The primary reflex effects of distension of the stomach on heart rate, arterial pressure and left ventricular contractility in the anaesthetized pig.

The present study was planned to investigate whether distension of the stomach primarily affects the heart rate, arterial blood pressure and left ventricular inotropic state and to explore the reflex mechanisms involved. In 16 anaesthetized pigs, distension of gastric balloons with 0.81 of Ringer solution (gastric transmural pressure of about 13 mmHg) without controlling any haemodynamic variable caused an increase in arterial blood pressure. When this response was prevented, an increase in heart rate was obtained in each animal. In five pigs, the increase in heart rate was graded by step increments of distension. No significant changes in maximum rate of change of left ventricular pressure were observed in the sixteen pigs during gastric distensions performed whilst preventing changes in heart rate and arterial blood pressure. The responses of arterial blood pressure and heart rate were not influenced by the administration of atropine (four and six pigs respectively), while they were abolished by the administration of bretylium tosylate (ten pigs) and by bilateral vagotomy (six pigs; three cervical, three subdiaphragmatic). The present study showed that gastric distension which was likely to be innocuous in the anaesthetized pig reflexly increased arterial blood pressure and heart rate. The afferent limb of the reflex was in the vagal nerves and the efferent limb involved sympathetic pathways.