CARDIOVASCULAR RESPONSES TO HYPERCAPNIA AND VARYING LEVELS OF ARTERIAL pH IN THE ANESTHETIZED CAT

Effects of acute hypercapnia on the cardiovascular system (CYS) were studied in the anesthetized cat. After surgery the animal was exposed to a gas mixture of 12% CO2 and 25% O2 in nitrogen, and hypercapnia with low levels of arterial pH (pHa) was produced for 20 minutes. In the second run the same level of hypercapnia was induced by ventilating the same cat from the above gas mixture but pHa was kept normal by a slow and continuous infusion of 1HAM (0.5 mM/ kg/min). Results of this study showed that hypercapnia increased aortic flow and induced peripheral vasodilation. Hypercapnia produced tachycardia in the presence of arterial acidosis whereas in its absence this response reversed to bradycardia. Hypercapnia increased mean arterial blood pressure (Pa) by 20% during low pHa, whereas this increase was only 10% in the absence of arterial acidosis. Therefore, it is concluded that hypercapnia in conjunction with arterial acidosis has a much stronger stimulatory influence on the CYS via different arterial chemoreceptors.