Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2001-04-19
2003-09-02
Schaetzle, Kennedy (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06615081
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to medical device therapy for diabetes, more specifically to a medical device system for adjunct therapy of diabetes by neuromodulation of a selected nerve or nerve bundle utilizing an implanted lead-receiver and an external stimulator.
BACKGROUND
Diabetes is a significant health problem affecting millions of Americans. It is the leading risk factor in coronary heart disease and stroke, leading cause of blindness, end-stage renal disease, and a major contributor to lower extremity amputations. Diabetes mellitus is a heterogeneous group of diseases, all of which ultimately lead to hyperglycemia (an elevation of glucose in the blood) and excretion of glucose in the urine as hyperglycemia increases. Diabetes mellitus is also characterized by the inability to reabsorb water, which results in increased urine production (polyuria), excessive thirst (polydipsia), and excessive eating (polyphagia).
The regulation of glucose levels in the body is by the hormone insulin. Insulin is produced by the beta cells of the pancreas from the tissue called islets of Langerhans (shown schematically in FIG.
1
). The pancreas is a flattened organ located just below the stomach. Insulin lowers blood sugar concentration by facilitating the movement of glucose into body tissues. Insulin is intimately involved in the regulation not only of glucose metabolism but also of protein and fat metabolism. Therefore, it is not suprising that all of the major foodstuffs play some role in regulating insulin release. Even though blood glucose level is the most important determinant that increases insulin secretion, other factors and conditions also influence insulin release. Among the other factors, and most notably for this invention is the condition that parasympathetic stimulation also increases insulin secretion.
Nerves have trophic influences on tissues, and the secretion of insulin is stimulated by vagal nerve fibers. Decreased glucose tolerance following vagotomy (interruption of the imulses carried by the vagus nerve) has been reported in human subjects, and sympathetic stimulation via the splanchnic nerve inhibits insulin release. The central nervous system also plays a role in regulating insulin secretion, and the outflow probably occurs via the hypothalamus and the autonomic nervous system.
In this invention diabetes is treated by electrical stimulation neuromodulation of the vagal nerve fibers with an implanted lead-receiver and an external stimulator with predetermined programs. The neuromodulation thus increasing the secretion of insulin by the pancreas, for adjunct (add-on) treatment of diabetes.
Observations on the profound effect of electrical stimulation of the vagus nerve on central nervous system (CNS) activity extends back to the 1930's. The vagus nerve
54
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
54
is preferred because of its easy accessibility. In the human body there are two vagus 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 vagus 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 vagus 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 vagus nerve does not cause any significant deleterious side effects.
Neuromodulation
One of the fundamental features of the nervous system is its ability to generate and conduct electrical impulses. These can take the form of action potentials, which is defined as a single electrical impulse passing down an axon, and is shown schematically in FIG.
2
. The top portion of the figure shows conduction over mylinated axon (fiber) and the bottom portion shows conduction over nonmylinated axon (fiber). These electrical signals will travel along the nerve fibers.
The nerve impulse (or action potential) is an “all or nothing” phenomenon. That is to say, once the threshold stimulus intensity is reached an action potential
7
will be generated. This is shown schematically in FIG.
3
. The bottom portion of the figure shows a train of action potentials.
Most nerves in the human body are composed of thousands of fibers of different sizes. This is shown schematically in FIG.
4
. The different sizes of nerve fibers, which carry signals to and from the brain, are designated by groups A, B, and C. The vagus nerve, for example, may have approximately 100,000 fibers of the three different types, each carrying signals. Each axon or fiber of that nerve conducts only in one direction, in normal circumstances.
In a cross section of peripheral nerve it is seen that the diameter of individual fibers vary substantially. The largest nerve fibers are approximately 20 &mgr;m in diameter and are heavily myelinated (i.e., have a myelin sheath, constituting a substance largely composed of fat), whereas the smallest nerve fibers are less than 1 &mgr;m in diameter and are unmyelinated. As shown in
FIG. 5
, when the distal part of a nerve is electrically stimulated, a compound action potential is recorded by an electrode located more proximally. A compound action potential contains several peaks or waves of activity that represent the summated response of multiple fibers having similar conduction velocities. The waves in a compound action potential represent different types of nerve fibers that are classified into corresponding functional categories as shown in the table below,
Conduction
Fiber
Fiber
Velocity
Diameter
Type
(m/sec)
(&mgr;m)
Myelination
A Fibers
Alpha
70-120
12-20
Yes
Beta
40-70
5-12
Yes
Gamma
10-50
3-6
Yes
Delta
6-30
2-5
Yes
B Fibers
5-15
<3
Yes
C Fibers
0.5-2.0
0.4-1.2
No
The diameters of group A and group B fibers include the thickness 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 in 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.
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. Because of their very slow conduction, C fibers would not be highly responsive to rapid stimulation. Selective stimulation of only A and B fibers is readily accomplished. The requirement of a larger and wider pulse to stimulate the C fibers, however, makes selective stimulation of only C fibers, to the exclusion of the A and B fibers, virtually unachievable inasmuch as the large signal will tend to activate the A and B fibers to some extent as well.
The vagus nerve is composed of somatic and visceral afferents and efferents. 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 vagus nerve fibers
Droesch Kristen
Schaetzle Kennedy
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