STROKE VOLUME AND SYSTOLIC-TIME INTERVAL ADJUSTMENTS DURING BICYCLE EXERCISE

By use of the impedance noninvasive method, cardiac output (Q), stroke volume (SV), heart rate (HR), Heather index (HI), and systolic time interval (STI) values were studied in 17 subjects working at 25, 50 and 75% of their maximal oxygen uptake (VO2(max)) on a Monark bicycle. A significant increase in SV at each work load and a concomitant decrease in positive expiratory pressure (PEP), left ventricular ejection time (LVET), and PEP/LVET were observed. The linear regression equation at 75% VO2(max) between LVET and HR and SV confirms the close relationship between these parameters. The significant increase of the contractility index (HI) showing the stress response of the myocardium is clearly assessed. At 75% work load, its correlation with SV is low; but the high level of the correlation (r = 0.90) between HI and HR from rest to recovery indicates the major role played by HR in the stress response. Consequently the changes in STI and HI, the relationship between STI and SV, and study of SV, HR, and Q provide valuable information about the adjustment of these parameters during calibrated efforts.