SUMMARY To determine the effect of respiration on systolic and diastolic time intervals, simultaneous phonocardiograms, carotid pulse tracings, M mode echocardiograms, and respiratory curve tracings were measured in 25 healthy subjects. The positioning of each cardiac cycle in relation to the phase of respiration was assessed and the dependency of heart rate and cardiac time intervals on respiration was examined. Heart rate clearly varied over the respiratory cycle. Where necessary the time intervals were corrected for heart rate or RR interval. The systolic time intervals showed a stronger dependency on respiratory group than the diastolic time intervals. The decrease in left ventricular ejection time and increase in pre-ejection period and isovolumic contraction time during inspiration support the idea that a relative increase in afterload in inspiration determines left ventricular systolic function. Isovolumic relaxation time also showed cyclic behaviour whereas the left ventricular filling time was affected by inspiration only. Filling time increased significantly when there was a transition from expiration to inspiration during left ventricular ejection. It seems that when isovolumic contraction takes place in expiration the diastolic intervals of this cycle take on an expiratory character. The

The effect of posture on the duration of systolic and diastolic time intervals and their dependency on cycle length (R-R interval) was investigated in 20 healthy subjects using simultaneous electrocardiograms, phonocardiograms, carotid pulse tracings, and M mode echocardiograms. The dependency of left ventricular ejection time and left ventricular filling time on the R-R interval did not change between the sitting and the supine position. Preejection period, preisovolumic interval, isovolumic contraction time, and isovolumic relaxation time displayed either weak or no dependency. Preejection period, its component intervals preisovolumic interval and isovolumic contraction time, as well as isovolumic relaxation time were prolonged in the sitting position, whereas the corrected left ventricular ejection time was shortened, and the corrected left ventricular filling time showed no significant change. These changes in the duration of the intervals can be understood as a depression of cardiac function in the sitting position due to the pooling of blood in the lower extremities: reduced filling leads to a diminished contractile and relaxation response on the basis of reduced fiber length.