Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2001-04-19
2003-05-13
Schaetzle, Kennedy (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S061000
Reexamination Certificate
active
06564102
ABSTRACT:
1. FIELD OF INVENTION
This invention relates generally to a medical device for the treatment of coma and brain injury, more specifically a medical device for adjunct (add-on) treatment of coma and traumatic brain injury by electrical stimulation neuromodulation of a selected nerve or nerve bundle utilizing an implanted lead-receiver and an external stimulator.
BACKGROUND
Coma is an abnormally deep state of unconsciousness with an absence of voluntary response to stimuli and with varying degrees of reflex activity. It represents the extreme of a graded continuum of impairment of consciousness, at the opposite pole of the spectrum from full alertness and awareness of the environment. It is not a single uniform disorder, but may stem from different causes such as trauma, disease, or their condition, and which may be characterized by different levels of consciousness. There are degrees of coma, but no varieties. Coma differs from both sleep and syncope (temporary suspension of consciousness due to generalized cerebral ischemia). Cerebral oxygen uptake is normal in sleep or actually increases during the rapid eye movement stage, but cerebral oxygen uptake is abnormally reduced in coma. The patient is incapable of sensing or responding adequately to external stimuli or inner needs, shows little or no spontaneous movement apart from respiration, and no evidence whatever of mental activity.
At the deepest state of coma there is no reaction to stimuli of any intensity, and corneal, pupillary, pharyngeal, tendon and plantar reflexes are absent. Respiration is slow and sometimes periodic (Cheyne-Stokes respiration) and cardiovascular regulating processes may show signs of failure. Lighter degrees of coma (‘semicoma’) allow partial response to stimulation, though this is imcomplete, mostly nonpurposive and usually consists of ineffectual movements or rubbing and scratching of the stimulated area. Bladder distension may call forth groaning or ill-coordinated motor stirring but the patient is still incontinent. Tendon refexes may or may not be obtainable, and the plantars may be either flexor or extensor. The Glasgow Coma Scale has proved its usefulness for the grading of depth of coma.
Coma needs to be distinguished from deep sleep and from stupor. In deep sleep and in coma the pictures may be closely similar on superficial observation. But the sleeper can be roused again to normal consciousness by the efforts of the examiner. He may wake spontaneously or unaccustomed stimuli, or in response to inner sensations such as hunger or bladder distension. In sleep there is sporadic continuing mental activity in the form of dreams that leave traces in memory. The distinguishing features usually accepted are that in coma the eyes remain shut even in response to strong arousal stimuli, do not resist passive opening, and do not appear to be watchful or follow moving objects; movements in response to stimulation are never purposeful, and there is no subsequent recall of events or inner fantasies from the time in question.
The Glasgow Coma Scale is now routinely used for acutely head-injured patients. It has proved to be of considerable predictive value in pointing to long-term outcome, in terms of both survival and ultimate levels of disability. The patient's clinical state is charted regularly on a number of graded parameters: motor responsiveness (no response, extensor response to pain, flexor response, localizing response, obeying commands), verbal performance (nil, without recognizable words, no sustained exchange possible, confused conversation, orientated for person, place and time) an eye opening (nil, in response to pain, in response to speech, spontaneously). Numerical scores are summated for the best responses obtained under each category at a defined point in time. In this way useful predictions can be made, often with 24 hours of injury and more certainly within the first week.
As shown in
FIG. 1
recovery from a moderate or severe brain trauma typically involves a progression through a sequence of neurobehavioral syndromes. The initial stage of severely head-injured patients is coma. When consciousness is recovered, a period of delirium and then post-traumatic amnesia is typically seen (stage II). The retrograde component of post-traumatic amnesia is the failure to recall events occurring before the head injury. The anterograde component of post-traumatic amnesia is the failure to store and recall ongoing events occurring since the head injury.
In the system and method of this invention, coma and the residual effects of traumatic brain injury are treated by electrical stimulation neuromodulation of the afferent vagal nerve fibers with an external stimulator with predetermined programs. Since a large percentage of patients with traumatic head injury eventually develop epilepsy which also impedes functional recovery, the anti-epileptic effects of vagus nerve stimulation would also be beneficial.
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
&
Droesch Kristen
Schaetzle Kennedy
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