In vivo measurement of feline esophageal tone

Using an isotonic recording device (barostat), we assessed feline esophageal smooth and striated muscle tone in vivo and determined the effects of a cholinergic agonist (bethanechol) and antagonist (atropine) and the effect of body position on this tone. Studies were performed on six cats under light intravenous ketamine anesthesia. Two parameters were analyzed: compliance and resistance to initial stretch (resting tone). Smooth muscle compliance (0.51 +/- 0.03 ml/mmHg) was significantly greater than that of the striated muscle section (0.26 +/- 0.02 ml/mmHg; P = 0.0260). Resting tone was low in both esophageal sections. Neither atropine nor bethanechol had any significant effect on the two tone parameters measured in smooth muscle. Change in body position had no influence on the intraesophageal balloon volume. We conclude that esophageal wall compliance varies according to location (smooth vs. striated muscle) and that esophageal smooth muscle tone is not under cholinergic excitatory control. Isotonic recording in vivo should allow further investigations of the nature of the neural and myogenic control of esophageal tone and of the relationships between phasic and tonic activity.