Is there a disassociation of maximal oxygen consumption and maximal cardiac output?

PURPOSE: The purpose of the present study was to determine whether maximal cardiac output (Q) is affected by the duration of the maximal exercise test. METHODS: Nine healthy men (N = 6) and women (N = 3) performed three separate maximal treadmill exercise tests, separated by at least 24 h, and underwent a body composition assessment by hydrostatic weighing, all within a 2-wk period. A baseline maximal exercise test was performed to establish VO(2max). The second and third tests, assigned randomly, were designed to elicit the subjects' predetermined VO(2max) in either 6 or 12 min. Heart rate (HR), blood pressure (BP), minutes of ventilation, and oxygen consumption (VO(2)) were measured during all tests. At the end of the 6- and 12-min tests, Q was measured using an acetylene rebreathing technique. Stroke volume (SV), mean arterial pressure (MAP), total peripheral resistance (TPR), and arteriovenous O(2) difference were calculated using standard equations. RESULTS: Repeated-measures ANOVA indicated that there were no significant differences in HR and VO(2max) between the baseline, 6-min, and 12-min tests. Paired t-tests revealed significantly greater Q (25.1 +/- 5.6 vs 23.7 +/- 5.2 L.min-1) and SV (138.3 +/- 31.5 vs 130.5 +/- 31.2 mL) in the 6- versus 12-min tests, respectively. There were no significant differences in systolic BP, diastolic BP, MAP, TPR, or arteriovenous O(2) difference. CONCLUSIONS: Despite there being no difference in VO(2max) between the two tests, the 6-min maximal exercise test resulted in a significantly greater Q than the 12-min test, because of a significantly greater SV. Thus, there was a disassociation between VO(2) and Q during maximal exercise.