Circulatory Responses to Intermittent Positive and Alternating Positive-Negative Pressure Respirators

Abstract
Exptl. animals with competent circulatory and respiratory systems tolerate either the pos.-neg. or the intermittent pos. type respirators without major alterations in blood or cardiac output. In the presence of respiratory failure and/ or circulatory embarrassment, or both, the intermittent pos. type machines cause a depression in cardiac output and blood pressure which is sometimes fatal. The pos.-neg. type machines are distinctly superior in such circumstances, since they maintain adequate cardiac output and blood pressure. This latter type of respirator owes its desirability to a more favorable effect on venous return to the heart. The objection that a negative pressure phase during expiration may produce pulmonary edema is not supported by exptl. findings or theoretical considerations.