The upper esophageal sphincter in the cat: the role of central innervation assessed by transient vagal blockade

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Abstract
Studies were performed on four cats to assess the role of extrinsic innervation via the cervical nerve trunks in the control of upper esophageal sphincter function. Transient vagal nerve blockade was accomplished by cooling the cervical vagosympathetic nerve trunks previously isolated in skin loops on each side of the neck. Upper esophageal sphincter pressure was measured using a multilumen oval manometry tube and a rapid pull-through technique. The upper esophageal sphincter response to cervical intraesophageal balloon distention and acid perfusion was assessed. The feline upper esophageal sphincter has a distinct asymmetric pressure profile, whereby anterior pressure > posterior pressure > left pressure > right pressure. Bilateral vagal nerve blockade lowered the mean upper esophageal sphincter pressure from 18.5 ± 1.5 to 12.0 ± 2.8 mmHg (1 mmHg = 133.3 Pa) (p < 0.001), with a significant reduction in pressure in all four quadrants. Intraesophageal balloon distention and acid perfusion both produced a significant increase in upper esophageal sphincter pressure. Bilateral vagal nerve blockade completely abolished the response of the upper esophageal sphincter to balloon distention and acid perfusion. We conclude that (i) normal upper esophageal sphincter tone in the cat is partially mediated by excitatory neural input via the cervical nerve trunks, presumably via the recurrent laryngeal nerves; and (ii) cervical intraesophageal balloon distention and acid perfusion produce reflex contraction of the upper esophageal sphincter, which is dependent on neural pathways via the cervical vagal nerve trunks, but the relative contribution of afferent and efferent pathways remains unknown.