Roles of hypercapnia and acidosis in the vasodilator response to hypercapnic acidosis.

KONTOS, HERMES A., DAVID W. RICHARDSON, AND JOHN L. PATTERSON, JR. Roles of hypercapniu and acidosis in the vasodilutor response to hyperc@c acidosis. Am. J. Physiol. 2 15 (6) : 1406-1408. 1968.-The importance of increased Pcoz and decreased pH in the mediation of the effects of hypercapnic acidosis on heart rate, blood pressure, and blood flow and vascular resistance of the human forearm were investigated in normal volunteers. The responses to hypercapnic acidosis produced by 7a/, CO2 breathing were compared to the effects of hypercapnia without acidosis produced by 7Y0 CO2 breathing while at the same time isotonic NaHCOa solution was infused intravenously to maintain arterial blood pH at the resting level, Hypercapnic acidosis (CO 2 breathing without NaHC03 infusion) was associated with increased heart rate, increased mean arterial blood pressure, no change in vascular resistance of the intact forearm, and decrease in vascular resistance of the forearm previously treated with phenoxybenzamine and propranolol. These responses were not significantly different from those seen during hypercapnia without acidosis (CO:! breathing plus NaHCOa infusion). The results indicate that the effects of hypercapnic acidosis on heart rate, blood pressure, and on forearm blood vessels are mediated by increased blood (and tissue) Pcoz rather than by the associated decrease in pH.