Cardiovascular control by medullary surface chemoreceptors.

The cardiovascular and respiratory effects of superfusion of the ventral surface of the medulla with acid hypercapnic or alkaline hypocapnic solutions have been studied in anaesthetized, paralyzed, artificially ventilated cats. Peripheral chemoreceptor and baroreceptor denervation was achieved by section of carotid sinus, aortic and cervical vagus nerves. Systemic arterial and central venous pressure, hindquarters blood flow, heart rate and phrenic nerve activity were recorded. Acid hypercapnic (pH 6.8, pCO2 85 mm Hg) superfusion caused increases in systemic arterial pressure, phrenic nerve activity and heart rate, and a decrease in hindquarters blood flow. Alkaline hypocapnic (pH u.i, pCO2 less than 10 mmHg) superfusion caused opposite effects. These experiments indicate a significant role of the chemoreceptors of the ventral surface of the medulla in cardiovascular control.