A pressure-sensitive switch apparatus for use in monitoring the position of a patient in a bed or chair is provided. The switch includes a resilient conductor disposed between first and second conductors located at opposite surface areas of the switch. The resilient conductor provides varying degrees of electrical contact between the first and second electrical conductors in response to pressure applied to either of these conductors by shifting of the patient's weight.

BACKGROUND OF THE INVENTION 
The present invention relates to a pressure-sensitive switch apparatus and, 
more particularly, to such an apparatus for use in monitoring the presence 
of a patient in a bed or chair. 
A problem of considerable concern to health care providers is that of 
patients leaving a bed or chair when the patient is not safely ambulatory. 
The use of restraints to ensure the safety and well-being of such patients 
is becoming impracticable in many instances, not only because of legal 
issues relating to patients' rights, but also because of a change to a 
more considered approach by medical and nursing staff toward patients. 
Concerns regarding the use of restraints are even more acute in the case 
of home care where patients are typically cared for by family members. 
There is a need, therefore, for a less invasive approach to monitor 
patients restricted to a bed or chair and to alert health care care 
providers when patients attempts movement on their own. 
It is, therefore, an object of the invention to provide a simple and 
reliable electronic device which automatically alerts nursing staff or 
other care givers should a patient attempt to exit a bed or chair 
unattended. 
It is further object of the invention to provide such a device which can be 
utilized in combination with standard monitoring devices such as home 
security systems. 
It is a still further object of the invention to provide such a device 
which can be used with commercially available equipment which permits the 
sensitivity of the device to be adjusted to optimize the performance of 
the device. 
SUMMARY OF THE INVENTION 
The invention meets these and other objects by providing a 
pressure-sensitive switch apparatus which is positioned beneath a patient 
lying or sitting in a bed or sitting in a chair. While the switch may be 
placed directly under the patient, it is preferably placed under or in the 
mattress or chair cushion or beneath a covering for the mattress or 
cushion. When the patient is present in the bed or chair, the patient's 
weight provides sufficient pressure to cause the switch to remain closed. 
On the other hand, when the patient attempts to exit the bed or chair, the 
resulting reduction of pressure applied to the switch causes it to open 
and alert nursing staff or other care givers that the patient is 
attempting movement on his or her own. 
A pressure sensitive switch apparatus embodying the invention includes a 
first electrical conductor, a second electrical conductor, and a resilient 
electrical conductor disposed between the first and second conductors. A 
substantially non-conductive member disposed between the resilient 
electrical conductor and either the first and second electrical conductors 
has at least one passageway which permits the passage of at least a 
portion of the resilient conductor in response to pressure applied to at 
least one of the first and second conductors. When sufficient pressure is 
applied to one of the first or second conductors, the resilient conductor 
is forced through the passageway and contacts the other of the conductors, 
thus establishing a closed electrical circuit between the first and second 
conductors. 
In practice, when the patient is present in the bed or chair, the patient's 
weight applies sufficient pressure to the first or second conductor to 
force the resilient conductor through the passageway and close the 
circuit. When the patient attempts to leave the bed or chair and pressure 
is reduced on the switch, the resilient conductor moves back through the 
passageway and the circuit opens. The opening of the circuit causes 
activation of an associated monitoring device, which may be a standard 
home security system, connected with the pressure-sensitive switch through 
associated electronic circuitry to alert the care giver that the patient 
is attempting movement on his or her own. The operation of the switch is 
enhanced by connecting the switch to existing monitoring equipment that 
contains controls which enable the user to select a specific desired 
pressure for activation. This enables the switch to be employed for 
determining if the patient is in a seated position versus a prone position 
which can be critical in, for example, a hospital trauma unit.

DETAILED DESCRIPTION 
Referring to FIGS. 1 and 2, a pressure-sensitive switch, generally 
indicated 10, embodying the invention includes a first base member 12, a 
second electrical conductor 14, a resilient base member 16 and a 
substantially non-conductive member 18. 
The base members 12 and 14 are formed from a non-electrically conductive, 
thin, flexible material. Preferably, this material is high-density 
polyethylene, although it should be understood that the invention is in no 
way limited in this regard and that a wide range of other non-conductive, 
flexible materials may be used. The base members 12 and 14 are generally 
of rectangular configuration, and in the illustrated embodiment measure 
about 0.023 inches thick, 3.500 inches wide and from about 4 to about 26 
inches long, depending on whether the switch is used for a chair or bed. 
Each of the base members 12 and 14 has, respectively, an outer surface 20 
and 22 and an inner surface 24 and 26. A conductive path 28 is processed 
on the inner surface 24 of base member 12, and conductive path 30 is 
processed on the inner surface 26 of base member 14. While the conductive 
paths 28 and 30 may be hard wired in a conventional manner, in the 
preferred embodiment they are formed from a conductive, carbon graphite 
ink or paint which is silk-screened or otherwise uniformly applied to the 
inner surfaces 24 and 26. The ink is combined with an acetate to enhance 
adhesion of the ink to the polyethylene, and with the ink in place, a 
conductive value is maintained regardless of bending or twisting of the 
base members 12 and 14. 
In the illustrated embodiment, conductive paths 28 and 30 are from about 
0.001 to about 0.003 inches thick, about 1.500 inches wide and from about 
4 to about 20 inches in length. The conductive paths are placed about 1 
inch from either side of base members 12 and 14, and about 2.500 inches 
from the left end of the switch apparatus 10 as shown in FIGS. 1 and 2 and 
about 1.500 inches from the opposite end of 15 and 23 base members. Of 
course, the dimensions of the ink path can be altered depending on the 
dimensions of the switch. 
Conductive wires 32 and 34 are adhered to the conductive paths 28 and 30, 
respectively, by adhesive areas 36 and 38. The wires are insulated close 
to the conductive paths to prevent contact with other conductive 
components of the switch apparatus and are jacketed to form a cable 40 to 
exit the switch apparatus. The cable 40 is adhered in place by two pads of 
adhesive polyethylene foam 42 and 44 mounted on inner surfaces 24 and 26, 
respectively. The foam pads are adhesive on all sides and surround the 
exiting cable to provide strain relief. In addition, the adhesive pads 42 
and 44 provide bonding between conductors 12 and 14. In the preferred 
embodiment of the invention, the pads 42 and 44 are 0.062 inches thick, 
about 2.0 inches wide and about 2.0 inches long. Two more adhesive pads 46 
and 48 are provided at the opposite end of the switch apparatus 10 to 
provide additional areas of bonding between the base members 12 and 14. In 
the preferred embodiment, the pads 46 and 48 are about 0.062 thick and 
measure about 0.75 inches in width and about 2.0 inches in length. Of 
course, other means for securing the wires 32 and 34 to the conductive 
paths and for bonding the base members 12 and 14 to one another could be 
substituted for the adhesive areas 36 and 38 and the adhesive pads 42-48 
without departing from the scope of the invention. 
As shown best in FIG. 2, when the switch apparatus is in its assembled 
condition, the resilient conductor 16 is disposed adjacent to and in 
contact with the conductive path 28. Accordingly, electric current applied 
to the conductive path 28 via the conductive wire 32 is transferred to the 
resilient conductor 16. In the preferred embodiment of the invention, the 
resilient conductor is formed from a conductive foam which is adhered 
directly to the base member 12 outside the area covered by the conductive 
path 28 by a thin layer of adhesive (not shown). The conductive foam 
provides consistent surface and volume resistivities and is commercially 
available from Foam Tech Inc. The foam comprises a homogenized mixture of 
carbon and polyethylene which is cellular in construction and about 0.125 
inches thick when uncompressed. When pressure is applied, the conductive 
foam compresses, condensing the cellular construction. Electrically, this 
causes the carbon elements to condense, thus densifying the conductive 
carbon structure and allowing more electrical current to pass than when 
the foam in uncompressed. 
Effectively, the foam is a variable resistor that responds to the pressure 
being applied. The more pressure that is applied, the more the foam 
condenses and the lower its resistive value allowing more current to pass 
through the area of the foam that is compressed. The lower the pressure 
that is applied to the foam, the less it is compressed and the higher its 
resistive value. Thus, a patient weighing 200 pounds sitting or laying on 
top of the switch apparatus would cause more electrical current to flow 
than would a patient weighing 100 pounds. In the illustrated embodiment, 
the resilient resistor 16 measures about 2 inches in width and about 20.0 
inches in length. Again, the length varies from about 4 to about 20 inches 
depending if the switch apparatus is utilized for a bed or a chair. 
Attached to base member 14 by means of adhesive is the non-conductive 
member 18. Member 18 is formed from a non-conductive, thin, flexible 
material which in the preferred embodiment is polyvinyl chloride. The 
material is about 0.010 thick, 3.500 inches wide and 4 to 20 inches in 
length. The non-conductive member 18 includes a plurality of apertures or 
openings 50, 50 which provide a passageway for the conductive foam when 
pressure is applied to the outer surface 20 or 22 of base members 12 and 
14, respectively. That is, if the patient's weight applies sufficient 
pressure to, for example, outer surface 20, the conductive foam is forced 
through one or several of the apertures 50 and contact is made with 
conductive path 30 on base member 14. Thus, a closed electrical circuit is 
established between the two conductive paths 28 and 30 through the foam 
conductor 16. When the pressure is released and the resilient foam 
retracts through the apertures 50, 50 the circuit is opened. In the 
illustrated embodiment, the apertures 50, 50 are about 0.190 inches in 
diameter and 0.010 in height, which are the preferred dimensions based on 
the weight of adolescent and adult patients, as apertures having these 
dimensions provide the appropriate amount of contact between the foam 
conductor 16 and the conductive paths 28 and 30. The switch can be adapted 
to monitor patients of lower weight, such as young children and infants, 
simply by enlarging the apertures 50, 50 allowing more of the foam to pass 
more easily therethrough, while at the same time requiring less pressure. 
The switch apparatus 10 is entirely enclosed in a vinyl covering 52, as 
shown in FIGS. 2 and 3. The cover is slightly larger in width and longer 
in length than the switch 10 to accommodate mounting holes 54. One end is 
tapered to allow cable 40 enclosing conductive wires 32 and 34 to exit the 
switch. The covering is made from a thin, flexible medical grade polyvinyl 
chloride about 0.012 thick, 3.750 inches wide and 4 to 28 inches long. A 
beading surrounds the covering where each side has been wielded to form 
the covering. 
As shown in FIG. 3, the cable 40 terminates with a connector 56 to 
facilitate hook-up and operation of an electronic control 58. The control 
58 monitors the variable resistive values of the conductive foam in 
response to pressure applied to and removed from the switch apparatus. 
With the switch apparatus 10 in place on, in or under a bed mattress or 
chair cushion, the control 58 is able to monitor shifting or other 
movement of the patient to a position that places the patient in potential 
danger of injury. 
As noted above, conventional monitoring equipment allows the sensitivity of 
the control 58 to be adjusted so that early warning of patient movement is 
provided. In addition, the sensitivity of the control 58 can be adjusted 
to compensate for the weight of the mattress, overlays or other bedding or 
distortions of the switch created by a patient laying or sitting on the 
switch while it is supported on an uneven surface. 
In practice, the switch is designed to remain open absent the presence of 
the patient in the bed or chair. When the patient is a proper laying or 
sitting position, the switch is closed. When the patient rises from the 
bed or chair or, based on the sensitivity setting, even shifts his or her 
weight to attempt such motion, the conductive foam retracts through the 
apertures 50, 50 to cause an open condition and sound an alarm through the 
control 5. 
An alternative embodiment of the switch apparatus is shown in FIG. 4, in 
which components corresponding to those shown in the first embodiment have 
been given like numbers. In the FIG. 4 embodiment of the switch apparatus 
10', the conductive path supported by the base member 12 is formed as a 
series of segments 60, 62, 64 and 66. Each of these segments has a 
separate conductive wire 68, 70, 72 and 74, respectively, supplied from 
the cable 40, and each of the conductive wires is monitored by separately 
by the control (not shown). The non-conductive member 18, the conductive 
path 30 and the base member 14 remain unaltered from the embodiment 
illustrated in FIGS. 1-3. Dividing the conductive path into a series of 
segments provides enhanced sensing of the patient's position, since the 
switch can be constructed so that individual segments are located beneath 
specific body parts. Accordingly, the position of a particular body part 
can be monitored while the patient lays or sits in a normal resting 
position. Having an individual sensor for a particular body part is 
especially important in, for example, head injury cases where a patient's 
head shifts to a medically compromising position while the patient lays in 
an otherwise normal resting position. 
While the invention has been described as it pertains to use in a patients 
bed or chair, in a hospital, nursing home or in the individual home 
setting, it can be seen that the invention can be for any other switching 
purpose where a variable pressure operating switch could be utilized. 
While the invention has been described with a certain degree of 
particularity, it is manifest that many changes may be made in the 
construction and arrangement of -components without departing from the 
spirit and scope of this disclosure. It is understood that the invention 
is not limited only by the scope of the attached of the attached claim or 
claims, including the full range of equivalency to which each element 
thereof is entitled.