Abstract:
An apparatus adjusts the pressures of a therapeutic mattress surface in accordance with the angular position of that surface. The apparatus comprises an angular position sensor and a rotation sensor which are housed together in an enclosure having a top surface in the form of a circular plate. The circular plate mounts either on the surface of the mattress or on the bottom of a bed frame supporting the mattress. The angular position and rotation sensors measure the horizontal plane referenced perpendicular to the direction of the force of gravity. The apparatus further comprises a controller blower valve assembly which processes data received from the angular position and rotation sensors to maintain, increase, or decrease the pressures within the mattress.

Description:
RELATED APPLICATION 
   This application is a continuation under 35 U.S.C. § 120 of Applicant&#39;s U.S. patent application Ser. No. 08/679,135 filed Jul. 12, 1996, now U.S. Pat. No. 6,353,950, which is a continuation of U.S. patent application Ser. No. 08/241,075 filed May 9, 1994, now U.S. Pat. No. 5,611,096. By this reference, the full disclosure of U.S. patent application Ser. No. 08/679,135 is incorporated herein as though now set forth in its entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to methods and apparatus for monitoring and/or controlling therapeutic beds and mattress systems and the patients supported thereon. More particularly, the invention relates to monitoring angular deviations of the mattress surface and patient from the flat, horizontal position and for controlling the system in response. 
   DESCRIPTION OF BACKGROUND ART 
   Therapeutic supports for bedridden patients have been well known for many years. Well known therapeutic supports include (without limitation) low air loss beds, lateral rotation beds and fluidized bead beds. Commercial examples are the “KinAir”, “RotoRest” and “FluidAir” beds, all of which are products manufactured and commercialized by Kinetic Concepts, Inc. of San Antonio, Tex. Similar beds are described in U.S. Pat. Nos. 4,763,463, 4,175,550 and 4,635,564, respectively. 
   Other examples of well-known therapeutic supports for bedridden patients are the inflatable mattresses, mattress overlays or mattress replacements that are commercialized independent of a rigid frame. Because of the simpler construction of these products separate from a costly rigid frame, they tend to be more versatile and economical, thereby increasing options for customers and allowing them to control costs. A specific example of one such mattress is the “TheraKair” mattress, described in U.S. Pat. No. 5,267,364, dated Dec. 7, 1993, also manufactured and commercialized by Kinetic Concepts, Inc. The TheraKair mattress is a composite mattress including a plurality of transversely-oriented inflatable support cushions that are controlled to pulsate and to be selectively adjustable in groups. Most therapeutic mattresses are designed to reduce “interface pressures”, which are the pressures encountered between the mattress and the skin of a patient lying on the mattress. It is well known that interface pressures can significantly affect the well-being of immobile patients in that higher interface pressures can reduce local blood circulation, tending to cause bed sores and other complications. With inflatable mattresses, such interface pressures depend (in part) on the air pressure within the inflatable support cushions. Although a number of factors are at play, as the cushion&#39;s air pressure decreases, the patient interface pressure also tends to decrease, thereby reducing the likelihood that the patient will develop bedsores and other related complications. Hence the long-felt need to have an inflatable mattress which optimally minimizes the air pressure in the inflated cushions. 
   The desired air pressure within a given cushion or group of cushions may also depend on inclination of the patient support, or portions thereof. For instance, it is known that when the head end of a bed is raised, a greater proportion of the patient&#39;s weight tends to be concentrated on the buttocks section of the mattress. Hence, it has long been known to divide inflatable therapeutic mattresses into groups of transversely-oriented inflatable cushions corresponding to different regions of patient&#39;s body, with the pressure in each group being separately controlled. Then, when a patient or attendant controls the bed to elevate the patient&#39;s head, pressure in the buttocks cushions is automatically increased to compensate for the greater weight concentration and to prevent bottoming of the patient. (“Bottoming” refers to any state where the upper surface of any given cushion is depressed to a point that it contacts the lower surface, thereby markedly increasing the interface pressure where the two surfaces contact each other.) 
   It is also well known in the field of treating and preventing bedsores, that therapeutic benefits may be obtained by raising and lowering (or “pulsating”) the air within various support cushions. The effectiveness of this therapy may be reduced or negated if the surface inclination of a region (i.e., angle of the region relative to a horizontal plane) changes, or if the pressure in the appropriate support cushions is not properly adjusted. As with bottoming, such a condition may occur when the head of the patient is raised to facilitate, for example, feeding of the patient. As the angle of the head end of the support mattress (and thus the angle of patient&#39;s head) becomes greater, the patient&#39;s weight redistributes. Consequently, a greater proportion of the patient&#39;s weight is concentrated on the patient&#39;s buttocks region, while less weight is concentrated on the head and back region. 
   It is also known to subject patients to gentle side-to-side rotation for the treatment and prevention of pulmonary problems. It is known to achieve such rotation therapy by alternating pressure in two inflatable bladders which are disposed longitudinally under the support mattress along the length of the left and right sides of the patient. Consequently, as one of the inflatable bladders inflates, the patient rotates by an angle up to approximately 45 degrees. Although references such as RWM&#39;s U.S. Pat. No. 4,769,584 have long taught the importance of sensing the actual angle of rotation, the actual rotation angle in inflatable supports was typically controlled by the amount of pressure applied to the pivot bladder without measuring the actual angle of rotation attained. Unfortunately, during this treatment, if too great of a rotation angle is achieved, then the patient tends to roll to the edge of the support mattress as one of the inflatable bladders inflates. Therefore, if an apparatus could be designed which would measure and control rotation angles of the therapeutic bed surface this would prevent attaining excess angles resulting in the patient rolling to the edge of the support mattress during side-to-side alteration, and possibly falling off the support mattress. Also, if a minimum rotation angle of about twenty five degrees is not attained, then minimal or no therapeutic value is received by the patient. 
   It has also long been known in the art to control other aspects of the patient surface in response to inclination of specific portions of the patient. For instance, the Eggerton “Tilt and Turn” bed popular in the 1980&#39;s was adapted to raise a restraining portion of the patient surface during lateral turning, in order to help prevent the patient from rolling off the bed. Another example is the automatic knee gatch feature popularized in Hill-Rom frames, particularly such as described in U.S. Pat. No. 3,237,212. Such knee gatch feature was adapted to automatically raise the knee section of the patient support whenever the patient or caregiver desired to raise the head section, hence compensating to pr event a patient from sliding toward the foot end of the bed when the head section was raised. 
   The concept of controlling air pressure inflatable support cushions in response to changes in the patient surface is at least plausible in bed systems which utilize a rigid frame structure beneath the patient. The frame structure provides an attractive location for mounting the transducers required for such control. With flexible mattresses, to position any foreign devices in closer proximity to a patient, because a patient might be injured by contact with the device would be steadfastly avoided, mounting a sensor to a rigid base board helps shield a patient from contact with the sensor. The result, though, is that a health care facility is inclined to acquire the entire bed system in order to gain the benefits of such technology—an acquisition which may not be readily affordable. Such acquisitions also limit the health care facility to using specific mattresses with specific frames, rather than separately selecting and interchanging the preferred mattresses and bed frames. Interchangeability, on the other hand, would tend to maximize the facilities cost containment and efficiency. 
   Unfortunately, conventional support mattresses fail to properly adjust the pressure within the support cushions as the surface angles of the support mattress vary. Therefore, if an apparatus could be implemented which would adjust the pressure within the support cushions as the mattresses surface angles change, the pressure points on the patient would be significantly reduced, thereby preventing or significantly reducing the number of bedsores. 
   Others have taught that the desired air pressure within the air cushions may depend in part on the angle to which the patient is desired to be rotated. For instance, U.S. Pat. No. 5,003,654 dated Apr. 2, 1991 described an oscillating low air loss bed which laterally rotates a patient to varying degrees depending in part on the pressure within the cushions which achieve the turn. 
   SUMMARY OF THE INVENTION 
   The present invention comprises a new and improved apparatus for measuring the angular positions of a therapeutic mattress surface and adjusting the pressures within the mattress in accordance with the angular position, and providing feedback to control rotation angles attained by the therapeutic mattress. The apparatus is particularly suited for use with a therapeutic mattress which comprises a plurality of inflatable support cushions positioned latitudinally under the patient&#39;s body. Typically, such a mattress is divided into four regions: The head region, the back region, the buttock region, and the legs/feet region. Furthermore, the mattress comprises two inflatable guard rails, each positioned on either side of the patient on the mattress surface. 
   The apparatus comprises an angular position sensor and a rotation sensor which are housed together in an enclosure having a top surface in the form of a circular plate. The circular plate mounts either on the surface of the mattress between two cushions or on the bottom of a bed frame supporting the mattress. The angular position and rotation sensors measure the angular position of the mattress&#39;s surface in relation to the horizontal and vertical planes, respectively. 
   The apparatus further comprises a controller which typically mounts on the bed frame. The controller processes the data received from the angular position and rotation sensors to maintain, increase, or decrease, when necessary, the pressure within the appropriate cushions of the mattress, the pivot bladders, or the inflatable guard rails. 
   It is, therefore, an object of the present invention to provide a feedback signal to a controller of a therapeutic mattress surface, on which a patient is receiving therapy, to cause compensations in the support surface pressures corresponding to changes in mattress surface angles. 
   Another object of the present invention is to provide an apparatus which measures and adjusts the pressure within the support cushions of the therapeutic mattress in relation to the changes in the mattresses surface angles. Such an apparatus may significantly reduce the prevalence number of bedsores. Another object is to provide an apparatus that measures and displays the rotation angle of a therapeutic bed surface to help prevent the patient from rolling to the edge of the support mattress during side-to-side alteration. Still another object is to control such rotation in response to current measurement, for various purposes. Such a system may help preclude the patient from falling off the support mattress, while ensuring that adequate rotation angles were achieved to provide the patient proper therapy. 
   It is still another object of the present invention to provide a feedback signal to the controller corresponding to changes in the rotation angle of the mattress surface to facilitate pressure compensations in the inflatable guard rails and to control the amount of rotation angle achieved by causing adjustments of pressures in the pivot bladders. 
   Another object of the present invention is to provide controlling feedback to the mechanism which adjust pressures in inflatable bladders located such as to cause side to side rotation of the therapeutic bed surface. 
   These and other objects, features, and advantages of the present invention will become evident to those skilled in the art in light of the following brief description of the drawings and detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view depicting a therapeutic bed  10  having a preferred embodiment of the present invention mounted thereon. 
       FIG. 2  is a perspective view off the therapeutic bed  10  of Fig., with its head section in an elevated position. 
       FIG. 3  is a diagram depicting the control system  38  of the preferred embodiment. 
       FIG. 4  is a front elevation view depicting the operator input and display of the preferred embodiment of the present invention. 
       FIG. 5  is a diagram depicting the mounting of the angular position and rotation sensors of the preferred embodiment on a circuit board. 
       FIG. 6  is a schematic diagram depicting the wiring of the angular position and rotation sensors of the preferred embodiment. 
       FIG. 7A  is a top view depicting the mounting of the angular position and rotation sensors of the preferred embodiment onto the mattress  13 . 
       FIG. 7B  is a side elevation view depicting the mounting of the angular position and rotation sensors of the preferred embodiment onto the therapeutic mattress  13 . 
       FIG. 7C  shows a detailed portion of the illustration in  FIG. 7B . 
       FIG. 7D  shows a detailed portion of the illustration in  FIG. 7A . 
       FIG. 8  is an end-on schematic elevation view, taken in cross-section, depicting the rotation bladders  90 ,  91  and guard bladders  92 ,  93  of the preferred embodiment. 
       FIG. 9  shows a perspective view of the embodiment of  FIG. 8  in use for supporting and turning patient  200 . 
       FIG. 10  shows a perspective view of an alternative embodiment, and  FIGS. 11 and 12  show schematic diagrams of the  FIG. 9  and  FIG. 10  embodiments, respectively. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Therapeutic bed  10 , as described herein, is an example of a presently preferred embodiment of the present invention. As illustrated generally in  FIGS. 1 and 2 , therapeutic bed  10  comprises mattress  13 , control unit  38 , and frame  11 . 
   Frame  11  in the illustrated embodiment is a conventional hospital bed frame. More particularly, frame  11  is commercially available through Amedco Health Care, Inc., of Wright City, Mo. under the designation “Futura Series Bed,” Model No. 2110. Such frames are equipped with conventional raise-and-lower mechanisms and sit-up mechanisms for adjusting the position of the patient surface. 
   Frame  11  includes sub-frame  12 , which is the portion of frame  11  that directly supports mattress  13 . As will be evident from viewing the frame itself, sub-frame  12  is subdivided into four sections  12   a - 12   d . More particularly, section  12   a  is the head section of sub-frame  12 , section  12   b  is the buttock section of sub-frame  12 , section  12   c  is the thigh section of sub-frame  12 , and section  12   d  is the foot section of sub-frame  12 . Sections  12   a - 12   d  are pivotally linked (or “hinged”) to one another at pivot joints  14   a - 14   c  to form an articulatable mattress support system, which supports mattress  13 . Sub-frame  12   b  is actually fixed relative to the remainder of frame  11 , whereas sections  12   a  and  12   c  are pivotable relative to section  12   b , with section  12   a  pivoting about pivot joint  14   a , and section  12   c  pivoting about joint  14   b  relative to section  12   b . Section  12   d , in turn, pivots relative to section  12   c  about pivot joint  14   c . Pivot joints  14   a - c , together with opposite pivot joints (not shown) which correspond to pivot joints  14   a - 14   c  along the opposite side of sub-frame  12 , provide three, mutually-parallel pivot axes about which sections  12   a, c  and  d  pivot. Each of said sections  12   a - 12   d  in the preferred embodiment are conventionally adapted with sheet metal (or “pan”) surfaces spanning across the width of sub-frame  12 . The pan surface of each of sections  12   a - 12   d  may be referred to as the “baseboard” of the respective section. 
   Frame  11  is equipped with a conventional drive device (not shown), such as a combination of electric motors together with mechanical linkage, for enabling elevation and articulation (i.e. angular movement) of sub-frame  12  relative to the horizontal. Conventional controls for such lifting device allow a user of bed  10  to raise and lower the entire sub-frame  12  and/or to articulate the mattress supporting surface of sub-frame  12 . “Articulation” of sub-frame  12  includes raising or lowering head section  12   a  relative to buttock section  12   b  and/or raising or lowering of thigh and foot sections  12   c  and  12   d  relative to buttock section  12   b . All such features of frame  11  are standard features with conventional hospital bed frames. 
   Other commercially available hospital bed frames may also be employed. For instance, in another embodiment of the present invention, the frame utilized is one manufactured by Stryker Medical of Kalamazoo, Mich. under the designation “Renaissance Series, Dual Control Critical Care Bed”. 
   Referring again to the embodiment shown in  FIG. 1 , mattress  13  comprises a foam submattress (or “pad”)  13   a , a plurality and inflatable tubular elements (or “cushions” or “air bags”) enclosed by cover  37 . Although certain details of the construction of mattress  13  are described here in detail, it will be evident that many details are not critical to the present invention. Various alternative constructions will be evident from the description of U.S. Pat. No. 5,168,589, entitled “Pressure Reduction Air Mattress and Overlay”, dated Dec. 8, 1992, as well as from a viewing or incorporation of various products commercialized by Kinetic Concepts, Inc. of San Antonio, Tex., including those marketed under the designations “DynaPulse”, “TheraKair”, FirstStep”, and “Homekair DMS”. All in a construction generally like U.S. Pat. No. 5,267,364, entitled “Therapeutic Wave Mattress”, dated Dec. 7, 1993. 
   In the presently preferred embodiment of mattress  13 , cover  37  contains inflatable support cushions  15 - 36 . Although not pictured in  FIG. 1 , cover  37  may be accompanied by opposite retaining sleeves  37   a ,  37   b  ( FIGS. 7A &amp; 7B ) for positioning cushions  15 - 36 . Each sleeve  37   a ,  37   b  includes twenty-one vertical baffles that divide cover  37  into twenty-two individual pockets  37   d  which each receive an end of one of cushions  15 - 36  to form mattress  13 . Each of such baffles  37   c  are formed integrally with the respective sleeve  37   a ,  37   b  by means of sewing the baffles  37   c  in the desired orientation. Such a construction is like that used in the commercially available “DynaPulse” product marketed by Kinetic Concepts, Inc. of San Antonio, Tex. Such a construction has the benefit of leaving the central region of mattress  13 , where sensor enclosure  86  is located, free of baffles so that sensor enclosure  86  can be mounted directly to the air cushions  33  and  34 . Various alternative constructions for sleeve  37   a  and  37   b  will be evident to those of ordinary skill in the art. For instance, a sleeve may be centrally oriented in mattress  13 , with each of the opposite ends of cushions  15 - 36  extending beyond the lateral limits of such a sleeve. Cover  37  may also include zippers and/or a releasable flap with hook and loop fastener material to help seal cushions  15 - 36  within their respective pockets. Such a flap may seal to the body of cover  37  using any suitable means. 
   Cushions  15 - 36  are arranged into four body support regions: the head region, the back region, the buttock region, and the leg/foot region. Illustratively, cushions  33 - 36  form the head region, cushions  29 - 32  form the back region, cushions  23 - 28  form the buttock region, and cushions  15 - 22  form the leg/foot region. 
   Control unit (or “controller”)  38  includes the components for inflating and controlling mattress  13 , and for interfacing with patient caregiver. As will be evident to those of ordinary skill in the art, such components (not shown) include a blower, a microprocessor or the equivalent, a heater, various valves and an equal number of pressure sensors, manifolds, connections, and insulation in such manner as may be desired. Controller  38  has a housing adapted with adjustable hooks for mounting on the footboard or siderail of frame  11 . Control unit  38  connects to each one of cushions  15 - 36  via a plurality of fluid lines (not shown) contained within trunk line  39  to supply cushions  15 - 36  with air as an inflating medium. Other inflating medium such as water will be evident to those of ordinary skill in the art. The fluid lines connect to their respective cushions using any suitable means such as a quick connect valve that includes a male member having a flange and a female member having a cavity about its inner surface for receiving the flange. Trunk line  39  enters cover  37  through an opening (not shown) to allow each individual fluid line to communicate the inflating medium to the cushions. Cushions  15 - 36  each include a cut-out portion (not shown) at their lower end on one side of mattress  13  to provide space for trunk line  39  to run through cover  37 . Although those of ordinary skill in the art will understand conventional means of connecting fluid lines to cushions  15 - 36  in the preferred embodiment, description of the fluid connections pictured in  FIG. 11  may be of further assistance in such understanding. 
   Referring to  FIG. 3 , controller  38  comprises operator input and display  41 , processor unit  42 , power supply  43 , angular position sensor  44 , rotation sensor  45 , temperature sensor  46 , blower  47 , blower relay  48 , heater  49 , heater relay  50 , analog to digital (A/D) converter  51 , and air controller valve bank  65 . Controller  38  connects to any suitable power source such as a  120  VAC public power line, preferably via a “hospital grade” outlet. Power supply  43  receives the 120 VAC input and converts it into a standard 5 VDC suitable for use by both processor  42  and operator input and display  41 . Power supply  43  also furnishes power to angular position sensor  44 , rotation sensor  45 , and temperature sensor  46 . Processor unit  42  comprises a microprocessor having associated RAM and ROM. 
   As illustrated in  FIGS. 3 and 4 , operator input and display  41  includes ON/OFF button  52  which allows a user to control power delivery to controller  38 . Upon the initial application of power, display  64  indicates that air is switched off. When the on/off button  52  is depressed, processor unit  42  generates a control signal that activates blower relay  48 , resulting in blower relay  48  delivering the 120 VAC input signal to blower  47 . Processor unit  42  also generates control signals that energize each air control valve in air control valve bank  65  to allow blower  47  to inflate each of cushions  15 - 36 . Air control valve bank  65  comprises 8 air control valves corresponding at least in part to the segregation of sections of cushions forming mattress  13 . 
   CPR button  58  provides the user with the option of automatically and completely deflating each of cushions  15 - 36 . If the user presses CPR button  58 , processor unit  42  deactivates blower relay  48  and generates control signals that energize each air control valve in air control valve bank  65  such that the individual air control valves open the fluid lines to the atmosphere. Consequently, the inflating medium in each of cushions  15 - 36  escapes to the atmosphere. Once cushions  15 - 36  vent their inflating medium to the atmosphere, processor unit  42  restores the valves in air control valve bank  65  to their previous settings. 
   Buttons  55 ,  56 ,  57 ,  58 ,  66  and  87  are soft keys whose functions are defined by text on the display to their left. Immediately following power up and depression of on/off button  52 , the label HT/WT appears next to button  57 . 
   Height/weight (HT/WT) button  57  permits the user to enter the height and weight of the patient  200  using therapeutic bed  10 . After the user presses HT/WT button  57 , the display shows test as follows: WT INCREASE next to button  55 , WT DECREASE next to button  56 , HT INCREASE next to button  57 , HT DECREASE next to  66 , and ENTER next to  87 . The user enters the height of patient  200  by pressing adjust buttons  55  and  56  until LCD  64  displays the correct height. The user enters the weight of patient  200  by pressing adjust buttons  57  and  66  until LCD  64  displays the correct weight. When LCD  64  displays the correct height and weight, the user presses save button  87  to store the patient&#39;s weight in processor unit  42 . Processor unit  42  utilizes the patient&#39;s height and weight to properly regulate the pressure of the inflating medium within cushions  15 - 36 . Illustratively, persons having smaller statures require lower pressures of the inflating medium within cushions  15 - 36 , while patient&#39;s having larger statures require greater pressures. 
   Pressure adjust buttons  59 - 62  provide the user with control over the pressure of inflating medium within the head region, the back region, the buttock region, and the leg/foot region of mattress  13 . During sustained operation, processor unit  42  displays bar graphs  67 - 70  on LCD  64  to provide the user with a visual indication of the inflating medium pressure in each region. Bar graphs  67 - 70  allow the user to quickly and easily determine which of the regions must be adjusted. Illustratively, to increase the inflating medium pressure within the head region, the user presses the plus side of pressure adjust button  59 . That pushing of pressure adjust button  59  furnishes processor unit  42  with a signal to indicate that pressure should be increased in the head section cushions. In response, processor unit  42  generates a control signal that increases the opening of valves corresponding to the head section in air control valve bank  65 . 
   Alternatively, to decrease the inflating medium pressure within the head region, the user presses the minus side of pressure adjust bottom  59 . That pushing of pressure adjust button  59  furnishes processor unit  42  with a signal to indicate that a portion of the inflating medium within the head region should be vented to the atmosphere. Consequently, processor unit  42  generates control signals that energize only the air control valves in air control valve bank  65  which are connected to the fluid lines communicating with cushions  33 - 36 . Those air control valves open the fluid lines so that the inflating medium in the head section cushions  22 - 26  escapes to the atmosphere. Once cushions  33 - 36  vent their inflating medium to the user selected pressure, processor unit  42  deactivates the activated air control valves. Pressure adjust buttons  60 - 62  operate identically to pressure adjust button  59  to either increase or decrease the pressure of the inflating medium within their respective body regions. 
   Notwithstanding that manual control of the inflating medium pressure within the body regions defined by cushions  15 - 36  provides the user with significant flexibility, processor unit  42  is adapted to perform the more important task of automatically adjusting such pressure. Particularly, the inflating pressure within the body regions is adjusted to compensate for weight shifts due to a changed body orientation commensurate with angular adjustment of the position of mattress  13 . For instance, as mattress  13  pivots from the position shown in  FIG. 1  to the position shown in  FIG. 2 , a patient  200  on therapeutic bed  10  will shift such that a larger portion of his body weight resides over the buttock region. To counter that shift, the pressure of the inflating medium within the buttock region (i.e. cushions  22 - 28 ) is increased while the pressure within the back regions (i.e., cushions  29 - 32 ) is decreased. The above is reversed if mattress  13  pivots from the position shown in  FIG. 2  to the position shown in  FIG. 1 . 
   As shown in  FIG. 3 , controller  38  includes angular position sensor  44  to furnish processor unit  42  with a signal representing the incline of mattress  13  so that processor unit  42  may automatically adjust the inflating medium pressure within each body region. Controller  38  further includes rotation sensor  45  which supplies processor unit  42  with a signal representing the rotation of mattress  13 . With such signal, controller  38  can determine the current angle of lateral rotation of mattress  13  and, hence, a patient  200  lying thereon. Once determined, such angle can be output by controller  38  via an appropriately-adapted display  64 , such as a digital or graphical representation thereon. Other uses of such output may also be employed, including feedback control of blower unit  38  and/or bed frame  11 . More particularly, processor unit  42  may automatically adjust the inflation medium pressures within guard rails  92 - 93  positioned longitudinally at each side of mattress  13  and pivot bladders  90 - 91  positioned longitudinally underneath mattress  13  along each side as shown in  FIG. 8 . 
   Referring to  FIG. 6 , angular position sensor  44  comprises inclinometer  77 , voltage regulator  71 , variable resistor  72 , resistor  73 , capacitor  74 , and diode  75 . Inclinometer  77  comprises a resistive element that changes value as inclinometer  77  rotates from a horizontal to an angular position. Voltage regulator  71  is configured as a current source to supply the current to inclinometer  77  which ultimately becomes the output signal from angular position sensor  44 . Variable resistor  72  establishes the output current from voltage regulator  71  and, further, provides a calibration adjustment for position sensor  44  that allows a user to normalize the relationship between the current produced from voltage regulator  71  relative to the ratio of change in resistance verses change in angular position of inclinometer  77 . Resistor  73  and capacitor  74  form a dampening filter to remove spurious transient outputs from inclinometer  77 , while diode  75  limits the output voltage of inclinometer  77  to the bias voltage received from power supply  43 . Header  76 , having pins  1  shorted to  2  and  3  shorted to  4  in normal operation, allows the disconnection of inclinometer  77  during the calibration of angular position sensor  44 . Connector  77  provides the electrical connection of angular position sensor to controller  38 . 
   Rotation sensor  45  comprises inclinometer  78 , voltage regulator  79 , variable resistor  80 , resistor  81 , capacitor  82 , and diode  83 . Inclinometer  78  comprises a resistive element that changes value as inclinometer  78  rotates about a central horizontal axis. Voltage regulator  79  is configured as a current source to supply the current to inclinometer  78  which ultimately becomes the output signal from rotation sensor  45 . Variable resistor  80  establishes the output current from voltage regulator  79  and, further, provides a calibration adjustment for rotation sensor  45  adjustment that allows a user to normalize the relationship between the current produced from voltage regulator  79  relative to the ratio of change in resistance verses change in angular position of inclinometer  78 . Resistor  81  and capacitor  83  form a dampening filter to remove spurious transient outputs from inclinometer  78 , while diode  83  limits the output voltage of inclinometer  78  to the bias voltage received from power supply  43 . Header  76 , having pins  1  shorted to  2  and  3  shorted to  4  in normal operation, allows the disconnection of inclinometer  78  during the calibration of rotation sensor  45 , while connector  77  provides the electrical connection  45  of rotation sensor  45  to controller  38 . 
   It has also been found that the tilt angle sensed by sensor  45  and the sit-up angle sensed by sensor  44  provide angular measurements relative to an imaginary vertical plane oriented along the longitudinal axis of bed  10 . The therapeutic objective, rather than determine the degree of rotation relative to such axis, is to determine the degree of rotation relative to the base board supporting the head section of mattress  13 . To achieve this objective, the sit-up angle is utilized in an algorithm to translate the angle measured by the tilt sensor from the universal coordinates of the earth to the coordinates of the base board of head section  12   a . The details of such algorithm will be evident to those of ordinary skill in the art. 
   As illustrated in  FIG. 5 , angular position sensor  44  and rotation sensor  45  each mount to circuit board  84 . Circuit board  84  includes electrical paths that interconnect the components of angular position sensor  44  and rotation sensor  45 . Additionally, circuit board  84  comprises a malleable material so that inclinometer  78  may be positioned at an angle of approximately 90 degrees relative to inclinometer  77  using bend zone  85 . That angular difference between inclinometers  77  and  78  permits inclinometer  77  to measure the movement of mattress  13  from a horizontal to an angular position and inclinometer  78  to measure the rotational movement of mattress  13  about a central horizontal axis. 
   Referring to  FIGS. 1 ,  2 , and  7 , circuit board  84  mounts into enclosure  86  using any suitable means, such as an adhesive to protect circuit board  84  and the components of angular position sensor  44  and rotation sensor  45 . Enclosure  86  mounts on mattress  13  between, for example, cushions  33  and  34  using any suitable means, such as snaps  88  and  89  or hook and loop fasteners (see  FIG. 7 ). Alternatively, enclosure  86  could mount underneath frame  11  near the head region of mattress  13  using any suitable means such as screws or nuts and bolts. With angular position sensor  44  and rotation sensor  45  positioned at the head region of mattress  13 , any elevation or lowering of mattress  13  or rotation of mattress  13  about its central horizontal axis will be registered. Alternately, enclosure  86  could be mounted under sub-frame  12 . 
   After the initial inflation of cushions  15 - 36 , controller  38  maintains their inflation at the user selected values. However, if a person in therapeutic bed  10  desires to elevate mattress  13  from a horizontal position to an angled position, controller  38  alters the inflation levels of certain cushions to compensate for the change in the weight distribution of the patient&#39;s body. Illustratively, as mattress  13  travels to the angled position depicted in  FIG. 2 , the resistance value of inclinometer  77  changes, resulting in a change in the current level of the signal delivered from angular position sensor  44  to processing unit  42 . However, A/D converter  51  first receives that signal and digitizes it into a signal readable by processor unit  42 . 
   Processor unit  42  receives and processes the signal from angular position sensor  44  to determine the necessary control required to supply cushions  15 - 36  with adequate inflating medium pressure to ensure proper support of the therapeutic bed user. In response to the above signal, processor unit  42  generates a control signal to activate air control valves in air control valve bank  65 . Because the buttock region requires inflation during the elevation of mattress  13 , processor unit  42  activates the air control valves in air control valve bank  65  which control inflating medium flow to cushions  23 - 38  (i.e., the buttock region). Consequently, blower  47  increases the inflation within cushions  23 - 28 , but not cushions  15 - 22  and  28 - 36 . Additionally, because the back region requires deflation during the elevation of mattress  13 , processor unit  42  generates control signals to activate the air control valves in air control valve bank  65  which control cushions  29 - 32 . Those air control valves open the fluid lines so that the inflating medium within cushions  29 - 32  escapes to the atmosphere. 
   Processor unit  42  maintains the activation of the valves controlling cushions  23 - 32  as long as it receives a changing signal from angular position sensor  44 . Once mattress  13  ceases to elevate, the output signal from angular position sensor  44  returns to a constant value. In response to the constant signal, processor unit  42  adjusts air control valves as necessary to maintain the steady state pressures. 
   Alternatively, if mattress  13  lowers, the resistance value of inclinometer  77  again changes, resulting in a change in the current level of the signal delivered from angular position sensor  44  to processing unit  42 . In response to the above signal, processor unit  42  generates a control signal to activate air control valves in air control valve bank  65 . Because only the back region requires inflation during the lowering of mattress  13 , processor unit  42  activates the air control valves in air control valve bank  65  which control inflating medium flow to cushions  29 - 32  (i.e., the back region). Consequently, blower  47  increases the inflation within cushions  29 - 32 , but not cushions  15 - 28  and  33 - 36 . Because the buttock region requires deflation during the lowering of mattress  13 , processor unit  42  generates control signals to activate the air control valves in air control valve bank  65  which control cushions  23 - 28 . Those air control valves open the fluid lines so that the inflating medium within cushions  23 - 28  escapes to the atmosphere. 
   Processor unit  42  adjusts air control valves controlling cushions  23 - 32  as long as it receives a changing signal from angular position sensor  44 . Once mattress  13  ceases to elevate, the output signal from angular position sensor  44  returns to a constant value. In response to the constant signal, processor unit  42  adjusts air control valves as necessary to maintain the steady state pressures. 
   Referring to  FIGS. 8 and 9 , an alternative feature of therapeutic bed  10  includes rotation bladders  90  and  91  and guard bladders  92  and  93  (not shown in  FIG. 9 ). Bladders  90  and  91  reside on frame  95  and are positioned underneath the sides of mattress  94  along its entire length. Mattress  94  comprises a similar mattress to mattress  13  except that its cover includes guard bladders  92  and  93  which extend along the entire length of mattress  94 . 
   Referring to  FIG. 11 , controller  38  connects to bladders  90  and  91  and guard bladders  92  and  93  via fluid lines  150 - 156  contained within trunk line  39  to provide an inflating medium to bladders  90  and  91  and guard bladders  92  and  93 . The fluid line of bladder  91  is connected to guard rail  92  and the fluid line of bladder  90  is connected to guard rail  93 . Processor unit  42  controls the inflation and deflation of bladders  90  and  91  concurrently with guard bladders  93  and  92  to rotate mattress  94  about its central horizontal axis, thereby imparting rotational motion and providing a restraining barrier to the therapeutic bed user. To select mattress rotation, a user pushes rotate button  100  to furnish processor unit  42  with a signal indicating that air control valves in air control valve bank  65  should supply bladders  90  or  91  with the inflating medium. 
   In response, processor unit  42  generates a control signal that activates air control valves in air control valve bank  65  associated with bladders  90  and  91 . However, to produce the rocking motion of mattress  94 , processor unit  42  must alternately inflate and deflate bladders  90  and  91 . Illustratively, to commence rotation beginning to the left, processor unit  42  generates a control signal to energize the air control valve controlling inflating medium flow to and from bladder  90 . As a result, blower  47  delivers the inflating medium to bladder  90 , thereby inflating it. Additionally, processor unit  42  generates a control signal to energize the air control valve controlling inflating medium flow to and from bladder  91 . However, the actuated air control valve opens the fluid line to bladder  91  to vent any inflating medium in bladder  91  to the atmosphere. With bladder  90  inflated and bladder  91  deflated, mattress  94  rotates to the left. Processor unit  42  generates the air control valve control signals until a predetermined angle is attained, as selected, to ensure the inducement of adequate therapy to the therapeutic bed user. At the attainment of the predetermined angle, after a preset time period, processor unit  42  reverses the energizations of the air control valves to inflate bladder  91  and deflate bladder  90 . Thus, processor unit alternately inflates and deflates bladders  90  and  91  to rotate mattress  94  about its central horizontal axis. 
   One issue to be addressed with rotation of a mattress  94  about its central horizontal axis consists of insuring sufficient inflation of bladders  90  and  91  to provide adequate therapy while also ensuring that patient  200  does not roll off mattress  94 . Therapeutic bed  10  includes guard bladders  92  and  93  to restrain the patient and prevent him from falling from mattress  94 . Guard bladders  92  and  93  comprise elongated pillows filled with an inflating medium which provide a barrier at the sides of mattress  94  to prevent a bed user from falling from mattress  94  during its rotation. 
   After commencement of mattress rotation, processor unit  42  must alternately inflate and deflate guard bladders  92  and  93 , concurrent with bladders  91  and  90 , to restrain the bed user within mattress  94 . To properly control the inflation and deflation of bladders  91  and  90  with guard bladders  92  and  93 , processing unit  42  must receive signals indicating the rotational position of mattress  94 . Thus, controller  38  includes rotation sensor  45  to provide a signal to processor unit  42  which indicates the rotational position of mattress  94 . Illustratively, as mattress  94  rotates to the position depicted in  FIG. 8 , the resistance value of inclinometer  77  changes, resulting in a change in the current level of the signal delivered from rotation sensor  45  to processing unit  42 . However, A/D converter  51  first receives that signal and digitizes it into a signal readable by processor unit  42 . 
   Processor unit  42  receives and processes the signal from rotation sensor  45  to determine the necessary control required to inflate and/or deflate the bladder  91 /guard rail  92  and bladder  90 /guard rail  93  pairs. In this instance, processor unit  42  generates a control signal to activate air control valves in air control valve bank  65  to energize and open the air control valve controlling inflating medium flow to and from bladder  90  with guard bladder  93 . Consequently, blower  47  delivers the inflating medium to bladder  90  and guard rail  93 , thereby inflating them. Additionally, processor unit  42  generates a control signal to energize the air control valve controlling inflating medium flow to and from bladder  91  with guard rail  92 . However, the actuated air control valve opens the fluid line to bladder  91  with guard bladder  92  to vent any inflating medium in bladder  91  and guard bladder  92  to the atmosphere. With bladder  90  and guard bladder  93  inflated and bladder  91  with guard bladder  92  deflated, a barrier on the left side of mattress  94  is formed to prevent a bed user from falling from mattress  94  as the bed surface is rotated to the left. 
   Processor unit  42  maintains the inflation of bladder  90  with guard bladder  93  and deflation of bladder  19  with guard bladder  92  until it receives a signal from rotation sensor  45  which indicates that the predetermined angle of rotation has been attained. In response to attaining the predetermined angle, after a preset time period, processor unit  42  generates a control signal to energize the air control valve controlling inflating medium flow to and from bladder  91  with guard bladder  92 . Consequently, blower  47  delivers the inflating medium to bladder  91  guard bladder  92 , thereby inflating them. Additionally, processor unit  42  generates a control signal to energize the air control valve controlling inflating medium flow to and from bladder  90  with guard bladder  93 . The actuated air control valve opens the fluid line to bladder  90  and guard bladder  93  to vent the inflating medium within bladder  90  and guard bladder  93  to the atmosphere. With bladder  91  with guard bladder  92  inflated and bladder  90  with guard bladder  93  deflated, a barrier on the right side of mattress  94  is formed to prevent a bed user from falling from mattress  94  as the bed surface is rotated to the right. Thus, processor unit  42  alternately inflates and deflates guard bladders  92  and  93  concurrently with bladders  91  and  90  to form a barrier which prevents a bed user from falling from mattress  94  as the bed surface is rotated to the left and right. 
   The foregoing description of a primary embodiment provides a detail example of the present invention. Many other embodiments, however, will be evident to those of ordinary skill in the art from the foregoing description, particularly when considered in view of the appended claims and accompanying drawings. 
   As an example of the alternatives, in one alternative embodiment, the sensors are moved from the central location (of  FIG. 1 ) to the very end of the head section of the mattress. This relocation not only aids in accessing the sensor but also ensures that the sensors do not interfere with the radio-luminescence of the chest section of the mattress. To aid in such relocation, the sensor circuit board  84  is rotated ninety degrees within enclosure  86 , and the extending flange  86   a  of enclosure  86  is oriented vertically at the head end of the bed mattress  13 . The flange  86   a  can also be extended in length to extend across most of the width of the head end of the bed. In such orientation, the flange  86   a  is removably inserted within an elongate pocket along the perimeter of the head end of the bed. The flange  86   a  then helps provide rigidity to the fabric border surrounding the mattress. The pocket itself is sleeve-like with hook and loop fastener closures at one longitudinal end thereof. Hence, the sensor housing with extended flange is selectively removable from said sleeve-like pouch for servicing the same and for laundering the remainder of the mattress  13 . A possible downside of such alternative embodiment relative to the first embodiment is that the sensors are less proximal to the chest of the patient and may not as accurately reflect the angle of rotation of the patient&#39;s chest. It is noted that the rotation of the chest is of particular interest because an important benefit of laterally rotating a patient is the prevention and therapy of nosocomial pneumonia, which obviously occurs primarily in the chest region. 
   Alternative configurations of guard bladders  92  and  93  in such alternative embodiment utilize a semi-rigid support integrated in the outer edge thereof. Such semi-rigid support comprises a section of relatively stiff plastic sheet within an adjacent foam pad adhered thereto. The pad itself is also inserted within rectangular pocket with hook and loop fastener material which is formed integral with the flexible perimeter surrounding the mattress. Such perimeter is simply a relatively stiff, upstanding border (or “wall”) formed of fabric, much like wall  7   a  described in U.S. Pat. No. 5,267,364. 
   In addition, the guard bladders  92  and  93  may be relatively short in length as compared to the length of the mattress as a whole. Other restraints and/or support bladders may also be utilized in various portions of the upper surface of the mattress, such as the flexible thoracic packs  37   a - 37   b  shown in  FIG. 10 . Such packs and other exemplary restraints are described in co-pending application Ser. No. 07/823,281, entitled “Patient Positioners For Use On Oscillating Air Support Surfaces”, filed Jan. 21, 1992, now U.S. Pat. No. 5,357,641. For instance, the packs may be secured to a cover sheet that is then secured over inflatable bolsters, and the patient lies directly on such cover sheet. Such cover sheet is fitted with excess material forming pockets for receiving and fitting directly on the inflatable bolsters. Such cover sheet is also provided with flexible thoracic packs having removable straps with hook and loop fastener material much as described in said co-pending application. 
   Although not shown in  FIG. 10 , releasable clips adjoining opposing straps, much like those described in U.S. Pat. No. 5,267,364, are also utilized in alternative embodiments such as that shown in  FIG. 10 . In such embodiment, various straps can also be utilized to ensure proper alignment in relationship between turning bladders  90  and  91 . Moreover, a side panel  90 - 90   a  may be secured at its lowermost portion by means of a zipper connection with another fabric layer  90   b  that is firmly connected to a base board of frame  11 . Screws are utilized in the preferred mode of such embodiment. 
   In addition, various safety features may also be incorporated into such embodiments. Amongst such safety features are the disabling of the rotation mode in various circumstances, including the lowering of a side rail or the raising of head section  12   a  of frame  11  beyond a comfort zone. Such comfort zone may be up to approximately 60°, or such other level as may be deemed safe while turning a patient from side-to-side to the degree selected. 
   The independent blower control unit  38  in the first embodiment is eliminated in various alternative embodiments, with its components being integrated into the frame in such alternative embodiments. The blower components and related hardware with connecting pneumatic hoses and the like, are mounted beneath the base boards of the bed in a suitable manner, and the display panel together with its control processor are integrated into the foot board of such alternative frame. Naturally, suitable electrical connections are also made. 
   Various other features may be added as desired in such alternative embodiments, including scales built in to the frame of such alternative embodiment, percussion controls for selectively controlling the transversely oriented air sacs to percuss the chest region of a patient during rotating modes, and various CPR features for deflating and leveling the patient surface for enabling CPR procedures. 
   With reference to  FIGS. 10 and 12 , other aspects of one such alternative embodiment include plumbing which enables counter rotation of the foot section of mattress  94 ′ relative to the head section of mattress  94 ′. More particularly, rather than a single left rotation bladder and a single right rotation bladder extending the full length of the bed (as shown in  FIGS. 9 and 11 ), two left rotation cells  90  prime and  191  for the head section and leg section of patient  200 , respectively, are utilized. Likewise two left pillows and/or retainers  92  prime and  193  are used in combination with two right pillows and/or retainers  192  prime and  93  prime. The plumbing for such alternative embodiment will be evident those of ordinary skill of the art from the schematic diagram shown in  FIG. 12 . A switch valve  199  is provided to allow selective switching of the configuration shown in  FIG. 12  to one more in line with that shown in  FIG. 11 . Appropriate modification of various retainers, cells and bladders will be evident to those of ordinary skill in the art. Such counter rotation may not only help retain patient  200  on the upper surface of mattress  13 ′, but is believed to also stimulate the lymphatic system of patient  200 . Such lymphatic stimulation, or twisting of patient  200  is believed to promote circulation of lymph throughout the lymphatic system of patient  200  by creating pressure differentials on such lymphatic system. Such lymphatic stimulation may be achieved, in part, by turning the head portion of patient  200  to a greater extent that the foot section of patient  200 , although greater lymphatic stimulation is thought to result from counter rotation of the foot section relative to the head section of the patient. It addition, the patient may be retained to a greater degree on the top surface of mattress  13 ′ by rotating only the head section thereof and leaving the foot section level, rather than rotating both the head and foot sections in the same direction. 
   Various prior U.S. patents and applications have been referenced in certain portions of this disclosure to possibly increase the reader&#39;s understanding of the invention and embodiments described and claimed herein. Each of such patents and applications is incorporated herein by this reference as though set forth in their entirety, particularly including (without limitation) U.S. Pat. Nos. 5,267,364, 5,168,589, and application Ser. No. 07/823,281. Further details of such patents have been referenced elsewhere herein. 
   Although the present invention has been described in terms of the foregoing embodiment, such description has been for exemplary purposes only and, there will be apparent to those of ordinary skill in the art, many alternatives, equivalents, and variations of varying degrees that will fall within the scope of the present invention. That scope, accordingly, is not to be limited in any respect by the foregoing description, rather, it is defined only by the claims which follow.