Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1998-10-26
2001-07-31
Schaetzle, Kennedy (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S059000
Reexamination Certificate
active
06269270
ABSTRACT:
BACKGROUND
1. Field of Invention
This invention relates generally to non-pharmacologic adjunct (add-on) treatment for Dementia, more specifically to adjunct treatment of Dementia including Alzheimer's disease by modulating electrical signals to a selected nerve or nerve bundle utilizing an easily implanted lead-receiver and an external stimulator.
2. Background
There is mounting scientific evidence that electrical stimulation has beneficial therapeutic effects for patients with Dementia and probable Alzheimer's disease. Most of the scientific studies are performed utilizing the technique of transcutaneous electrical nerve stimulation (TENS). In the TENS method (such as 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 for stimulation with varying frequency and pulse widths. 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 nerve is to use 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.
Two recent studies reported by Scherder et al., using TENS as the method of stimulation, described the benefits on memory and affective behavior in patients with probable Alzheimer's disease. There was a partial disappearance of the treatment effects on memory and affective behavior after a treatment-free period of 6 weeks, suggesting that continuation of the stimulation is necessary for maintaining or even further improving the treatment effects.
The rationale underlying the TENS study was that peripheral nerve stimulation would activate the hippocampus and hypothalamus structures which are affected in Alzheimer's disease (AD). This assumption is based upon animal experimental studies in which hippocampal activity was found to increase after peripheral tactile stimulation and the activity of the hypothalamus was enhanced by electro-acupuncture, a type of peripheral electrical stimulation. The hippocampus is highly involved in memory processes, in close association with other brain regions such as the inferomedial temporal cortex and the ventromedial prefrontal cortex. The hypothalamus plays a crucial role in affective behavior in Alzheimer's disease.
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 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. Myelinated fibers also 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. 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.
A-Beta fibers respond very well to high frequency stimulation, e.g., 100 Hz with an intensity just above threshold. In a recent study, A-Beta fibers also appeared to respond to low-frequency stimulation (2 Hz) with a higher intensity. Activation of A-Delta and C fibers is usually caused by low-frequency stimulation (less than 10 Hz) with higher intensity. To activate all three types of afferent nerve fibers, high-frequency and low-frequency stimulation can be combined in one treatment.
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 hypothalamus, hippocampus, and amygdala. See
FIG. 1
(from:
Epilepsia
, vol. 31, suppl. 2: 1990, page S2).
An activation of higher-level areas, e.g. the hippocampus and hypothalamus, by TENS or cranial nerve (such as vagal nerve) stimulation might be transmitted by afferent nerve fibers, i.e. thick-myelinated A-Beta fibers, thin-myelinated A-Delta fibers, and Unmyelinated C fibers. The basic premise of vagal nerve stimulation is that vagal visceral afferents have a diffuse central nervous system (CNS) projection, and activation of these pathways has a widespread effect on neuronal excitability.
Observations on the profound effect of electrical stimulation of the vagus nerve on central nervous system (CNS) activity, extends back to 1930's. Intermittent vagal stimulation has been relatively safe and well tolerated. The minimal side effects of tingling sensations and brief voice abnormalities have not been distressing. 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 res
Schaetzle Kennedy
Sheridan & Ross P.C.
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