Key programmed transcutaneous electric stimulator

A transcutaneous electrical stimulator for applying therapeutic electrical impulses to the living body of a patient, where at least some of the electrical parameters of the electrical impulses are actuated by the use of a key. When this key is inserted in the housing of the stimulator and rotated, the several wards actuate corresponding switches, activating a controller which operates a generator to deliver the therapeutic impulses. At least one parameter of the therapeutic impulses may be determined by the pattern of the wards.

FIELD OF THE INVENTION 
This invention relates to medical stimulators and the control of the 
electrical parameters used in the medical stimulators to deliver 
therapeutic electrical impulses. 
BACKGROUND OF THE INVENTION 
In recent years, transcutaneous electrical nerve stimulation (TENS) has 
been developed to provide relief of pain without the use of systemic 
analgesic drugs. Stimulators used for this purpose deliver therapeutic 
electrical impulses to the skin surface of a living patient through lead 
wires from the stimulator to body contacting electrodes. Typically, 
transcutaneous electrical stimulators control at least the therapeutic 
parameters of electrical pulse width, electrical pulse rate, and 
electrical pulse amplitude. Sometimes, the same stimulator may have dual 
controls for operating two separate transcutaneous electrical output 
channels. 
Also in recent years, neuromuscular stimulation (NMS) has been developed to 
provide muscle re-education (maintenance, strengthening, or 
rehabilitation) transcutaneously. 
Conventionally, the electrical pulse parameters have been controlled in the 
stimulator using either potentiometers or with momentary contact rocker 
switches. The latter are shown in coassigned U.S. Pat. No. 4,803,986 
(Dufresne et al.), which is hereby incorporated by reference. 
For purposes of describing this invention, a "transcutaneous electrical 
stimulator" includes at least a TENS stimulator, a NMS stimulator, or any 
other medical stimulator used to deliver therapeutic electrical impulses. 
One difficulty with using conventional stimulators is dealing with the 
problem of setting the various electrical pulse controls for the proper 
and unique operation of the transcutaneous electrical stimulator for a 
patient because the stimulator is used therapeutically by untrained 
personnel. Sometimes, the stimulator is used by a patient apt to alter the 
controls in ignorance of the effect of such alteration. 
The desired therapeutic effect of the electrical impulses can not occur if 
the controls are not properly set by trained personnel. Unfortunately, 
misapplication of the stimulator through improper setting of the controls 
can be painful to the patient at the very location requiring pain relief 
therapy. 
Previously, the operation of electrical switches by a token using a 
plurality of multiple contact switches for use in dispatching systems has 
been disclosed in U.S. Pat. No. 3,046,364 (De Kramer et al). 
Also, U.S. Pat. No. 4,647,734 (Dana) discloses a key activated switch 
providing binary coded switching outputs for use with microprocessor based 
equipment. An arrangement of actuators is also disclosed. 
Also, U.S. Pat. No. 3,415,087 (Kramasz et al) discloses a plurality of 
electrical switches disposed in spaced relation to the cylinder of a pin 
tumbler lock. A special key is provided wherein one edge has conventional 
serrations for operating the pin tumbler, and the other edge has a 
plurality of lobes or notches formed into it which cooperate with a link 
mechanism that activates on or more of the electrical switches. 
None of these prior activities has contemplated the circumstances unique to 
pain relief therapy using transcutaneous electrical stimulators. 
SUMMARY OF THE INVENTION 
The present invention solves the problems found in the operation of 
conventional transcutaneous electrical stimulators by providing a 
stimulator having a apertured housing which may receive an actuator such 
as a key having wards or other actuating means to control one or more of 
the electrical pulse parameters vital to the proper transcutaneous 
electrical therapy. Trained personnel having a variety of keys may select 
one key to provide the proper setting of the electrical pulse controls. 
The controls may not be reset by untrained personnel unless a different 
key is possessed. 
The transcutaneous electrical stimulator comprises an apertured housing, 
means for generating therapeutic impulses of electrical energy, means for 
delivering the electrical energy to a location for therapy, and means for 
controlling the generating means, and a key insertable into the housing 
through the aperture and having a plurality of wards, at least one of 
which is configured to actuate the controlling means. 
Typically, transcutaneous electrical stimulators control at least the 
parameters of electrical pulse width, electrical pulse rate, and 
electrical pulse amplitude. 
Preferably, a stimulator of the present invention comprises a controller 
including several switches mounted within the housing but in communication 
with the aperture or keyhole. The operation of the stimulator involves a 
key to engage or otherwise actuate at least one of the switches. 
Preferably, the key has several wards, at least one of which is configured 
to engage at least one of the switches. 
To use the stimulator, the key is inserted into the aperture and moved, 
e.g., rotated into a stationary position, so that the appropriate ward 
actuate the appropriate switches through direct contact or otherwise. 
Depending on the presence or length of each ward in communication with a 
corresponding switch, some of the switches are closed. The various 
combinations of ward-switch contacts sets the electrical pulse parameters 
desired for proper therapy. With the key maintained in a stationary 
position, the controller is activated so as to induce the therapeutic 
regimen of electrical stimulation from the generator selected by trained 
personnel for the patient. 
The invention may also be embodied so that the electrical parameters of 
pulse rate and pulse width are determined by the pattern of the wards, 
while the electrical parameter of pulse amplitude is controlled by the 
patient using a potentiometer dial provided at the exterior surface of the 
stimulator housing. 
Another embodiment of the invention provides that the key will be 
constructed with frangible wards which can be removed by hand or with a 
tool by the trained personnel. Selection of which wards to remove 
establishes the proper transcutaneous electrical therapy for the patient. 
By choosing which of the wards to remove, the practitioner can easily 
prepare a key which will invoke exactly the regimen of therapy believed to 
be most appropriate. 
An object of the invention is to provide a mechanism so that the electrical 
parameters of the therapeutic impulses generated by a transcutaneous 
electrical stimulator can be quickly and simply set to pre-selected values 
without threat of misapplication of the transcutaneous electrical therapy 
through alteration of the values set. 
A feature of the invention is a transcutaneous electrical stimulator having 
a keyhole and a matching key so that insertion and rotation of the key 
invokes these pre-selected values. 
An advantage of the invention is that the stimulator with appropriate key 
may be provided to a patient without undue concern as to misuse of the 
transcutaneous electrical stimulator. 
A further advantage of the invention is that the medical practitioner can 
specify a particular therapeutic mode by the selection of a particularly 
patterned key for a particular patient. When a key with a plurality of 
frangible wards is provided, that key is easily converted to a patterned 
key by breaking off the appropriate wards on the key. 
A related advantage is that trained personnel providing a different key to 
a patient may alter the therapeutic regimen without other alteration to 
the transcutaneous electrical stimulator. 
Yet another advantage of the invention is that the cost of providing 
transcutaneous electrical therapy can be reduced without loss of providing 
appropriate therapy for each patient.

EMBODIMENTS OF THE INVENTION 
Referring to FIG. 1, a transcutaneous electrical stimulator of the present 
invention is shown. The stimulator 10 includes a housing 12 and a key 14. 
The key 14 bears at least one ward 15. The pattern of the wards 15 encodes 
information about the therapeutic regimen specified by that particular key 
used in the housing 12. The key 14 has a flange 16 at its head to 
facilitate grasping and turning. 
The housing 12 has an aperture 18 adapted to receive the key 14. A support 
block 20 may be optionally provided to support and protect the key 14 when 
the key 14 is in its operating position. Optionally, the support block 20 
may be configured to provide a detent mechanism (not shown) to resist 
movement of the key 12 in aperture once the key 12 is in its operating 
position. 
Optionally mounted on the housing 12 is one or more potentiometer dials 22, 
used by the patient to adjust the pulse amplitude in certain embodiments 
of the invention. 
Also mounted on the housing 12 is at least one output jack 24 which are 
used to convey the repetitive electrical pulses to the patient. Typically, 
a pair of lead wires 25 adapted to connect to output jack 24 conveys the 
repetitive electrical pulses to a pair of body contacting electrodes 27. 
Referring to FIG. 2, a cross section view along section lines 2--2 in FIG. 
1, the interaction of the key with the switches is illustrated. The 
housing 12 has been removed from the view for clarity, although it should 
be understood that the housing 12 would preferably include a structure, 
e.g., a keyway, aligned with the aperture 18, to support and align the key 
14 when and while it is inserted in the housing 12. In this figure, the 
key 14 is being held supported but at liberty to rotate axially through an 
arc. At some point during rotation of the key 14, one or more wards 15 on 
the key 14 will actuate one or more switches 26, preferably by directly 
contacting the switches 26. 
Each switch 26 may be formed from a spring contact 28 mounted on a printed 
circuit board 32 and a fixed contact 30, conveniently, an electrically 
conducting pad on a printed circuit board 32. Preferably, the wards 15 
contact the spring contacts 28 which thereby contact fixed contacts 30. 
Optionally, when at the point where rotation of the wards 15 contact the 
spring contacts 28, a detent mechanism on the support block 20 may 
releasably hold the key 14 in engagement with the switches 26. 
Depending on the pattern of the wards 15 on the key 14, one or more of the 
switches 26 will be actuated. The arrangement of the switches actuated by 
the key determine the functioning of electrical circuitry in the 
stimulator 10 for providing pain relief therapy. 
Referring to FIG. 3, a general block diagram of the electrical circuit 36 
required to supply high voltage/current output pulses 38 of the stimulator 
10 is illustrated. Generally, battery power 40 is supplied to a switched 
inductor circuit 42. A clock 44 drives a control circuit 46, which in turn 
controls a programmable logic block 48. Programmable logic block 48 
supplies switching signals 51 to switched inductor circuit 42 for 
generating a high-voltage supply 52 to output stages 54, which then 
utilizes programmed logic signal 50 to generate electrical stimulation 
signal 38. Programmable logic block 48 receives external status 
information 56 and uses this information to create the programmed logic 
signal 50 appropriate to the desired output conditions. Included in the 
external status information 56 is the condition of the switches 26 created 
by the pattern of contact between spring contact(s) 28 and fixed 
contact(s) 30 (these status conditions denoted collectively by the 
reference numeral 56a), and optionally, information on the condition of 
other controls and sensors (these status conditions denoted collectively 
by the reference numeral 56b) such as the potentiometer 22 (shown in FIG. 
1.) 
The block diagram of the electrical circuit 36 shown in FIG. 3 is 
illustrative of an electrical circuit of a transcutaneous electrical 
stimulator 10 of the present invention. It is to be recognized and 
understood that electrical circuits for use in transcutaneous electrical 
nerve stimulators are well known in the art and may include other 
circuitry or alterations to the circuitry shown here. 
The particular electrical circuit 36 illustrated in FIG. 3 is preferred for 
use with the stimulator 10 of the present invention and is additionally 
described in coassigned U.S. Pat. application Ser. No. 042,166, filed Apr. 
24, 1987, and now abandoned but continued in U.S. Pat. application Ser. 
No. 361,784, filed May 30, 1989, now U.S. Pat. No. 4,926,864, the contents 
of which are hereby incorporated by reference. 
However, in an alternate embodiment of the invention, where low component 
count is particularly desired, the output stages can incorporate a 
transformer coupling, obviating the need for the switched inductor circuit 
42 for the generation of high voltage. Exemplary output stages of this 
type are also well known to those skilled in the art. 
Referring to FIG. 4, a key 60 bearing frangible wards 62 is illustrated. In 
this embodiment, the key 60 has been constructed so that the wards 62 are 
frangible at score lines 64. The score lines are formed on the wards 62 
during the process of manufacturing the key 60. These score marks 64 are 
of such nature so that one or more wards 62 can be deliberately removed by 
hand or with a tool with some effort by the trained medical practitioner, 
in order to create the pattern of wards 62 on the key 60 desired to 
actuate the stimulator 10 to provide the appropriate pain relief therapy. 
However, the wards 62 should have sufficient mechanical strength at the 
score lines 64 to minimize inadvertent or accidental breaking. Other 
aspects of the key 60 are similar to key 14, such as the presence of a 
flange 66 corresponding to flange 16. 
In preferred embodiments, the key 14 or 60 will be formed of a 
non-conductive material to prevent electrical conduction between the 
various switches 26 through the key. Polymeric materials are preferred, 
with polycarbonate considered particularly preferred. Such a key is 
advantageously made using injection molding techniques well known to those 
skilled in that art. 
The spring contacts 28 of the preferred switches 26 are advantageously 
formed from hardened beryllium copper, optimally covered with a nickel or 
nickel/gold plating to improve conductivity. The fixed contacts 30 may be 
an electrically conductive pad of copper on the printed circuit board, 
optimally covered with gold plating to improve conductivity. 
The remaining portions of the stimulator 10 may be made of materials 
conventionally used for transcutaneous electrical stimulators and the 
electrical circuitry therefor. 
While certain embodiments of the present invention have been described in 
detail herein and as shown in the accompanying Drawing, it will be evident 
that various further modifications are possible without departing from the 
scope of the invention.