Gender differences in the oxygen transport system during maximal exercise in hypertensive subjects

Study objectives: To analyze gender differences in the oxygen transport sys tem at peak exercise with particular emphasis on the difference in systemic arteriovenous oxygen extraction and in mixed venous oxygen saturation. Patients and methods: Cardiopulmonary graded exercise testing and hemodynam ic assessment were performed on a cycle ergometer in 64 hypertensive patien ts (32 female and 32 male) varying in age from 23 to 64 years. Female and m ale patients were matched for age and BP, Measurements and results: Peak oxygen uptake was significantly lower in wom en than in men, and when expressed in absolute units (L/min: -39%) and when normalized for body mass (mL/min/kg: -33%) or statistically adjusted for h eight and weight (-29%). This resulted essentially from a significantly low er cardiac output in women, both when expressed in absolute units and when adjusted for body size. lit the peripheral level, female patients had a low er arteriovenous oxygen content difference at peak exercise, which resulted from a lower hemoglobin concentration and the inability to decrease mixed venous oxygen saturation to the same Ie rd as in men. Conclusion: The lower peak oxygen uptake of women results from both central and peripheral factors. The significantly higher value for mixed venous ox ygen saturation, which contributes to the lower arteriovenous oxygen differ ence of women, could result from their smaller muscle mass, lower capillary density, and lower oxidative potential.