Central nervous system mechanisms in deglutition and emesis

Feasibility study of the Nox-T3 device to detect swallowing and respiration pattern in neurologically impaired patients in the acute phase

Dysphagia is a frequent complication in neurologically impaired patients, which can lead to aspiration pneumonia and thus prolonged hospitalization or even death. It is essential therefore, to detect and assess dysphagia early for best patient care. Fiberoptic endoscopic and Videofluoroscopy evaluation of swallowing are the gold standard exams in swallowing studies but neither are perfectly suitable for patients with disorders of consciousness (DOC). In this study, we aimed to find the sensitivity and specificity of the Nox-T3 sleep monitor for detection of swallowing. A combination of submental and peri-laryngeal surface electromyography, nasal cannulas and respiratory inductance plethysmography belts connected to Nox-T 3 allows recording swallowing events and their coordination with breathing, providing time-coordinated patterns of muscular and respiratory activity. We compared Nox-T3 swallowing capture to manual swallowing detection on fourteen DOC patients. The Nox-T3 method identified swallow events with a sensitivity of 95% and a specificity of 99%. In addition, Nox-T3 has qualitative contributions, such as visualization of the swallowing apnea in the respiratory cycle which provide additional information on the swallowing act that is useful to clinicians in the management and rehabilitation of the patient. These results suggest that Nox-T3 could be used for swallowing detection in DOC patients and support its continued clinical use for swallowing disorder investigation.

Physiology of the Digestive Tract Correlates of Vomiting

Emesis is composed of 3 independent digestive tract correlates that are individually organized by a brainstem neural network and all 3 hierarchically organized by a central pattern generator. The central pattern generator may be in the Bötzinger nucleus of the brain stem. The digestive tract sensory mechanisms that activate vomiting are the digestive tract mucosa or chemoreceptive trigger zone of the area postrema. Regardless of the initial stimulus, the area postrema may be activated in order to inhibit orthograde digestive tract motility and reflux blocking reflexes that would interfere with anterograde movement, which is the basic purpose of vomiting. The digestive tract correlates are (1) relaxation of the upper stomach and contraction of the lower pharynx, (2) retrograde giant contraction, and (3) the pharyngo-esophageal responses during retching and vomitus expulsion. The proximal gastric response allows gastroesophageal reflux, the lower pharyngeal response prevents supra-esophageal reflux, and both last the duration of the vomit process. The retrograde giant contraction empties the proximal digestive tract of noxious agents and supplies the stomach with fluids to neutralize the gastric acid which protect the esophagus from damage during expulsion. The retch mixes the gastric contents with acid neutralizer and gives momentum to the expelled bolus. During vomitus expulsion the esophagus is maximally stretched longitudinally which stiffens its wall to allow rapid transport as the suprahyoid muscles and diaphragmatic dome contract, and the hiatal fibers relax.

Neural mechanisms of swallowing and effects of taste and other stimuli on swallow initiation

Swallowing involves several motor processes such as bolus formation and intraoral transport of a food bolus (oral stage) and a series of visceral events that occur in a relatively fixed timed sequence but are to some degree modifiable (pharyngeal stage or swallow reflex). Reflecting the progressive aging of society, patients with swallowing disorders (i.e., dysphagia) are increasing. Therefore, there is expanding social demand for the development of better rehabilitation treatment of dysphagic patients. To date, many dysphagia diets have been developed and are available commercially to help bring back the pleasure of mealtimes to dysphagia patients. Texture modification of food to make the food bolus easier to swallow with less risk of aspiration is one of the important elements in dysphagia diets from the viewpoint of safety assurance. However, for the further development of dysphagia diets, new attempts based on new concepts are needed. One of the possible approaches is to develop dysphagia diets that facilitate swallow initiation. For this approach, an understanding of the mechanisms of swallow initiation and identification of factors that facilitate or suppress swallow initiation are important. In this review, we first summarize the neural mechanisms of swallowing and effects of taste and other inputs on swallow initiation based on data mainly obtained from experimental animals. Then we introduce a recently established technique for eliciting swallowing using electrical stimulation in humans and our ongoing studies using this technique.

Antiaversive properties of opioids in the conditioned taste aversion test in the rat

The antiaversive effect of mu-, kappa- and delta-opioid receptor agonists against conditioned taste aversion (CTA) induced by apomorphine, lithium chloride and copper sulphate in the rat was studied, in order to evaluate whether prevention of CTA is a suitable model for the study of antiemetics. Anti-aversion was not a general characteristic of all opioid substances tested. Only one dose of the mu-agonist morphine and only one dose of the kappa-agonist ethylketocyclazocine had a consistent antiaversive effect against CTA induced by apomorphine; one dose of the delta-agonist [D-Ala2, Met5]enkephalinamide antagonized the aversion induced by lithium chloride. As the results do not correspond to our previous findings on the antiemetic effects of these opioids in the dog (all mu- and kappa-agonists tested having an antiemetic effect), we conclude that the CTA test cannot be used as a screening test for potentially antiemetic drugs.

Emetic and antiemetic effects of opioids in the dog

The emetic and antiemetic effects of opioid agonists were studied in awake dogs. The mu-agonists morphine, fentanyl and methadone, in sedative doses, prevented the emetic response to apomorphine and copper sulphate; only morphine induced emesis, at doses lower than those required to prevent emesis. The delta-agonist [D-Ala2,Met5]enkephalinamide (DALA) and [Leu5]enkephalin induced emesis in some of the dogs studied but had no antiemetic activity. The kappa-agonists bremazocine and ethylketocyclazocine (EKC) did not induce emesis but, at sedative doses, prevented the emetic response to apomorphine. The emetic effect of DALA was antagonized by naloxone in some dogs; the antiemetic effect of morphine, bremazocine and EKC was blocked by both naloxone and MR 2266. The non-opioid sedatives diazepam, phenobarbital and xylazine, administered in sedative doses, did not prevent apomorphine-induced emesis. Our results suggest that a delta-receptor is involved in the emetic effect and a mu- and/or or kappa-receptor in the antiemetic effect of opioids.