Stroke volume increases by similar mechanisms during upright exercise in normal men and women

To define the effects of gender on stroke volume control during upright exercise in normal subjects, we examined central hemodynamics in 34 men and 27 women during staged bicycle ergometry. Central hemodynamics were assessed by right-sided cardiac catheterization and simultaneous radionuclide angiography. Left ventricular end-diastolic and end-systolic volumes were calculated from the stroke volume (by direct Fick) and the corresponding left ventricular ejection fraction. Men were larger than women (1.85 ± 0.11 vs 1.65 ± 0.13 m², p < 0.001) but groups were matched for age (39 ± 12 vs 36 ± 9 years, P = 0.27). Oxygen consumption at peak exercise was higher in men than in women (2.51 ± 0.50 vs 1.74 ± 0.30 liters/min, p < 0.001) but was not different when adjusted for body weight (31.5 ± 8.1 vs 28.4 ± 6.4 ml/kg/min, P = 0.14), indicating similar levels of overall fitness in the 2 groups. At rest and during submaximal and maximal exercise, stroke volume and left ventricular end-diastolic and end-systolic volumes were higher in men than in women, but there were no intergroup differences in stroke volume index, left ventricular ejection fraction, and left ventricular end-diastolic or end-systolic volume indexes. Comparison of derived regression equations of cardiac index, stroke volume index and left ventricular end-diastolic and end-systolic volume indexes revealed no differences in the time course or magnitude of changes with respect to oxygen consumption, expressed as percentage of peak oxygen consumption, in the 2 groups. The major increase in left ventricular end-diastolic volume from upright rest in both men and women occurred during early exercise and accounted for most of the increase in stroke volume with relatively small increases in pulmonary wedge pressure. With moderate to intense exercise, stroke volume was maintained because of decreases in left ventricular end-systolic volume, as left ventricular end-diastolic volume did not change or decreased slightly from 50 to 100% of peak oxygen consumption in both men and women. Our data indicate that in normal subjects, gender, independent of body size and physical fitness, is not an important determinant of cardiac output or left ventricular volume response to upright exercise.