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

STUDY OBJECTIVES: To analyze gender differences in the oxygen transport system 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 hemodynamic assessment were performed on a cycle ergometer in 64 hypertensive patients (32 female and 32 male) varying in age from 23 to 64 years. Female and male patients were matched for age and BP. MEASUREMENTS AND RESULTS: Peak oxygen uptake was significantly lower in women 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 height and weight (-29%). This resulted essentially from a significantly lower cardiac output in women, both when expressed in absolute units and when adjusted for body size. At the peripheral level, female patients had a lower 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 level 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 oxygen saturation, which contributes to the lower arteriovenous oxygen difference of women, could result from their smaller muscle mass, lower capillary density, and lower oxidative potential.