Cardiovascular response to oxygen inhalation in the anesthetized cat

¹ Department of Pharmacology, University of California Medical Center, Los Angeles, California

An analysis of the cardiovascular response to short periods of inhalation of O₂ is presented. In cats anesthetized with chloralose, an immediate acute fall in arterial pressure, accompanied by a varying degree of bradycardia was followed by an equilibrium state lower than the control value. Following bilateral vagotomy the initial hypotension was still present but the arterial pressure during the second phase returned to the preoxygen value. With inactivation of the caroticoaortic chemoreceptor regions, no hypotensive effect was seen, but a small, slowly developing hypertension was observed, originating peripherally. A similar, but significantly smaller hypotensive effect was seen in cats under sodium pentobarbital anesthesia. No significant difference in the arterial O₂ saturation between animals anesthetized with chloralose and pentobarbital was noted, but in both groups the largest fall in arterial pressure occurred with the greater degree of anoxia. Experiments in which an increased degree of anoxemia was induced demonstrated the significantly different reactivity of the chemoreflex system under the anesthetics studied and suggests the presence of a central selective depression of the tonic anoxic chemoreceptor drive with barbiturate anesthesia.