Abstract
SUMMARY Moderate hypocapnia (arterial carbon dioxide tension about 25 mm Hg) was produced in closed-chest anaesthetized dogs using two methods—firstly by increasing minute ventilatory volume, and secondly by withdrawing carbon dioxide gas which had been added to the inspired gas mixture during hyperventilation. Myocardial blood flow was measured by estimating the rate of clearance of radioactive xenon from the myocardium after its selective injection into one of the two main branches of the left coronary artery. Hypocapnia was associated with a highly significant reduction in myocardial blood flow and oxygen availability but myocardial oxygen extraction increased so that oxygen consumption by the myocardium was unaffected. Mean arterial blood pressure, heart rate and cardiac output did not change significantly. Hypocapnia caused an increase in systemic blood lactate level but myocardial consumption of glucose, lactate, pyruvate and non-esterified fatty acid was not significantly altered.
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