Studies on the carotid body and the carotid sinus. Circulatory effects of the carotid chemoreflex.

Abstract

Previously, carotid chemoreflex and baroreflex have been reported, although for the most part of these mechanisms have not been clarified.In this experiments, circulatory effects of the carotid chemoreflex were investigated in the anesthetized dogs. Chemoreflex was performed with Lobeline (0.02mg, 1ml) and potassium cyanide (KCN, 1%, 1ml) through the catheter inserted to the carotid sinus. Continuously, during experiments, systolic blood pressure (S. P), diastolic blood pressure (D. P), systolic pulmonary blood pressure (SPaP), diastolic pulmonary blood pressure (DPaP), respiration and pulse rate were recorded simultaneously in the closed chest dogs. Cardiac output, pulmonary blood flow, coronary blood flow, S. P, D. P, SPaP, DPaP, and pulse rate were examined in the controlled breathing of the open chest dogs.In each experiment, during and after reflex, blood gas, HCO3-, and pH were measured. However, none of them were changed by these reflexes.In the case of the closed chest dogs, chemoreflex by Lobeline did not change S. P and D. P, but SPaP was increased by 22.54%, significantly. DPaP was increased by 18.14%. Respiration rate was increased by 26.46% significantly. Heart rate was decreased by 9.15%.In the open chest dogs, chemoreflex by Lobeline increased S. P and D. P by 13.05% and 14.58% significantly. SPaP and DPaP were increased by 22.19% and 21.97% significantly. Pulmonary resistance was increased by 28.57% significantly. Pulmonary blood flow was decreased by 9.7% significantly.In the open chest dogs, chemoreflex with KCN increased S. P, D. P, and SPaP by 21.59%, 21.39%, and 41.02% significantly. Pulmonary resistance was increased by 20% significantly. Pulmonary blood flow was decreased by 10.43%. Cardiac output was not changed but coronary blood flow was increased by 6.50% significantly.It should be noted here that the carotid chemoreflex caused the hyperrespiration, the changes of pulmonary arterial blood pressure, pulmonary resistance, and pulmonary blood flow significantly, but these hemodynamic changes are capable of being separated from the effects of hyperrespiration through the chemoreflex mechanism.