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.
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.
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.
(av)o2 = arteriovenous oxygen content
difference; NS = not significant; R = respiratory gas exchange
ratio; V̇co2 = carbon dioxide output;
V̇o2 = oxygen uptake (units per minute)