Effect of a reduction in arterial oxygen content (carbon monoxide) on coronary flow

Mongrel dogs were chronically instrumented for ventricular pacing, to measure left circumflex coronary flow (CF), left ventricular and arterial pressure, and to obtain blood samples from the left atrium and coronary sinus. Following a 3- to 4-week recovery period, the animals were subjected to a 30% reduction in arterial oxygen saturation by exposure to low levels of carbon monoxide. Three types of experiments were performed: 1) control, 2) pacing at 150 bpm, and 3) double blockade with propranolol and atropine. Reduction in arterial oxygen saturation in the three conditions studied resulted in a significant increase in CF and no change in myocardial oxygen consumption. The relationship between CF and arterial saturation demonstrated that double blockade produced a difference in the magnitude of the CF response. These results indicate a neurogenic mechanism to regulate coronary flow that may aid in maintaining oxygen availability during stressful conditions.