Hemodynamic effects of continuous positive and negative pressure breathing in normal man.

Abstract

Alterations in cardiac output, central blood volume, and arterial and central venous pressures were studied in 36 young men subjected to continuous negative or continuous positive pressure breathing. Negative pressure breathing increased cardiac output, stroke volume, and, to a lesser extent, central blood volume. Positive pressure, without overbreathing, decreased both cardiac output and central blood volume, but hyperventilation reversed these effects. On the basis of these observations, it is concluded that decreased intrathoracic pressure is important in maintaining or increasing the blood available to the heart in man, particularly during circulatory stress.