The effect of hypercapnia on the blood supply to the heart

Summary Experiments were carried out on dogs under morphine-urethane anesthesia. A thermoelectric method was used to study the coronary circulation. Simultaneous records were made of the respiration, blood pressure, and ECG while 3, 5, 7, 10, 15, 20, and 30% CO₂ and oxygen were added to the air breathed. Breathing was maintained for from 30 sec to one hour. It was found that in most cases the change of coronary flow was biphasic: in the first phase it was reduced and in the second increased. For a given CO₂ concentration the extent to which the second phase was manifested depended on the time for which the mixture was breathed, there being no effect for periods for less than three minutes. From the curves of the blood pressure and coronary circulation it could be seen that the coronary vessels were constricted in the first and dilated in the second phase.(Presented by Active Member AMN SSSR V. V. Parin) Translated from Byullenten' Éksperimental'noi Biologii i Meditsiny, Vol. 55, No. 4, pp. 9–14, April, 1963