Apparatus and method for controlling pain by transcutaneous electrical stimulation (TES)

Apparatus and method are described for controlling pain by transcutaneous electrical stimulation (TES), the apparatus comprising a pulse generator for generating periodic electrical pulses, skin electrodes coupled to the pulse generator and adapted to be placed in contact with the skin of the patient for applying the pulses thereto, and a pulse-width modulator for modulating the width of the pulses applied by the electrodes to the patient's skin. The skin electrodes include a survey electrode having a handle for moving it over the surface of the skin to locate the relevant nerve. The pulses applied are unsymmetrical, nearly square-shape, bipolar current pulses width-modulated 25-50% per period of 0.1 to 1.0 seconds.

BACKGROUND OF THE INVENTION 
The transcutaneous electrical stimulation (TES) treatment for controlling 
pain involves the application of periodic electrical pulses to the skin of 
the patient in the painful region. The equipment presently in use applies 
the pulses via skin electrodes coupled to a pulse generator which 
generates symmetrical (e.g. sine wave, square-wave, bell-shaped or 
triangular) pulses of fixed frequency and width. This treatment has been 
found effective to reduce pain in many (but not all) cases, and many 
theories have been proposed attempting to explain the mechanism of action 
by which it accomplishes this. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide apparatus and method to 
make the TES treatment even more effective for controlling pain. 
According to a broad aspect of the invention, the TES treatment for 
controlling pain is made more effective by modulating the width (duration) 
of the pulses applied to the patient via the skin electrodes. It has been 
found that particularly good results can be obtained by modulating the 
width of the pulses 25-50% per period of 0.1 to 1.0 seconds, and by 
applying the pulses at a frequency of 50-150 Hz, a width of 68-740 
microseconds, and a voltage of 60-150 volts. 
Clinical data is set forth below showing that modulating the width of the 
pulses as described above increases the effectiveness of the TES treatment 
for reducing or aleviating pain. It is believed that the increased 
effectiveness of this treatment can be explained as follows: First, the 
width-modulation of the pulses prevents or decreases habituation to the 
stimulus. In addition, the width-modulated pulses are also believed to 
enhance muscle stimulation which increases the blood flow and decreases 
the local stagnant anoxia (a cause of pain) in the small blood vessels. 
The modulations activate the monosynaptic reflex and, in addition, produce 
a deep somatic and visceral effect which has a benefit in aleviating pain. 
Further features and advantages of the invention will be apparent from the 
description below.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The apparatus illustrated in FIG. 1 is basically a pulse generator having 
pulse-width modulating means for applying width-modulated pulses to a 
plurality of external skin electrodes which are to be applied to the skin 
of the patient in the painful region. In the apparatus of FIG. 1, the skin 
electrodes include two reference electrodes RE1, RE2 each having a 
relatively large surface area; an active electrode AE having a smaller 
surface area; and a survey electrode SE of even smaller surface area. The 
latter electrode has a handle 12 to facilitate its movement over the skin 
of the patient in order to locate the trigger point or the relevant nerve, 
as will be described more particularly below. 
The pulse generator of FIG. 1 includes a chargeable battery PS as the power 
supply, the battery (e.g. 5-6 volts) being charged via a connector 14 and 
a resistor R1 (e.g. 68 ohms). The battery power supply is applied, via 
power switch PWR, filter capacitor C1 (100 ufd), and a 
light-emitting-diode indicator LED having a voltage-dropping resistor R2 
(390 ohms) connected in series therewith, to a master oscillator circuit 
including a unijunction transistor Q1 (2N4871), variable resistor R3 (15 
Kohms) another resistor R4 (390 ohms), and capacitor C2 (0.47 ufd). The 
output of the oscillator of transistor Q1 is applied via conductor 16 to 
Terminal-2 of an integrated circuit chip IC555 which acts as a one-shot 
monostable. 
The power supply PS is also applied via modulator switch MOD to a modulator 
oscillator circuit including a second unijunction transistor Q2 
(2N4871Q2), resistors R5 (15 Kohm) and R6 (680 ohm), and a capacitor C3 
(4.7 ufd). The output of this oscillator circuit drives a transistor Q3 
(2N4400) having a resistor R7 (3 Kohm) in its collector circuit connected 
to the power supply PS, and a base connected to the oscillator transistor 
Q2 via another variable resistor R8 (110 Kohm). The output of transistor 
Q3 is connected, via resistor R9 (3 Kohm) and conductor 18, to Terminal-6 
of the integrated circuit chip IC55. 
The output of integrated circuit chip IC555 is taken from its Terminal-3 
and is applied via conductor 20 and resistor R10 (47 ohm) to the base of a 
further transistor Q4 (MJE 520) acting as a current amplifier. Its output 
is fed to the primary winding TP of a transformr TR connected across the 
collector of transistor Q4 and its base via resistor R11 (510 ohm). 
Transformer TR includes two secondary windings TS1, TS2, each connected at 
one side together via jumper wire 22, and to one of the reference 
electrodes RE1, RE2. The opposite side of transformer secondary winding 
TS1, is connected, via a voltage-divider resistor R12 (100 Kohm), to the 
survey electrode SE; and the opposite side of transformer secondary 
winding TS2 is connected, via voltage-divider resistor R13 (100 Kohm), to 
the active electrode AE. 
IC555 is a well known integrated circuit chip, and therefore its specific 
construction and mode of operation are not described herein. When 
connected as illustrated in FIG. 1, with its Terminal-2 coupled to the 
output of the master oscillator circuit of transistor Q1, it acts as 
one-shot monostable multivibrator which is reset by the pulses from the 
master oscillator applied via conductor 16 to its Terminal-2. The 
frequency of the pulses is determined by the frequency of the master 
oscillator, which may be varied resistor R3. The width or duration of the 
pulses outputted by the one-shot monostable is determined by the pulses 
applied to its Terminal-6 via conductor 18 from transistor Q3 driven by 
the modulator oscillator circuit of transistor Q2; and the percent of 
modulation of this circuit may be varied by varying resistor R8. IC555 
further includes resistors R14 (4.7 Kohm) and R15 (3 Kohm) connected 
between its Terminals 6,8 and 4, and capacitor C4 (0.47 ufd) connected 
between its Terminals 1, 7 and 6, as shown. 
The provision of the two reference electrodes RE1, RE2, cooperable with the 
survey electrode SE and the active electrode AE, respectively, provides 
two separate channels for pain treatment. The reference electrodes RE1, 
RE2 are of large surface area, in this case being 15.times.5 cm, and are 
adapted to be placed on the skin at the part of the spinal column closest 
to the pain area. The active electrode AE is of smaller surface area, 
being in this case 3.5.times.2.5 cm, and is adapted to be placed on the 
skin at the painful region. Before using the active electrode AE, however, 
it is preferred to locate the painful area by the use of the survey 
electrode SE, which is of circular configuration 2 cm. in diameter, this 
electrode being provided with the handle 12 to facilitate its manipulation 
for locating the painful region. 
All the electrodes are preferably made of vulcanized silicone rubber 
compound having an electrical resistance of 700 ohm/cm.sup.2 and are 
preferably first coated with tap water or a conductive paste before 
application to the skin. 
It will be appreciated that the output amplifier Q4 is a constant current 
amplifier as it has an output impedance many times higher than the 
interface resistance of the skin electrodes. 
FIG. 2 illustrates the use of the apparatus for treating one form of 
headache, wherein one of the reference electrodes RE1 is placed at the top 
of the spinal column, and the active electrode AE is placed at the back of 
the head adjacent to the painful region. 
FIG. 3 is a wave form diagram illustrating the train of width-modulated 
pulses produced by the pulse generator of FIG. 1. Thus, the pulses P1-Pn, 
outputted by the generator and applied by the skin electrodes to the 
patient, are of the same general shape but are width-modulated so that 
their widths continuously increase a predetermined percentage for a fixed 
period of modulation. In the waveforms illustrated in FIG. 3, the 
percentage of modulation is 25%, and the period of modulation is 0.2 
seconds. Thus, the first pulse P1 has a width of 0.5 milli-seconds (i.e. 
500 microseconds), the second pulse P2 10 milli-seconds thereafter has a 
pulse width of 0.5065 milli-seconds (506.5 microseconds), and the last 
pulse Pn 190 milliseconds after pulse P2 (i.e., 0.2 seconds from the start 
of the initial pulse P1) has a pulse width of 0.625 millseconds (625 
microseconds). 
It will be further seen from FIG. 3 that each of the pulses P1-Pn is 
unsymmetrical, bipolar, and nearly square-shaped. FIG. 3 shows the 
negative portion of the pulse waveform above the O-axis, since this is the 
more active phase. This pulse shape, resulting mainly from the reactance 
of the transformer TR, has a nearly square-shaped negative or polarising 
phase and an exponentially decaying positive or depolarising phase, and 
has been found to be more effective than the symmetrical or monopolar 
pulses heretofore used in TES treatment. 
Preferably, the apparatus is first operated in the modulator-disable Mode, 
i.e. with the MOD switch open. After a predetermined time interval, for 
example 5-15 minutes of treatment, the MOD switch is closed to enable the 
modulator which effects the pulse-width modulation described above and 
illustrated in FIG. 3. 190 Ambulatory patients (107 men and 83 women, aged 
16 to 80) suffering from various pain conditions, received the 
above-described TES treatment alone, or combined with other forms of pain 
therapy. All patients were referred by their treating physician with 
established diagnosis, each subsequently confirmed by clinical findings. 
Eighty five patients had tension-headache, migraine or post-traumatic 
headache; 27 had pain due to previous nerve injury or amputation; and 13 
had herpes zoster. Of the latter, seven were treated in the acute phase 
(the first 3-5 weeks of the disease) while the others had long-standing 
post herpetic neuralgia. Of the remaining 65 patients, eight had severe 
localized pain due to bone metastases; nine had post-operative pain, 
namely chest pain after open heart surgery and thoracotomy, incisional 
pain after renal operation, mastectomy and plastic surgery; six were 
young, healthy athletes suffering from sudden muscle spasms in the legs; 
three had undergone chordotomy; and one had undergone thalamotomy. The 
rest of the patients were diagnosed as various forms of neuralgias, 
namely, meralgia paresthetica, trigeminal, intercostal and sciatic pain. 
These 65 patients also include three post C.V.A. with hemisparesis and 
pain in the affected arm, and two patients with pain in the foot after 
embolectomy. 
The majority of the 190 patients had previously received various drugs for 
pain alleviation; they were directed to continue the same medication 
during the first T.E.S. sessions. 
A trial of stimulation was initially given in order: (a) to find the 
optimal placement of the electrodes, e.g., to cover and concentrate the 
current stimulation over the affected area; and (b) to select a current 
strength that would give a comfortable vibrating sensation. The TES was 
administered for 20-30 minutes. After the first few minutes, there usually 
was habituation so the stimulus could be increased without discomfort, 
even to a point where sometimes muscle contractions followed. The 
treatment was repeated 2-3 times weekly up to about 10 sessions, depending 
on the therapeutic progress. If effective (the patient's subjective 
evaluation being the most important guide), the TES was continued either 
in the hospital or at home by self-administration. 
Switch MOD was closed to produce pulse-width modulation during the TES 
treatment after adequate current had been reached. The current activated 
by the pulse modulation prevents habituation to the stimulus as described 
above, and thus obviates the need of changing of the current intensity 
during treatment. In addition, the pulse modulation is also effective as a 
muscle stimulator as described above. 
With two electrodes of the same size, the current density beneath each of 
them is equal. Whenever stimulation of local skin receptors is intended, 
two electrodes of the same size should therefore be used. If the pain is 
diffuse and spread over a large area, the two big electrodes RE1, RE2 are 
applied. With two electrodes of unequal size, the current density under 
the small electrode (e.g. AE or SE) is higher than under the large one 
(RE1 and RE2). When stimulation of trigger points or of an accessible 
superficial nerve is the treatment of choice, a large (e.g. RE1) and a 
small (e.g. AE) electrode should be used. The two electrodes are placed at 
a distance of 5-30 cm from one another, depending on the localization of 
the pain. 
To assess the effects of the TES treatment, a pain profile and scoring 
system was determined before the treatment, and repeated after a series of 
sessions. This profile included (1) pain intensity; (2) pain duration and 
its frequency; (3) degree of medication; (4) limitation of movement; (5) 
daily activity level; (6) mood. Each feature was given a score between 0-4 
(4 being the more severe condition), the total score being 24. The results 
were classified as "moderate" if pain relief was obtained only during the 
TES treatment or if the scoring decreased up to four points. The results 
were considered "good" if pain relief was obtained for various periods 
after treatment and the initial scoring was reduced by 6-8 points. It must 
be noted that the results represent the effect during a series of 
treatment, and long-term follow-up was not available in most patients. 
Good effects were obtained in 50.6% of the patients, moderate in 27.8%, and 
no effect in 21.6%. There is no significant overall difference between the 
various groups, except for herpes zoster with 38.5% "good" results (five 
out of 13 patients; these five patients were all the acute stage). 
Although there were only a small number of patients in each sub-group, and 
many individual variations were seen, some cases are worthy of comment. 
Two aged patients with hemiparesis and two after embolectomy had good 
results with the TES treatment and continued the treatment at home. (The 
importance of a non-invasive prolonged method of treatment in elderly 
patients suffering from severe systemic diseases and in whom a number of 
drugs are contraindicated or ineffective, is obvious). The same was true 
in one patient with sternal pain after surgery for double valve 
replacement, and two others with severe metastatic pain. The latter 
operated the stimulator continuously during the day. A number of patients 
activated the stimulation to the point where it elicited muscle 
contractions. The results were poor in trigeminal neuralgia and facial 
pain. 
If effective at all, the pain generally diminished soon after the 
application of the current. Thus, if there is no effect during the first 
few sessions, treatment may be discontinued. However, it should not be 
stopped before it has been ascertained that the painful area has been well 
covered by the stimulation. 
Some patients returned to the clinic every few months for repeated TES 
sessions. Since the introduction of this treatment, the number of nerve 
blocks appreciably decreased. It seems that when TES and nerve blocks were 
combined, the patient could be easier weaned from the blocks. In other 
instances, where nerve blocks were considered, but TES was applied first 
as a trial treatment, blocks became superfluous. The treatment had no side 
effects even after prolonged application. 
While the invention has been described above with respect to one preferred 
embodiment, it will be appreciated that many variations may be made. For 
example, the frequency of application of the pulses may generally be 
varied from 50-150 Hz, the apparatus described above operating at a 
frequency of 90 Hz. In addition, the pulse width may be from 68-740 
microseconds, the apparatus described above producing pulses of a width of 
500 microseconds. The pulse voltage may generally be from 60-150 volts, 90 
volts having been found most effective in the above apparatus. The current 
peak of the pulses depends on the pulse width; thus, pulses having a width 
of 68 microseconds preferably should have a peak of about 60 milliamps, 
and pulses having a width of 740 microseconds preferably should have a 
peak of about 15 milliamps. The apparatus described above operates at a 
pulse width of 500 microseconds and a peak of 20 milliamps. The modulation 
period may generally vary from 100 milliseconds (0.1 second) to 1000 
milliseconds (1 second), the preferred example described above having a 
modulation period of 0.2 seconds. The modulation percentage may vary from 
25-50% per period, the preferred modulation being 25% in the example 
described above. 
While the invention has been found particularly effective in the TES 
treatment for controlling pain, it will be appreciated that it could also 
be used as a muscle stimulator since it has a muscle stimulating effect as 
described above. 
Further, the optional attachment illustrated in FIG. 4 may also be included 
to provide a capability of producing anesthesia in addition to analgesia. 
The unit of FIG. 4 is adapted to be plugged into terminals TAE and TREI, 
respectively, of FIG. 1 to produce a voltage between a needle electrode NE 
and a skin electrode AE.sup.1 of the size of electrode AE in FIG. 1. The 
needle electrode in this case receives positive potential and is adapted 
to penetrate the skin and to be inserted into the nerve anesthesized. The 
needle is insulated except for the tip which is bare. The potential 
applied to the nerve by needle electrode NE is derived across the 
plugged-in terminals TAE and TREI via resistors R20 (100 Kohm), R21 (10 
Kohm), and R22 (10 Kohm), which together divide, by 5-10, the voltage 
applied between electrodes NE and AE.sup.1. The circuit further includes a 
diode D20 which limits the negative phase of the pulse. The use of 
width-modulated pulses for anesthesia has also been found advantageous in 
that it requires less average energy than non-modulated pulses. 
Many other variations, modifications and applications of the invention will 
be apparent.