Electricity: circuit makers and breakers – Weight
Reexamination Certificate
2001-06-07
2004-02-24
Enad, Elvin (Department: 2832)
Electricity: circuit makers and breakers
Weight
C200S08600A, C340S573300
Reexamination Certificate
active
06696653
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to binary switches for use in the medical monitoring field and to methods for manufacturing same. More particularly, the instant invention involves the construction, manufacture, and operation of pressure sensitive patient monitors of the sort commonly used in medical settings to detect when a patient has, for example, left a chair or a bed.
BACKGROUND OF THE INVENTION
It is well documented that the elderly and post-surgical patients are at a heightened risk of falling. 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.
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.
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.
Of course, direct monitoring of 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's circumstance to a care giver who might be located either nearby or remotely at a central monitoring facility, such as a nurse's station. The obvious advantage of an electronic monitoring arrangement is that it frees the care giver to pursue other tasks away from the patient. Additionally, when the monitoring is done at a central facility a single person can monitor multiple patients which can result in decreased staffing requirements.
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 electronic monitor which conventionally contains a microprocessor of some sort. In a common arrangement, a patient'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 similarly 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) or both. Additionally, many variations of this arrangement are possible and electronic monitoring devices that track changes in other patient variables (e.g., wetness/enuresis, patient activity, etc.) are available for some applications.
General information relating to mats for use in patient monitoring may be found in 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). Additional information may be found in 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.
By way of general background, in a typical arrangement, a pressure-sensing mat of the sort discussed herein is a sealed “sandwich” composed of three layers: two outer layers and an inner (central) layer positioned between the two outer layers. 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 help 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 one or more 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 via a simple continuity (or low voltage) check whether a weight is present on the sensor (e.g., 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 moved from a seated or prone position.
One disadvantage of the current generation of pressure sensitive mats is that they cannot be completely (e.g., hermetically) sealed around their perimeters 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”). Of course, the fact that the interior of the mat must be 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 that enters when the switch expands 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 a conventional mat together, thereby ruining the sensor. Thus, cleaning soiled mats becomes problematic. In summary, what is needed is a pressure sensitive mat that is more resistant to invasion by fluids than has heretofore been available.
Methods of manufacturing conventional pressure sensitive mats for use in medical applications of this sort of sensing device typically begin at a single station punch, wherein the upper and lower plastic
onconductive members are cut from a larger sheet of material. This step would typically be followed by the application of a conductive material to one face of each member. For example, the conductive material could be printed onto the surface usin
Blaker Margaret S.
Cooper Craig L.
Fitzgerald Sanford G.
Keck Richard R.
Smith Toby E.
Bed-Check Corporation
Enad Elvin
Fellers Snider Blankenship Bailey & Tippens, P.C.
Lee K.
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