Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-11-30
2002-03-12
Kamm, William E. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06356788
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to electrical stimulation therapy for neurologic and neuropsychiatric disorders, more specifically to neuromodulation therapy for depression, migraine, and neuropsychiatric disorders, as well as adjunct treatment for partial complex, generalized epilepsy and involuntary movement disorders utilizing an implanted lead-receiver and an external stimulator.
BACKGROUND
It has been observed clinically that electrical stimulation therapy for seizures produced mood improvement independent of the anti-seizure effects. This discovery led to medical research into the therapeutic effects of electrical stimulation for depression. Medical research has shown beneficial medical effects of vagus nerve stimulation (VNS) for severely depressed patients.
Vagus nerve stimulation, and the profound effects of electrical stimulation of the vagus nerve on central nervous system (CNS) activity, extends back to the 1930's. Medical studies in clinical neurobiology have advanced our understanding of anatomic and physiologic basis of the anti-depressive effects of vagus nerve stimulation.
Some of the somatic interventions for the treatment of depression include electroconvulsive therapy (ECT), transcranical magnetic stimulation, vagus nerve stimulation, and deep brain stimulation. The vagus nerve is the 10
th
cranial nerve, and is a direct extension of the brain.
FIG. 1A
, shows a diagram of the brain and spinal cord
24
, with its relationship to the vagus nerve
54
and the nucleus tractus solitarius
14
.
FIG. 1B
shows the relationship of the vagus nerve
54
with the other cranial nerves.
Vagus nerve stimulation is a means of directly affecting central function and is less invasive than deep brain stimulation (DBS). As shown in
FIG. 1C
, cranial nerves have both afferent pathway
19
(inward conducting nerve fibers which convey impulses toward the brain) and efferent pathway
21
(outward conducting nerve fibers which convey impulses to an effector). The vagus nerve is composed of 80% afferent sensory fibers carrying information to the brain from the head, neck, thorax, and abdomen. The sensory afferent cell bodies of the vagus reside in the nodose ganglion and relay information to the nucleus tractus solitarius (NTS)
14
.
As shown schematically in
FIGS. 1A and 1D
, the nucleus of the solitary tract relays this incoming sensory information to the rest of the brain through three main pathways; (1) an autonomic feedback loop, (2) direct projection to the reticular formation in the medulla, and (3) ascending projections to the forebrain largely through the parabrachial nucleus (PBN)
20
and the locus ceruleus (LC)
22
. The PBN
20
sits adjacent to the neucleus LC
22
(FIG.
1
A). The PBN/LC
20
/
22
sends direct connections to every level of the forebrain, including the hypothalamus
26
, and several thalamic
25
regions that control the insula and orbitofrontal
28
and prefontal cortices. Perhaps important for mood regulation, the PBN/LC
20
/
22
has direct connections to the amygdala
29
and the bed nucleus of the stria terminalis—structures that are implicated in emotion recognition and mood regulation.
In sum, incoming sensory (afferent) connections of the vagus nerve
54
provide direct projections to many of the brain regions implicated in nueropsychiatric disorders. These connections reveal how vagus nerve stimulation is a portal to the brainstem and connected regions. These circuits likely account for the neuropsychiatric effects of vagus nerve stimulation.
Increased activity of the vagus nerve is also associated with the release of more serotonin in the brain. Much of the pharmacologic therapy for treatment of migraines is aimed at increasing the levels of serotonin in the brain. Therefore, non-pharmacologic therapy of electrically stimulating the vagus nerve would have benefits for adjunct treatment of migraines and other ailments, such as obsessive compulsive disorders, that would benefit from increasing the level of serotonin in the brain.
The vagus nerve provides an easily accessible, peripheral route to modulate central nervous system (CNS) function. Other cranial nerves can be used for the same purpose, but the vagus nerve is preferred because of its easy accessibility. In the human body there are two vagal nerves (VN), the right VN and the left VN. Each vagus nerve is encased in the carotid sheath along with the carotid artery and jugular vein. The innervation of the right and left vagal nerves is different. The innervation of the right vagus nerve is such that stimulating it results in profound bradycardia (slowing of the heart rate). The left vagal nerve has some innervation to the heart, but mostly innervates the visceral organs such as the gastrointestinal tract. It is known that stimulation of the left vagal nerve does not cause any significant deleterious side effects.
Complex partial seizure is a common form of epilepsy, and some 30-40% of patients afflicted with this disorder are not well controlled by medications. Some patients have epileptogenic foci that may be identified and resected; however, many patients remain who have medically resistant seizures not amenable to resective surgery. Stimulation of the vagus nerve has been shown to reduce or abort seizures in experimental models. Early clinical trials have suggested that vagus nerve stimulation has beneficial effects for complex partial seizures and generalized epilepsy in humans. In addition, intermittent vagal stimulation has been relatively safe and well tolerated during the follow-up period available in these groups of patients. The minimal side effects of tingling sensations and brief voice abnormalities have not been distressing.
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 Diameter
Conduction 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 myelinted 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.
Compared to unmyelinated fibers, myelinated fibers are typically larger, conduct faster, have very low stimulation thresholds, 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. Selective stimulation of only A and B fibers is readily accomplished. The requirement of
Kamm William E.
Sheridan & Ross P.C.
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