THE EFFECTS OF VAGOTOMY ON VENTILATION AND BLOOD GAS COMPOSITION IN DOG, SHEEP AND RABBIT

The influence of vagotomy on resting arterial blood gases ( P aCO 2 and P aO 2 ) and on the ventilatory responses to hypercapnia and hypoxia was studied in three different species of anaesthetized animals. After bilateral cervical vagotomy resting P aCO 2 generally declined. In the dog, where this was studied more fully, resting P aCO 2 declined significantly (8·13±0·67 mm Hg) over several hours, but P aO 2 changes were not significant. After vagotomy tidal volume ( V T), but not frequency ( f ), increased with increasing chemical drive. It is concluded that the increase in frequency in response to increased CO 2 or decreased O 2 is dependent on the vagal mechanisms. Minute volume, fractional inspiratory CO 2 ( V E, F ICO 2 ) and minute volume, fractional inspiratory O 2 ( V E, F 10 2 ) relationships have been determined. Although vagotomy may not decrease the response of minute volume of ventilation in the lower part of V E, F ICO 2 curves (mild hypercapnia), it flattened the upper parts of the curves in sheep and rabbits, and to a lesser extent in dogs; it seemed that there was little species difference in this respect. Ventilatory responses to graded hypoxia were close to or slightly higher than pre‐vagotomy values throughout the V E, F IO 2 , curves in all animals.