# Patent

## Title
Esophageal activity modulated obesity therapy

## Abstract

Methods and devices for delivering electrical stimulation to the sympathetic nervous system in response to the onset of eating. In some methods, swallowing is detected which then initiates a dose of stimulation which can vary in intensity, frequency, or both over the dose length. In some methods, the dose length is between about one quarter hour and one hour. The dose frequency may increase, hold steady, then decrease over the dose duration so as to mimic the response of the gut stretch and nutrient receptors to receiving food. The dose can drive biomarkers indicative of eating, for example glucagon, glucose, FFA or glycerol to at least about half of their normal post eating levels and then stop so as to retain stimulation effectiveness for subsequent doses and to prolong battery life.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application claims priority from U.S. provisional application 61/170,964, filed Apr. 20, 2009, which is herein incorporated by reference in its entirety.


FIELD OF THE INVENTION
The invention is related generally to neuromodulation, in particular to stimulating the sympathetic nervous system to treat obesity.
BACKGROUND
Obesity results from an imbalance between food intake and energy expenditure, such that there is a net increase in fat reserves. Excessive food intake, reduced energy expenditure, or both may contribute to this in balance. Clinically, obesity is defined relative to body mass index (BMI), a measure of body weight to body surface (kg/m2). A normal BMI is considered to be in the range from greater than 30 kg/m2. A BMI in the range from 25-30 is considered overweight, while obese is classified as having a BMI >30. Obesity is classified into 3 subcategories: Class I—moderate; Class II—severe; and Class III very severe.
It is well established that patients with elevated BMIs are at increased risk for a variety of diseases including hypertension and cardiovascular disease, kidney disease, diabetes, dyslipidemia, sleep apnea, and orthopedic problems. Obesity has become pandemic in the U.S. with a prevalence exceeding 30%. The increased demand on health care resources due to obesity and the health problems associated with it are estimated in the U.S. to exceed $200 billion annually.
Appetite and satiety, which control food intake, are partly regulated by the hypothalamus region of the brain. Energy expenditure is also controlled in part by the hypothalamus. The hypothalamus regulates the autonomic nervous system of which there are two branches, the sympathetic and the parasympathetic. The sympathetic nervous system generally prepares the body for action by increasing heart rate, blood pressure, and metabolism. The parasympathetic system prepares the body for rest by lowering heart rate, lowering blood pressure, and stimulating digestion. Destruction of the lateral hypothalamus results in hunger suppression, reduced food intake, weight loss, and increased sympathetic activity. In contrast, destruction of the ventromedial nucleus of the hypothalamus results in suppression of satiety, excessive food intake, weight gain, and decreased sympathetic activity.
The splanchnic nerves carry sympathetic neurons that innervate the organs of digestion and the adrenal glands, while the vagus nerve carries parasympathetic neurons that innervate the digestive system, and as experiments involving hypothalamic destruction have shown, those neurons involved in the feeding and weight gain response.
Experimental and observational evidence suggests that there is a reciprocal relationship between sympathetic nervous system activity and food intake, with an increase in sympathetic activity generally leading to a reduction in food intake. These effects are mediated by specific neuropeptides (e.g., neuropeptide Y, galanin) known to decrease sympathetic activity, which in turn triggers an increase food intake. Other peptides such as cholesystokinin, leptin, and enterostatin, increase sympathetic activity, thus decreasing food intake. Ghrelin is a peptide that is secreted by the stomach and which is associated with hunger. Peak plasma levels of this peptide occur just prior to mealtime, and ghrelin levels are increased after weight loss. Sympathetic activity can suppress ghrelin secretion. PYY is a hormone released from the intestine that also plays a role in satiety. PYY levels increase after meal ingestion. Sympathetic activity can increase PYY levels. Similarly, drugs such as nicotine, ephedrine, caffeine, subitramine, dexfenfluramine, which lead to an increase in sympathetic activity, also reduce food intake.
Appetite is stimulated by various psychosocial factors, but also by low blood glucose levels, as well as mechanical receptors in the gastrointestinal tract. For example, cells in the hypothalamus that are sensitive to glucose levels are thought to play a role in the hunger response, increasing the sensation of hunger as glucose levels decrease. In response, activation of the sympathetic nervous system leads to an increase in plasma glucose levels. Similarly, a feeling of satiety can be promoted by distention of the stomach and delayed gastric emptying. Sympathetic nerve activity reduces gastric and duodenal motility, causes gastric distention, and can increase contraction of the pyloric sphincter, which can result in distention and delayed emptying of the stomach contents.
The sympathetic nervous system also plays a role in energy expenditure and thus the tendency towards obesity. Genetically inherited obesity in rodents is characterized by decreased sympathetic activity in adipose tissue and other peripheral organs. Catecholamines and cortisol, which are released by the sympathetic nervous system, cause a dose-dependent increase in resting energy expenditure. In humans, a negative correlation between body fat and plasma catecholamine levels has been reported.
Over- or under-feeding lean human subjects can have significant effects on sympathetic nervous system activation and energy expenditure. For example, weight loss in obese subjects is associated with a compensatory decrease in energy expenditure, which promotes regaining previously lost weight, a common problem that limits the effectiveness of classic diet and exercise weight loss programs. Conversely, drugs that activate the sympathetic nervous system, such as ephedrine, caffeine, or nicotine, are known to increase energy expenditure. Smokers are known to have lower body fat stores and increased energy expenditure relative to non-smokers. Weight gain is a commonly reported consequence of quitting smoking. The sympathetic nervous system also plays an important role in regulating energy substrates such as fat and carbohydrate. Metabolism of glycogen and fat, needed to support increased energy expenditure, is increased by sympathetic activation.
Animal research shows that acute electrical activation of the splanchnic nerves causes a variety of physiologic changes. Electrical activation of a single splanchnic nerve in dogs and cows causes a frequency dependent increase in catecholamine, dopamine, and cortisol secretion, and circulating plasma levels of these compounds that lead to increased energy expenditure can be achieved. In adrenalectomized pigs, cows, and dogs, acute single splanchnic nerve activation causes increased blood glucose levels with concomitant reduction in liver glycogen stores. In dogs, single splanchnic nerve activation causes increased pyloric sphincter tone and decreased duodenal motility, reducing the rate of food passage through the gastrointestinal tract, and in turn leading to a sensation of satiety. Moreover, sympathetic, and specifically splanchnic nerve, activation can result in suppression of insulin and leptin hormone secretion.
First-line therapy for obesity treatment is typically behavior modification involving reduced food intake and/or increased exercise. However, these approaches frequently fail and behavioral treatment is commonly supplemented by administration of pharmacologic agents known to reduce appetite and/or increase energy expenditure. Commonly used pharmacologic agents include dopamine and a dopamine analogues, acetylcholine and cholinesterase inhibitors. Pharmacologic therapy is typically delivered orally. However, treating obesity with drugs frequently results in undesirable side effects, including systemic effects such as tachycardia, sweating, and hypertension. In addition, tolerance can develop such that the response to the drug is reduced even one higher doses are used.
More radical forms of therapy involve surgical intervention. In general, these procedures are designed to reduce the size of the stomach and/or reroute the gastrointestinal tract to substantially avoid the stomach, the net effect being either a reduction in the amount of food that can be consumed before feeling full, reduction in absorption, or both. Representative procedures include gastric bypass surgery and gastric banding. While these procedures can be effective in treating obesity, they are highly invasive, require significant lifestyle changes, and may have significant postoperative complications.
More recent experimental forms for treating obesity have involved electrical stimulation of the stomach (gastric pacing) and the vagus nerve (parasympathetic stimulation). These therapies make use of a pulse generator to electrically stimulate the stomach or nerves via implanted electrodes. The object of these therapies is to reduce food intake through the promotion of satiety and/or reduction of appetite. For example, U.S. Pat. No. 5,423,872 (Cigaina) discloses a method for treating eating disorders by electrically pacing the stomach. Similarly, U.S. Pat. No. 5,263,480 (Wernicke) discloses a method for treating obesity by likely activating the vagus nerve. However, while these methods are suggested to be effective in reducing food intake, neither is believed to affect energy expenditure.
SUMMARY
There are significant limitations in prior art methods and apparatus used in treating obesity that limit their effectiveness. In first line therapeutic approaches, such as simple regulation of food intake combined with exercise, compliance and discipline are primary pitfalls. In neuromodulatory therapies, the application of electrical signals to nerves in order to regulate food consumption and/or energy expenditure, are not necessarily linked to the subject's individual physiology, and thus may fail to maximize the benefits of this approach as an obesity treatment method. In addition, essentially all prior art neuromodulatory methods are subject to limitations inherent to neurons, specifically the fact that chronic stimulation leads to neural accommodation, and thus reduced effectiveness of the neuromodulation program.
What are needed, therefore, are systems and methods for the treatment of obesity that overcome compliance problems inherent in first-line therapeutic approaches such as diet and exercise programs. In addition, what are needed are systems and methods of controlling obesity that are effectively self-regulating, such that the need for patient compliance becomes either irrelevant or significantly reduced. In particular, systems and methods of treating obesity that self-regulate in response to normal physiological parameters, for example timing of meals and or timing of rest or sleep periods, will be able to avoid compliance issues that arise when the subject is left in control of a diet and/or exercise regimes.
Without being limited by theory, it is believed that to achieve weight loss over time, the generation of false satiety signals coincident with the timing of normal body functions will either escape, or substantially avoid, some of the effects of habituation (i.e., neural accommodation) to a therapeutic signal. In particular limiting the use of neuromodulation to induce satiety to periods slightly preceding or concomitant with eating (i.e., meals) will be effective to reduce food intake. Similarly, using a stimulatory pattern designed to increase metabolism during intervals between meals will be effective to further enhance weight loss by increasing energy expenditure. In effect, these methods provides a dual stimulatory program that (a) mimics satiety at a time most effective to reduce food consumption; and (b) mimics exercise, by increasing energy expenditure during intervals between periods of nutrient consumption. Furthermore, it is believed that by generating a false satiety signal during food intake, a “safe harbor” will provided by effectively “hiding” the neuromodulatory signal behind a natural event, in turn producing a more pronounced satiety signal and in turn more effectively reducing food intake.
The present invention includes methods and apparatus for treating obesity, and potentially other disorders by electrically stimulating the sympathetic nervous system in response to detection of a period of nutrient consumption in such a way as to simulate satiety, and during the intervals between successive periods of food intake in such a way as to increase energy expenditure. By differentially applying stimulatory patterns configured to either mimic satiety, or increase energy expenditure, obesity can be more successfully treated than would be possible using a single stimulatory paradigm. Further, the invention provides that the alternating “satiety” and “energy” programs are regulated automatically, removing compliance issues that occur when a subject is left to regulate their own obesity therapy program.
The present invention includes a method for treating obesity or other disorders by electrically activating the sympathetic nervous system. Satiety can be induced by stimulating afferent fibers in the sympathetic nervous system, and in particular fibers in the splanchnic nerve. Likewise, activating efferent fibers can be used to increase energy expenditure and reducing food intake.
Stimulation is accomplished using a pulse generator and electrodes implanted near, or attached to, various areas of the sympathetic nervous system, such as the sympathetic chain ganglia, the splanchnic nerves (greater, lesser, least), or the peripheral ganglia (e.g., celiac, mesenteric). Ideally, the obesity therapy can employ electrical activation of the sympathetic nervous system that innervates the digestive system, adrenals, and abdominal adipose tissue, such as the splanchnic nerves and/or celiac ganglia.
A method of obesity treatment may reduce food intake by a variety of mechanisms, including general increased sympathetic system activation and increasing plasma glucose levels upon activation. Satiety may be produced through direct affects on the pylorus and duodenum that cause stomach distension and delayed stomach emptying. In addition, limiting ghrelin secretion can be used to reduce food intake.
A method of obesity treatment may also increase energy expenditure by causing catecholamine, cortisol, and dopamine release from the adrenal glands, and may be titrated to vary the rate of release of these hormones. Fat and carbohydrate metabolism, which is also increased by sympathetic nerve activation, will accompany the increased energy expenditure. Other hormonal effects induced by this therapy may include reduced insulin secretion. Alternatively, this method may be used to normalize catecholamine levels, which are reduced with weight gain.
Electrical sympathetic activation for treating obesity is ideally accomplished without causing a rise in mean arterial blood pressure (MAP). During activation therapy, a sinusoidal-like fluctuation in the MAP may occur with an average MAP that is within safe limits. Alternatively, an alpha sympathetic receptor blocker, such as prazosin, could be used to blunt the increase in MAP.
Electrical modulation (inhibition or activation) of the sympathetic nerves might also be used to treat other eating disorders such as anorexia or bulimia. For example, inhibition of the sympathetic nerves may be useful in treating anorexia. Electrical modulation of the sympathetic nerves may also be used to treat gastrointestinal diseases such as peptic ulcers, esophageal reflux, gastroparesis, and irritable bowel syndrome. For example, stimulation of the splanchnic nerves that innervate the large intestine may reduce the symptoms of irritable bowel syndrome, characterized by diarrhea. Pain may also be treated by electric nerve modulation of the sympathetic nervous system, as certain pain neurons are carried in the sympathetic nerves. This therapy may also be used to treat type II diabetes. These conditions may require varying degrees of inhibition or stimulation.
The present invention provides that satiety mimicking signals are applied to the sympathetic nervous in response to swallowing, or some other physiological parameter directly associated with the intake of food, or temporally coordinated with the perception that food is, or is about to be, consumed. Between periods of feeding, the invention provides that signals designed to increase energy expenditure are applied to the sympathetic nervous system. Collectively, the invention provides increased effectiveness in inducing satiety, as well as increasing energy expenditure, which together provide that the invention improves on prior methods and apparatus for treating obesity. In addition, the neural stimulation paradigms in the present invention reduce the likelihood of neural accommodation, and can be titrated to maximize effectiveness of the generated signals with respect to reducing food intake and increasing energy expenditure.
Therefore, in some embodiments a method of modulating a component of the nervous system of a mammal, the method comprising: providing a sensor, wherein the sensor is configured to produce a first sensor output signal associated with the onset of a period of nutrient consumption, and a second sensor output signal, associated with the end of a period of nutrient consumption; providing a stimulator configured to output a first therapeutic signal in response to the first sensor output signal, and a second therapeutic signal in response to the second sensor output signal; wherein applying the first therapeutic signal to a first component of the nervous system is effective to mimic satiety in the mammal; and wherein applying the second therapeutic signal to a second component of the nervous system is effective to produce an increase in energy expenditure in the mammal.
In some embodiments, the sensor is configured to produce the first sensor output signal in response to at least one of swallowing, a blood glucose level, a neurological signal associated with olfaction, a stomach pH level, an electrical impedance of saliva, an electromyographic signal in the esophagus, and a change in intrathoracic pressure.
In some embodiments, the sensor is configured to produce the second sensor output signal in response to at least one of cessation of swallowing, a blood glucose level, a neurological signal associated with loss of an olfactory signal, a stomach pH level, an electrical impedance of saliva, an electromyographic signal in the esophagus, and a change in intra-thoracic pressure.
In some embodiments, the first therapeutic signal is applied to a component of the sympathetic nervous system. In some embodiments, the component of the sympathetic nervous system comprises afferent nerve fibers of a splanchnic nerve.
In some embodiments, the second therapeutic signal is configured to modulate a component of the sympathetic nervous system. In some embodiments, the component of the sympathetic nervous system comprises efferent fibers in a splanchnic nerve.
In some embodiments, the first therapeutic signal comprises at least one electrical pulse train; wherein the at least one electrical pulse train is applied for a duration ranging from about 2.5 minutes to about 30 minutes; wherein the at least one electrical pulse train is followed by a time interval ranging from about 2.5 minutes to about 30 minutes during which no electrical signal is applied to the component of the nervous system; wherein the at least one electrical pulse train comprises a frequency ranging from about 0 Hz to about 20 Hz; and wherein the at least one electrical pulse train comprises a current ranging from about 0.1 to about 3 mA.
In some embodiments, the first therapeutic signal comprises a plurality of electrical pulse trains, wherein pulse trains are separated from each other by an interval comprising substantially no signal. In some embodiments, at least one of the electrical pulse trains varies in duration from the remaining electrical pulse trains. In some embodiments, at least one of the electrical pulse trains varies in frequency from the remaining electrical pulse trains. In some embodiments, at least one of the electrical pulse trains varies in current from the remaining electrical pulse trains. In some embodiments, each of the electrical pulse trains are of substantially equal duration. In some embodiments, each of the electrical pulse trains are of substantially equal frequency. In some embodiments, each of the electrical pulse trains are of substantially equal current.
In some embodiments, the second therapeutic signal comprises at least one electrical pulse train; wherein the at least one electrical pulse train is applied for a duration ranging from about 5 minutes to about 120 minutes; wherein the at least one electrical pulse train is followed by a time interval ranging from about 5 minutes to about 180 minutes during which substantially no electrical signal is applied; wherein the at least one electrical pulse train comprises a frequency ranging from about 10 Hz to about 30 Hz; and wherein the at least one electrical pulse train comprises a current ranging from about 1 to about 5 mA.
In some embodiments, the second therapeutic signal comprises a plurality of electrical pulse trains, and wherein pulse trains are separated from each other by an interval comprising substantially no signal. In some embodiments, at least one of the electrical pulse trains varies in duration from the remaining electrical pulse trains. In some embodiments, at least one of the electrical pulse trains varies in frequency from the remaining electrical pulse trains. In some embodiments, at least one of the electrical pulse trains varies in current from the remaining electrical pulse trains. In some embodiments, each of the electrical pulse trains are of substantially equal duration. In some embodiments, each of the electrical pulse trains are of substantially equal frequency. In some embodiments, each of the electrical pulse trains are of substantially equal current.
In some embodiments there is provided, an implantable apparatus configured to modulate a component of the nervous system of a mammal, the apparatus comprising: a sensor, wherein the sensor is configured to produce a first sensor output signal associated with the onset of a period of nutrient consumption, and a second sensor output signal, associated with the end of a period of nutrient consumption; a stimulator configured to output a first therapeutic signal in response to the first sensor output signal, and a second therapeutic signal in response to the second sensor output signal; wherein the first therapeutic signal is effective to mimic satiety in the mammal; and wherein the second therapeutic signal is effective to produce an increase in energy expenditure in the mammal.
In some embodiments, the sensor is configured to produce the first sensor output signal in response to at least one of swallowing, a blood glucose level, a neurological signal associated with olfaction, a stomach pH level, an electrical impedance of saliva, an electromyographic signal in the esophagus, and a change in intra-thoracic pressure.
In some embodiments, the sensor is configured to produce the second sensor output signal in response to at least one of cessation of swallowing, a blood glucose level, a neurological signal associated with loss of an olfactory signal, a stomach pH level, an electrical impedance of saliva, an electromyographic signal in the esophagus, and a change in intra-thoracic pressure.
In some embodiments, the first therapeutic signal is applied to a component of the sympathetic nervous system. In some embodiments, the component of the sympathetic nervous system comprises afferent nerve fibers of a splanchnic nerve.
In some embodiments, the second therapeutic signal is configured to modulate a component of the sympathetic nervous system. In some embodiments, the component of the sympathetic nervous system comprises efferent fibers in a splanchnic nerve.
In some embodiments, the apparatus is configured be implanted in the thoracic cavity of the mammal. In some embodiments, the stimulator is configured to be programmable after implantation in the mammal.
The novel features of this invention, as well as embodiments of the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which:



DESCRIPTION OF THE FIGURES
FIG. 1 is a diagram of the efferent autonomic nervous system;
FIG. 2 is a diagram of the sympathetic nervous system;
FIG. 3 is an elevation view of the splanchnic nerves and celiac ganglia;
FIG. 4 is a schematic of an exemplary prior art stimulation pattern which can be used in the present method of the invention;
FIG. 5 is schematic of an exemplary prior art pulse generator which can be used in the method of the present invention;
FIG. 6 depicts an exemplary prior art catheter-type lead and electrode assembly which can be used in the method of the present invention;
FIG. 7 is a graph of known plasma catecholamine levels in response to various physiologic and pathologic states;
FIGS. 8A, 8B, and 8C are exemplary graphs of the effect of splanchnic nerve stimulation on catecholamine release rates, epinephrine levels, and energy expenditure, respectively, expected to be achievable in the practice of the present invention;
FIG. 9 is a graph of known plasma ghrelin level over a daily cycle;
FIG. 10 is a section view of an exemplary instrument placement which can be used in the method of the present invention for implantation of an electrode assembly;
FIGS. 11A and 11B illustrate a first dosing pattern that can be delivered in some embodiment methods, having an intensity ramp and substantially constant frequency over the dose length.
FIG. 12 is a bar chart having an experimental result from canines showing rises in biomarkers using four variations in stimulation.
FIG. 13 is a bar chart having an experimental result from canines showing repeatable rises in biomarkers over a series of three doses.
FIGS. 14 and 15 are current and frequency plots for a second dosing algorithm.
FIGS. 16 and 17 are current and frequency plots for a third dosing algorithm.



DETAILED DESCRIPTION
Weight control can be viewed in relatively simple terms as the net difference between energy intake and expenditure. Where intake exceeds expenditure an individual will gain weight over time, and conversely where expenditure exceeds intake, net weight loss is realized. The goal in any weight control paradigm is thus finding a way in which to reduce intake and/or increase expenditure in order to create a net caloric deficit. This is the basis of all diet and exercise programs. While conceptually simple, for a variety of reasons, most diet and/or exercise programs are generally ineffective, typically because of the difficulty in maintaining compliance with the diet and/or exercise regime. However, since appetite and energy expenditure are ultimately regulated by the nervous system, it is hypothetically possible to control weight not by voluntary adherence to a diet/exercise program, but rather through direct modulation of components of the nervous system that are involved in appetite and metabolism.
The human nervous system is a complex network of nerve cells, or neurons, found centrally in the brain and spinal cord and peripherally in various nerves of the body. Neurons comprise a cell body, dendrites and an axon. Clusters of neuronal cell bodies are termed ganglia. A nerve is a collection of neurons that are generally organized to serve a particular part of the body. A single nerve may contain several hundred to several hundred thousand neurons. Nerves often contain both afferent and efferent neurons. Afferent neurons carry signals back to the central nervous system (CNS) while efferent neurons carry signals away from the CNS to the periphery. Electrical signals are conducted via neurons and nerves. Neurons release neurotransmitters at synapses (connections) with other nerves to allow continuation and modulation of the electrical signal. In the periphery, synaptic transmission often occurs at ganglia. Nerves can also release transmitters at their termini permitting neuromodulation of target tissues (e.g., adrenal gland).
The electrical signal generated by a neuron is known as an action potential. Action potentials are initiated when a voltage potential across the neuronal cell membrane exceeds a certain threshold, resulting in the opening of ion channels in the neuronal cell membrane. The action potential is then propagated down the length of the neuron. The action potential of a nerve is complex and represents the sum of action potentials of the individual neurons within it.
Neurons can be myelinated, un-myelinated, of large axonal diameter, or small axonal diameter. In general, the speed of action potential conduction increases with myelination and with neuron axonal diameter. Accordingly, neurons are classified into type A, B and C neurons based on myelination, axon diameter, and axon conduction velocity. In terms of axon diameter and conduction velocity, A conduct faster than B, which in turn conduct faster than C neurons.
The autonomic nervous system is a subsystem of the human nervous system that controls involuntary actions of the smooth muscles (blood vessels and digestive system), the heart, and glands, as shown in FIG. 1. The autonomic nervous system is divided into the sympathetic and parasympathetic systems. The sympathetic nervous system generally prepares the body for action by increasing heart rate, increasing blood pressure, and increasing metabolism. The parasympathetic system prepares the body for rest by lowering heart rate, lowering blood pressure, and stimulating digestion.
The hypothalamus controls the sympathetic nervous system via descending neurons in the ventral horn of the spinal cord, as shown in FIG. 2. These neurons synapse with preganglionic sympathetic neurons that exit the spinal cord and form the white communicating ramus. The preganglionic neuron can either synapse in the paraspinous ganglia chain or pass through these ganglia and synapse in a peripheral, or collateral, ganglion such as the celiac or mesenteric. After synapsing in a particular ganglion, a postsynaptic neuron continues on to innervate the organs of the body (heart, intestines, liver, pancreas, etc.) or to innervate the adipose tissue and glands of the periphery and skin. Preganglionic neurons of the sympathetic system are typically myelinated type A and B neurons, while postganglionic neurons are typically unmyelinated type C neurons.
Mechano receptors and chemoreceptors in the gut often transmit their sensory information using frequency encoding, typically over A and B type fibers. The distended gut can distend the stretch receptors which generate a higher frequency signal when stretched compared to when they are not stretched, in one example. Nutrient receptors in the gut can generate different frequency signals in the presence of a specific nutrient, in another example. These frequency encoded signals travel afferently to the brain, and can indicate fullness and/or the presence of nutrients.
Several large sympathetic nerves and ganglia are formed by the neurons of the sympathetic nervous system, as shown in FIG. 3. The greater splanchnic nerve (GSN) is formed by efferent sympathetic neurons exiting the spinal cord from thoracic vertebral segment numbers 4 or 5 (T4 or T5) through thoracic vertebral segment numbers 9 or 10 or 11 (T9, T10, or T11). The lesser splanchnic (lesser SN) nerve is formed by preganglionic sympathetic efferent fibers from T10 to T12 and the least splanchnic nerve (least SN) is formed by fibers from T12. The GSN is typically present bilaterally in animals, including humans, with the other splanchnic nerves having a more variable pattern, being present unilaterally, bilaterally and sometimes even absent.
The splanchnic nerves run along the anterior-lateral aspect of the vertebral bodies and pass out of the thorax entering the abdomen through the crus of the diaphragm. The nerves run in proximity to the azygous veins. Once in the abdomen, neurons of the GSN synapse with postganglionic neurons primarily in celiac ganglia. Some neurons of the GSN pass through the celiac ganglia and synapse on in the adrenal medulla. Neurons of the lesser SN and least SN synapse with post-ganglionic neurons in the mesenteric ganglia.
Postganglionic neurons, arising from the celiac ganglia that synapse with the GSN, innervate primarily the upper digestive system, including the stomach, pylorus, duodenum, pancreas, and liver. In addition, blood vessels and adipose tissue of the abdomen are innervated by neurons arising from the celiac ganglia/greater splanchnic nerve. Postganglionic neurons of the mesenteric ganglia, supplied by preganglionic neurons of the lesser and least splanchnic nerve, innervate primarily the lower intestine, colon, rectum, kidneys, bladder, and sexual organs, and the blood vessels that supply these organs and tissues.
In the treatment of obesity, one embodiment involves electrical activation of the greater splanchnic nerve of the sympathetic nervous system. In some embodiments unilateral activation can be used, although bilateral activation can also be used. The celiac ganglia can also be activated, as well as the sympathetic chain or ventral spinal roots.
Electrical nerve modulation (nerve activation or inhibition) can be accomplished by applying an energy signal (pulse), at a certain frequency, amplitude, and current, to the neurons of a nerve (nerve stimulation). Where the energy pulse exceeds the activation threshold for neurons in the nerve, those neurons will depolarize, resulting in the production of action potentials. The cumulative action potential for the nerve will depend on the extent of recruitment of individual neurons within the nerve (i.e., the number of neurons who are provoked to depolarize). The amount of energy applied is a function of the current amplitude and pulse width duration. Activation or inhibition can be a function of the frequency, with low frequencies on the order of 1 to 50 Hz resulting in activation, and high frequencies greater than 100 Hz generally resulting in inhibition. Inhibition can also be accomplished by continuous energy delivery resulting in sustained depolarization, which leads to neuronal accommodation (de-sensitization). Different neuronal types may respond to different frequencies and energies with activation or inhibition.
Each neuronal type (A, B, or C neurons) has a characteristic pulse amplitude-duration profile (energy pulse signal) that leads to activation. Myelinated neurons (types A and B) can generally be stimulated with relatively low current amplitudes on the order of 0.1 to 5.0 milliamperes, and short pulse widths on the order of 50 to 200 microseconds. Unmyelinated type C fibers typically require longer pulse widths, on the order of 300 to 1,000 microseconds, and higher current amplitudes. This difference in energy for activation can be advantageously exploited in order to selectively stimulate certain subsets of neurons in a nerve containing mixed neuronal types. This is of particular use in modulating nerves such as the splanchnic, as the splanchnic nerves contains both afferent pain neurons, which are typically type C neurons, and efferent preganglionic neurons, which are myelinated type B neurons. Thus, in a therapy such as obesity treatment involving splanchnic nerve activation, it is desirable to activate the efferent type B neurons and not the afferent type C pain neurons. This can be effectively accomplished by varying the energy pulse signal.
A fibers are an integral part of the afferent stimulation and signaling. The A fibers can be activated at relatively low stimulation intensity and are often activated in early, lower current portions of some therapies and doses according to the present invention.
Two important parameters related to stimulation of peripheral nerves of mixed neuronal type are the rheobase and chronaxie. These two parameters are a function of the stimulus duration and stimulus strength (current amplitude). The rheobase is the lower limit of the stimulus strength below which an action potential cannot be generated, regardless of the stimulus duration. The chronaxie is the stimulus duration corresponding to twice the rheobase. This is a measure of excitability of the mixed peripheral nerve. It is generally not desirable to stimulate a peripheral nerve at stimulus intensities greater than the chronaxie. The chronaxie of the splanchnic nerve is estimated to be between approximately 150 microseconds and 400 microseconds.
Various stimulation patterns, ranging from continuous to intermittent, can be utilized. With intermittent stimulation, energy is delivered for a period of time at a certain frequency during the signal-on time as shown in FIG. 4. The signal-on time is followed by a period of time with no energy delivery, referred to as signal-off time.
Superimposed on the stimulation pattern are the parameters of pulse frequency and pulse duration. The treatment frequency may be continuous or delivered at various time periods within a day or week. The treatment duration may last for as little as a few minutes to as long as several hours. For example, in some embodiments splanchnic nerve activation to treat obesity may be delivered at a frequency of three times daily, coinciding with meal times. Treatment duration with a specified stimulation pattern may last for one hour. Alternatively, treatment may be delivered at a higher frequency, say every three hours, for shorter durations, say 30 minutes. The treatment duration and frequency can be tailored to achieve the desired result.
In some embodiments, neural activation by an electrical stimulator is regulated by an output signal received from a sensor. The sensor may either be external, or internally implanted in the subject. In some embodiments, the sensor is configured to detect swallowing indicative of the consumptions of food. In some embodiments, the sensor may be configured to produce an output signal in response to, and without being limiting, a change in blood glucose levels, a neurological signal associated with olfaction (i.e., the smell of food), a change in stomach pH (indicating the presence of food and release of stomach acid as part of the digestion process), a change in impedance in the saliva of the oral cavity, detection of an electromyographic signal in or near the esophagus indicative of swallowing, and a change in intrathoracic pressure detected for example by a sensor placed at the suprasternal notch.
Upon sensing a swallowing event, the sensor is configured to produce an output signal that can be relayed directly or via remote means (e.g., wirelessly) to a neural stimulator, which in turn will respond to the sensor signal by applying a signal to a component of the nervous system, such as a splanchnic or other nerve, or directly to a portion of the gastrointestinal tract. In some embodiments, the signal, which in this case can be described as a first therapeutic signal, can be configured with respect to frequency, amplitude, and duration to mimic satiety and induce the subject to either reduce or cease food intake on feeling a sense of fullness. In some embodiments, the first therapeutic signal can take the form of a train of electrical pulses. A pulse train can range in duration from about 2.5 minutes to about 60 (or 30 in another embodiment) minutes; pulse frequency can range from about 0 Hz to about 20 Hz; and pulse current can range from about 1 to about 5 mA.
In some embodiments, the first therapeutic signal can comprises a plurality of such pulse trains, which may be of equal or varying duration, frequency, or current amplitude. In some embodiments, pulse energy (total power inherent in a pulse train) can be ramped up or down over time in order to effectively titrate the response of the nervous system to the applied neuromodulatory signal.
In some embodiments, individual pulse trains can be separated by a period of no stimulation greater, lesser, or equal to the length of a pulse train. In addition, the first therapeutic signal can be configured to terminate upon cessation of eating, or can be continued for a period of time following eating in order to ensure that the subject does not resume food consumption until a period of time has elapsed.
Pulse generation for electrical nerve modulation can be accomplished using a pulse generator. Pulse generators can use conventional microprocessors and other standard electrical components. A pulse generator for this embodiment can generate a pulse, or energy signal, at frequencies ranging from approximately 0 Hz (i.e., constant current) to 300 Hz, a pulse width from approximately 10 to 1,000 microseconds, and a constant current of between approximately 0.1 milliamperes to 20 milliamperes. The pulse generator can be capable of producing a ramped, or sloped, rise in the current amplitude and/or frequency. In some embodiments, a pulse generator can communicate with an external programmer and/or monitor. Passwords, handshakes and parity checks can be employed for data integrity. The pulse generator can be battery operated or operated by an external radiofrequency device. Because the pulse generator, associated components, and battery may be implanted they are preferably encased in an epoxy-titanium shell.
A schematic of an implantable pulse generator (IPG) is shown in FIG. 5. Components can be housed in the epoxy-titanium shell. A battery supplies power to the logic and control unit. A voltage regulator controls the battery output. A logic and control unit can control the stimulus output and allow for programming of the various parameters such as pulse width, amplitude, and frequency. In addition, stimulation pattern and treatment parameters can be programmed at the logic and control unit. A crystal oscillator provides timing signals for the pulse and for the logic and control unit. An antenna is used for receiving communications from an external programmer and for status checking the device. An output section couples to the electrodes and leads that carry the energy pulse to the nerve. A reed switch allows manual activation using an external magnet. Devices powered by an external radiofrequency device can be used to limit the components to primarily a receiving coil or antenna.
The IPG can be coupled to a lead and electrode assembly. The lead can comprise a bundle of electrically conducting wires insulated from the surroundings by a non-electrically conducting coating. Where used, wires of the lead connect the IPG to the stimulation electrodes, which transfers the energy pulse to the nerve. A single wire may connect the IPG to the electrode, or a wire bundle may connect the IPG to the electrode. Wire bundles may or may not be braided. Wire bundles are preferred because they increase reliability and durability. Alternatively, a helical wire assembly could be utilized to improve durability with flexion and extension of the lead. In some embodiments, power could be transmitted from the pulse generator to an end effector electrode wirelessly.
The electrodes can comprise platinum or platinum-iridium ribbons or rings as shown in FIG. 6. The electrodes are capable of electrically coupling with the surrounding tissue and nerve. The electrodes may encircle a catheter-like lead assembly. The distal electrode may form a rounded cap at the end to create a bullet nose shape. Ideally, this electrode serves as the cathode. A lead of this type may contain 2 to 4 ring electrodes spaced anywhere from 2.0 to 5.0 mm apart with each ring electrode being approximately 1.0 to 10.0 mm in width. Catheter lead electrode assemblies may have an outer diameter of 0.5 mm to 1.5 mm to facilitate percutaneous placement using an introducer.
Bipolar stimulation of a nerve can be accomplished with multiple electrode assemblies with one electrode serving as the positive node and the other serving as a negative node. In this manner nerve activation can be directed primarily in one direction (unilaterally), for example, to selectively activate efferent nerve fibers. Alternatively, a nerve cuff electrode can be employed. Helical cuff electrodes, such as those described in U.S. Pat. No. 5,251,634 (Weinberg), can be used. Cuff assemblies can similarly have multiple electrodes and direct and cause unilateral nerve activation.
Unipolar stimulation can also be performed. As used herein, unipolar stimulation means using only a single electrode on the lead, while the metallic shell of the IPG, or another external portion of the IPG, essentially functions as a second electrode, remote from the first electrode. In some embodiments, unipolar stimulation may be more suitable for splanchnic nerve stimulation than the bipolar stimulation method, particularly if the electrode is to be placed percutaneously under fluoroscopic visualization. With fluoroscopically observed percutaneous placement, it may not always be possible to place the electrodes immediately adjacent the nerve, which is often required for bipolar stimulation.
With unipolar stimulation, a larger energy field is created in order to electrically couple the electrode on the lead with the remote external portion of the IPG, and the generation of this larger energy field can result in activation of the nerve even in the absence of close proximity between the single lead electrode and the nerve. This allows successful nerve stimulation with the single electrode placed only in “general proximity” of the nerve. This allows for significantly greater separation between the electrode and the nerve than the “close proximity” required for effective bipolar stimulation. The magnitude of the allowable separation between the electrode and the nerve will necessarily depend upon the actual magnitude of the energy field that the stimulator generates with the lead electrode in order to couple with the remote electrode. Patch electrodes, cuff electrodes, and transvascular/intravascular electrodes may be used in various embodiments.
In multiple electrode assemblies, some of the electrodes may be used for sensing nerve activity. This sensed nerve activity could serve as a signal to commence stimulation therapy. For example, afferent action potentials in the splanchnic nerve, created due to the commencement of feeding, could be sensed and used to activate the IPG to begin stimulation of the efferent neurons of the splanchnic nerve. Appropriate circuitry and logic for receiving and filtering the sensed signal would be required in the IPG. Thus, in some embodiments, electrodes within the assembly can be used to provide the sensor functionality as described herein with respect to detecting swallowing or some other physiological parameter associated with eating as has been described above.
Because branches of the splanchnic nerve directly innervate the adrenal medulla, electrical activation of the splanchnic nerve results in the release of catecholamines (epinephrine and norepinephrine) into the blood stream. In addition, dopamine and cortisol, which also raise energy expenditure, can be released. Catecholamines can increase energy expenditure by 15% to 20%. By comparison, subitramine, a pharmacologic agent used to treat obesity, increases energy expenditure by only 3% to 5%.
Human resting venous blood levels of norepinephrine and epinephrine are approximately 300 picograms (pg)/milliliter (ml) and 25 pg/ml, respectively, as shown in FIG. 7. Detectable physiologic changes such as increased heart rate occur at norepinephrine levels of approximately 1,500 pg/ml and epinephrine levels of approximately 50 pg/ml. Venous blood levels of norepinephrine can reach as high 2,000 pg/ml during heavy exercise, and levels of epinephrine can reach as high as 400 to 600 pg/ml during heavy exercise. Mild exercise produces norepinephrine and epinephrine levels of approximately 500 pg/ml and 100 pg/ml, respectively. It may be desirable to maintain catecholamine levels somewhere between mild and heavy exercise during electrical sympathetic activation treatment for obesity.
In anesthetized animals, electrical stimulation of the splanchnic nerve has shown to raise blood catecholamine levels in a frequency dependent manner in the range of 1 Hz to 20 Hz, such that rates of catecholamine release/production of 0.3 to 4.0 mug/min can be achieved. These rates are sufficient to raise plasma concentrations of epinephrine to as high as 400 to 600 pg/ml, which in turn can result in increased energy expenditure ranging from 10% to 20% as shown in FIG. 8. During stimulation, the ratio of epinephrine to norepinephrine is 65% to 35%. It may be possible to change the ratio by stimulating at higher frequencies. This may be desired to alter the energy expenditure and/or prevent a rise in MAP.
Energy expenditure in humans ranges from approximately 1.5 kcal/min to 2.5 kcal/min. A 15% increase in this energy expenditure in a person with an expenditure of 2.0 kcal/min would increase energy expenditure by 0.3 kcal/min. Depending on treatment parameters, this could result in an additional 100 to 250 kcal of daily expenditure and 36,000 to 91,000 kcal of yearly expenditure. One pound of fat is approximately 3500 kcal, yielding an annual weight loss of 10 to 26 pounds.
Increased energy expenditure is typically fueled by fat and carbohydrate metabolism, and in extreme cases of weight loss by metabolism of protein. Postganglionic branches of the splanchnic nerve innervate the liver and fat deposits of the abdomen. Activation of the splanchnic nerve can result in fat metabolism and the liberation of fatty acids, as well as glycogen breakdown and the release of glucose from the liver. Fat metabolism coupled with increased energy expenditure may result in a net reduction in fat reserves.
The present invention takes advantage of the known relationship between sympathetic activation and energy expenditure. As a result, in some embodiments, a second therapeutic signal can be produced that is configured to increase energy expenditure. The second therapeutic signal can be generated in response to the sensing of the end of a period of eating. This can be, for example, after the cessation of a patter of swallowing typical of eating, upon achieving a desired blood glucose level, upon loss of olfactory signals, where stomach pH begins to rise, a change in impedance of saliva in the oral cavity, or a cessation of changes in intrathoracic pressure detected in the vicinity of the suprasternal notch. Alternatively, the second therapeutic signal could be generated upon cessation of electromyographic signals on or near the esophagus that are normally associated with swallowing of food. In some embodiments the second therapeutic signal may be generated immediately after the end of a meal period. In some embodiments, the second therapeutic signal may be delayed in time until some pre-determined time following eating, or in response to sensing some pre-determined physiological parameter (e.g., catecholamine levels, blood glucose levels, signaling molecule levels).
Analogously to the first therapeutic signal, the second therapeutic signal can be configured, without limitation, with respect to duration, frequency, and current amplitude. Similarly, the second therapeutic can be applied in the form of an electrical pulse train, or plurality of such pulse trains. Pulse trains can be of similar or varying duration, frequency, and/or current amplitude. In some embodiments, an electrical pulse train can comprise a duration ranging from about 5 to about 120 minutes, a frequency ranging from about 10 to about 30 Hz, and a current amplitude ranging from about 1 to about 5 mA. In some embodiments, pulse trains within a plurality of pulse trains can be separated from each other by period during which no signal is applied. These intervals can be of greater, lesser, or equal duration to individual pulse trains.
In some embodiments, signal intensity of the second therapeutic signal can be ramped up or down as desired in order to achieve a desired physiological parameter or outcome. For example, and without being limiting, signal intensity may be modulated in order to maintain blood glucose levels, or catecholamine levels (or as described below to levels of ghrelin or some other signaling molecule), at concentrations that enhance increased energy expenditure, in effect providing a way of titrating neuromodulation to achieve a desired result.
It may also be desirable to titrate obesity therapy to plasma ghrelin levels. In humans, venous blood ghrelin levels range from approximately 250 pg/ml to greater than 700 pg/ml as shown in FIG. 9. Ghrelin levels rise and fall during the day with peak levels typically occurring just before meals. In patients with gastric bypass surgery, an effective treatment for obesity, ghrelin levels are more static and typically stay in a low range of 100 to 200 pg/ml. Splanchnic nerve activation, in the treatment of obesity, could be titrated to keep ghrelin levels in the low range below 250 to 300 pg/ml. Reductions in food intake comparable to the increases in energy expenditure (i.e., 100 to 250 kcal/day), could yield a total daily kcal reduction of 200 to 500 per day, and 20 to 50 pounds of weight loss per year.
In anesthetized animals, electrical activation of the splanchnic nerve has also been shown to decrease insulin secretion. In obesity, insulin levels are often elevated, and insulin resistant diabetes (Type II) is common. Down-regulation of insulin secretion by splanchnic nerve activation may help correct insulin resistant diabetes.
Electrical activation of the splanchnic nerve can cause an increase in mean arterial blood pressure (MAP) above a baseline value. A drop in MAP below the baseline can follow this increase. Because a sustained increase in MAP is undesirable, the stimulation pattern can be designed to prevent an increase in MAP. One strategy would be to have a relatively short signal-on time followed by a signal-off time of an equal or longer period. This would allow the MAP to drop back to or below the baseline. The subsequent signal-on time would then raise the MAP, but it may start from a lower baseline. In this manner a sinusoidal-like profile of the MAP could be set up during therapy delivery that would keep the average MAP within safe limits. The rise in MAP can be accompanied by a decrease in heart rate which is a compensatory mechanism that may also normalize MAP with sustained stimulation for more than approximately 10 minutes.
Alternatively, in some embodiments, an alpha-sympathetic receptor blocker, such a prazosin could be used to blunt the rise in MAP. Alpha-blockers are commonly available antihypertensive medications. The rise in MAP seen with splanchnic nerve stimulation is the result of alpha-receptor activation, which mediates arterial constriction. Because the affects of this therapy on reduced food intake and energy expenditure are related to beta-sympathetic receptor activity, addition of the alpha-blocker would not likely alter the therapeutic weight loss benefits. Given the potential for relatively short period of stimulation with the present method, however, it may be possible to avoid altogether the increase in MAP that attends other stimulatory programs, an additional advantage provided by the present invention.
Implantation of the lead/electrode assembly for activation of the greater splanchnic nerve can ideally be accomplished percutaneously using an introducer as shown in FIG. 10. The introducer can be a hollow needle-like device that would be placed posteriorly through the skin between the ribs para-midline at the T9-T12 level of the thoracic spinal column. A posterior placement with the patient prone is preferred to allow bilateral electrode placement at the splanchnic nerves, if required. Placement of the needle could be guided using fluoroscopy, ultrasound, or CT scanning. Proximity to the splanchnic nerve by the introducer could be sensed by providing energy pulses to the introducer to electrically activate the nerve while monitoring for a rise in MAP. All but the very tip of the introducer would be electrically isolated so as to focus the energy delivered to the tip of the introducer. The lower the current amplitude required to cause a rise in the MAP, the closer the introducer tip would be to the nerve. Ideally, the introducer tip serves as the cathode for stimulation.
Alternatively, a stimulation endoscope could be placed into the stomach of the patient for electrical stimulation of the stomach. The evoked potentials created in the stomach could be sensed in the splanchnic nerve by the introducer. To avoid damage to the spinal nerves, the introducer could sense evoked potentials created by electrically activating peripheral sensory nerves. Once the introducer was in proximity to the nerve, a catheter type lead electrode assembly would be inserted through the introducer and adjacent to the nerve.
Percutaneous placement of the lead electrode assembly could be enhanced using direct or video assisted visualization. An optical port could be incorporated into the introducer. A separate channel would allow the electrode lead assembly to be inserted and positioned, once the nerve was visualized. Alternatively, a percutaneous endoscope could be inserted into the chest cavity for viewing advancement of the introducer to the nerve. The parietal lung pleuron is relatively clear, and the nerves and introducer can be seen running along the vertebral bodies. With the patient prone, the lungs are pulled forward by gravity creating a space for the endoscope and for viewing. This may avoid the need for single lung ventilation. If necessary, one lung could be collapsed to provide space for viewing. This is a common and safe procedure performed using a bifurcated endotracheal tube. The endoscope could also be placed laterally, and positive CO2 pressure could be used to push down the diaphragm, thereby creating a space for viewing and avoiding lung collapse.
Alternatively, stimulation electrodes could be placed along the sympathetic chain ganglia from approximately vertebra T4 to T11. This implantation could be accomplished in a similar percutaneous manner as above. This would create a more general activation of the sympathetic nervous system, though it would include activation of the neurons that comprise the splanchnic nerves.
Alternatively, the lead/electrode assembly could be placed intra-abdominally on the portion of the splanchnic nerve that resides retroperitoneally on the abdominal aorta just prior to synapsing in the celiac ganglia. Access to the nerve in this region could be accomplished laparoscopically, using typical laparoscopic techniques, or via open laparotomy. A cuff electrode could be used to encircle the nerve unilaterally or bilaterally. The lead could be anchored to the crus of the diaphragm. A cuff or patch electrode could also be attached to the celiac ganglia unilaterally or bilaterally. Similar activation of the splanchnic branches of the sympathetic nervous system would occur as implanting the lead electrode assembly in the thoracic region.
An alternative lead/electrode placement can be via a transvascular approach. Due to the proximity of the splanchnic nerves to the azygous veins shown in FIG. 10, and in particular the right splanchnic nerve and right azygous vein, modulation could be accomplished by positioning a lead/electrode assembly in this vessel. The venous system and azygous vein can be accessed via the subclavian vein using standard techniques. The electrode/lead assembly can be mounted on a catheter. A guidewire can be used to position the catheter in the azygous vein. The lead/electrode assembly would include an expandable member, such as a stent. The electrodes can be attached to the stent, and using balloon dilation of the expandable member, can be pressed against the vessel wall so that energy delivery can be transferred to the nerve. An expandable member would allow fixation of the electrode lead assembly in the vessel. The IPG and remaining lead outside of the vasculature can be implanted subcutaneously in a manner similar to a heart pacemaker.
Various doses can be delivered in response to the detection of eating. Three different dosing strategies are described below. Individual or multiple doses from these strategies may be utilized as part of various embodiments of the present invention.
FIGS. 11A and 11B illustrate one algorithm according to the present invention. In this algorithm, labeled as “Algorithm A” in the figure, the series of doses are delivered in a diurnal pattern, are delivered during typical waking hours, and are not delivered in the typical sleeping hours. In this example, the doses are delivered about 12 times per day. The doses are about a half hour long, with an inter-dose no (or substantially reduced intensity) stimulation period of about one hour in between. Algorithm A, in this example, has a substantially constant frequency, of about 20 Hz. The stimulation intensity ramps up at the beginning of the dose, ramps down at the end of the dose, and has a substantially constant intensity plateau portion in between the up ramp and down ramp.
The intensity is shown as a percent of Maximum Tolerable Current (MTC), a measure of tolerable stimulation intensity. MTC can be measured in various ways, depending on the embodiment. In one embodiment, the patient is stimulated at various intensities and asked which intensity is the maximum they could tolerate after leaving the session. In another method, which can be used in animals and humans, the blood pressure is observed during stimulation and compared to a blood pressure base line the day before the stimulation. The Mean Arterial Pressure (MAP) may be used, which may be approximated as 1⁄3 times the systolic plus 2⁄3 times of the diastolic, to give each a proper weighting. A MTC in this embodiment may be the intensity at which MAP increases 20 percent above the baseline.
In one embodiment, the pulse width is held at about 1⁄2 ms (500 usec) while the current is varied. In another embodiment, the current is held constant while the pulse width is varied. In still other embodiments, both current and pulse width are varied to vary the pulse width*current product, which is the intensity, having units of time*current which is charge, typically mSec*mA. In some embodiments the MTC has a pulse width of about 1⁄2 msec (512 usec in one embodiment) and a current of about 1, 2, or even 3 mA.
In FIGS. 11A and 11B, the current increases in a ramp over the first 10 minutes, holds constant for 15 minutes, and decreases over the next 5 minutes. This is followed by 60 minutes of no stimulation, followed by another dose, during typical waking hours. In the embodiment illustrated, the first dose occurs at 4:00 and the last dose stops at about 21:00. In this embodiment, the first dose occurs in pre-waking hours, which may act to inhibit morning appetite and/or stimulate metabolism prior to waking In some embodiments, the first dose does not occur until the patient is normally awake, and the last dose ends at least about one, two, or three hours before sleep is expected, in various embodiments.
Algorithm A thus has a dose time of at least about 15 minutes and less than about 60 minutes, or at least about 20 minutes and less than 40 minutes, or between about 20 and 30 minutes, or about a half hour. The inter dose interval can last at least about one half hour and less than about 3 hours, or at least about 3⁄4 hour and less than about 2 hours, or at least about one hour and less than about two hours, and combinations thereof. The dose can act to drive a sensation of satiety and/or increase metabolism for a period sufficient to initiate this sensation and metabolic rate increase, but not so long as to significantly reduce the same effects later, when the dose is repeated again. The dose length can be such that there is no short term degradation in the response. The dose length can be such that there is no decrease in an otherwise increasing biomarker, for example, Free Fatty Acids (FFA), Glucagon, Glycerol, and Glucose, during the dose. This can be explicitly measured on a per patient basis or based on the expected response for a patient, based on other patient responses. In this way, the same dose delivered again during the day can have the same effective result, rather than a blunted response as previous excessive stimulation has caused an accommodation response by the body. The diurnal, lack of stimulation during sleeping hours may also aid in the anti-accommodation performance of the therapy. In this way, the same dose delivered a day later will have substantially the same physiological response as the dose the previous day.
FIG. 12 illustrates the beneficial effect of even short stimulation doses (of 5-7 minutes) followed by about a half hour of off-time. The increases in Free Fatty Acids (FFA), Glucagon, Glycerol, and Glucose (GLU) are all seen.
FIG. 13 illustrates the beneficial effect of a 30 minute dose having a 60 minute inter-dose interval in between. This stimulation used a 60 second on/60 second off duty cycle, at 2 mA and 20 Hz. The change in glycerol and FFA both at 10 minutes after the start of the dose are seen to be significant. The liberation of FFA and glycerol, indicative of lipolysis, is seen to repeat in doses 2 and 3. This indicates there is some recovery and lack of significant accommodation to the repeated doses. There may well be beneficial effects in addition to the burning of fat stores. The circulating FFA and glucose which result from the dose may well reduce appetite as well, as glucose is added to the blood stream and sensed, for example, by the brain. This can thereby reduce hunger and blunt appetite, apart from any direct satiety signaling by the dose, and lasting after the dose has ceased.
FIG. 14 illustrates another family or group of algorithms, labeled as “Algorithm B” in the figures. In this algorithm, the current is held substantially constant, while the frequency is ramped up and down in a dose. In this example, intensity (here current) is held constant for a half hour period, while frequency is ramped up and down for three ramps within a half hour long dose. In this example, current is held at 100 percent of MTC, while the frequency ramp is a linear ramp from 0 to 20 Hz for 5 minutes, then a ramp down from 20 Hz to 0 over 5 minutes, then two repeats of same. The inter-dose interval can be about 60 minutes, or the same times discussed with respect to Algorithm A, both for the doses and inter-dose intervals. The duty cycle can be 5 seconds on and 5 seconds off, in some embodiments.
FIG. 15 shows the doses delivered over a day, for the entire day and night. In some embodiments, stimulation is stopped during expected sleeping hours.
Algorithm B can be used to deliver variations of afferent signaling which may mimic the nutrient and mechanoreceptors which normally indicate the presence of food. The increasing and/or decreasing may aid in overcoming or preventing accommodation to the stimulation. Different populations of neurons may be effectively stimulated by different frequencies at the different times into each frequency ramp. In various embodiments, the dose/inter-dose times may be 10/20, 30/60, 80/160, and the like, with the times given in minutes. The frequency increasing portions may be about 5, 10, or 15 minutes long in some embodiments, as may the frequency decreasing portions in some embodiments. The frequency ramp portions can be configured such that the subsequent frequency ramps have substantially similar results as the first such ramps in the dose and/or compared to the same ramp in the next dose.
FIGS. 15 and 16 illustrate another algorithm, labeled “Algorithm C.” The dose and inter-dose times can be as previously described with respect to Algorithms B and C. Algorithm C can have a substantially constant stimulation intensity, shown here as 100 percent of MTC. Algorithm C can also have an increasing frequency ramp portion followed by a substantially constant frequency portion, followed by a decreasing frequency ramp portion. In this example, the frequency increases from about 0 to 20 Hz over about 15 minutes, then remains at about 20 Hz for 35 minutes, and then decreases back to about 0 Hz over about 10 minutes. In some embodiments, the frequency ramp up is about 1⁄4 hour, the constant portion about 1⁄2 hour, and the ramp down about 1⁄4 hour. In this example, the stimulation can either be run day and night or discontinued in expected sleeping times.
Algorithm C may be viewed as a combination or blending of algorithms A and B. The frequency ramp up, plateau and ramp down are believed to at least partially replicate normally satiety curves as induced by a meal followed by a normal post meal decline, as seen by the nutrient and mechano receptors in the stomach and lower gut. Such mimicry can be used to sneak under the body's accommodation response that could otherwise reduce response to subsequent doses.
Other algorithms may also be used in some aspects of the present invention. Algorithm C can be varied having an 80 minute dose and a 160 minute inter-dose interval, with a 30 minute current ramp to maximum dose. The 30 minute ramp may provide a beneficial CV response at the dose onset, and has shown that in some tests. In another embodiment, Algorithm A is varied, to have a 30 min dose/60 minute inter-dose interval, with 24 hour application.
While the particular invention as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that this disclosure is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended other than as described in the appended claims.
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## Claims

1. A method of modulating a component of the nervous system of a mammal, the method comprising:
providing a sensor, wherein the sensor is configured to produce a first sensor output signal associated with the onset of a period of nutrient consumption, and a second sensor output signal, associated with the end of a period of nutrient consumption;
providing a stimulator configured to output a first therapeutic signal in response to the first sensor output signal, and a second therapeutic signal in response to the second sensor output signal;
wherein applying the first therapeutic signal to a first component of the nervous system is effective to mimic satiety in the mammal; and
wherein applying the second therapeutic signal to a second component of the nervous system is effective to produce an increase in energy expenditure in the mammal.

2. The method of claim 1, wherein the sensor is configured to produce the first sensor output signal in response to at least one of swallowing, a blood glucose level, a neurological signal associated with olfaction, a stomach pH level, an electrical impedance of saliva, an electromyographic signal in the esophagus, and a change in intrathoracic pressure.

3. The method of claim 1, wherein the sensor is configured to produce the second sensor output signal in response to at least one of cessation of swallowing, a blood glucose level, a neurological signal associated with loss of an olfactory signal, a stomach pH level, an electrical impedance of saliva, an electromyographic signal in the esophagus, and a change in intra-thoracic pressure.

4. The method of claim 1, wherein the first therapeutic signal is applied to a component of the sympathetic nervous system.

5. The method of claim 4, wherein the component of the sympathetic nervous system comprises afferent nerve fibers of a splanchnic nerve.

6. The method of claim 1, wherein the second therapeutic signal is configured to modulate a component of the sympathetic nervous system.

7. The method of claim 6, wherein the component of the sympathetic nervous system comprises efferent fibers in a splanchnic nerve.

8. The method of claim 1, wherein the first therapeutic signal comprises at least one electrical pulse train;
wherein the at least one electrical pulse train is applied for a duration ranging from about 2.5 minutes to about 30 minutes;
wherein the at least one electrical pulse train is followed by a time interval ranging from about 2.5 minutes to about 30 minutes during which no electrical signal is applied to the component of the nervous system;
wherein the at least one electrical pulse train comprises a frequency ranging from about 0 Hz to about 20 Hz;
wherein the at least one electrical pulse train comprises a current ranging from about 1 to about 5 mA.

9. The method of claim 8, wherein the first therapeutic signal comprises a plurality of electrical pulse trains, wherein pulse trains are separated from each other by an interval comprising substantially no signal.

10. A method of modulating a component of the nervous system of a mammal, the method comprising:
sensing the onset of eating in the mammal; and
stimulating a splanchnic nerve responsive to the eating sensing by applying at least one electrical stimulus dose,
in which the dose has a stimulation duration of at least about 1⁄4 hour and has a frequency which varies much more than the intensity;
in which the method has a reduced intensity or no intensity interval after the dose at least about 1 hour in length.

11. The method of claim 10, in which the dose stimulation duration is less than about 1 hour.

12. The method of claim 11, in which the dose stimulation duration is less than about 1⁄2 hour.

13. The method of claim 10, in which the dose frequency increases at the beginning of the dose for at least about 1⁄5 of the dose and decreases at the end of the dose for at least about 1⁄5 of the dose.

14. The method of claim 13, in which the dose frequency remains substantially constant in the middle of the dose for at least about 1⁄5 of the dose.

15. The method of claim 10, in which the dose frequency increases and decreases over the dose in a pattern which mimics a normal eating response.

16. The method of claim 10, in which the dose frequency has a maximum frequency in the dose in between about 10 Hz and 20 Hz.

17. The method of claim 10, in which the dose stimulation intensity has a maximum intensity in between about 1⁄2 mSec-mA and about 2 mSec-mA.

18. The method of claim 10, in which the dose stimulation intensity and frequency are configured sufficient to raise biomarkers indicative of eating food to levels substantially the same or least half of the level indicative of eating food.

19. The method of claim 18, in which the dose stimulation duration is sufficient to raise biomarkers indicative of eating food to levels substantially the same or least half of the level indicative of eating food, and the stimulation stops or substantially reduces upon the biomarkers raising to the level indicative of eating food.

20. A method of modulating a component of the nervous system of a mammal, the method comprising:
sensing the onset of eating in the mammal; and
stimulating a splanchnic nerve responsive to the eating sensing by applying at least one electrical stimulus first dose,
in which the first dose has a stimulation duration of at least about 1⁄4 hour and has a frequency which varies much more than the intensity;
in which the method follows the varying frequency first dose with an increasing intensity second dose configured to stimulate more efferently than the first dose and to capture more fibers than the first dose.