation of the zones of the air support
layer in
15 accordance with the present invention;
Fig. 9 is a flow diagram of the algorithm for a max inflate mode for
controlling the inflation of the zones of the air support layer in accordance
with the
present invention;
Fig. 10 is a front view of the controller of Fig. 1 showing various
20 switches and indicators for monitoring and controlling force optimization
surface; and
Fig. 11 is a back view of the controller with back panel removed to
show the valve assembly, compressor, and blower used in controlling the
pressure in
zones of the force optimization surface.
25 Detailed Description of the Drawings
Referring to Fig. 1, a force optimization surface 10 includes a support
surface assembly 11, a control interface assembly or controller 18, and a
lead/tubing
assembly 13. Support surface assembly 11 includes a bottom cover 34, a
modifiable
support surface or modifiable support layer 9, a sensor layer 14, a fire
barrier 38, an
30 anti-sheer layer 40, and a top cover 42 as shown, for example in Figs. 3
and 4. In the
illustrated embodiment modifiable support layer 9 includes a lower or foam/air
support
layer 36 and an upper or controllable air mattress layer 12. Air mattress 12
includes
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one or more independently controllable air zones or chambers. An alternative
support
surface assembly 11 which can be modified by the addition of sensor layer 14
and fire
barrier 38 as described herein for use as support surface assembly 11 in
accordance
with the present invention is described in U.S. Patent Application No.
09/281,888,
filed on March 31, 1999, assigned to Hill-Rom, Inc., the assignee of the
present
invention, the disclosure of which is incorporated herein by this reference.
While the
illustrated embodiment increases and decreases pressure in air mattress 12 to
modify
modifiable support layer 9 in two different manners, it is within the teaching
of the
disclosure to provide mechanically or electrically modifiable support layers 9
made of
foam, springs, or other suitable material which modify the firmness or surface
configuration of the support layer in different manners to affect the force
between the
support surface 1 l and a patient 16.
In the illustrated embodiment, air mattress 12 includes individual
cylindrical cushions 44 divided into four independently controllable zones or
groups
referred to as head chamber 46, upper torso chamber 48, lower torso chamber 50
and
foot chamber 52, two headers or plenums 54 per chamber, and four side bladders
56
per chamber (not shown in Fig. 3, only two of which are shown in Fig. 4). Each
cushion 44 and plenum 54 is illustratively 4.0 inches (10.16 cm) in diameter
58. Each
plenum 54 is fluidly coupled to each cylindrical cushion 44 in its associated
chamber
such as by opening 60 formed through end wall 62 of cylinder 44 and sidewall
64 of
plenum 54 as shown, for example, in Fig. 4. Each plenum 54 is also coupled to
an air
supply 23 including a pump 31 and a blower 33 in controller 18 via mattress
plumbing
(not shown) coupled to lead/tubing assembly 13. Appropriate mattress plumbing
is
known and a specific embodiment applicable to the present invention is
disclosed in
U.S. Patent Application Serial No. 09/281,888. Each side bladder 56 is 1.5
inches
(3.81 cm) in diameter 66. Illustratively each cushion 44, plenum 54, and side
bladder
56 is fabricated from urethane coated nylon twit! material radio frequency
welded to
join and seal the fabric in the illustrated geometry.
Illustratively head chamber 46 includes four individual cushions 44 and
upper torso chamber 48 includes four individual cushions 44 so that each
chamber 46,
48 has an overall length of sixteen inches (40.64 cm). Lower torso chamber 50
includes seven individual cushions 44 and thus has an overall length of twenty-
eight
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inches (71.12 cm), Foot chamber 52 includes five individual cushions 44 and
thus has
an overall length of twenty inches (50.8 cm).
The manner of inflation of side bladders 56 is not illustrated but may be
accomplished through manual inflation valves (not shown) or by having side
bladders
56 in fluid communication with one of the chambers 46, 48, 50, 52. Side
bladders 56
allow the width of mattress 12 to be adjusted to accommodate common intensive
care
unit ("ICU" ) and medical-surgical ("med-Surg") frames. Typical ICU and Med-
Surg
frames include patient support surfaces having a width of 32-35 inches (81.28-
88.9
cm). Illustratively air mattress 12 has a length of approximately 80 inches
(203.2 cm)
and a width adjustable between thirty-two inches (81.28 cm)(with side bladders
deflated) and thirty-five inches (88.9 cm)(with side bladders inflated).
As shown in Fig. 3, bottom layer 36 includes a plurality of foam
segments 70 and air support segment 72. As with air mattress layer 12, bottom
layer
36 is divided into four segments, a head zone 76, an upper torso zone 78, a
lower
15 torso zone 80, and a foot zone 82. Illustratively head zone 76, upper torso
zone 78,
and lower torso zone 80 each include a plurality of urethane foam segments 70
inserted into urethane coated nylon twill sleeves. The sleeves are joined at
regular
intervals. This joining may be accomplished in the manner disclosed in U.S.
Patent
Application Serial No. 09/281,888. Foot zone 82 includes air support segment
72
having a plurality of air bladders 88 and plenums 90 underlying foot chamber
52 of air
mattress 12.
Each foam segment 70 of head, upper torso, and lower torso zones 76,
78, 80 is thirty-two inches (81.28 cm) in overall length and includes a mid-
section 84
extending between two end caps 86. Each foam segment 70 is four inches (10.16
cm)
25 wide by four inches (10.16 cm) tall. Head and upper torso zone 76, 78
illustratively
include four foam segments 70 each and thus each zone 76, 78 has an overall
length of
sixteen inches (40.64 cm). The mid-sections 84 of the foam segments 70 in the
head
and upper torso zones 76, 78 are a High Resiliency ("HR") grade foam of 2.25-
2.5
density, support factor 2.4 minimum, 17-21 IL,D, CAL 117, antimicrobial foam.
30 Lower torso zone 80 illustratively includes seven foam segments 70 and thus
has an
overall length of twenty-eight inches (71.12 cm). The mid-sections 84 of the
foam
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segments 70 in the lower torso zone 80 are a HR grade foam of 2.25-2.5
density,
support factor 2.5 minimum, 31-34 ILD, CAL 117, antimicrobial foam.
End caps 86 of all of foam segments ?0 of zones 76, 78, 80 combine to
form side rails on lower support 36 and are thus referred to as side rail
foam. These
side rails facilitate patient ingress to and egress from surface 10. In
addition, end caps
86 and mid-sections 84 combine to create a cradle zone to facilitate adequate
centering
of patient to assist in keeping patient from sliding into the side rail and
reducing the
need for the caregivers to frequently reposition the patient. End caps 86 are
bonded to
mid-sections 70 with acetone heptane and resin base spray adhesive. Each end
cap 86
10 is two inches (5.08 cm.) in overall length, four inches (10.16 cm) wide,
and four inches
(10.16 cm) tall to conform to the mid-section 70 to which it is attached. End
caps 86
are made of conventional foam grade such as Foam Grade H45XF, 1.8-1.9 PCF, 53-
60
II,D, support factor 2.0, Cal 117, antimicrobial foam.
Illustratively foot zone 82 includes air support segment 72 having five
1 S air bladders 88 extending between and fluidly coupled to two spaced apart
plenums 90.
Bladders 88 and plenums 90 are four inches (10.16 cm) in diameter. Thus foot
zone
82 has an overall length of twenty inches (50.8 cm). Bladders 88 and plenums
90 are
made of urethane coated nylon twill material, IAW material specification 100-
001-
0032. Bladders and plenums 90 are in fluid communication with the two plenums
54
20 that supply air to the foot chamber 52 of air mattress 12.
Force optimization surface 10 provides for sensing multiple interface
pressures or forces exerted by the modifiable support surface 9 on a patient
16 atop
sensor layer 14. Those skilled in the art will recognize that interface
pressure
measured in a defined area is the integral over the area of all of the forces
exerted
25 normal to the area. Therefore, the term force or interface force will be
used to refer to
the interface force or interface pressure unless otherwise stated to avoid
confusion
between pressure in an air bladder and the interface pressure. Support
surfacel l is
coupled to a controller 18 configured with software for regulating air
pressure within
each chamber 46, 48, 50, 52 of mattress 12 based on measured interface force
values
30 exerted by the chambers 46, 48, 50, 52 on the patient 16. Various interface
sensors 15
are known which detect the interface pressure and the interface force. In the
illustrated embodiment of the invention, zones of the modifiable support
surface 9 are
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modified in response to the maximum force exerted within the zone using
resistive
force sensors located on each zone. A multiplicity of sensors detecting
interface
pressure can be used to detect this maximum force exerted within the zone,
however in
the illustrated embodiment an interface force sensor is described. To avoid
confizsion,
the term interface sensor will be used to refer to both a multiplicity of
interface
pressure sensors or an interface force sensor.
Force optimization surface 10 with its controller 18 uses multiple
interface sensor readings to decide how to modify pressure within a given
chamber or
chambers within mattress 12 to optimally reduce the interface force. The
nature of the
optimization can vary as desired, such as controlling air pressures to achieve
a
minimum average value for all interface sensor signal values, to maintain all
interface
sensor values below a threshold, or to achieve certain force profiles over
various
surface areas, etc.
Illustratively sensor layer 14 includes a peripheral downwardly
extending sidewall 92 and a surface 94 extending between and combining with
sidewall
92 to form a modifiable support surface-receiving cavity much like a fitted
sheet, as
shown for, example, in Figs. 3 and 4. Nevertheless, it is within the teaching
of this
disclosure for sensor layer 14 to include a mat disposed between air mattress
12 and
top cover 42. Incorporated within surface 94 is a plurality of sensing zones
which in
the illustrated embodiment include head zone 96, upper torso zone 98, lower
torso
zone 100, and foot zone 102. In the illustrated embodiment, each sensing zone
includes a peripherally extending non-sensing border 104 having a width 106 of
one
inch (2.54 cm), an outer covering 108, and an interface sensor 15.
Illustratively,
interface sensor i 5 includes a top conductive layer 110 and a bottom
conductive layer
112 separated by a semiconductor material 114, a first wire 116 coupled at one
end to
top conductive layer 110 and at the other end to controller 18, and a second
wire 118
coupled at one end to bottom conductive layer 112 and at the other end to
controller
18, as shown for, example, in Figs. 3, 4 and 5. Illustratively outer covering
108 is
0.002 in (.051 mm) thick aromatic polyether polyurethane film available from
Deerfield Urethane (Route S-10 Box 185, South Deerfield, Massachusetts 01373)
PT9200U or equivalent. Each conductive layer 110, 112 is illustratively
Monsanto
Flextron~ nickel coated copper rip stop nylon fabric. Semiconductor material
114 is
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a piezo-resistive sheet available from Verg, Inc, Winnipeg, Canada.
Illustrated
interface sensor 15 acts to sense the maximum force exerted anywhere within
the zone.
In the illustrated embodiment of sensor layer 14, head zone 96 is
sixteen inches (40.64 cm) long and thirty-two inches (81.28 cm) wide and is
positioned
to lie adjacent to head chamber 46 of air mattress 12. Upper torso zone 98 is
sixteen
inches (40.64 cm) long and thirty-two inches (81.28 cm) wide and is positioned
to lie
adjacent to upper torso chamber 48 of air mattress 12. Lower torso zone 100 is
twenty-eight inches (71.12 cm) long and thirty-two inches (81.28 cm) wide and
is
positioned to lie adjacent to lower torso chamber SO of air mattress 12. Foot
zone 102
10 is twenty inches (50.8 cm) long and thirty-two inches (81.28 cm) wide and
is
positioned to lie adjacent to foot chamber 52 of air mattress 12.
Alternative integrated interface sensing material in sensor layer 14 can
be any material that provides multiple interface sensors 15 such as a
resistive or
capacitive film providing a grid or matrix of interface sensors. These
interface pressure
15 mapping technologies are well known to those of skill in the art, and
provide for
sensing and mapping interface pressures against the entire body contact area
of patient
16. Illustrative interface pressure sensing and mapping devices include
capacitive
devices such as the X-SENSORTM pad available from the X-sensor company in
Calgary, Canada or the EMEDTM system from Novel GmbH in Munich, Germany,
20 resistive force sensing devices such as those available from Vista Med in
Winnipeg,
Canada or Tekscan in Boston, Massachusetts, or other sensor types such as
pneumatic
pressure sensors, etc. It will be understood that in order to determine the
maximum
force exerted within a zone, like the illustrated interface sensor does, a
multiplicity of
capacitive or pneumatic sensors would be required within each specific zone.
25 It will be understood that in the illustrated embodiment, lower support
layer 42, air mattress 12, and sensor layer 14 are all divided into the same
number and
size of segments, chambers, or zones. Each segment, chamber, or zone
corresponds
and is associated with the chamber, segment, or zone underlying or overlying
it. Thus,
hereinafter the terms zones of modifiable support surface or zones of support
surface
30 assembly are occasionally used.
Refernng again to Fig. 3 and 4, fire barrier 3 8 is designed to receive
and substantially totally encompass lower foam/air layer 36 and upper air
mattress
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support layer 12. Fire barrier 38 is illustratively formed of stretchable 1 x
1 rib knit
that is constructed of fiberglass and modacrylic fabric or equivalent IAW raw
material
specification 240-02-0019. Anti-shear lining 40 is formed to have a downwardly
opening cavity to receive the fire barrier 38 lower support layer 36 and air
mattress
5 layer support i 2 assembly in the manner of a fitted sheet. Anti-sheer
lining 40 is
constructed of a low coefficient of friction nylon, polyester twill, or an
equivalent.
Anti-sheer lining 40 is installed over the fire barrier 38 and air mattress 12
and under
the top cover 42 to reduce sheer force to the patient.
Illustratively, top cover 42 and bottom cover 34 each include one half
of a peripherally extending zipper 35. The half of the zipper 35 coupled to
top cover
42 is sewn to urethane strips for sealing to the host material of top cover
42.
Illustratively the host material of top cover 42 is a polyurethane coated, bi-
directional
stretch nylon substrate material. The half of the zipper 35 coupled to bottom
cover 34
is sewn directly to the host material of bottom cover 34. The host material of
bottom
1 S cover is illustratively a monomeric vinyl laminate fabric. The zipper
starts and ends on
the center line of the patient foot end 29. Anti shear lining 40, fire barrier
38, upper
and lower support layers 12, 36 are received between top and bottom covers and
enclosed therein by joining halves of zipper 35 to form support surface
structure 11.
Controller 18 includes a smart board 19, a power supply 21, an air
20 supply 23, a control I/O panel 25, and a pneumatic system 27. The
illustrated power
supply 21 is one of a 220 volt 50 Hz input, 24 volt DC, 110 volt AC output
power
supply or a 110 volt 50 Hz input, 24 volt DC, 110 volt AC output power supply
coupled to power cord 17. Air supply 23 includes an air pump 31 such as a
Thomas
.35 cfm 24 VDC air pump and a blower 33 such as Amatec centrifugal blower each
of
25 which are mounted in controller 18, electrically connected to power supply
21 and
fluidly coupled to pneumatic system 27. Blower 33 is a high volume low
pressure
blower used for rapid inflation of the air mattress 12 to bring the mattress
to initial set
pressures and to bring all zones of the mattress to maximum pressure during a
max
inflate mode 134. Pump 31 is a high pressure low volume pump used to increase
30 pressures in chambers of air mattress 12.
Illustratively, control I/O panel 25 includes an alarm silence button 37,
an alarm silence LED 39, a max inflate button 41, a max inflate LED 43, a zone
1 LED
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45 which blinks when selected, a zone 2 LED 47 which blinks when selected, a
zone 3
LED 49 which blinks when selected, a zone 4 LED 51 which blinks when selected,
and
a call for service LED 53. Illustratively, panel 25 is a membrane keypad
adhesively
secured to controller 18 and is connected to control electronics (not shown)
on smart
5 board 19 through a ribbon cable and PCB connector (not shown). Control panel
25
will provide operator feed back via the use of LEDs 39, 43, 45, 47, 49, 51, 53
including alarms and sensor malfunctions.
To meet CPR requirements, a one step manual emergency dump valve
55 is incorporated in a known manner into support surface assembly 11. The
purpose
10 of valve 55 is to dump air in the head, upper torso, and lower torso
chambers 46, 48,
50 in fifteen seconds. Once CPR is completed, dump valve 55 is reset.
Pneumatic system 27 includes four stepper motor controlled zone
selector needle valves (not shown), five pressure transducers 7 (shown
diagrammatically in Fig. 2 only), a stepper motor controlled vent needle valve
(not
15 shown). Pneumatic system 27 is coupled to smart board 19 which includes a
processor
and firmware (not shown). Pneumatic system 27 includes air supply lines 57
fluidly
coupled to each chamber 46, 48, S0, 52. Each supply line 57 is also coupled to
the air
supply 23 through a designated zone valve (not shown). A pressure sensing line
(not
shown) is connected to each supply line 57 and to a pressure transducer 7
electrically
20 coupled to smart board 19. A vent line 59 is coupled to each supply line 57
through
vent valve (not shown) to vent chambers 46, 48, 50, 52 when appropriate.
Controller 18 provides for measuring sensed interface forces in real
time and modifying the modifiable support surface 9, i.e., controlling chamber
pressures in air mattress 12 in the illustrated embodiment, as required to
reduce
25 interface forces between a patient and support surface assembly 11.
Controller 18 is
illustratively coupled to a mattress control system 20 that regulates pressure
within
chambers of mattress 12. For an example of a system that determines an index
using
pressures for evaluating interface pressure performance of a support surface
see
application serial no. 08/752,796, entitled Method and Apparatus for
Evaluating a
30 Support Surface, which is hereby incorporated by reference.
Controller 18 can be provided within force optimization surface 10 or
as a separate component coupled to force optimization surface 10 via an
appropriate
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communication interface, such as wires or a wireless communication link. In
the
illustrated embodiment top and bottom wires 116, 118 from each sensor zone are
coupled into an eight wire bundle 120 forming a portion of lead/tubing
assembly 13
extending between support surface assembly 11 and terminating in a 9-pin D sub-
s miniature connector with finger twist lock screws 122 coupled to controller
18.
Controller 18 further provides for coupling force optimization surface 10 to
other
external systems (not shown) over various types of links, such as a peer-to-
peer
communication network.
Software in controller 18 is configured to scan or monitor interface
10 forces from interface sensors 15 to maintain desired support
characteristics, such as
minimizing the force between the patient and each zone of support surface
assembly
11, regardless of the body position or the bed position. Thus, for example, if
patient
16 rolls over onto his or her side, or if support surface assembly 11 is
coupled atop an
articulated bed frame that assumes a non-flat orientation, controller 18 will
adjust
15 pressures in air mattress 12, i.e., modify modifiable support surface 9,
automatically to
minimize forces between each zone and the patient. These adjustments can be
made at
a predetermined periodic rate or can be event-driven as required. The rate at
which
adjustments are made can further be limited or filtered as desired.
The software or firmware loaded into controller 18 includes a start
20 phase 130, a force management phase 132, a max inflate mode 134, and a
service
mode 136. In describing these phases the term "zone" will be used to refer to
the
sensing zone 96, 98, 100, 102 and the underlying associated chamber 46, 48,
50, 52
respectively. These zones are referred to as zone 1 (head zone 96 and head
chamber
46), zone 2 (upper torso zone 98 and upper torso chamber 48), zone 3 (lower
torso
25 zone 100 and lower torso chamber 50) and zone 4 (foot zone 102 and foot
chamber
53). "Pressure in a zone" refers to the air pressure in the chamber underlying
and
associated with the sensing zone. "Force on a zone" refers to the interface
force or
pressure sensed by interface sensor 15.
The algorithm for start phase 130 is shown, for example, in Fig. 6.
30 Start phase 130 includes the steps of turning the blower on 138, sensing
the current
pressure in zones 1, 2, 3, and 4 (P,~) 140, comparing the current pressure in
each zone
to a set pressure for each zone 141, blowing air into each zone so long as the
pressure
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in all chambers is not greater than the respective set pressure for the
chamber 142, and
turning off the blower when the pressure in all zones is greater than a set
initial
pressure (P,~~ 144. Typically after turning the blower off 144, one or more of
the
following steps of going to the max inflate mode 136 if the max inflate flag
exists 146,
going to the service mode 138 if the service flag exists 148, and continuing
to the force
management phase 132 after completion 150 are included in start phase 130.
The software includes a force management phase 132 which operates
after the start phase 130 to adjust the pressure within each of the chambers
underlying
the sensor zones to minimize the force exerted between the surface and the
patient. As
10 shown, for example, in Fig. 7, at a high level, force management phase 132
includes a
first manner of modification of modifiable support surface 9 or pumping
procedure 131
and a second manner of modification of modifiable support surface 9 or venting
procedure 133. Illustratively, the pumping procedure 131 includes the steps of
ensuring that the pressure in a zone (P~) does not exceed a maximum pressure
15 established for the chamber underlying the zone (Pa"",~ before performing
any pumping
operation 152, and incrementally pumping air into the zone so long as the
current force
(F~) in the zone is lower than the force recorded prior to the last
incremental pumping
(Fog) 154. The venting procedure 133 includes the steps of insuring that the
pressure
in a zone does not fall below a minimum pressure established for the zone
(P",~
20 before performing any venting operation 156 and incrementally venting the
zone when
the current force in the zone (F#) exceeds the force recorded prior to the
last pumping
step (Fob 158. The venting procedure 133 is continued so long as the current
force
(F~) in the zone is less than the force recorded prior to last incremental
venting (F~),
and the venting procedure 133 ceases when the current force in the zone (F#)
exceeds
25 the force recorded prior to the last venting step (F~~. When pumping
procedure 131
terminates the force management phase 132 goes to venting procedure 133 and
when
the venting procedure 133 terminates force management phase 132 returns to
pumping
procedure 131.
It will be understood that with a plurality of zones overlying a plurality
30 of associated independently inflatable chambers that each zone and its
associated
chamber could be simultaneously controlled with a dedicated pump, valves and
controller or with a single controller, valve manifold, pump, and control
algorithm
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which cycles through the zones. It will also be understood that if modifiable
support
surface 9 is not an inflatable surface but an otherwise modifiable surface,
similar
subroutines will be included in pumping and venting procedure 131, 133 to
ensure that
limits of the modifiable surface are not exceeded and to modify the surface in
different
manners to facilitate reduction in forces between the surface and the patient.
At a very
high level force management phase 132 performs a first modification to the
support
surface so long as it continues to reduce the force between the surface and
the patient
and then performs a second modification to the surface for so long as it
continues to
reduce the force between the surface and the patient. Typically after
performing the
second modification, force management phase returns to the first modification,
however if the modifiable support surface 9 can be modified in more than two
manners, a third or more modifications may be performed.
One algorithm for implementing force management phase 132 for
multiple zones and a single vent valve and pump is shown in Fig. 8 and
includes the
pumping procedure 131 and venting procedure 133. Pumping procedure 131
includes
the steps of turning on the pump 170, selecting the valve to the next zone
which is not
in a no pump mode 172, measuring the current pressure (P*) in the selected
zone 174,
comparing the current pressure (P#) in the selected zone to a predetermined
max
pressure for that zone (P"m"t 176. If the current pressure is less than the
max pressure
(P~<P~,~ for the zone the step of reading the current force (F~) on the zone
178 is
performed, however, if the current pressure is greater than the maximum
pressure then
the step of putting the zone into no pump mode by setting the no pump flag for
the
zone 180 is performed as part of a loop described later either returning to
the zone
selection step 172 of pumping procedure 131 or exiting to venting procedure
133.
As long as the current pressure does not exceed the maximum pressure
for the zone, the step of comparing the current force to the last recorded
force on the
zone 182 is performed. If the current force on the zone is less than the last
recorded
force, the goal of minimizing forces is being achieved by what is currently
being
performed, i.e., pumping, so the steps of replacing the recorded force with
the current
force (F#~d F#) 184 and pumping the zone for a set period of time 186 are
performed
during a loop that returns to the select zone step 172 of pumping procedure
131.
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If during the comparison step 182 it is determined that the current force
is not lower than the previously recorded force (F~zF,~~, then whatever is
currently
being performed, i.e., pumping, is not working to achieve the desired results
for the
selected zone. Therefore the zone is not pumped anymore and the step of
setting a No
5 Pump Flag (NPF~) to establish that the zone is in a "no-pump mode" 180 is
performed
as part of a possible pumping procedure exit loop. Anytime the No pump mode
step
180 is performed for a zone, that zone cannot be selected anymore during the
current
pumping procedure as the zone will no longer be a zone without a no pump flag.
To
avoid a continuous loop, the step of determining whether all of the zones are
in no
10 pump mode 188 is performed. If all zones are not in the no pump mode then
the select
zone step 172 is performed. However if all zones are in the no pump mode, the
pumping procedure 131 is exited and the venting procedure 133 is performed.
During
the exit from pumping procedure 131 to venting procedure 133 the steps of
clearing
each zone out of no pump mode by clearing the no pump flags 190 and turning
off the
15 pump 192 are performed.
Venting procedure 133 includes the steps of opening the vent valve
200, selecting the valve to the next zone which is not in a no vent mode 202,
measuring the current pressure (P#) in the selected zone 204, comparing the
current
pressure (P~) in the selected zone to a predetermined min pressure for that
zone (P,~
20 206. If the current pressure is greater than the min pressure (P#>P~,,N,~
for the zone the
step of reading the current force (F~) on the zone 208 is performed, however,
if the
current pressure is less than the minimum pressure then the step of putting
the zone
into no vent mode by setting the no vent flag for the zone 210 is performed as
part of a
loop described later either returning to the zone selection step 202 of
venting
25 procedure 133 or exiting to pumping procedure 131.
As long as the current pressure does not dip below the minimum
pressure fox the zone, the step of comparing the current force to the last
recorded
force on the zone 212 is performed. If the current force on the zone is less
than the
last recorded force, the goal of minimizing forces is being achieved by what
is currently
30 being performed, i.e., venting, so the steps of replacing the recorded
force with the
current force (F#aa F~) 214 and venting the zone for a set period of time 216
are
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performed during a loop that returns to the select zone step 202 of venting
procedure
133.
If during the comparison step 212 it is determined that the current force
is not lower than the previously recorded force (F~zF~o~, then whatever is
currently
5 being performed, i.e., venting, is not achieving the desired results for the
selected zone.
Therefore the zone is not vented anymore and the step of setting a No Vent
Flag
(NVF~) to establish that the zone is in a "no-vent mode" 210 is performed as
part of a
possible venting procedure exit loop. Anytime the no vent mode step 210 is
performed
for a zone, that zone cannot be selected anymore during the current venting
procedure
10 as the zone will no longer be a zone without a no vent flag. To avoid a
continuous
loop, the step of determining whether all of the zones are in no vent mode 218
is
performed. If all zones are not in the no vent mode then the select zone step
202 is
performed. However, if all zones are in the no vent mode, then the venting
procedure
133 is exited and the pumping procedure 131 is performed. During the exit from
I S venting procedure 133 to pumping procedure 131 the steps of clearing each
zone out
of no vent mode by clearing the no vent flags 220 and closing the vent valve
222 are
performed.
The control algorithm also includes a max inflate mode 134, shown, for
example, in Fig. 9. The max inflate mode 134 includes the steps of closing the
vent
20 valve 230, opening the valve for all of the zones 232, turning the pump on
234, turning
the blower on 236, measuring the pressure in each zone 238, and averaging the
pressures in all of the zones (Pa~ 240. Then the step of comparing the average
pressure to the maximum pressure 242 is performed. If the average pressure is
not less
than the maximum pressure (P"~zP""~, then the steps of closing all of the
valves 244,
25 turning off the pump and blower 246, and illuminating the max inflate LED
248 are
performed. If the average pressure is less than the maximum pressure (P"~<P~
then
max inflate mode returns to the measuring pressure step 238.
The control algorithm also includes a call for service mode. A
maximum service time will be selected. If the maximum service time has
elapsed, the
30 return from any pressure transducer equals zero, or if pressure does not
rise in any
zone after max service time, or if force readings are open or short circuit
for max
service time, the. call for service LED 53 is illuminated.
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While the invention thus far has been described as including four
chambers and four sensing zones positioned between the four chambers and a
surface
on which a patient is located with each zone being responsive to changes in
interface
pressure or force over an associated chamber, it is within the teaching of the
invention
to include more or less than four chambers and four zones. Those skilled in
the art to
which this invention relate will recognize that higher resolution and greater
control can
be achieved by increasing the number of independently inflatable chambers or
modifiable zones and associated sensor zones. It should also be recognized
that
independently inflatable chambers or modifiable zones and associated sensor
zones can
assume any configuration, orientation, or arrangement to facilitate
controlling interface
forces between patient and a surface on which patient is situated. In other
words,
zones can extend along a separate the support surface along both a length
dimension
and a width dimension of the support surface.
Controller 18 is configured to monitor peak interface force on a zone
15 between patient 16 and mattress 12 and can reduce that force by adjusting
pressure in
one or more chambers. Controller 18 includes memory for storing and recording
data
such as sensor values and adjustments made over time. The data recorded by
controller 18 can be used to analyze system performance and make assessments
regarding patient 16. Controller 18 is further configured to interface with a
display
and/or printer output device 22 to provide for either visual or hard copy
output both
for recorded data and for data as it is acquired in real time.
Force optimization surface 10 further can be configured with a
weighing system to sense, monitor, record, display, and print patient 16's
weight.
When a large number of force sensors are used, by integrating measured force
values,
interface sensors 15 can be used to derive weight information. However in the
illustrated embodiment separate weight sensors 24 (diagrammatically
illustrated only)
are provided, such as force sensors in a bottom layer (not shown) of surface
10. One
such force sensor includes a single bladder (not shown) internally lined with
conductive
material to indicate bottoming out so that the pressure in the bladder will be
30 proportional to the weight of the patient when bottoming out is not
indicated. A
separate reference chamber is provided to determine the weight differential.
As with
interface sensors 15, a grid of weight sensors 24 can capture patient weight
without
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adverse effect from either the orientation of force optimization surface 10
atop an
articulated frame or the orientation of patient 16 atop surface 10. Although
weight
sensors 24 can provide an absolute weight value, controller 18 can be
configured to
determine accurate weight change values from weight sensors 24 even if a
precise
absolute weight is not easily obtained. Even without an accurate absolute
weight of
patient 16, a caregiver can derive meaningful information concerning patient
16 based
on knowledge of weight changes over time. Controller 18 can further be
configured to
detect a bed exit by patient 16 based on information from weight sensors 24,
and
provide an alert to caregivers accordingly.
An embodiment of force optimization surface 10 also includes
integrated diagnostic sensors such as heart rate, respiration, and temperature
sensors
26, 28, 30. Interface sensors 15 are used to obtain this information by
monitoring
pressure changes in real-time and analyzing the data to derive the vital
characteristics.
Software filters detect the appropriate respiration or heart rate signals. Non-
invasive
sensor systems for obtaining these patient parameters as are known in the art
can also
illustratively be integrated into force optimization surface 10 by embedding
them into
sensor layer 14. Temperature can be obtained through temperature sensing
transducers or fabrics as are also known in the art. For example, thermistors
may be
provided in the piezo resistive sensing layer discussed above. These
technologies
provide diagnostic capabilities in that controller 18 can monitor and display
vital signs
of patient 16 such as heart rate, respiration rate, and skin temperature.
Useful
information about a patient 16 is provided both by display of the current
values of
these parameters and by analysis of this information recorded by controller 18
over a
period of time.
Controller 18 includes software to monitor these conditions and
provide alerts 32 when vital signs go out of predefined bounds. Various levels
of
alerts 32 can be provided, ranging from informational alerts for relatively
minor
deviations to emergency alerts upon detection of life threatening conditions.
Controller 18 can be coupled to other systems to signal these alerts, such as
a system
at a nurse station, an automated paging system, etc.
Controller 18 uses information from sensors 15, 26, 28, 30 to derive
other diagnostic-information related to patient 16, such as an apnea condition
based on
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monitoring of respiration rate based on interface pressure sensors 15 or from
respiration sensor 28. Vital sign information from sensors 15, 26, 28, 30 can
also be
correlated to other measurements such as patient core temperature, pulse
oximetry,
etc. Force optimization surface 10 can further be configured with a vibrating
mechanism that is activated by controller 18 upon detection of an apnea
condition, in
order to vibrate patient 16 gently to induce recovery. An alarm can be
indicated if the
apnea condition persists beyond a predetermined amount of time.
Force optimization surface 10 can further be configured to measure
interface shear forces or pressures between patient 16 and surface 10 which
can also
10 restrict blood flow to patient 16 and contribute to development of pressure
ulcers.
Interface pressure sensors 15 as discussed above provide measuring a normal
force.
By providing sensors 1 S that also sense shear forces, or separate shear force
sensors
(not shown), controller 18 can be configured to adjust air pressures in
chambers of
mattress 12 based on both normal and shear forces if the anti-shear layer 40
is not
15 incorporated in support surface assembly 11.
Although the invention has been described in detail with reference to
certain illustrated embodiments, variations and modifications exist within the
scope and
spirit of the invention as described and defined in the following claims.
