Inspiratory gas flow induced by cardiac systole.

This study was made to quantify the inspiratory gas flow pulse produced by cardiac systole. Ten adults (9 men, 1 woman; age 24-65 yr) were studied, of whom two had respiratory muscle weakness. The inspiratory flow pulse commenced 50-60 msec after the R wave of the ECG and lasted 106 (SD22) msec. In eight subjects seated and breathing through a mouthpiece, the flow pulse reached a peak of 120 (SD 58) ml sec-1 and displaced a volume of 6.6 (SD 2.3) ml (range 3.6-9.9 ml). Similar results were obtained using a nasal mask. By adding an external airway resistance, the effective intrathoracic pressure responsible for inspiratory flow was estimated to be -0.21 (SD 0.03) cm H2O. Duplicate studies showed little variation in pulse volume. The mechanism of the inspiratory gas flow pulse and its contribution to gas exchange is discussed.