Systemic circulatory responses to hypocapnia in man.

RICHAKDSON, DAVID Mr., HERMES A. KONTOS, A. JARRELL RAPER, AND JOHN L. PATTERSON, JR. Systemic circulatory responses to hypocapnia in man. Am. J. Physiol. !223(6): 1308-1312. 1972.Hypocapnic alkalosis, induced by voluntary hyperventilation in normal man, was associated with increases in cardiac output and in heart rate and decreases in mean arterial blood pressure and in systemic vascular resistance. These changes were most pronounced 1 min following the onset of hyperventilation, were less pronounced at 4 min, and subsided completely 7 min following the onset of hyperventilation. The circulatory effects of hyperventilation were largely dependent on the associated chemical changes rather than on mechanical or reflex effects, since isocapnic hyperventilation produced no significant changes except a small increase in heart rate. Beta-adrenergic receptor blockade with propranolol did not alter the circulatory responses to hypocapnic hyperventilation. Administration of the antihistamine promethazine significantly reduced the increases in cardiac output and in heart rate and the decrease in systemic vascular resistance associated with hyperventilation, and it abolished the decrease in mean arterial blood pressure, signifying that release of histamine may be an important factor in the production of the circulatory responses to hyperventilation.