Abstract:
This invention relates generally to patient monitoring systems and more particularly concerns devices and systems used to monitor bed patients in hospital or other care-giving environments. In accordance with a first aspect of the instant invention, there is provided a pressure sensitive mat which has been completely sealed around its exterior edges. The interior of the mat is kept in communication with the atmosphere by way of a section of flexible tubing which encloses the attached electrical line. One end of the tubing is sealed inside of the mat and the other end is open to the atmosphere, thereby providing a passageway for air to reach the interior of the mat. This arrangement, however, protects the interior of the mat from exposure to fluids near the perimeter of the mat and allows the mat-portion of the invention to be completely submersed without adverse effect, if that should become necessary.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 60/184,424 filed Feb. 23, 2000, the disclosure of which is incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to monitoring systems and, more particularly, concerns pressure-sensitive devices and systems used to monitor patients in hospital or other care giving environments.  
         BACKGROUND OF THE INVENTION  
         [0003]    It is well documented that the elderly and post-surgical patients are at a heightened risk of falling. There are many reasons for this but, broadly speaking, these individuals are often afflicted by gait and balance disorders, weakness, dizziness, confusion, visual impairment, and postural hypotension (i.e., a sudden drop in blood pressure that causes dizziness and fainting), all of which are recognized as potential contributors to a fall. Additionally, cognitive and functional impairment, and sedating and psychoactive medications are also well recognized risk factors.  
           [0004]    A fall places the patient at risk of various injuries including sprains, fractures, and broken bones—injuries which in some cases can be severe enough to eventually lead to a fatality. Of course, those most susceptible to falls are often those in the poorest general health and least likely to recover quickly from their injuries. In addition to the obvious physiological consequences of fall-related injuries, there are also a variety of adverse economic and legal consequences that include the actual cost of treating the victim and, in some cases, caretaker liability issues.  
           [0005]    In the past, it has been commonplace to treat patients that are prone to falling by limiting their mobility through the use of restraints, the underlying theory being that if the patient is not free to move about, he or she will not be as likely to fall. However, research has shown that restraint-based patient treatment strategies are often more harmful than beneficial and should generally be avoided—the emphasis today being on the promotion of mobility rather than immobility. Among the more successful mobility-based strategies for fall prevention include interventions to improve patient strength and functional status, reduction of environmental hazards, and staff identification and monitoring of high-risk hospital patients and nursing home residents.  
           [0006]    Of course, monitoring high-risk patients, as effective as that care strategy might appear to be in theory, suffers from the obvious practical disadvantage of requiring additional staff if the monitoring is to be in the form of direct observation. Thus, the trend in patient monitoring has been toward the use of electrical devices to signal changes in a patient&#39;s circumstance to a caregiver who might be located either nearby or remotely at a central monitoring facility, such as a nurse&#39;s station. The obvious advantage of an electronic monitoring arrangement is that it frees the caregiver to pursue other tasks away from the patient. Additionally, when the monitoring is done at a central facility a single nurse can monitor multiple patients which can result in decreased staffing requirements.  
           [0007]    Generally speaking, electronic monitors work by first sensing an initial status of a patient, and then generating a signal when that status changes, e.g., he or she has sat up in bed, left the bed, risen from a chair, etc., any of which situations could pose a potential cause for concern in the case of an at-risk patient. Electronic bed and chair monitors typically use a pressure sensitive switch in combination with a separate monitor/microprocessor. In a common arrangement, a patient&#39;s weight resting on a pressure sensitive mat (i.e., a “sensing” mat) completes an electrical circuit, thereby signaling the presence of the patient to the microprocessor. When the weight is removed from the pressure sensitive switch, the electrical circuit is interrupted, which fact is  10  sensed by the microprocessor. The software logic that drives the monitor is typically programmed to respond to the now-opened circuit by triggering some sort of alarm—either electronically (e.g., to the nursing station via a conventional nurse call system) or audibly (via a built-in siren).  
           [0008]    General information relating to mats for use in patient monitoring may be found in patent application 09/285,956 filed Apr. 2, 1999 the disclosure of which is specifically incorporated herein by reference. Additionally, U.S. Pat. Nos. 4,179,692, 4,295,133, 4,700,180, 5,600,108, 5,633,627, 5,640,145, and 5,654,694 (concerning electronic monitors generally) contain further information generally pertinent to this same subject matter, as do U.S. Pat. Nos. 4,484,043, 4,565,910, 5,554,835, and 5,623,760 (switch patents), the disclosures of all of which are all incorporated herein by reference.  
           [0009]    By way of general background, in a typical arrangement, a pressure-sensing mat is a sealed “sandwich” composed of three layers: two outer layers and an inner (central) layer positioned therebetween. The outer layers are usually made of some sort of plastic and are impermeable to fluids and electrically non-conductive on their outer faces, where “outer” is determined with respect to the middle layer. The inner surface of each of the outer layers—which inner surfaces are oriented to face each other from opposite sides of the central layer—is made to be electrically conductive, usually by printing a conductive (e.g., carbon-based) ink on that surface. The compressible middle “central spacer” is made of a non-conductive material and serves to keep the two conductive faces apart when a patient is not present on the sensor. The central spacer is discontinuous, which makes it possible for the two conductive inner surfaces to be forced into contact through the discontinuities when weight is applied to the switch. By attaching a separate electrical lead to each of the conductive inner faces, it can readily be determined (e.g., via a simple continuity check) whether a weight is present on the sensor (e.g., whether a patient is seated thereon). Removal of the weight causes the central spacer to expand and press apart the two conducting faces, thereby breaking the electrical connection between them. Thus, a device that monitors the resistance across the two electrical leads may determine when a patient has risen to his or her feet.  
           [0010]    One disadvantage of the current generation of pressure sensitive mats is that they cannot be completely (e.g., hermetically) sealed against the external environment. The reason for this should be clear: if the interior of the mat were completely sealed, air pressure inside of the mat would tend to oppose the urging of the mat faces into contact, thereby making it difficult or impossible to complete the circuit (e.g., think of compressing an “air pillow”). Thus, it is customary to intentionally leave gaps in the seal between the two halves of the mat which allow for movement of air into and out of the switch.  
           [0011]    Another disadvantage of the prior art is that partial sealing of the perimeter of the mat can cause it to resist expansion after weight is removed therefrom. That is, when a patient places weight on a conventional mat, air is slowly expelled from the mat interior, typically through a small opening in the perimeter of the mat. However, when the patient rises the opening in the mat can collapse or narrow in response to air pressure on the now-deflated mat body, thereby retarding the process of reinflating it. As a consequence, the mat may continue to signal that the patient is still present on the mat for a time after he or she has risen.  
           [0012]    Of course, the fact that the interior of the mat must kept open to the atmosphere results in a mat that is highly susceptible to invasion by bodily fluids or cleaning solutions, as the in-rushing air tends to carry fluids along with it into the interior of the mat. Further, it is well known that some common disinfecting cleaners can loosen the adhesives that hold the layers of the mat together, thereby ruining the sensor. Thus, cleaning soiled mats that have air passages placed therein becomes problematic. In summary, what is needed is a pressure sensitive mat that is more resistant to invasion by fluids than is presently available.  
           [0013]    Heretofore, as is well known in the patient monitoring arts, there has been a need for an invention to address and solve the above-described problems. Accordingly, it should now be recognized, as was recognized by the present inventors, that there exists, and has existed for some time, a very real need for pressure sensitive mat and monitoring system that would address and solve the above-described problems.  
           [0014]    Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.  
         SUMMARY OF THE INVENTION  
         [0015]    In accordance with a first aspect of the instant invention, there is provided a pressure sensitive mat which has preferably been completely sealed around its exterior edges except where a breathing tube passes therethrough. The interior of the mat is kept in communication with the atmosphere by way of a section of flexible tubing which encloses the attached electrical line. One end of the tubing is sealed inside of the mat and the other end is open to the atmosphere, thereby providing a passageway for air to reach the interior of the mat. This arrangement, however, protects the interior of the mat from exposure to fluids that might be present near its perimeter. In fact, this innovation allows the mat-portion of the invention to be completely submersed without adverse effect, if that should be come necessary.  
           [0016]    According to another aspect of the instant invention, there is provided a pressure sensitive mat and breathing tube combination wherein the wires that transmit status information from the interior of the mat to a separate electronic monitor are not inside of the breathing tube, but instead are adjacent to it through at least part of their length. One example of such an arrangement would be found in a multi-lumen tube of the sort that are well known to those skilled in the medical arts, wherein the electrical wires are preferably placed in one tube (or lumen), with one or more other tubes being kept clear to permit the passage of air therethrough.  
           [0017]    Finally, according to still another aspect of the instant invention, there is provided a pressure sensitive mat and breathing tube combination, wherein the breathing tube is completely separated from the electrical wires and separately penetrates the mat perimeter to reach its interior.  
           [0018]    The foregoing has outlined in broad terms the more important features of the invention disclosed herein so that the detailed description that follows may be more clearly understood, and so that the contribution of the instant inventor to the art may be better appreciated. Although the instant invention will be described in connection with a preferred embodiment, it is to be understood that it is not intended to limit the invention to that embodiment. That is, the instant invention is not to be limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. Rather, the invention is capable of other embodiments and of being practiced and carried out in various other ways not specifically enumerated herein. Further, it should be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting, unless the specification specifically so limits the invention. Finally, the disclosure that follows is intended to apply to all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:  
         [0020]    [0020]FIG. 1 illustrates the general environment of the invention.  
         [0021]    [0021]FIG. 2 contains a schematic illustration of a convention pressure sensitive mat.  
         [0022]    [0022]FIG. 3 contains a cross-sectional view of a pressure sensitive mat.  
         [0023]    [0023]FIG. 4 illustrates a preferred embodiment of the instant invention.  
         [0024]    [0024]FIG. 5 contains a cross-sectional view of a preferred connecting tube arrangement of the instant invention, wherein the tube encloses the electrical wire.  
         [0025]    [0025]FIGS. 6A and 6B illustrate cross sections of another wire/tube configuration, wherein the electrical wire and tube are run roughly in parallel.  
         [0026]    [0026]FIG. 7 contains a plan view of another preferred embodiment, wherein the electrical wire and breathing tube are run roughly in parallel.  
         [0027]    [0027]FIG. 8 illustrates another preferred arrangement, wherein the electrical wire and breathing tube enter the mat in different locations.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     General Background  
       [0028]    Turning first to FIG. 1 wherein the general environment of the instant invention is illustrated, in a typical arrangement a sensing mat  100  is placed on a hospital bed  20  where it will lie beneath a weight-bearing portion of the reclining patient&#39;s body, usually the buttocks and/or shoulders. It should be noted at the outset, however, that although the language that follows is largely confined to illustrations involving bed-type sensors, the range of application of the instant invention is much broader and could include chair sensors, potty sensors, and any other type of pressure-sensitive switch that is used in a patient monitoring environment where invasion by fluids is a concern.  
         [0029]    Generally speaking, the mat  100 /monitor  50  combination works as follows. When a patient is placed atop the mat  100 , the patient&#39;s weight compresses the mat  100  and closes an electrical circuit, which closure is sensed by the attached electronic patient monitor  50  through electrical line  10  and connector  40  (FIG. 2). When the patient attempts to leave the bed, weight is removed from the sensing mat  100 , thereby breaking the electrical circuit. The patient monitor  50  senses the change in electrical continuity and signals the caregiver per its pre-programmed instructions. Note that additional electronic connections not pictured in this figure might include a monitor  50  to nurse-call-station connection, a monitor  50  to computer connection, and an A/C power cord—although the monitor  50  can certainly be configured to be battery operated.  
         [0030]    [0030]FIG. 2 contains a schematic drawing of a prior art pressure sensitive patient mat. As is indicated in that figure, a typical pressure sensitive mat  100  includes upper and lower non-conductive outer members  220  and  240  (FIG. 3), respectively, which serve to protect the interior from contact with the environment. These members are usually made of a flexible impermeable electrically non-conductive material such as plastic, with polyester being the preferred material. These two members are separated by an internal non-conductive spacer  260 , which has at least one aperture therethrough  250 . In FIG. 2, the central spacer  260  is shown in phantom because it is hidden from view within the assembled product.  
         [0031]    As is further indicated in FIG. 3, the typical pressure sensitive switch is a “sandwich” type arrangement with the two outer members surrounding the inner non-conductive spacer  260 . The perimeters of the upper  220  and lower  240  members are conventionally sealed together by a heat activated adhesive (such as polyethylene) or by some form of pressure sensitive adhesive.  
         [0032]    Affixed to the inner surface of each of the outer members  220  and  240  is a conductive layer ( 320  and  340 , respectively) which, for safety purposes, preferably does not extend to the edges of the mat. As should be clear, pressure on the mat  100  tends to urge the conductive faces  320  and  340  into contact through aperture  250 , thereby completing an electrical circuit. When pressure is released, the central spacer  260 , which is preferably constructed of a compressible and resilient material, expands and pushes the conductive layers apart. As is suggested in FIG. 2, when the electrical line  10  enters the mat it is typically separated into two electrically isolated elements, one of which is placed in electrical communication with the conductive layer  320  atop of the spacer  260  and the other which is placed in electrical communication with the conductive layer  340  underneath the spacer.  
         [0033]    As is generally illustrated in FIG. 3, the central spacer  260  usually fits loosely within an envelope formed by the two outer layers  220  and  240 . This arrangement allows air to move freely throughout the interior of the mat  100 . Fluid communication between the interior of the mat and the atmosphere is typically provided in the form of one or more breaches in the seal between the upper  220  and lower  240  members. These breaches are created during the manufacturing process and provide a means for the mat  100  to “breathe” when compressed. A first natural breach occurs at the point where electrical line  10  enters the mat between the upper  220  and lower  240  mat members. Typically, the mat material fits loosely around the electrical line  10 , thereby providing a ready passageway for air (and fluids) to enter and exit the mat. Where more airways are needed, it is possible to create gaps between the outer members along their common perimeter. One way of doing this involves placing a piece of monofiliment line between the upper  220  and  240  members before they are sealed. After the two members have been sealed together, the line is withdrawn, leaving behind a small gap  230  in the seal between the layers.  
       Preferred Mat Embodiments  
       [0034]    A first preferred embodiment of the instant mat is illustrated in FIG. 4, which contains a plan view of the device. As is illustrated there, the mat portion of the sensor  400  is configured in a “sandwich” arrangement as has been described above. However, the instant embodiment differs from the prior art in that it contains a separate open-ended “breathing tube”  420  which loosely encloses the electrical line  10 . This tube  420  enters the mat between the upper  220  and lower  240  members. The upper  220  and lower  240  members may now be completely sealed along their perimeters, including where the tube  420 /electrical line  10  combination enters the mat  400 . When pressure is applied to the mat  400 , the air inside of the mat  400  is pushed toward and out of the breathing tube  420 , thereby allowing the mat  400  to compress. Similarly, when pressure is removed, air returns from the atmosphere to the interior of the mat  400  via the same conduit, thereby allowing the mat  400  to quickly expand to its un-weighted configuration which separates the upper  220  and lower  240  members.  
         [0035]    [0035]FIG. 5 illustrates a preferred embodiment of the breathing tube  420  in cross section. As can be seen in this figure, tube  420  is sized so that the electrical line  10  fits loosely therein, thereby providing at least a partially unobstructed air passageway. The breathing tube  420  is preferably round or oval, although obviously the precise shape of the tube  420  is unimportant, so long as an air-tight seal may be created around the perimeter of the tube  420  where it enters the mat  400  between the two outer mat members. Within electrical line  10  will typically be found two or more electrically isolated conductors  510 , with the use of a four-conductor wire being a common arrangement. It should be apparent that the number of electrical conductors  510  that might be found within the electrical line  10  is unimportant to the practice of the instant invention. As has been described previously, it is customary to use two of these conductors  510  to establish separate electrical communications between the monitor  50  and the upper  320  and lower  340  conducting members inside of the mat.  
         [0036]    In operation, the sensing portion of the instant invention  400  may be completely submerged without risk of fluid invasion, so long as the outer terminus of the breathing tube  420  (i.e., the end nearest the connector  40 ) is kept clear of the fluid. Further, the instant mat  400  may be fully compressed and then released while held under water without risk of drawing fluid into its interior, provided that the perimeter has been completely sealed. Finally, in a patient monitoring situation where there has been a release of fluid into the bed or chair, the mat  400  can be cleaned and reused without endangering its structural integrity.  
         [0037]    [0037]FIG. 7 contains another preferred arrangement. In this variation, the tube  420  and electrical wire  10  run roughly in parallel into the mat  700 . A cross sectional view of this arrangement may be found in FIGS. 6A and 6B, these two figures differing only in the size of the breathing tubes  420  and  620  attached thereto. This configuration of breathing tube/electrical conductors  510  is sometimes referred to as a “multi-lumen” cable by those skilled in the art. Of course, the diameter of the breathing tube  420  is unimportant to the operation of the instant invention, except that it should be large enough to convey sufficient air into and out of the interior of the mat  700  to allow it to be readily compressed and then expanded again. The best tube  420  diameter will ultimately depend on the specifics of the mat to which it is attached and will need to be determined empirically for each type of mat.  
         [0038]    [0038]FIG. 8 contains still another variation, wherein the electrical line  10  and the breathing tube  420  enter the mat  800  independently. As should be clear from this figure, this arrangement suffers from the disadvantage that two different breaches of the mat perimeter would need to be sealed. However, having the electrical line  10  and breathing tube  420  separated might be advantageous in some circumstances.  
         [0039]    Finally, it should be noted and remembered that although it is preferable that the mat be completely sealed along its perimeter except where the breathing tube penetrates it, that is not strictly required. The breathing tube acts to assist in reinflation of the any sort of mat when weight is removed therefrom, so it would also be useful with a conventional mat which is not hermetically sealed. However, if the mat is not completely sealed along its perimeter there is a risk that fluid will enter the interior of the mat through those breaches, as has been a problem in the past.  
         [0040]    Clearly, many variations of this and the previous arrangements are possible and have been specifically contemplated by the instant inventor.  
         
       [0041]    Conclusions  
         [0042]    Although the preceding text has occasionally referred to the sensor of the instant invention as a “bed” mat that was done for purposes of specificity only and not out of any intention to limit the instant invention to that one application. In fact, the potential range of uses of this invention is much broader than bed-monitoring alone and might include, for example, use with a chair monitor, urinal monitor, or other pressure sensitive patient monitor application which is configurable as a binary switch, a binary switch being one that is capable of sensing at least two conditions and responding to same via distinct electronic signals. In the preferred embodiment, those two conditions would be the presence of weight on the switch. Additionally, it should be noted that the use of the term “binary” is not intended to limit the instant invention to use only with sensors that can send only two signal types. Instead, binary switch will be used herein in its broadest sense to refer to any sort of sensor that can be utilized to sense the condition or location of a patient, even if that sensor can generate a multitude of different signals.  
         [0043]    Thus, it is apparent that there has been provided, in accordance with the invention, a patient sensor and method of operation of the sensor that fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art and in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit of the appended claims.