A polygraphic study of systolic time intervals and their correlations with heart rate and workload during supine ergometry in one hundred normal subjects.

The present study was designed to investigate systolic time intervals (STI) in 100 normal subjects undergoing continuous-maximal supine cycle ergometry and to search for possible linear correlations between STI (dependent variables) and heart rate, diastolic blood pressure, systolic blood pressure, age, sex, weight, and height (independent variables), by stepwise regression analysis. The only significant correlation discovered in the study was between the contractility index (isometric contraction time-ICT) and the total work produced by each participant. Exercise tolerance was limited primarily by shortening of the ICT interval, all subjects discontinuing the test when ICT reached 13.7 +/- 7 ms.