Effect of hypercapnia on the blood supply to the heart in chronic experimental conditions

Summary

Experiments were staged on dogs in chronic conditions without anesthesia. The changes in the volume velocity of the coronary circulation were recorded by the thermoelectric method. Respiration, blood pressure and ECG were registered simultaneously. Hypercapnia of different degrees was provoked by inhalation of gas mixtures with 3, 5, 7, 10 and 15% CO₂ for 1–10 min.

The changes in the coronary circulation in response to hypercapnia were either biphasic (reduction at the beginning of the action, replaced by its gradual increase, as in dogs under anesthesia), or—monophasic (increase only). During the first phase there was constriction of the coronary vessels, and during the second—dilatation. Characteristic of dogs without anesthesia were inconstancy, a lesser degree and a shorter duration of constriction (during, the first phase). Evidently while awake the animals possessed greater compensatory powers for overcoming the vasoconstrictor effects of CO₂ on the coronary vessels than did dogs under anesthesia.