The effects of oesophageal distension on diaphragm and laryngeal muscle activity in the anaesthetized cat.

The electromyographic (EMG) activities of diaphragm and laryngeal muscles were recorded during oesophageal distension in anesthetized cats. The responses to distension of the thoracic oesophagus differed from those evoked by distension of the cervical oesophagus. The crural component of the diaphragm (CD) was inhibited by distension of the thoracic oesophagus; distension of the cervical oesophagus did not affect CD EMG. Thyroarytenoid (TA) muscle EMG increased markedly and consistently in response to distension of the cervical oesophagus. Distension of the thoracic oesophagus only produced statistically significant increases in TA EMG with high distending volume (10 ml) at the level of the gastro-oesophageal junction. The main abductor of the vocal cords, the posterior cricoarytenoid (PCA) was either unchanged or decreased by oesophageal distension. The electrical activities of left paratendinous diaphragm, left costal diaphragm, internal intercostal and external intercostal muscles remained unchanged. The entire pattern would appear to constitute a means to aid passage of a bolus into the stomach, and simultaneously guard the respiratory tract from reflux or aspiration.