Systolic time intervals: the effect of stroke volume in healthy young men.

1. Positional change and exercise were used to gain a range of heart rates and stroke volumes in 20 healthy male subjects, and a regression plane computed for the 3 principal systolic time intervals. The addition of stroke volume as a second physiological variable was shown to result in an increase in the coefficient of determination of 13% for the LVET and 10% for the PEP. The QS2 was found to be dependent only on heart rate. It is concluded from this preliminary study that the addition of stroke volume and the derivation of a planar regression equation would allow calculation of potentially more useful index values for the LVET and PEP.