Transcutaneous electrical nerve stimulation (TENS) device

An improved transcutaneous electrical nerve stimulator (TENS) involving a microcurrent (typically 25 to 900 microamps) monophase D.C. carrier signal (typically 10,000 to 19,000 Hz, preferably 15,000 Hz) that is modulated on and off in time (typically at 0.3 Hz up to 10,000 Hz, preferably 9.125 Hz followed by 292 Hz) and further inverted about every second by reversing the polarity of the signal at the electrodes. Such a device has been found to be useful in alleviating pain very rapidly.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an improved transcutaneous electrical nerve 
stimulation (TENS) apparatus for symptomatic relief and management of 
chronic (long term) intractable pain and adjunctive treatment in the 
management of postsurgical traumatic acute pain. More specifically, the 
invention relates to a TENS device that operates in the electrical current 
range of about 25 microamps to less than 1 milliamp using a chopped (e.g., 
9.125 Hz or 292 Hz) carrier frequency (e.g., 15,000 Hz) having typically a 
monophasic wave profile which is preferably inverted (reversed polarity) 
approximately every second. 
2. Description of the Prior Art 
It is generally known and an accepted practice to administer transcutaneous 
energy in the form of light and/or electrical current as a therapeutic 
treatment particularly to alleviate certain types of pain. Such treatments 
are frequently compared to acupuncture both in terms of application and 
results. It is also generally known in both types of transcutaneous 
radiation therapy that the body will favorably respond to certain 
preselected discrete beat frequencies. Thus for example in U.S. Pat. No. 
4,232,678; 4,553,546 and 4,646,743 and French patent No. 2371935 various 
types of infrared (IR) and/or near IR light sources are chopped (modulated 
on and off in time) at selected frequencies to produce a pulsating source 
of IR radiation as a transcutaneous energy to be applied to mammalian 
tissue. Analogously, U.S. Pat. Nos. 3,785,383 and 3,902,502 disclose a 
transcutaneously applied capacitively coupled electrostatic electrode 
system and a microcurrent conductivity coupled electrode system, 
respectively, for the purpose of reducing sensitivity to pain. In the 
later disclosure the concept of modulating the carrier frequency by 
superimposing a beat frequency is employed. Instruments specifically 
designed to accomplish this type of electric current therapy are now 
commonly referred to as transcutaneous electrical nerve stimulators 
(TENS). 
SUMMARY OF THE INVENTION 
The improved transcutaneous electrical nerve stimulator according to the 
present invention is categorically a microcurrent TENS which operates 
using a unique wave form. The instrument is constructed such that it will 
operate from about 25 microamps up to about 900 microamps current during 
therapeutic use with a peak current of the order of 6 milliamps. Typically 
the current is applied through a pair of electrodes in the form of a high 
frequency, monophasic, burst of a D.C. carrier signal (e.g., at lest 
10,000 Hz to 19,000 Hz)that is chopped or modulated at a relatively lower 
frequency (e.g., from about 0.3 Hz up to 10,000 Hz). The burst of the 
modulated carrier signal are typically from about 0.05 seconds to about 10 
seconds in duration with about one second in duration being preferred. 
Preferably, successive bursts are inverted relative to the previous burst 
by reversing the polarity at the electrodes thus simulating a biphasic 
wave form, yet the carrier is a monophasic D.C. signal. Preferably, the 
modulating frequency is selected from pairs of frequencies which exhibit 
specific therapeutic action (e.g., 292 Hz and 9.125 Hz). Advantageously 
the TENS can be performed synchronously with light stimulation and has 
been found to relieve pain extremely fast (typically in 1 to 3 minutes) 
under conditions that are below the level of human sensation. 
Thus the present invention provides an improved transcutaneous electrical 
nerve stimulator comprising: 
(a) a pair of electrode means for making surface contact and supplying 
electrical current to mammalian tissue; and 
(b) an electrical circuit means for supplying to the pair of electrode 
means from about 25 microamps up to about 900 microamps of a monophasic 
sequence of bursts of a D.C. carrier signal selected from the frequency 
range of at least 10,000 Hz to about 19,000 Hz which is modulated on and 
off in time at a frequency selected from the range of about 0.3 Hz up to 
10,000 Hz and said bursts are characterized as having a periodicity 
greater in duration than that associated with the modulation frequency. 
Preferably the microcurrent TENS device inverts the D.C. carrier signal 
between bursts by reversing the polarity at the pair of electrodes means. 
Most preferably this occurs about every second with the modulating 
frequency being selected from the group consisting of 9.125, 18.25, 73, 
146, 292, 584, 168, 2336, and 4672 Hz with a D.C. carrier frequency of 
typically 15,000 Hz. For routine pain management the use of 9.125 Hz 
followed by 292 Hz is particularly useful. The present invention also 
provides a unique LED electrode that produces electromagnetic radiation 
synchronously with the electrical current therapy. 
It is an object of the present invention to provide an improved TENS device 
that operates in the microcurrent range using a unique wave form. It is a 
further object to provide such a TENS device that exhibits enhanced 
ability to quickly manage pain. It is still a further object to provide 
such a TENS device that is highly compatible with other pain management 
therapies. Fulfillment of these objects and the presence and fulfillment 
of other objects will become apparent upon complete reading of the 
specification and claims taken in conjunction with the attached drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The improved microcurrent transcutaneous electrical nerve stimulator 
according to the present invention, how it operates and how it is used, 
how it differs from previously known instruments and the advantages of 
using the improved device can perhaps be best explained and understood by 
reference to the drawings. FIG. 1 illustrates one particularly preferred 
embodiment of the present invention wherein the TENS unit (generally 
designated by the numeral 10) consists of a portable housing 12 with two 
external electrodes 14 and 16. In this particular embodiment the case or 
housing 12 is equipped with a clip 18 that allows the unit to be worn on 
the belt or the like during use. The other side of the case 12 relative to 
the belt clip 18 is equipped with a slot 20 that allows a sliding selector 
switch 22 to be used to set the beat frequency (i.e., the modulating 
frequency for turning the carrier signal on and off at a predetermined 
frequency characteristic of the therapeutic treatment being performed). In 
this particular illustrated embodiment only two frequency settings are 
available to the user (typically 9.125 Hz or 292 Hz). As such this 
particular embodiment is easily operated by the patient. In a more complex 
embodiment, a greater number of preselected discrete frequency settings 
are provided (for example, by making the slot 20 of the sliding selector 
switch 22 longer) thus producing a clinical or physician's version of the 
instrument. 
The top face of the case 12 is further provided with an on/off switch 24 
and a monitor light 26 along with an electrical current selector switch 
28. Also there are two electrode connector terminals 30 and 32 provided on 
the top face of the case 12 which in this illustrated embodiment involve 
two separate types of energy emitting electrode systems. The first system 
involves two electrically conductive electrodes 34 and 36. Electrode 34 is 
a conventional self adhering neurostimulation electrode which is 
adhesively pressed to the skin or the like. The second current electrode 
36 is a conductive pad that represents the outer skin contacting surface 
of both the second electrical current electrode and the light emitting 
diode (LED) system (the second type of energy emitting electrode system). 
As shown in FIG. 1, there is a set of four light emitting diodes 38 
protruding through the current carrying electrode surface 36. Thus, in 
this particular embodiment, both the unique electrical wave form of the 
present invention and synchronous light radiation can be simultaneously 
applied transcutaneously at the same physical location. Typically this 
second electrode 36 is held adhesively to the skin or the like during use 
by the use of a transparent, conductive, double adhesive electrode patch 
(not shown). 
The actual use of the TENS unit 10 illustrated in FIG. 1 is relatively 
simple and straightforward. The electrodes, typically either a pair of 
self adhering neurostimulation electrodes of approximately 32 millimeters 
in diameter such as supplied by Axelgaard Manufacturing Co. of Fallbrook, 
Calif., or one such electrode plus the specialized light/current electrode 
of FIG. 1 adhesively held by a 38.4 millimeter in diameter model 
4.times.4sp electrode patch supplied by AcuData Software Medical Products 
Division of Petaluma, Calif., are positioned on mammalian skin tissue in 
accordance with a health care professional or physician's instructions. 
During use there are only two adjustments that need to be made. The 
current selector switch 28 on the top face of the housing 12 can be 
adjusted from 25 microamps up to a 6 milliamp peak output. The frequency 
selector 22 can be positioned wither high, e.g. 292 Hz, or low, e.g. 9.125 
Hz. The on/off switch 24 when turned on will activate the on light 26 
which flashes or blinks faster as the current setting is increased. As 
such, visual confirmation of the instrument being on and the particular 
current setting can be readily determined by looking at the light 26. 
During use the current can be adjusted by the user by use of switch 28. 
Typically the current is initially elevated until the perception of 
electrical stimulation is perceived. The current is then decreased until 
perception of stimulation is undetectable. Readjustment during treatment 
can be repeated as needed. Typically a setting of about three tenths of 
full scale for switch 28 represents an optimum effective setting. 
One particularly preferred method of use for pain involving muscle spasms, 
tightness or chronic problems, starts with 9.125 Hz and the current turned 
up until it can be felt. The current setting is then lowered until the 
sensation is gone. The current is continuously lowered each time the 
sensation of stimulation becomes apparent until a setting is found where 
no further sensation appears for two minutes. The TENS unit is then 
switched to the high frequency setting. For acute pain such as post 
surgical pain or pain involving inflammation and/or swelling rather than 
muscle tightness or spasm, start with 292 Hz. Such procedures have been 
found to alleviate pain in as little as 1 to 3 minutes. Application of the 
TENS unit for periods in excess of twenty minutes is not generally needed 
although longer or even continual stimulation may be beneficial in 
selected cases. 
FIG. 2 is a block diagram of the individual components making up a typical 
electrical circuit for the embodiment of the TENS device shown in FIG. 1. 
The respective function of the individual components are indicated on the 
block diagram. As shown, the device is powered by a battery 40 supplying 
current to a voltage step-up converter 42. The voltage step-up converter 
typically produces a 30 volt source which is part of a precision constant 
current source 44 (for details see FIG. 2). The 30 volt is applied to the 
skin and a precision constant current sync regulates the current through 
the skin. 
As further illustrated on the left side of FIG. 2, the electrical circuit 
involves a modulation oscillator 46, a carrier oscillator 48 and a 
bi-phase oscillator 50. The bi-phase oscillator 50 is typically a 0.05 
second to 10 second oscillator that drives a polarity switcher 52 which in 
turn reverses the polarity of the current supplied by the precision 
constant current source 44 at the current electrodes 54 and 56. The 
carrier oscillator 48 is typically a 10,000 Hz to 19,000 Hz signal 
(preferably about 15,000 Hz) generator that drives one of the input sides 
of the gating circuit 58. The modulation oscillator 46 and frequency 
divider 60 are the source of the beat frequency that chops the carrier 
frequency on and off in time at preselected frequencies known to be 
beneficial for therapeutic purposes. As suggested in FIG. 2, the output 
from the frequency divider 60 is either 292 Hz or 9.125 Hz. This signal 
drives both the LED driver 62 and the other input side of the gating 
circuit 58. The LED driver 62 then drives the LED electrode 64 at the 
selected frequency synchronously with the current electrodes 54 and 56. 
The gating circuit 58 output is directed through attenuator 64 before the 
signal is directed to the precision constant current source 44 and 
polarity switcher 52. The output from the attenuator is also used to drive 
the feedback monitor LED flasher 66 thus alerting the patient that the 
TENS device is operating by flashing at a rate proportional to the 
current. 
FIG. 3 is a detailed schematic of one preferred embodiment of the 
electrical circuitry according to the present invention. This particular 
circuitry is generic to both the 292 Hz/9.125 Hz modulated embodiment of 
FIGS. 1 and 2 as sell as the physician's version having eight different 
selectable modulation frequencies. In presenting the schematic of FIG. 3, 
conventional electrical notation is employed to identify all components 
and relevant electrical component values. A single 9 volt portable radio 
type battery is employed as the current source. The following table of 
components categorizes and identifies the individual elements and 
associated circuitry corresponding to the functional block circuit 
description of FIG. 2. 
TABLE 
______________________________________ 
(FIG. 2) (FIG. 3) 
______________________________________ 
Battery, 40 BT1 9V Alk 
Voltage Step-Up Converter, 42 
U2, Q10, L1 
Precision Constant Current Source 44 
U3, Q2 
Modulation Oscillator, 46 
U1 
Carrier Oscillator, 48 U4D 
Bi-Phase Oscillator, 50 U4B 
Polarity Switcher, 52 V4A, Q5-9 
Current Electrodes, 54 & 56 
J2 
Gating Circuit, 58 U4C 
Frequency Divider, 60 U1 
LED Driver, 62 Q1 
Attenuator, 64 Q3, VR1 
Feedback Monitor LED Flasher, 66 
V5 (vco) 
______________________________________ 
FIG. 4 illustrates the essential features of the unique wave form of the 
electrical signal employed in the improved TENS according to the present 
invention. As illustrated the vertical axis is D.C. current wherein the 
center line represents ground and the displacement upwards represents one 
polarity and displacement downward represents the inverse or reverse 
polarity at the pair of conductive electrodes. The horizontal axis is 
time. As seen in FIG. 4, the instantaneous current at maximum power is 
plotted as a function of time with insufficient resolution to perceive the 
carrier frequency (i.e., typically 15,000 Hz). What can be clearly seen is 
the inversion or more specifically the reversing of polarity at the 
electrode approximately every second in this specific illustration. Also, 
the monophasic character of the D.C. carrier signal is evident in that 
during any given one second burst of the 15,000 Hz carrier signal, current 
flows in only one direction (i.e., amplitude either above or below the 
center ground but not both). The on/off time modulation of the carrier 
signal at 9.125 Hz is suggested in that a sequence of 110 millisecond 
bursts chops the one second interval into approximately 9 cycles with 
approximately 50% duty cycle (i.e., current transmission during half of 
the cycle). In the case of 292 Hz a 3.4 millisecond burst chops the one 
second into 292 cycles. As further suggested in the first reversed 
polarity modulation cycle a burst of the 15,000 Hz carrier frequency would 
represent some 822 individual pulses within a given duty cycle at 9.125 Hz 
or 25.7 individual pulses, at 292 Hz. As further suggested in FIG. 4, the 
normal treatment range is confined to a current of up to about 900 
microamps which is represented in the drawing as a central band well below 
the maximum current amplitude of 6 milliamps. It should be appreciated 
that the illustration of FIGS. 4 and 5 are not to scale and will vary 
depending on the selection and rate of polarity reversal at the 
electrodes. 
FIGS. 5a and 5b illustrate the printed circuit associated with the novel 
combined LED/current electrode according to the present invention. As 
illustrated in FIG. 5a, the back side of the printed circuit involves 
leads 68 and 70 which connect fours LED's (not shown) in series. The other 
leads 72 supply current to the tissue contacting current electrode 74 of 
FIG. 5b. Current electrode 74 is provided with four openings for insertion 
of the LED's into the light emitting circuitry 68 and 70. This circuit 
board is then incorporated into an appropriate housing as illustrated in 
FIG. 1. 
The advantages of the improved TENS unit according to the present invention 
are viewed as being numerous and significant. The fact that the unit is a 
microcurrent TENS powered by a single 9 volt battery means the unit is 
highly portable, readily serviceable and safe under all normal operating 
conditions. The fact that the polarity at the electrodes is systematically 
reversed reduces the likelihood of any detrimental tissue damage in the 
vicinity of the electrodes. In this regard reversal of polarity every 0.05 
seconds up to about 10 seconds (preferably from about 0.1 seconds to 8 
seconds and most preferably about every second) is useful for purposes of 
this invention but other periodical reversal schemes including 
asynchronous, random and-or time delayed or interruption of the carrier 
signal should be considered equivalent. The unique wave profile results in 
extremely fast management of pain under treatment conditions that are 
virtually undetectable to the user. And, the overall therapeutic procedure 
is highly compatible with simultaneous treatment using IR and near IR 
pulsed therapy again accelerating the process of pain management. 
Having thus described and exemplified the preferred embodiments with a 
certain degree of particularity, it is to be understood that the invention 
is not to be limited to the embodiments set forth herein for purposes of 
exemplification, but is to be limited only by the scope of the attached 
claims, including a full range of equivalents to which each element 
thereof is entitled.