What is the medical device being studied?
The study device is similar to a pacemaker and will send tiny electrical signals to the nerve in your abdomen regulating the activity of the stomach during digestion as shown in the picture.
These tiny signals may reversibly block nerve signals in your abdomen. This in turn, relaxes the parts of your digestive system, such as your stomach and your pancreas, both of which are active in processing food and digesting calories. However, until this research study is done, it is not known whether or not the Maestro™ System will cause weight loss.
This experimental, or, investigational device has some parts that are placed inside your abdomen and under your skin by your surgeon and some parts you will wear outside your body.
An investigational device is one that is not approved by the US Food and Drug Administration(FDA). Your study surgeon will show you the parts that will be placed inside your abdomen and the parts that you will wear on the outside of your body.
In previous studies with the Maestro™ System, safety results showed no important findings or concerns. The average excess weight loss at 6 months from implant was 14.2%.
Other surgical treatments for obesity include adjustable gastric bands and gastric bypass. They report excess weight loss at 6 months ranging from 26% (bands) and 54% (bypass).
What is the vagus nerve and what does it do?
The vagus nerve originates in the brain and is the longest of the twelve cranial nerves. In fact, the vagus can be thought of as the “spinal cord” of the nervous system that controls the stomach, intestine and many other organs.
Together with three sacral nerves, the vagus nerve is also the principal pathway for parasympathetic nervous system communication to the brain from those organs. Vagal efferent nerve transmission (from the brain to the body) regulates a broad range of the body’s functions. Furthermore, vagal afferent fibers (from the body to the brain) comprise approximately 80% of the fibers of the vagus nerve.
The vagus nerve has the most extensive distribution of all the cranial nerves, affecting many essential physiologic functions involved in food ingestion, processing, and digestion — including the following functions relevant to this approach to treating obesity:
- Ability of the stomach to enlarge to accommodate a larger volume of food (known to doctors as accommodation).
- Contraction of the stomach pump (the antrum) which grinds up food and mixes it with stomach enzymes.
- Acid secretion by the stomach
- Stomach emptying
- Secretion of digestive enzymes by the pancreas and emptying of the gallbladder
- Modulation of sensations of being full (satiation), hunger, nausea, dull pain and discomfort
How might blockage of the vagus nerve by the Maestro™ system produce weight loss?
Unlike drug therapies that focus on a single mechanism of action (e.g. suppression of appetite or inhibition of fat/calorie absorption or increase in metabolic rate) or bariatric surgery which simply tries to mechanically limit food intake (lapband) or both limit food absorption and restrict food intake by irreversibly altering normal gastrointestinal tract anatomy and physiology (gastric bypass), EnteroMedics’ Maestro™ System is intended to offer potential weight loss that treats obesity by intermittently down-regulating or blocking the vagal nerve function in the abdomen.
The Maestro™ System utilizes blocking principles documented in historical studies that report weight loss following interruption of the vagus nerve (vagotomy) and the resulting
vagal block. These publications, which are summarized below, provide substantial data supporting these conclusions:
Cutting the Vagus Nerve for Treatment of Duodenal Ulcer Prevented Weight Gain:
A series of 120 patients with duodenal ulcers underwent either complete or partial cutting of the vagus nerve to reduce stomach acid secretion. The treatment goals were to reduce gastric acid, to reduce ulcer symptoms and to permit increases in body weight. Less than 50% of those with complete interruption of the vagus nerve achieved the desired body weight, while 94% of those with partial vagal nerve interruption gained weight, a demonstration that vagus nerve block by surgery inhibits gain in body weight.
Chang TM, Chan D, Liu YC et al. Long-term Results of Duodenectomy with Highly Selective Vagotomy in the Treatment of Complicated Duodenal Ulcers. Amer J Surg 2001;181:372-376.
Cutting the Vagus Inhibits Fat Absorption:
A series of 48 patients was admitted to a hospital to study fat absorption. Sixteen were studied prior to severance of the vagus nerve, and the remaining 32 patients were studied at least one year after complete or partial interruption of the vagus nerve. Patients with only the stomach branches of the vagus nerve severed had similar fat absorption to pre-operative patients, while the remaining patients with complete vagal interrruption continued to demonstrate poor fat absorption (and therefore absorption of fewer fat-derived calories) one year or more afterward.
Edwards JP, Lyndon PJ, Smith RB et al. Faecal Fat Excretion after Truncal, Selective, and Highly Selective Vagotomy for Duodenal Ulcer; Gut 1974;15:521-525.
Cutting the Vagus Nerve Decreased Food Intake:
Seven obese patients underwent truncal vagotomy (complete interruption of the vagus nerve). At three and nine months following vagotomy, body weights, as well as dietary intake of food were significantly decreased. The authors’ concluded that this study demonstrated an appetite-suppressant effect following truncal vagotomy, particularly with regard to liquid calorie intake.
Gortz L, Bjorkman AC, Andersson H et al. Truncal Vagotomy Reduces Food and Liquid Intake in Man. Physiol and Behav 1990;48:779-781.
Cutting the Vagus Nerve During Stomach Stapling Improved Weight Loss:
A series of 69 obese patients underwent stomach stapling (vertical band gastroplasty) either with or without truncal vagotomy. In patients followed for one year or longer, the vagotomy group had an average excess body weight loss that was twenty percent higher than the non-vagotomy patients. In patients followed for over five years, the differences were even greater.
Kral JG, Gortz L, Hermansson G. Gastroplasty for Obesity: Long-Term Weight Loss Improved by Vagotomy. World J Surg 1993;17:75-79.
Cutting the Vagus Nerve For Ulcer Decreased Appetite
A series of 27 male patients who had undergone vagotomy 15-20 years previously for peptic ulcers were compared with patients who had undergone stomach removal without vagotomy for the same condition. Higher proportions of the vagotomy patients continued to have decreased appetite, and loss of weight.
Johnson HD. The Late Nutritional and Haematological Effects of Vagal Section. Brit J Surg 1969;56:4-9.