Influence of carbon dioxide tension in the cephalic circulation on hind-limb vascular resistance in anaesthetized dogs.

In dogs anaesthetized with chloralose, the effects were determined of changes in cephalic blood PCO2 on vascular resistance and on the reflex vascular responses to stimulation of baroreceptors and chemoreceptors. Both vagus nerves were cut above the nodose ganglia, both carotid sinus regions were perfused with blood at controlled pressures and the cephalic circulation was perfused with blood, equilibrated with various levels of CO2, through the brachiocephalic and left subclavian arteries. Increases in cephalic blood PCO2 between 4 and 6 kPa resulted in increases in arterial perfusion pressure in a vascularly isolated hind limb. These responses were inhibited at high carotid sinus pressures and the responses to changes in carotid pressure were enhanced at high levels of cephalic PCO2. The reflex increase in vascular resistance resulting from stimulation of carotid chemoreceptors, however, was unaffected by the level of cephalic blood CO2. These results indicate that the carbon dioxide tension in the cephalic circulation is of importance in the control of vascular resistance in the hind limb.