Influence of decrease in the muscle activity during mastication on occurrence of the Stage II transport.

PURPOSE: The purpose of this study was to examine the hypothesis that in the process from food ingestion to swallowing, intentional decrease in the muscle activity during mastication would affect the number of chewing strokes, and thus the occurrence of Stage II transport (St2Tr) or the number of swallowing. METHODS: Twenty adults with healthy dentition were instructed to make (1) normal mastication and (2) mastication with 50% muscle activity (50% mastication), controlled by visual feedback with electromyogram. Gummy jelly was selected as a test food. The oropharynx was observed during the sequence of events from the start of mastication until swallowing using a nasal endoscope. The number of chewing strokes was calculated by rhythmical masseter muscle activity on electromyogram. RESULTS: The number of chewing strokes increased with 50% mastication. There was a particularly noticeable increase in the number of pre-St2Tr strokes. No effect on the number of additional swallows was seen as a result of 50% mastication. CONCLUSIONS: The present study supported the hypothesis that intentional decrease in the muscle activity during mastication affected the number of chewing strokes and the occurrence of St2Tr. Particularly, this tendency was noticeable during the mastication before the start of St2Tr. However, our results did not support a question as to the number of swallowing.

[Medulla and upper cervical cord compression by bilateral vertebral artery presented with myelopathy and drop attack: case report].

A 51-year-old man had suffered from attacks of quadri-paresis and unconsciousness for previous three years prior to presentation. Prior to admission, he had been received anticonvulsants, but his symptoms showed no improvement. Neurological examination revealed hyper-reflexia of his left lower extremity and moderate decrease of sense of pain, temperature, and tactile sensation in his left extremities and trunk, while vibratory sensation was normal. Magnetic resonance(MR) imaging revealed a flow-void area in the craniocervical junction and marked narrowing of the medulla oblongata and upper cervical cord by compression of the vertebral arteries(VA). CT myelography also showed the compression and narrowing of the spinal cord. Vertebral angiography demonstrated symmetrical running course of the arteries, which curved medially at the level of craniocervical junction. Suboccipital craniectomy and C1 and upper half of C2 laminectomies were performed. After dural opening, the ventrolateral aspects of the lower medulla oblongata and the upper cervical cord were found to be compressed by the VA. The arteries were retracted dorsolaterally by GORE-TEX tapes so as to decompress the medulla oblongata and cervical cord, and the tapes were anchored to the residual part of C1 posterior arch. Postoperative MR imaging and CT myelography showed complete decompression, and the patient was relieved of his previous neurological symptoms.