Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1998-10-26
2001-03-27
Kamm, William E. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S061000
Reexamination Certificate
active
06208902
ABSTRACT:
BACKGROUND
1. Field of Invention
This invention relates generally to non-pharmacologic adjunct (add-on) treatment for pain, more specifically to adjunct treatment of pain by modulating electrical signals to a selected nerve or nerve bundle utilizing an easily implanted lead-receiver and an external stimulator.
2. Background
Analgesia by neural stimulation, either transcutaneously or through inserted needles (electro-acupuncture), has been demonstrated in humans. In the transcutaneous electrical nerve stimulation (TENS) method (such as with a device manufactured by Xytron Medical), two standard carbon rubber electrodes with gel are fixed on patient's skin across the tissue to be stimulated. One electrode being the negative pole and other being the positive pole. Utilizing the two electrodes, asymmetric biphasic pulses are used, with the frequency and pulse width being adjustable. Because the skin has high impedance, relatively large outputs are required to stimulate, and the site to be stimulated is not very specific. Other tissues including muscle, between the two skin electrodes will be stimulated.
Another method of stimulating a nerve is by using a percutaneous needle, or a lead with one end (distal end) being next to the nerve and utilizing a patch somewhere on the skin as the return electrode. Such a method is not feasible for long term stimulation because of the potential for infection, but can be useful for short term testing.
The time course and the distribution of the analgesic effect vary with the stimulus frequency used. The analgesic effect of high-frequency (40-400 Hz), low-intensity stimulation is largely confined to the spinal segment stimulated and the effect has a relatively short time course. The response is explained by events at the level of the spinal cord, as expressed in the spinal gate-control theory, which suggests an inhibition of cells transmitting information from nociceptors (receptors for pain) by activation of low-threshold afferents. Analgesia by low-frequency (2-5 Hz) peripheral stimulation is characterized by a slower time course with a long induction time (15-30 min.) and an effect outlasting the stimulation period from 20 min. to several hours. Furthermore, the effect is widespread and not confined to the spinal segment being stimulated. This suggests a different, presumably humoral mechanism, possibly due to b-endorphin. This slow time course is not only found with low-frequency peripheral nerve stimulation but also with classical needle acupuncture. The two modes of stimulation are assumed to act through similar mechanisms.
To understand the basics, it is instructive to see what happens when one accidentally hits their thumb with a hammer. A common sequence is to withdraw the thumb, yell (via limbic connections), and then apply pressure to the injured thumb. The first scientific explanation of how pressure and other external stimuli inhibit pain transmission was the gate theory of pain, proposed by Melzack and Wall in 1965. They hypothesized that information from first-order low-threshold mechanical afferents and from first-order nociceptive afferents converges into the same second-order neurons. They proposed that the preponderance of activity in the primary afferents determines the pattern of signals the second-order neuron transmits. Thus, if the low-threshold mechanical afferents are more active than the nociceptive afferents, the mechanoreceptive information is transmitted and the nociceptive information inhibited. According to their theory, transmission of pain information is blocked in the dorsal horn, closing the gate to pain. Lamina II, the substantia gelatinsosa, was suggested as the site of interference with pain massage transmission. The gate theory is important because it inspired inquiry into the mechanics and control of pain. One result of these investigations was the clinical application of transcutaneous electrical nerve stimulations (TENS). TENS uses electrical current applied to the skin to interfere with the transmission of pain information.
Another theory that has incorporated findings from research stimulated by the gate theory is the counterirritant theory. According to the counterirritant theory, inhibition of nociceptive signals by stimulation of non-nociceptive receptors occurs in the dorsal horn of the spinal cord, as shown in
FIG. 1
(from: Neuroscience-Fundamentals for Rehabilitation, Page 119. W. B. Saunders Company).
For example, as shown in
FIG. 1
, pressure stimulates mechanoreceptive afferents
24
. Theoretically, proximal branches of the mechanoreceptive afferents
24
activate interneurons
22
that release the neurotransmitter enkephalin. Enkephalin binds with receptor sites on both the primary afferents and interneurons
22
of the pain system. Enkephalin binding depresses the release of substance P and hyperpolarizes the interneurons
22
, thus inhibiting the transmission of nociceptive signals to the spinothalamic tract
27
.
FIG. 1
also shows tissue damage
25
and a pathway to the dorsal column
26
.
Most nerves in the human body are composed of thousands of fibers, of different sizes designated by groups A, B and C, which carry signals to and from the brain. The vagus nerve, for example, may have approximately 100,000 fibers of the three different types, each carrying signals. Each axon (fiber) of that nerve conducts only in one direction, in normal circumstances. The A and B fibers are myelinated (i.e., have a myelin sheath, constituting a substance largely composed of fat), whereas the C fibers are unmyelinated.
A commonly used nomenclature for peripheral nerve fibers, using Roman and Greek letters, is given in the table below,
External
Conduction
Diameter
Velocity
Group
(&mgr;m)
(m/sec)
Myelinated Fibers
A&agr; or IA
12-20
70-120
A&bgr;:IB
10-15
60-80
II
5-15
30-80
A&ggr;
3-8
15-40
A&dgr; or III
3-8
10-30
B
1-3
5-15
Unmyelinted fibers
C or IV
0.2-1.5
0.5-2.5
The diameters of group A and group B fibers include the thicknesses of the myelin sheaths. Group A is further subdivided into alpha, beta, gamma, and delta fibers in decreasing order of size. There is some overlapping of the diameters of the A, B, and C groups because physiological properties, especially the form of the action potential, are taken into consideration when defining the groups. The smallest fibers (group C) are unmyelinated and have the slowest conduction rate, whereas the myelinated fibers of group B and group A exhibit rates of conduction that progressively increase with diameter. Group B fibers are not present in the nerves of the limbs; they occur in white rami and some cranial nerves. Myelinated fibers are typically larger, conduct faster and have very low stimulation thresholds, compared to the unmyelinated type, and exhibit a particular strength-duration curve or respond to a specific pulse width versus amplitude for stimulation. The A and B fibers can be stimulated with relatively narrow pulse widths, from 50 to 200 microseconds (&mgr;s), for example. The A fiber conducts slightly faster than the B fiber and has a slightly lower threshold. The C fibers are very small, conduct electrical signals very slowly, and have high stimulation thresholds typically requiring a wider pulse width (300-1,000 &mgr;s) and a higher amplitude for activation.
The vagus nerve is composed of somatic and visceral afferents (i.e., inward conducting nerve fibers which convey impulses toward the brain) and efferents (i.e., outward conducting nerve fibers which convey impulses to an effector). Usually, nerve stimulation activates signals in both directions (bi-directionally). It is possible, however, through the use of special electrodes and waveforms, to selectively stimulate a nerve in one direction only (unidirectionally). The vast majority of vagal nerve fibers are C fibers, and a majority are visceral afferents having cell bodies lying in masses or ganglia in the skull. The central projections terminate largely in the nucleus of the solitary tract which sends fibers to various regions of the brain, e.g., the hypot
Kamm William E.
Sheridan Rose P.C.
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