A dysphagia model with denervation of the pharyngeal constrictor muscles in guinea pigs: functional evaluation of swallowing

To determine the incidence of dysphagia and associated pulmonary compromise in stroke patients through a systematic review of the published literature. Databases were searched (1966 through May 2005) using terms "cerebrovascular disorders," "deglutition disorders," and limited to "humans" for original articles addressing the frequency of dysphagia or pneumonia. Data sources included Medline, Embase, Pascal, relevant Internet addresses, and extensive hand searching of bibliographies of identified articles. Selected articles were reviewed for quality, diagnostic methods, and patient characteristics. Comparisons were made of reported dysphagia and pneumonia frequencies. The relative risks (RRs) of developing pneumonia were calculated in patients with dysphagia and confirmed aspiration. Of the 277 sources identified, 104 were original, peer-reviewed articles that focused on adult stroke patients with dysphagia. Of these, 24 articles met inclusion criteria and were evaluated. The reported incidence of dysphagia was lowest using cursory screening techniques (37% to 45%), higher using clinical testing (51% to 55%), and highest using instrumental testing (64% to 78%). Dysphagia tends to be lower after hemispheric stroke and remains prominent in the rehabilitation brain stem stroke. There is increased risk for pneumonia in patients with dysphagia (RR, 3.17; 95% CI, 2.07, 4.87) and an even greater risk in patients with aspiration (RR, 11.56; 95% CI, 3.36, 39.77). The high incidence for dysphagia and pneumonia is a consistent finding with stroke patients. The pneumonia risk is greatest in stroke patients with aspiration. These findings will be valuable in the design of future dysphagia research.

Swallowing movements are produced by a central pattern generator located in the medulla oblongata. It has been established on the basis of microelectrode recordings that the swallowing network includes two main groups of neurons. One group is located within the dorsal medulla and contains the generator neurons involved in triggering, shaping, and timing the sequential or rhythmic swallowing pattern. Interestingly, these generator neurons are situated within a primary sensory relay, that is, the nucleus tractus solitarii. The second group is located in the ventrolateral medulla and contains switching neurons, which distribute the swallowing drive to the various pools of motoneurons involved in swallowing. This review focuses on the brain stem mechanisms underlying the generation of sequential and rhythmic swallowing movements. It analyzes the neuronal circuitry, the cellular properties of neurons, and the neurotransmitters possibly involved, as well as the peripheral and central inputs which shape the output of the network appropriately so that the swallowing movements correspond to the bolus to be swallowed. The mechanisms possibly involved in pattern generation and the possible flexibility of the swallowing central pattern generator are discussed.

The aim of this study was to map the viscerotopic representation of the upper alimentary tract in the sensory ganglia of the IXth and Xth cranial nerves and in the subnuclei of the solitary and spinal trigeminal tracts. Therefore, in 172 rats 0.5-65 microliters of horseradish peroxidase (HRP), wheat germ agglutinin-HRP, or cholera toxin-HRP were injected into the trunks and major branches of the IXth and Xth cranial nerves as well as into the musculature and mucosa of different levels of the upper alimentary and respiratory tracts. The results demonstrate that the sensory ganglia of the IXth and Xth nerves form a fused ganglionic mass with continuous bridges of cells connecting the proximal and distal portions of the ganglionic complex. Ganglionic perikarya were labeled in crude, overlapping topographical patterns after injections of tracers into nerves and different parts of the upper alimentary tract. After injections into the soft palate, pharynx, esophagus, and stomach, anterograde labeling was differentially distributed in distinct subnuclei in the nucleus of the tractus solitarius (NTS). Palatal and pharyngeal injections resulted primarily in labeling of the interstitial and intermediate subnuclei of the NTS and in the paratrigeminal islands (PTI) and spinal trigeminal complex. Esophageal and stomach wall injections resulted in labeling primarily of the subnucleus centralis and subnucleus gelatinosus, respectively. The distribution of upper alimentary tract vagal-glossopharyngeal afferents in the medulla oblongata has two primary groups of components, i.e., a viscerotopic distribution in the NTS involved in ingestive and respiratory reflexes and a distribution coextensive with fluoride-resistant acid-phosphatase-positive regions of the PTI and spinal trigeminal nucleus presumably involved in visceral reflexes mediated by nociceptive or chemosensitive C fibers.