Air-operated body support device

Airtight sacks are installed in parallel array to support a patient. A blower supplies air to the sacks through a function control valve system and a multi-tap high flow pressure selector. The pressure selector defines discrete zones of air pressure between its inlet and its exhaust to atmosphere. An adjustable tap communicating with individual sacks or group of sacks may be selectively placed in communication with any of the pressure zones to independently establish the pressure maintained in the corresponding sacks. The sacks may be connected to the line from the pressure tap at a single valve. The slide valve has one state permitting communication between the blower and the sacks, a second state sealing all sacks and third state venting all sacks. A detector and indicator of the patient's depth of deflection is provided for at least one sack. The blower may be used also to operate adjunctive air devices such as air pillow overlays for imparting desired movement to a patient.

FIELD OF THE INVENTION 
This invention relates to body support devices utilizing inflatable air 
sacks, and has particular application to hospital beds for patients at 
risk to pressure sores. 
BACKGROUND OF THE INVENTION 
Much attention has been directed for many years to the design of reduced 
pressure patient support systems for maximizing patient comfort and 
reducing the risks of pressure sores in bedridden patients. One of the 
early widely used therapies in this field was a floatation system marketed 
under the trademark "CLINATRON." This device is a large tub containing an 
air permeable sack filled with micron-sized silicon spheres. The spheres 
are formed into a fluidized bed by massive introduction of air into the 
bottom of the tub. This device marked the early stages of hospital rental 
equipment for patients at risk because of skin grafts, burns or pressure 
sores. The equipment was bulky and weighed almost one thousand pounds. An 
extremely large blower was required to effectuate the system, and any 
tears in the sack containing the silicon spheres could cause spheres to be 
blown out around the area of the apparatus. Despite its problems, and the 
great expense associated with utilization of the equipment, it has been 
widely used for patients at risk from excessive bed pressure. 
In more recent years, a class of devices has been introduced which the 
industry has come to designate as "low air loss". A typical low air loss 
support system has a plurality of upstanding parallel vapor-permeable air 
sacks inflated to provide support for the patient. Such devices are 
marketed under the trademarks "Monarch," "Air Plus," "Flexicair," and "Kin 
Air". The approach of this class of equipment is to provide gradual 
leakage of air from the sacks, either by perforating them at selected 
locations or by providing a "breathable" sack material which is permeable 
to the passage of vapor. Typically, air is pumped from a manifold on one 
side of the bed through the sacks extending transversely of the bed. The 
air is wholly or partially exhausted through holes or pores in the sacks 
and at least in some instances, through an exhaust port. The air losses 
necessitate the use of a rather large air pump or blower, and the systems 
constructed of this type tend to be bulky and expensive. To seek to avoid 
infection problems stemming from the holes or open pores of the sack 
material, special sterilization precautions are necessary. Some of these 
commercial beds are provided with special sack configurations to impart 
desired movements to the patient. The beds are not easily adaptable to 
acute care hospital use and are not radiolucent so as to permit taking 
X-rays of a patient lying in one. This class of beds includes permanent 
electrical circuitry making its use unacceptable in certain hospital 
environments. Because of their air loss characteristic, these beds cannot 
support the patient when blower operation is terminated. Thus, if the 
patient is to be transported to another hospital area, the sacks will be 
deflated unless battery power backup is provided. Despite their 
deficiencies, these beds have grown to dominate the market, which is 
predominantly served by the temporary leasing of these special purpose 
beds to hospitals as required for particular patients, generally at a rate 
to the hospital of about $100.00 per day. For reference, U.S. patents 
issued to makers of such commercial beds include U.S. Pat. No.3,822,425, 
3,909,858, 4,099,276, 4,488,322, 4,525,585 and 4,638,519. 
Other simple approaches to providing reduced pressure patient support 
systems include water mattresses, air mattresses (including types with 
varying air pressure in alternating sections of the mattress) and 
"egg-crate" mattresses. 
The utilization of the present invention is believed to present a 
substantial advance over the technology known in this industry. By 
providing essentially zero air-loss sacks in a system adapted to permit 
the clinician to carefully and quickly control the air pressure in all 
parts of the support system and to quickly carry out procedures required 
for care of the patient, the invention overcomes many of the problems of 
the art. The air sacks and electrical components of the system can quickly 
be installed or removed from a radiolucent intensive care bed. On removal, 
there are no electrical components remaining on the bed, and the bed may 
be utilized efficiently in acute care hospital use. Because the invention 
does not utilize air sacks with holes or permeable pores, problems of 
infection and sterilization are minimized. The no-air loss sack approach 
permits the utilization of a much more compact air flow source. The end 
result is a system which is lightweight and relatively simple and 
inexpensive. The bed may be transported without air pump operation while 
still maintaining air pressure in the sacks to support the patient. In one 
preferred embodiment, this "transport" mode isolates each sack, or 
selected adjacent groups of sacks such as sack pairs, from others so that 
the pressure profile established among the sacks by the clinician is 
preserved during the transport mode. This configuration also permits 
efficient use of the air blower, since the blower can be turned off for 
long periods of time by placing the apparatus in this sealed-off transport 
configuration. This may be particularly beneficial in providing economical 
use of beds of this type in the home environment. Because of the ability 
to preserve the support pressure profile without full use of the blower, 
the blower also can be used to drive adjunctive air devices useful in 
other aspects of patient therapy. For example, the blower may be used with 
adjunctive devices such as air pillow overlays for rolling the patient, 
and/or for flexing portions of the patient's body such as knees or feet. 
The system is readily adaptable to automatic, timevarying rhythmic pressure 
variance therapies. It also may be adapted to automatic pressure control 
in feed back loops responsive to the weight and position of a patient. 
SUMMARY OF THE INVENTION 
In accordance with the invention, there is provided a body support device 
comprising a plurality of upstanding parallel elongated air sacks abutting 
to form a support surface, the material of the sacks being substantially 
impervious to the passage of air and other fluids. Each sack is provided 
with an inlet communicating with its interior, and all of the inlets are 
connected to an air flow production means to provide pressurized air to 
all of the sacks. Thus, each sack, in cooperation with the air flow 
production means, forms a support pressure system for the part of the 
person's body on the sack. Means are provided for selecting and 
establishing the pressure maintained in each sack or in individual groups 
of sacks such as adjacent sack pairs, and for closing the pressure support 
systems to retain air pressure in the sacks. 
In a specific embodiment, there are provided valve means to permit rapid 
switching of connections between the air flow production means and the 
sacks from a first state in which the inlet of the air flow production 
means communicates with atmosphere and the outlet communicates with the 
sack inlets to pressurize the sacks, and a second state in which the 
intake of the air flow production means communicates with the sack inlets 
and the outlet is vented to atmosphere, so that rapid pump down of the 
device may be achieved by causing the valve means to move to the second 
state. 
Devices constructed in accordance with the invention may also include means 
for sensing the distance that the top of one of the air sacks is 
supporting the patient above a reference point, thus sensing the depth of 
the patient's deflection of the sack to enable optimal setting of the 
system pressure level. 
In one form of the invention, each sack is free of every other sack, so 
that it may be removed from the array, and there is provided check valve 
means associated with the bed adjacent the sack inlet which is operable on 
removal of the sack to stop the flow of air at the check valve. 
The invention contemplates that the means for selecting and establishing 
the pressure maintained in the sacks may consist of a high flow conduit 
with an inlet connected to the outlet of the air flow production means. 
The conduit has discrete zones, each zone being maintained at a different 
pre-selected percentage of the inlet pressure. Means are provided for 
selectively connecting the inlet of each sack, or group of sacks, to a 
selected one of the zones. 
Particularly adapted to the purpose of controlling the pressure in the 
sacks is a multi-tap pressure selector having an inlet connected to the 
air flow source and a first block on one face of the selector having a 
plurality of channels, one of which is connected to the inlet. A second 
block on the opposite face of the selector also has a plurality of 
channels. A tap block interposed between the first and second blocks has a 
plurality of restricted passageways, each of which interconnects a 
different pair of channels on opposite sides of the selector. Each 
restricted passageway produces a pressure drop between the two channels of 
its interconnected pair. The channels and restricted passageways form a 
continuous sealed air flow conduit leading from the inlet, with each 
channel defining a zone of discrete and unique pressure. A plurality of 
pressure taps are slidably positioned in the tap block, each of the taps 
communicating with a different sack or group of sacks. Each tap may be 
moved to selectively connect its air sack or air sack group to any one of 
the channels in the first and second block, and thus to any selected one 
of the discrete pressure zones. The selector has an outlet connected to 
one of the air flow channels at the end of said air flow conduit remote 
from the inlet. 
In one embodiment, the invention incorporates a valve interposed between 
the pressure selector and the air sack inlets. The valve may be moved 
between a first state in which the sack inlets are open to fluid 
communication from the air flow source through the pressure selector, and 
a second state closing the sack inlets so that the pressure profile among 
the sacks established by the air flow source and the pressure selector 
when the valve is in the first state may be substantially preserved upon 
movement to the second state. In a particular form, the valve is a slide 
valve having a first surface in which air passages from the pressure 
selector terminate, and a confronting second surface on which the air sack 
inlets are arrayed, and the valve operates by relative sliding motion 
between the two valve surfaces. The valve may have a third state venting 
the sacks to atmosphere for deflation. 
The invention also contemplates a valve which is biased to the state 
sealing the air sack inlets to preserve the pressure profile among the 
sacks, and an automatic valve actuator causing the valve to switch to the 
state connecting the sacks to the air flow source through a pressure 
selector only during times when the air pressure produced by the air flow 
source for use in the air sacks exceeds a threshold pressure. 
A multimode system employs the invention for both supporting a patient on 
air sacks having a desired pressure profile and for intermittently causing 
movement of the patient. This system employs a single air flow source and 
at least one pressure selector, and a movement overlay removably 
positioned on the air sacks having a plurality of inflatable compartments, 
the inflation and deflation of which are adapted to cause selected 
movement of the patient. In this aspect, the invention includes flow 
control means for exposing air from the air flow source to the sack inlets 
and also for directing air into and from the compartments of the movement 
overlay to produce desired movements while preserving a desired pressure 
profile among the sacks. 
The advantages of the invention can be appreciated more fully by reference 
to the enclosed drawings which depict embodiments of the invention in more 
detail.

DETAILED DESCRIPTION 
A critical care hospital bed to which the invention has been applied is 
indicated by the reference numeral 10 in FIG. 1. Bed 10 includes a 
segmented platform 12 lying generally horizontally between folding side 
rails 14 and 16. The articulated segments of platform 12 are adjusted by a 
hydraulic system to various positions dictated by patient comfort or 
clinical considerations, including medical procedures to be carried out on 
the patient. The hydraulic adjustments are controlled by the clinician 
through a control panel 18 located at the foot of the bed. The bed is of a 
radiolucent character, minimizing elements extending through the central 
area of a vertical projection of the patient lying in the bed which would 
interfere with the taking of x-rays of the patient. A bed having the 
general characteristics thus far described, which is appropriate for 
application of this invention, is a critical care bed marketed by 
Humanetics, Inc. of Carrollton, Tex. under the trademark "CardioSystems". 
As depicted in FIG. 1, the ordinary mattress of bed 10 has been removed and 
replaced by an array of twenty air sacks 20 forming part of a body support 
system in accordance with this invention. The support sacks 20 are 
fluid-tight, and are arranged in parallel array extending generally 
between the side rails 14 and 16. The sacks 20 are not perforated by 
sewing or any other means, so that the material's airtight characteristic 
is preserved. The sacks may be formed from any suitable impermeable 
material by heat sealing. One sack material preferred for the application 
of the invention is a nylon to the inside of which a heat sealable 
urethane coating is applied. Each sack 20 is independent and separate from 
every other sack in the array, so that it may be removed and/or replaced 
by itself. The sacks are held in position by a series of snaps 22 located 
along each side of platform 12. 
As seen in FIG. 2, each sack is formed with an inlet 24 extending into the 
interior of the sack at one end thereof. An array of horizontally-oriented 
quick connection check valve couplings 26, each having a release lever 27, 
is spaced along the margin of the platform 12 in mounting brackets 28 
adjacent to side rail 14, one corresponding to each of the sacks 20. The 
mating connector portion for the coupling is located on inlet 24 of each 
sack, so that each sack may be quickly provided with connection through a 
check valve to the air supply system of the bed described below. Check 
valve 26 and its complimentary connection portion associated with the 
inlet 24 may, for example, be the quick connect couplings marketed under 
the trade name "CPC" by Colter Products Company. 
Only one check valve coupling 26 is illustrated in FIG. 2 for clarity of 
illustration, but the array of check valves corresponds on a one-to-one 
basis with the number of sacks provided in the system. A cover 30 is 
provided for each segment of platform 12 along the margin of the platform 
containing the check valve connectors 26. Cover 30 is provided with 
horizontal apertures 32 for access to each of the check valve connectors 
26. Disconnection of sack inlet 24 from the check valve 26 may be quickly 
affected by raising inlet 24 to press lever 27 against the top of cover 
30, releasing air sack 20 from the array and enabling the check valve 26 
to stop all passage of air. Cover 30 minimizes the possibility of fluid 
spill interference with the connector's functioning. 
In order to provide a level base for the sacks 20, and to provide some 
margin of comfort in the base of the bed at times when the support system 
is not functional, a foam pad 34 approximately equal to the height of 
cover 30 covers the remainder of platform 12. A conventional comforter 
(not shown) may be placed over the air sacks to promote evaporation of 
perspiration or other liquids, and to help manage problems created by 
incontinence. 
FIG. 3 schematically illustrates the manner in which support sacks 20 are 
interconnected in a system in accordance with the invention to provide 
easily controlled support for the body. The major operative elements of 
the system are an airflow production source such as air pump or blower 40, 
a function control valve system 41, a high flow multi-tap pressure 
selector 42, and the array of support sacks 20. 
The function control valve system 41 and pressure selector 42 are, as will 
be seen, compact units which can be installed underneath bed platform 12 
along one edge of the bed behind control panel 43. Blower 40 may be very 
compact and placed in a portable box (not shown) to be removably hung 
under the bed and connected to the function control valve system 41. A 
suitable method of connection is by a quick disconnect arrangement of 
sliding confronting plates having a pair of ports on each plate. The ports 
on the box are associated with the inlet and outlet of the blower 40, and 
are matched to the two ports communicating with system 41. System 41 
includes five on/off valves, 44, 46, 48, 50, and 52. Valves 44-52 may be 
operated by a single control shaft carrying a series of five cams such as 
the one indicated at numeral 54, to operate the valves between their on 
and off positions. The cams 54 may be controlled by the clinician 
utilizing function control knob 56 on the control panel 43, shown in FIG. 
4, to turn this shaft. Although cam operation of the valves is a 
convenient and simple one for construction and use, other valve activation 
mechanisms may be employed, including solenoids. Valve 44 blocks or 
enables communication between the positive or outlet side of pump 40 and 
inlet 58 of the pressure selector 42. Valve 46 gates the connection 
between the pump outlet and atmosphere. Valve 48 provides on/off 
connection between the negative side or inlet of pump 40 and atmosphere. 
Valve 50 is also connected to the inlet of pump 40, and provides on/off 
communication with the inlet 58 of selector 42. Valve 52 simply permits 
connection of the outlet 59 of selector 42 to atmosphere. Function control 
system 41 also includes a pressure gauge 60 and a bleed valve 62 
permitting the outlet side of pump 40 to be selectively bled to atmosphere 
by the setting of weight selection knob 64 located on control panel 43 as 
shown in FIG. 4. This setting establishes the pressure at selector inlet 
58. 
The structure and operation of pressure selector 42 is best understood in 
conjunction with FIGS. 5-7. Selector 42 includes a front block 70 having a 
series of channels 72, 74, 76, 78 and 80 formed in the rear face thereof. 
Channel 72 is the high pressure entrance plenum communicating with 
selector inlet 58. A rear block 81 is formed substantially identically to 
the front block 70. Channels 82, 84, 86, 88 and 90 formed in the face of 
block 81 confront, but are spaced from, the channels 72-80 of block 70. 
Interposed between block 70 and block 81 is a tap block 92 which is 
sealingly engaged with blocks 70 and 81 by suitable means such as gaskets 
(not shown). 
Channel 72, which communicates with selector inlet 58 at one end thereof 
(FIG. 7), communicates at the opposite end (FIG. 8) through restricted 
passageway 102 with its corresponding channel 82 in the rear block 81. 
Likewise, at that same end, as seen in FIG. 8, channels 74 and 84 are 
connected by restricted passageway 104; channels 76 and 86 are connected 
by restricted passageway 106; channels 78 and 88 are connected by 
restricted passageway 108; and channels 80 and 90 are connected by 
restricted passageway 110. The ends of certain channels of the first and 
second blocks 70 and 81 are also interconnected at section 7--7 by slanted 
passageways, as indicated in FIG. 7. Restricted passageway 114 connects 
channels 82 and 74; restricted passageway 116 connects channels 84 and 76; 
restricted passageway 118 connects channel 86 to channel 78; and 
restricted passageway 120 passes between channel 88 and channel 80. The 
end of channel 90 at the cross-section taken in FIG. 7 communicates in 
turn with outlet 59 from the selector 42. It will be appreciated that the 
circuitry thus defined in blocks 70 and 81 together with the tap block 92, 
is a sealed airflow conduit extending from the selector inlet 58 to outlet 
59. The conduit passes through the length of each channel 72-90 in series, 
with a restricted passageway providing communication across tap block 92 
between each channel in the series. Each restricted passageway, by its 
restricted size in comparison to the flow cross-section of the channels 
themselves, provides a pressure drop between each of the ten sections of 
the flow conduit. Thus, each of the ten channels defines a unique pressure 
which is a preselected percentage of the inlet pressure, with pressures 
declining from channel 72 to channel 90. A suitable restriction size is 
established depending on the desired balance between two competing 
characteristics: (1) smaller size will increase the maximum pressure 
available to the system; and (2) larger size will increase flow rates and 
thus decrease the time required to inflate or deflate the sacks. 
The pressure zones defined in the channels of blocks 70 and 81 may be 
communicated with individual ones of the air sacks 20 by means of a series 
of pressure taps 130 carried in shafts 131 in tap block 92. A tap 130 and 
shaft 131 are provided to correspond with each sack 20. A representative 
tap 130 and shaft 131 are shown in FIG. 6. Tap 130 is formed with a bore 
132 extending through the tap from its upper end 133. The shaft 131 may be 
sealed toward its top and bottom by O-rings (not shown). A series of 
tapping ports communicates between each shaft 131 and each channel of 
blocks 70 and 81. Shaft 131 is connected to channels 72, 74, 76, 78, 80, 
82, 84, 86, 88 and 90 by tapping ports 142, 144, 146, 148, 150, 152, 154, 
156, 158 and 160, respectively. An orifice 162 is formed in the wall of 
tap 160 facing the series of tap ports 152-160. A second orifice 164 in 
the opposite side of tap 130 faces the series of tap ports 142-150. 
Orifices 162 and 164 are on diametrically opposed sides of the tap 130, 
and are axially spaced from one another by one-half the distance between 
adjacent tapping ports in the series 142-150 or 152-160. In this way, as 
any tap 130 is axially moved, the user may expose the central bore 132 of 
that tap for communication with any one of the ten channels defined in 
blocks 70 and 81. In the apparatus depicted, manual movement is enabled by 
horizontally extending lever 166 located near the lower end of tap 130. 
Each tapping shaft 131 communicates adjacent end 133 of tap 130 to a 
fitting 170. Fitting 170 of each tap is connected by hose 172 to one of 
the check valves 26 mounted on the bed platform 12. Thus, there is 
one-to-one correspondence of taps 120 to sacks 20. Alternatively, each tap 
may be connected to the inlets of an adjacent pair of sacks, an 
arrangement which reduces the number of taps and other parts required, and 
thus makes fabrication more economical. 
Reference is now made to the valve position table illustrated in FIG. 3. 
The control shaft 54 has four different positions defining different 
combinations of open and closed states for the five valves 44-52. These 
combinations are shown in the table. In normal operation, valves 44, 48 
and 52 are open, while valves 46 and 50 are closed. Air is taken into the 
pump through open valve 48, and pumped to selector inlet 58 via open valve 
44. It passes through the 10 pressure zones of the selector 42 and out 
open valve 52. Each tap 130 is adjusted to cause its corresponding sack to 
maintain the pressure of a selected one of the zones. Individual 
adjustment of pressure in one sack by manipulating one of the taps 130 has 
no long term effects on the pressure of the other sacks and only minimal 
transient effects. 
A second functional position of control shaft 54 is a rapid pump down or 
deflation of the air sacks 20 denominated as "CPR", as rapid deflation may 
be desired for the emergency administration of CPR. In this functional 
setting, each of the valves assumes the opposite state from that which it 
maintains during normal setting, so that the pump positively pumps down 
the sacks. The third functional setting is maximum inflate, which is to 
rapidly fill all of the air sacks in the system. This may be desired 
simply to set up the system or may be called for by radiographic 
procedures. In this functional setting, all valves except for valve 52 are 
in their normal operational state. On maximum inflate, valve 52 closes the 
exhaust port 59 from selector 42. Finally, the fourth functional setting 
is the transportation mode, which implies the cessation of airflow 
production in the system. In this mode, all valves are closed to preserve 
air pressure in the sacks. In the three non-normal function settings, it 
is possible that the blower could be run air-starved. Suitable protection 
to prevent harm to the blower, as by a time or temperature cut-off or 
relief valve, may be provided. 
Referring to FIG. 4, it can be seen that a readily understandable control 
panel 43 is mounted on one side of the bed in front of selector 42 and 
function control system 41. The left hand portion of the panel includes 
the twenty individual tap levers 166 mounted for vertical sliding movement 
to produce the axial movement of each tap 130. By manual adjustment of 
each lever, each individual air sack may be communicated to a different 
one of the pressure zones in pressure selector 42. Preferably, the tracks 
174 guiding levers 166 are provided with ten detent positions 
corresponding to each of the ten axial positions of each tap. 
At the right end of panel 43, the function control knob 56 permits the 
clinician to place the system into any one of the four functional modes. 
Pressure gauge 60 reflects the pressure generated at the outlet of the 
pump, as regulated by the setting of bleed valve 62. 
The setting of weight selector 64 to control bleed valve 62 is further 
enabled by the deflection indicator system schematically illustrated in 
FIG. 9. A central sack 20 in the array is provided with a rectangular 
sheet 180 stretched across its upper surface. Four cords 182 extend 
downwardly from sheet 180 over pulleys 184 to a common point of joinder 
186 to cord 188. The common cord 188 is guided by indicator pulleys 190 
behind an indicator scale 192 mounted on the side of the bed. Tension is 
provided to cords 182 and 188, to hold sheet 180 firmly to the sack 20, by 
spring 194. Cord 188 carries a pointer 196 which slides in a slot 198 in 
scale 192. This guides the clinician in adjusting the overall system 
pressure by turning weight selection knob 64 to change the setting of 
bleed valve 62. The adjustment is made until the pointer 196 is in the 
central range of scale 192, indicating sufficient pressure to maintain the 
patient well above the platform 12, but sufficient softness to enjoy the 
benefits of low pressure support. 
Of course, for any given air pressure in the sacks, a heavier person will 
sink deeper in the sacks than a lighter one. Little or no penetration 
would mean that the weight of the patient is being supported by a minimum 
contact area, maximizing contact pressure. By reducing air sack pressure 
and permitting the contact area to increase, the contact pressure is 
reduced. Eventually, the contact area is maximized by pressure reduction, 
and further pressure reduction will produce no additional benefit. The 
scale 192 and pointer 196 should be aligned so that the central range of 
indication is in the zone of maximized contact area. 
While adjustment of pressure at selector inlet 56 by adjusting weight 
selector knob 64 has been illustrated to effect proper patient depression 
of the sacks, other structural techniques may be used. For example, by 
providing valves 44-52 with continuous adjustment capability between their 
"on" and "off" states, and by modifying cam 54, the bleed valve 62 can be 
eliminated and the adjustment be performed by manipulation of the function 
selector knob 56 in a range around the normal function setting. The cams 
54 would be configured to gradually move valves 44-52 between their normal 
functional states and their opposite states as the knob 56 is turned from 
"normal" to "CPR". This gradually reduces the pressure at selector inlet 
58. The cam 54 controlling valve 52 would gradually increase the 
restriction of valve 52, as knob 56 moves from "normal" to "maximum", thus 
increasing the pressure at 58. 
Other forms of detecting and indicating the depth of the patient's 
deflection may be used. For example, an ultrasonic emitter/sender may be 
mounted below a sack 20 in the center of platform 12. Reflected energy 
signals returning to the platform 12 can be detected to ascertain the 
depth of the patient's depression of the top of the sack. Such a system 
producing electrical data signals could be used in a feedback loop to 
automatically control the overall system pressure, as by adjusting bleed 
valve 62. 
The system of this invention is readily adapted to automatic pressure 
control modalities. A multiple feedback control system for the individual 
pressure taps is schematically illustrated in FIG. 10. The individual 
pressure taps 200 are set in response to signals from individual 
deflection detectors 202 mounted with each sack, such as ultrasonic 
emitter/sensors described above. The signals from each detector 202 are 
sent individually to a processor 204 which controls individual stepper 206 
for adjusting each tap 200. Each signal is continuously compared by 
processor 204 to a desired valve for the particular sack, and any error 
signal generated causes the processor to activate the particular stepper 
206 corresponding to the detector causing the signal. Stepper 206 moves 
tap 200 in a direction to minimize the error signal. 
Although this multiple feed-back system is optimally operated on deflection 
signals, it will be appreciated that individual sack pressures could be 
sensed to produce the error signals. The pressure to be maintained in a 
sack to produce the desired range of deflection, however, will vary from 
patient to patient. A pressure sensing system should have as its base line 
desired pressure a value which is established after observing the patient 
in position. 
This invention may also be utilized in a system for producing time-varying 
rhythmic pressure therapies, as schematically illustrated in FIG. 11. 
Rhythmic variation in pressures, with each individual sack passing through 
a range of available pressure with the passage of time, is often desired 
and can be easily accomplished by the system of this invention. Taps 220 
are adjusted by individual cams 222 on cam shaft 224 driven by stepper 226 
under the control of timer 228. By selection of cam shape and timing of 
stepper commands, the clinician can vary the pressures in individual 
portions of the bed as desired. 
It will be appreciated from the foregoing description that many benefits 
and advantages flow from application of this invention to the hospital 
environment. Adjustment of the pressure taps gives a quick way of 
establishing the desired firmness or softness in each supporting sack. 
Adjustment of one tap does not cause variations in the pressure of other 
sacks. The system can be quickly switched from normal function to rapid 
deflation or pump-down. The device can be deprived of its air flow 
operation and still support the patient with an air cushion. The 
elimination of passage of air or other vapor through the sacks reduces the 
risks of infection and simplifies cleaning and sterilization. The 
fastening of sacks to bed is done with connectors concealed from the 
hazards of fluid spills. The sack connectors permit removal of any sack 
without compromising the integrity of the air circuit. 
The sacks and blower box may be readily removed to permit use as an 
ordinary bed, eliminating the necessity for a single use rental bed which 
is costly and of limited versatility. The air flow circuitry components 
are compact and do not compromise the radiolucent characteristics of the 
bed. The system is adaptable to automatic control of pressures including 
control in response to deflection detection as well as time-varying 
rhythmic pressure adjustment. 
A preferred system embodying the invention, employing a slide valve 
connecting pressure selector taps to air sacks, and enabling multiple uses 
of a single blower, is illustrated in FIG. 12. As depicted in FIG. 12, an 
array of air-tight support sacks 240 is connected to an air flow source 
such as a blower or air pump 242 which provides the pressurized air to 
inflate the sacks at selectable pressures to provide a support pressure 
profile desired by the clinician. The output 244 of air flow source 242 is 
alternatively directed by two position valve 246 to the system for 
supplying the air sacks 240 or to a patient movement overlay system 248, 
which will be described in more detail below. In the position illustrated 
in FIG. 12, the output of the blower air pump 242 is connected by valve 
246 to the air supply system for air sacks 240. Air is supplied to the 
inlet 248 of a high-flow pressure selector 250. Pressure selector 250 is 
constructed, as described above in detail in connection with FIGS. 4-8, to 
define zones of distinct pressure which are predetermined percentages of 
the maximum pressure at inlet 248. The outlet 252 of selector 250 extends 
through two position maximum inflate valve 254. Valve 254, in its normal 
setting depicted in FIG. 12, simply exhausts the output, but may be moved 
to a closed position for rapid inflation of sacks 240 at startup. 
The maximum pressure of selector 250 in operation may be optimized by the 
user by means of weight control valve 256 operated in conjunction with 
pressure gauge 258. Weight control valve 256 and gauge 258 correspond to 
similar elements indicated by the reference numerals 60 and 62 in FIG. 4. 
Their operation may be assisted by one or more deflection detectors such 
as described in conjunction with FIG. 9. 
The output of blower 242 may also be connected through valve 260 to a 
closed air bellows 262 which will be described in more detail below. A 
Fowler boost valve 264 is also placed in parallel with pressure selector 
250. Valve 264 has a normal setting depicted in FIG. 12 and a second 
setting which directs the output of valve 264 through a restricted orifice 
266 for increasing the air pressure at selector inlet 248 by approximately 
fifty percent. This conveniently permits the operator to quickly increase 
the pressures in the pressure zones of selector 250, and thus in the air 
sacks 240 by approximately fifty percent, to facilitate positioning the 
patient in an upright sitting position in the bed, which requires higher 
sack pressures. 
A slide valve 268 provides the interface between pressure selector 250 and 
the air sacks 240. The pressure selector taps 270 extending from pressure 
selector 250 are connected to a sliding valve member 272 in valve 268. The 
inlet lines 274, each extending from an adjacent sack pair, connect to the 
stationary member 276 of valve 268. Valve 268 operates by relative sliding 
motion of the confronting surfaces of members 272 and 276 between three 
discrete positions. The first is a normal position, in the middle setting 
of slide valve 268, which connects each pressure tap 270 to a 
corresponding sack pair inlet 274. When the valve member 272 is moved to 
the right as shown in FIG. 12, the sack pair inlets 274 are all sealed 
against the confronting face of member 272, so that the pressure in sacks 
240 is maintained in substantially the profile set by the user prior to 
movement to this transport mode. The third position of valve 268 is the 
"CPR" mode in which the sack pair inlets 274 are aligned with vent ports 
in member 272 so that the sacks 240 are vented to atmosphere, permitting 
their deflation. 
Valve 268 is biased into the transport mode, in which each sack pair is 
isolated from the remainder of the system, by biasing spring 278. Manual 
selection of the positions of valve 268 may be made by one or more control 
levers such as depicted at 280 in FIG. 12. Automatic movement of the valve 
from the transport mode into the normal mode, connecting the pressure 
selector taps 270 to the sack pairs 274, is effected by bellows 262 upon 
its inflation by pump 242. 
Construction of a suitable slide valve 268 is illustrated in more detail in 
FIGS. 13 and 14. In these figures, movement of sliding valve member 272 to 
the left produces the transport mode, while movement to the right gives 
the vented CPR mode. Stationary valve member is provided with a spaced 
array of passages 282 passing completely therethrough. Each of passages 
282 is connected on the outer side of valve 268 to an inlet line 274, each 
of which communicates with a pair of support sacks 240. Sealing O-rings 
284 surround each passage 282 at the surface of stationary valve member 
276 confronting sliding valve member 272. A spaced array of corresponding 
passages 286 is formed through sliding valve 272 corresponding exactly to 
passages 282 of stationary valve member 276. These passages 286 are 
connected on their outside to pressure selector tap lines 270. In FIG. 14, 
the valve 268 is shown in its normal operating position, with the passages 
282 and 286 aligned to communicate the air pressure from each tap 270 to 
its corresponding air sack pair 240. In this way, the pressure provided by 
the setting of each tap 270 is communicated to its corresponding sack pair 
to establish a pressure profile among the sacks as desired by the 
clinician. An equal number of vent ports 288 are provided through sliding 
valve member 272 just to the left of each passage 286. By movement of 
sliding valve member 272 to the right into the "CPR" position, all sacks 
are vented to atmosphere through the vent ports 288. Movement of sliding 
valve 272 to the left creates the "transport" made, blocking off the 
proximal ends of passages 282 so that the sacks are sealed and each sack 
pair is isolated from every other sack pair. 
As depicted in FIG. 13, the valve 268 may be positioned transversely of the 
bed so that control knobs 280 may be provided for manual movement of the 
valve among its three states from either side of the bed. Knobs 280 are 
secured to suitable levers 290 for effecting the sliding movement of 
member 272. Detents 292 and 294 are provided for the extreme positions of 
valve 268, being the transport and CPR modes, respectively. 
The automatic valve actuator bellows 262 is positioned against a stationary 
portion of the bed structure 296. Upon its inflation, bellows 262 exerts a 
force upon actuating paddle 298 connected by lever arm 300 the valve 
actuating lever 290. Biasing spring 278 connected between lever arm 300 
and stationary structure 296 biases valve 268 through lever arm 300 and 
lever 290 to the transport mode. When air from the pump 242 inflates the 
bellows 262, automatic movement of valve 268 into the normal mode is 
effected. Upon any cessation of operation of the blower 242, the bellows 
pressure will be depleted and valve 268 will automatically return to the 
transport mode, sealing the individual support sack pairs. 
As depicted in FIG. 12, the entire operation may be controlled through a 
central controller/timer 310. Controller 310 communicates with valve 260 
through line 312, so that the automatic actuating bellows 262 may be 
disabled by moving valve 260 to its exhaust position, disconnecting 
bellows 262 from the air supply. Controller 310 also controls system 
selector valve 246 through line 314. The air supply system may be 
converted by controller 310 to periodic activation of the movement overlay 
system 248, either by manual selection or by automatic time cycling. When 
activation of the movement overlay system 248 is desired, valve 260 is 
first moved to the exhaust position so that the support sacks 240 are 
locked into their sealed transport mode to preserve the pressure profile 
established by the clinician among the array of air sacks. Then, valve 246 
is switched over so that blower 242 is supplying its output through line 
316 to the movement overlay pressure selector 318. 
The overlay system 248 employs one or more inexpensive air mattress 
overlays. As depicted in FIG. 12, three overlays used on top of the 
support sack array may be used, either individually or all at once. The 
first, overlay 320, effects side to side roll or positioning of the 
patient's body as well as providing for knee flexure. Overlay 322 may be 
positioned against a moveable foot board to produce foot flexing. Overlay 
324 provides a plurality of small volume sacks for lower leg stimulation. 
Overlay 320 is divided into five separate air compartments. Pillow 
compartment 326 extends across one end of overlay 320. Immediately below 
the pillow 326 are two side-by-side roll compartments 328 and 330. At the 
lower end of overlay 320 are two transverse leg flexure compartments 332 
and 334. The foot flexure overlay 322 includes a single compartment to be 
placed between the patient's feet and a vertical board such as a moveable 
foot board. Lower leg stimulation overlay 324 includes a plurality of 
transverse compartments 336. 
Each of the compartments of overlay 320, 322 and 324 is connected through a 
two position valve 338 to a path leading from a selected zone of the 
pressure selector 318 through a pressure tap 340. Controller 310, via line 
314, can alternate the valves 338 between venting the compartment and 
connecting it to its corresponding pressure tap 340. Controller 310 may 
also control, via line 342, the pressure setting of each tap 340. 
Thus, with the system supplying air to line 316, any selected periodic 
inflation or deflation of the compartments of overlays 320, 322 and 324 
may be effected. Roll compartments 328 and 330 may be utilized to position 
the patient on the bed. With compartments 328 and 330 deflated, no bias to 
the patient is provided. By inflating either of these compartments, the 
patient may be rolled to one side or the other. Flexing of the patient's 
legs may be affected by periodic inflation of compartments 332 and 334. 
The patient's foot may be flexed by inflation and deflation of 
compartments 322. A periodic ripple or wave through the compartment 336 of 
lower leg stimulation overlay 324 may be effected to advantageously 
stimulate circulation. 
Rather than time share the blower by alternating selection of positions of 
valve 246, it is within the scope of this invention to simultaneously 
operate a support sack array 240 and overlay system 248. If the air 
movement demands of a selected overlay are small, this may be achieved by 
singly adding additional taps to selector 250 to drive the overlay. 
Otherwise, it may be accomplished by dividing the air output of blower 242 
to drive both systems simultaneously. Even when use of an overlay is not 
desired, the isolation of air sack pairs in the transport mode permits the 
blower to be turned off for the majority of the time of operation. The 
blower need be turned on only briefly at infrequent intervals to insure 
maintenance of the desired pressure profiles. 
Although specific embodiments of the invention have been illustrated in the 
accompanying drawings and described in the foregoing detailed description, 
it will be understood that the invention is not limited to the embodiments 
disclosed, but is capable of numerous rearrangements, modifications and 
substitutions of parts and elements without departing from the spirit of 
the invention.