Patent Publication Number: US-2021186784-A1

Title: Support surface overlay with vacuum enclosure and method of operation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit under 35 U.S.C. § 120 of U.S. Provisional Patent Application No. 62/949,961, filed on Dec. 18, 2019, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND AND SUMMARY OF THE DISCLOSURE 
     Alternating pressure support surface overlays are known in the art. Some such overlays include a bladder having first and second selectively and independently inflatable and deflatable compartments. The first compartment may be inflated while the second compartment is deflated and vice versa so that the bladder selectively applies and relieves pressure to different parts of the body of a patient or other user disposed thereon. 
     It also is known in the art to enclose such a bladder within an envelope, the envelope including a lower panel below the overlay bladder and an upper panel above the bladder. In some instances, the upper and lower panels of the envelope are imperforate. In others, at least one of the upper and lower panels (usually the upper panel) is perforated to allow pressurized air to flow from within the envelope to outside the envelope, thereby providing ventilating air to the body of a user thereon. 
     A drawback to such an arrangement is that the bladder may be loosely enclosed within the envelope so that at least one panel of the envelope is prone to shifting laterally with respect to the overlay when the assembly is manipulated, particularly with a patient or other user disposed thereon. This can lead to bunching or wrinkling of the panel(s) of the envelope, thereby creating pressure points adversely affecting patient comfort and the efficacy of the overlay. Alternatively or additionally, the bladder may shift or bunch up within the envelope, also thereby creating pressure points adversely affecting patient comfort and the efficacy of the overlay. 
     It would be desirable to control such shifting of the panel(s) of the envelope and shifting of the bladder therein. The disclosure shows and describes illustrative embodiments of a system configured and operable to do so. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top is a top plan view of an illustrative system according to the present disclosure, the system including a bladder having first and second selectively and independently inflatable compartments disposed within an interior region of an envelope, the envelope including a first panel, a second panel, and a seam joining the first panel and the second panel to the overlay; 
         FIG. 2  is a bottom plan view of the system of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the system of  FIG. 1 ; 
         FIG. 4  is a detail view of a portion of the bladder of  FIG. 1 ; 
         FIG. 5  is a side elevation view of the system of  FIG. 1 ; 
         FIG. 6  is a partial top plan view of the system of  FIG. 1  according to the present disclosure, showing some of the features thereof in greater detail; 
         FIG. 7  is a schematic diagram of an illustrative pneumatic system configured to selectively pressurize the first and second inflatable compartments and to selectively draw air from the interior region of the envelope; 
         FIG. 8  is a cross-sectional end elevation view of the system of  FIG. 1  showing the layers of the envelope in relation to the bladder with both of the inflatable compartments of the bladder shown schematically in a deflated condition, and the envelope at atmospheric pressure; 
         FIG. 9  is a cross-sectional end elevation view of the system of  FIG. 1  with one of the inflatable compartments of the bladder in an inflated condition, the other of the inflatable compartments of the bladder in a deflated condition, and the envelope at atmospheric pressure; 
         FIG. 10  is a perspective and a cross-sectional end elevation view of the system of  FIG. 1  with both of the inflatable compartments of the bladder in an inflated condition, and the envelope at atmospheric pressure; 
         FIG. 11  is a cross-sectional end elevation view of the system of  FIG. 1  with one of the inflatable compartments of the bladder in an inflated condition, the other of the inflatable compartments of the bladder in a deflated condition, and a first proportion of air removed from the interior region of the envelope so that the first panel of the envelope conforms to the surfaces of the bladder to a greater degree than does the second panel of the envelope; 
         FIG. 12  is a perspective and a cross-sectional end elevation view of the system of  FIG. 1  with both of the inflatable compartments of the bladder in an inflated condition, and a first proportion of air removed from the interior region of the envelope so that the first panel of the envelope conforms to the surfaces of the bladder to a greater degree than does the second panel of the envelope; 
         FIG. 13  is a cross-sectional end elevation view of the system of  FIG. 1  with one of the inflatable compartments of the bladder in an inflated condition, the other of the inflatable compartments of the bladder in a deflated condition, and a second proportion of air greater than the first proportion of air removed from the interior region of the envelope so that the first panel of the envelope conforms to the surfaces of the bladder to a similar degree as does the second panel of the envelope; and 
         FIG. 14  is a cross-sectional end elevation view of the system of  FIG. 1  with one of the inflatable compartments of the bladder in an inflated condition, the other of the inflatable compartments of the bladder in a deflated condition, and a third proportion of air greater than the second proportion of air removed from the interior region of the envelope so that the first panel of the envelope conforms more closely to the surfaces of the bladder to a similar degree as does the second panel of the envelope. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The drawings show an illustrative embodiment of a system including a support surface overlay  10  having a bladder  100  and an envelope  200  containing the bladder  100 . The system also includes a control system  300  configured to selectively pressurize the bladder  100  and withdraw air from the envelope  200 , as will be discussed further below. 
     The bladder  100  includes a first (or upper) flat, flexible sheet  102  overlying a second (or lower) flat, flexible sheet  104 . One or both of the first and second sheets  102 ,  104  may be imperforate. The first and second sheets  102 ,  104  are joined together by a generally sinusoidal seam  106 , thereby defining first and second interdigitated inflatable compartments  108 ,  110 . As best shown in  FIG. 4 , the seam  106  may define one or more relief cuts  124 , for example, as further described in U.S. Pat. No. 9,216,122, the disclosure of which is incorporated by reference herein. 
     The first and second compartments  108 ,  110  may be selectively and independently inflated and deflated. The first compartment  108  may define a first plurality of inflatable cells  112  arranged in rows, each of the first plurality of inflatable cells  112  defining a corresponding contact node  114  when inflated. The second compartment  110  may define a second plurality of inflatable cells  116  arranged in rows interdigitated with the rows of the first plurality of inflatable cells  112 , each of the second of inflatable cells  116  defining a corresponding contact node  118  when inflated. As best shown in  FIGS. 1 and 6 , the rows of first and second inflatable cells  112 ,  116  may extend in a side-to-side direction of the overlay  100 . In other embodiments, the rows of first and second inflatable cells  112 ,  116  may extend in an end-to-end direction of the overlay  100 , perpendicular to that shown. In further embodiments, the rows of first and second inflatable cells  112 ,  116  could extend in other directions. 
     In other embodiments, the bladder  100  could take any number of alternative forms. 
     A first bladder tube  120  defining a lumen therethrough extends from the first compartment  108  in fluid communication therewith. A second bladder tube  122  defining a lumen therethrough extends from the second compartment  110  in fluid communication therewith. The first and second bladder tubes  120 ,  122  are joined or otherwise connected to one or both of the first and second sheets  102 ,  104  in sealed engagement therewith. The free ends of the first and second bladder tubes  120 ,  122  are configured for connection to the control system  300 , for example, via an intervening connector  308 , as will be discussed further below. 
     The envelope  200  includes a first (or upper) flexible panel  202  overlying a second (or lower) flexible panel  204 . (In  FIGS. 1 and 6 , the upper panel  202  is shown as being transparent for clarity.) The first and second panels  202 ,  204  are joined together by at least one generally circumferential seam  206 , thereby defining an interior region  208  of the envelope. The first and second panels  202 ,  204  of the envelope  200  may be joined together directly. Alternatively, the first and second panels  202 ,  204  of the envelope  200  may be joined together through an intervening structure. For example, the first panel  202  of the envelope  200  may be joined to the first sheet  102  of the bladder  100  by a seam  206 , and the second panel  204  of the envelope  200  may be joined to the second sheet  104  of the bladder  100  by the seam  206  or another seam. 
     One or both of the first and second panels  202 ,  204  of the envelope  200  are made of flat, flexible sheets of material. One or both of the first and second sheets are imperforate or sufficiently imperforate that a vacuum may be drawn upon the interior region  208  thereof, as will be discussed further below. 
     The first and second panels  202 ,  204  may be configured so that the first panel  202  stretches elastically to a greater degree than does the second panel  204  when the first panel  202  and the second panel  204  are subjected to the same or similar tensile load, as will be discussed further below. To this end, the first and second panels  202 ,  204  could be made of different materials having different material properties, or they could be made of the same material of different thicknesses, or both. In an embodiment, the first panel  202  is substantially thinner than the second panel  204 , for example, half the thickness of the second panel  204 , so that the first panel  202  stretches elastically to a greater degree than does the second panel  204  when the first panel  202  and the second panel  204  are subjected to the same or similar tensile load. In other embodiments, the envelope  200  could take any number of alternative forms. 
     An envelope tube  210  defining a lumen therethrough extends from the interior region  208  in fluid communication therewith. The envelope tube  210  is joined or otherwise connected to either or both of the first and second panels  202 ,  204  in sealed engagement therewith. The envelope tube  210  includes an optional in-line envelope filter  212  configured to capture biohazardous material that may be present in the interior region  208  of the envelope  200  and mitigate a likelihood of such biohazardous material from contaminating the controller  300 . The envelope tube  210  also includes an in-line calibrated envelope check valve  214  outboard of the optional in-line envelope filter  212 , and configured to preclude undesired entry of air from atmosphere to the interior region  208  of the envelope  200 . In other embodiments, the locations of the in-line calibrated envelope check valve  214  and the optional in-line envelope filter  212  could be reversed with respect to each other. The free end of the envelope tube  210  is configured for connection to the control system  300 , for example, via an intervening connector  308 , as will be discussed further below. 
     The control system  300  is operable to selectively and independently force pressurized air (or another medium) into, and relieve the air (or other medium) from, the first and second compartments  108 ,  110  to selectively and independently inflate and deflate the corresponding inflatable cells  112 ,  116  through the first and second bladder tubes  120 ,  122 . The control system  300  also is operable to selectively withdraw air (or another medium) from the interior region  208  of the envelope  200  to selectively collapse the first and second panels  202 ,  204  of the envelope  200  against the first and second sheets  102 ,  104  of the bladder  100  within the envelope  200 . As shown in  FIG. 7 , the control system  300  includes a pump  302 , which may be a pneumatic pump. The control system  300  also includes a pneumatic circuit including a valve or manifold arrangement configured to selectively align the suction of the pump  302  in fluid communication with the interior region  208  of the envelope  200 , and to selectively align the discharge of the pump  302  in fluid communication with one or both of the first and second inflatable compartments  108 ,  110  of the bladder  100 . 
     More specifically, the pneumatic circuit includes a pump input (or suction) line  304  in selective fluid communication with an input (or suction) port of the pump  302 . The pump suction line  304  also is in selective fluid communication with the atmosphere via a calibrated vacuum relief valve  310 . The calibrated vacuum relief valve  310  is in parallel with the calibrated envelope check valve  214 . A filter  324  may be provided on the side of the calibrated vacuum relief valve  310  opposite the pump  302  to filter air drawn from the atmosphere into the controller  300 . 
     The calibrated vacuum relief valve  310  is configured to be closed when the pressure in the suction line  304  is at or above a predetermined suction line pressure (which may be referred to herein as the calibrated vacuum relief valve setpoint pressure), and to open when the pressure in the suction line  304  is below the predetermined suction line pressure. 
     The pneumatic circuit also includes a pump output (or pressure) line  306  in selective fluid communication with an output (or pressure) port of the pump  302 . The pump pressure line  306  is in selective fluid communication with the first inflatable compartment  108  of the bladder  100  via the first bladder tube  120  and an intervening, three-way, first compartment isolation valve  314 . The first compartment isolation valve  314  is power-operated, for example, solenoid-operated. Also, the first inflatable compartment  108  of the bladder  100  is in selective fluid communication with the atmosphere through an air outlet  328  via the first bladder tube  120  and the intervening first compartment isolation valve  314 . With the first compartment isolation valve  314  in a first position, the first inflatable compartment  108  of the bladder  100  is in fluid communication with the pump pressure line  306  and not with the atmosphere. With the first compartment isolation valve  314  in a second position, the first inflatable compartment  108  of the bladder  100  is in fluid communication with the atmosphere and not with the pump pressure line  306 . A first inflatable compartment pressure sensor  316  is configured to sense pressure in a pneumatic line connecting the first inflatable compartment  108  to the first inflatable compartment isolation valve  314 . 
     Similarly, the pump pressure line  306  is in selective fluid communication with the second inflatable compartment  110  of the bladder  100  via the second bladder tube  122  and an intervening, three-way, second compartment isolation valve  318 . The second compartment isolation valve  318  is power-operated, for example, solenoid-operated. Also, the second inflatable compartment  110  of the bladder  100  is in selective fluid communication with the atmosphere through an air outlet  328  via the second bladder tube  122  and the intervening second compartment isolation valve  318 . With the second compartment isolation valve  318  in a first position, the second inflatable compartment  110  of the bladder  100  is in fluid communication with the pump pressure line  306  and not with the atmosphere. With the second compartment isolation valve  318  in a second position, the second inflatable compartment  110  of the bladder  100  is in fluid communication with the atmosphere and not with the pump pressure line  306 . A second inflatable compartment pressure sensor  320  is configured to sense pressure in a pneumatic line connecting the second inflatable compartment  110  to the second inflatable compartment isolation valve  318 . 
     As suggested above, one or more pneumatic connectors  308  may be provided to facilitate connection and disconnection of the control system  300  pneumatic lines to and from the first bladder tube  120 , the second bladder tube  122 , and the envelope tube  210  of the bladder  100 . 
     The control system  300  includes a controller  350  configured to receive inputs from a user interface panel  352 , to receive inputs from the first inflatable compartment pressure sensor  316 , and from the second inflatable compartment pressure sensor  320 . The controller  350  also is configured to provide control outputs to the pump  302 , to the first compartment isolation valve  314 , and to the second compartment isolation valve  318  to thereby selectively turn the pump  302  on and off and to selectively change the states of the first compartment isolation valve  314  and the second compartment isolation valve  318  valve between respective open and closed positions, as will be discussed further below. 
     The user interface panel  352  may include user input devices, for example without limitation, sensors, switches, touchscreens, and the like, enabling user control of the control system  350  and/or components thereof. The user input devices may be operable to enable user control of any number of system functions, for example, on/off, cycle time, cycle programs, and inflatable compartment pressures, among others. The controller  350  may selectively cause the pump  302  to turn on and off based on any or all of user input from the user input devices, input from hardware or software resident in the controller  350  or elsewhere, and input from the first inflatable compartment pressure sensor  316  and the second inflatable compartment pressure sensor  320 . Also, the controller  350  may be configured to selectively effect various alignments of the first compartment isolation valve  314  and the second compartment isolation valve  318  valve between respective open and closed positions, as will be discussed further below. 
     As mentioned above, the control system  300  is operable to selectively provide pressurized air to the first and second compartments  108 ,  110  of the bladder  100  to thereby inflate and deflate the first and second compartments  108 ,  110 . More specifically, the control system  300  is configured to selectively provide pressurized air to, and relieve pressurized air from, the first and second compartments  108 ,  110 . The control system  300  may provide pressurized air to either or both of the first and second compartments  108 ,  110  at the same time or alternatingly, and to relieve pressurized air from either or both of the first and second compartments  108 ,  110  at the same time or alternatingly. As such, at any time, both of the first and second compartments  108 ,  110  may be fully or partially inflated at the same time, both of the first and second compartments  108 ,  110  may be fully or partially deflated at the same time, one of the first and second compartments  108 ,  110  may be fully or partially inflated while the other is fully or partially deflated, both of the first and second compartments  108 ,  110  may be becoming inflated at the same time, both of the first and second compartments  108 ,  110  may be becoming deflated at the same time, one of the first and second compartments  108 ,  110  may be becoming inflated while the other is becoming deflated, and so on. The control system  300  may be operable to selectively pressurize the first and second compartments  108 ,  110  as desired to any one or more predetermined pressures. 
     The control system  300  also is operable to selectively withdraw air from the interior region  208  of the envelope  200  independent of any inflation and/or deflation of the first and second compartments  108 ,  110  of the bladder  100 . More specifically, the control system  300  is configured to selectively withdraw air from the interior region  208  of the envelope  200 , thereby causing the first and second panels  202 ,  204  of the envelope to collapse against and conform to the bladder  100  to varying extents, as will be discussed further below. With the first and second panels  202 ,  204  of the envelope collapsed against the bladder  100 , lateral (that is, end-to-end and side-to-side) motion of the bladder  100  with respect to the envelope  200 , with respect to a user disposed thereon, and/or with respect to a support surface (for example, a hard surface or a foam or other flexible and resilient underlayment) upon which the bladder is disposed is inhibited or substantially eliminated. 
     For example, the control system  300  is operable in a first mode of operation to vent both of the first inflatable compartment  108  and the second inflatable compartment  110  to atmosphere. In the first mode of operation, the control system  300  may or may not draw a vacuum on the interior region  208  of the envelope  200 , as will be discussed further below. In the first mode of operation, the first compartment isolation valve  314  is in its second position so that the first inflatable compartment  108  is vented to the atmosphere through the air outlet  328  and isolated from the pump  302 . Similarly, the second compartment isolation valve  318  is in its second position so that the second inflatable compartment  110  is vented to the atmosphere through the air outlet  328  and isolated from the pump  302 . The pump  302  may or may not be running. If the pump  302  is running, the pump  302  draws a vacuum on the interior region  208  of the envelope  200  via the pump suction line  304 . The first and second inflatable compartments  108 ,  110  may be de-pressurized or evacuated more quickly with the pump  302  running than with the pump  302  not running. If the pressure in the pump suction line  304  drops below the calibrated vacuum relief valve set point pressure, the calibrated vacuum relief valve  310  opens, thereby coupling the suction of the pump  302  to the atmosphere through the calibrated vacuum relief valve  310  and the filter  324 . Because the first compartment isolation valve  314  and the second compartment isolation valve  318  are in their second positions, thereby isolating the pump  302  from the first inflatable compartment  108  and the second inflatable compartment  110 , respectively, the discharge of the pump  302  is routed to the atmosphere via the calibrated pressure relief valve  322  once the pressure in the pump output line  306  upstream of the first and second compartment isolation valves  314 ,  318  exceeds the calibrated pressure relief valve setpoint pressure. 
     The control system  300  is operable in a second mode of operation to inflate and pressurize the first inflatable compartment  108 , vent the second inflatable compartment  110  to atmosphere, and draw a vacuum on the interior region  208  of the envelope  200 . In the second mode of operation, the first compartment isolation valve  314  is in its first position so that the first inflatable compartment  108  is in fluid communication with the outlet of the pump  302  via the pump output line  306  and isolated from the atmosphere. The second compartment isolation valve  318  is in its second position so that the second inflatable compartment  110  is vented to the atmosphere through the air outlet  328  and isolated from the pump  302 . In the second mode of operation, the pump  302  is running, thereby inflating and pressurizing the first inflatable compartment  108  with air discharged from the pump  302  via the pump discharge line  306  and the first compartment isolation valve  314 . When the pressure in the pneumatic line connecting the first compartment isolation valve  314  to the first inflatable compartment  108  exceeds a predetermined pressure, as may be sensed by the first inflatable compartment pressure sensor  316 , the controller  350  may cause the pump  302  to turn off. If the pressure in the pump output line  306  upstream of the first and second compartment isolation valves  314 ,  318  exceeds the calibrated pressure relief valve setpoint pressure, the calibrated pressure relief valve  322  opens, thereby venting the pump discharge line  306  upstream of the first and second compartment isolation valves  314 ,  318  to the atmosphere. Also, the pump  302  draws a vacuum on the interior region  208  of the envelope  200  via the pump suction line  304 . If the pressure in the pump suction line  304  drops below the calibrated vacuum relief valve set point pressure, the calibrated vacuum relief valve  310  opens, thereby coupling the suction of the pump  302  to the atmosphere through the calibrated vacuum relief valve  310  and the filter  324 . 
     The control system is operable in a third mode of operation to vent the first inflatable compartment  108  to atmosphere, inflate and pressurize the second inflatable compartment  110 , and draw a vacuum on the interior region  208  of the envelope  200 . In the third mode of operation, the first compartment isolation valve  314  is in its second position so that the first inflatable compartment  108  is vented to the atmosphere through the air outlet  328  and isolated from the pump  302 . The second compartment isolation valve  318  is in its first position so that the second inflatable compartment  110  is in fluid communication with the outlet of the pump  302  via the pump output line  306  and isolated from the atmosphere. In the second mode of operation, the pump  302  is running, thereby inflating and pressurizing the second inflatable compartment  110  with air discharged from the pump  302  via the pump discharge line  306  and the second compartment isolation valve  318 . When the pressure in the pneumatic line connecting the second compartment isolation valve  318  to the second inflatable compartment  110  exceeds a predetermined pressure, as may be sensed by the second inflatable compartment pressure sensor  320 , the controller  350  may cause the pump  302  to turn off. If the pressure in the pump output line  306  upstream of the first and second compartment isolation valves  314 ,  318  exceeds the calibrated pressure relief valve setpoint pressure, the calibrated pressure relief valve  322  opens, thereby venting the pump discharge line  306  upstream of the first and second compartment isolation valves  314 ,  318  to the atmosphere. Also, the pump  302  draws a vacuum on the interior region  208  of the envelope  200  via the pump suction line  304 . If the pressure in the pump suction line  304  drops below the calibrated vacuum relief valve set point pressure, the calibrated vacuum relief valve  310  opens, thereby coupling the suction of the pump  302  to the atmosphere through the calibrated vacuum relief valve  310  and the filter  324 . 
     The control system  300  is operable in a fourth mode of operation to inflate and pressurize both the first inflatable compartment  108  and the second inflatable compartment  110 , and to draw a vacuum on the interior region  208  of the envelope  200 . In the fourth mode of operation, the first compartment isolation valve  314  is in its first position so that the first inflatable compartment  108  is in fluid communication with the outlet of the pump  302  via the pump output line  306  and isolated from the atmosphere. The second compartment isolation valve  318  is in its first position so that the second inflatable compartment  110  is in fluid communication with the outlet of the pump  302  via the pump output line  306  and isolated from the atmosphere. In the fourth mode of operation, the pump  302  is running, thereby inflating and pressurizing the first inflatable compartment  108  with air discharged from the pump  302  via the pump discharge line  306  and the first compartment isolation valve  314 , and thereby inflating and pressurizing the second inflatable compartment  110  with air discharged from the pump  302  via the pump discharge line  306  and the second compartment isolation valve  318 . When the pressure in the pneumatic line connecting the first compartment isolation valve  314  to the first inflatable compartment  108  exceeds a predetermined pressure and the pressure in the pneumatic line connecting the second compartment isolation valve  318  to the second inflatable compartment  110  exceeds a predetermined pressure, the controller  350  may cause the pump  302  to turn off. If the pressure in the pump output line  306  upstream of the first and second compartment isolation valves  314 ,  318  exceeds the calibrated pressure relief valve setpoint pressure, the calibrated pressure relief valve  322  opens, thereby venting the pump discharge line  306  upstream of the first and second compartment isolation valves  314 ,  318  to the atmosphere. Also, the pump  302  draws a vacuum on the interior region  208  of the envelope  200  via the pump suction line  304 . If the pressure in the pump suction line  304  drops below the calibrated vacuum relief valve set point pressure, the calibrated vacuum relief valve  310  opens, thereby coupling the suction of the pump  302  to the atmosphere through the calibrated vacuum relief valve  310  and the filter  324 . 
     The control system  300  may be operable to selectively inflate the first and second inflatable compartments  108 ,  110 , to any desired pressures, for example, any pressures between one psi or less and fifteen psi or more, including but not limited to 1.0 psi, 1.5 psi, 2.0 psi, 2.5 psi, 3.0 psi, 3.5 psi, 4.0 psi, 4.5 ps, 5.0 psi, 5.5 psi, 6.0 psi, 6.5 psi, 7.0 psi, 7.5 psi, 8.0 psi, 8.5 psi, 9.0 psi, 9.5 psi, 10.0 psi, 10.5 psi, 11.0 psi, 11.5 psi, 12.0 psi, 12.5 psi, 13.0 psi, 13.5 psi, 14.0 psi, 14.5 psi, and 15.0 psi, and any intervening pressures. Any or all of the capacity of the pump  302 , the setpoint pressures of the first and second pressure sensors  316 ,  320 , the calibrated pressure relief valve setpoint, and operational parameters of the controller  350  may be varied to select the desired pressures. 
     The control system  300  may be operable to control the proportion of air withdrawn from the interior region  208  of the envelope  200  (compared to, for example, the maximum volume of the envelope  200 ), thereby controlling the degree of collapse of the panels  202 ,  204  of the envelope  200  against the bladder  100 . Any or all of the capacity of the pump  302 , the calibrated vacuum relief valve setpoint, and operational parameters of the controller  350  may be varied to select the desired proportion of air withdrawn from the interior region  208  of the envelope  200  and the degree of collapse of the panels  202 ,  204  of the envelope  200  against the bladder  100 . 
       FIGS. 8-14  show the bladder  100  and envelope  200  in various states of inflation and vacuum, respectively. 
       FIG. 8  shows the bladder  100  with both of the first and second inflatable compartments  108 ,  110  fully deflated, and the interior region  208  of the envelope  200  at atmospheric pressure. The first and second panels  202 ,  204  are shown exaggeratedly spaced from the bladder  100  for clarity. 
       FIG. 9  shows the bladder  100  with the first inflatable compartment  108  fully inflated, and the interior region  208  of the envelope  200  at atmospheric pressure. The first and second panels  202 ,  204  are shown exaggeratedly spaced from the bladder  100  for clarity. 
       FIG. 10  shows the bladder  100  with both of the first and second inflatable compartments  108 ,  110  fully inflated, and the interior region  208  of the envelope  200  at atmospheric pressure. The first and second panels  202 ,  204  are shown exaggeratedly spaced from the bladder  100  for clarity. 
       FIG. 11  shows the bladder  100  with the first inflatable compartment  108  fully inflated, and a partial vacuum drawn on the interior region  208  of the envelope  200 . The first panel  202  of the envelope  200  conforms to the first inflatable cells  112  of the first inflatable compartment  108  to a first degree. The second panel  202  of the envelope  200  conforms to the first inflatable cells  112  of the first inflatable compartment  108  to a second degree less than the first degree. The first panel  202  of the envelope  200  conforms to the first inflatable cells  112  of the first inflatable compartment  108  to a greater degree than does the second panel  202  of the envelope  200  because the first panel  202  has greater elasticity than the second panel  204 , as discussed further above. 
       FIG. 12  shows the bladder  100  with both the first and second inflatable compartments  108 ,  110  fully inflated, and a partial vacuum drawn on the interior region  208  of the envelope  200 . The first panel  202  of the envelope  200  conforms to the first inflatable cells  112  of the first inflatable compartment  108  and to the second inflatable cells  114  of the second inflatable compartment  110  to a first degree. The second panel  202  of the envelope  200  conforms to the first inflatable cells  112  of the first inflatable compartment  108  and to the second inflatable cells  114  of the second inflatable compartment  110  to a second degree less than the first degree. The first panel  202  of the envelope  200  conforms to the first and second inflatable cells  112 ,  114  of the first and second inflatable compartment  108 ,  110 , respectively, to a greater degree than does the second panel  202  of the envelope  200  because the first panel  202  has greater elasticity than the lower panel  204 , as discussed further above. 
       FIG. 13  shows the bladder  100  with the first inflatable compartment  108  fully inflated, and a greater vacuum drawn on the interior region  208  of the envelope  200  than represented in  FIGS. 11 and 12 . The first panel  202  of the envelope  200  conforms to the first inflatable cells  112  of the first inflatable compartment  108  to a first degree. The second panel  202  of the envelope  200  conforms to the first inflatable cells  112  of the first inflatable compartment  108  to a third degree. The third degree may be less than the first degree and greater than the second degree, or it may be substantially similar to the first degree. This phenomenon may occur because the relatively greater vacuum has greater effect on further collapsing the second panel  204  against the cells  112  of the bladder  100  (compared to the state represented in  FIGS. 11 and 12 ) than it does on further collapsing the second panel  204  against the cells  112  of the bladder  100  (compared to the state represented in  FIGS. 11 and 12 ). This phenomenon may be a consequence of relevant properties of the materials of which the first and second panels  202 ,  204  are made and or the relative thicknesses of the first and second panels  202 ,  204 . 
       FIG. 14  is similar to  FIG. 13  but shows both the first and second panels  202 ,  204  of the envelope more closely conforming to the first inflatable cells  112  of the bladder  100  because a still greater vacuum is drawn on the interior region  208  of the envelope  200 . 
     In some embodiments, the first panel  202  of the envelope  200  may have elasticity similar to that of the second panel  204  of the envelope  200 . In such embodiments, the first panel  202  of the envelope  200  could conform to the first inflatable cells  112  of the first inflatable compartment  108  to the same degree or a similar degree that the second panel  202  conforms to the first inflatable compartment  108  in the various states of operation as discussed above. 
     In modes of operation wherein one of the first and second inflatable compartments  108 ,  110  is inflated and the other of the first and second inflatable compartments  108 ,  110  is deflated, the upper and lower panels  202 ,  204  of the envelope  200  would conform to the bladder  100  in manners similar to those described above during the various modes of operation as described above. 
     The embodiments shown and described herein are illustrative and should not be construed to limit the scope of the invention as may be claimed herein or in any related application.