Cardiac mechanisms underlying normal exercise tolerance: gender impact.

The aim of this study is to test our hypothesis that normal exercise tolerance differs according to gender and to identify potential functional cardiac relationships, which could explain those differences. A total of 44 healthy individuals with mean age of 49 ± 12 years (28-74 years, 22 males) constituted the study cohort. All individuals underwent resting and exercise Doppler echocardiogram simultaneously with peak oxygen uptake analysis (pVO(2)). At equal pVO(2), males achieved higher peak exercise workload (p < 0.001) and females higher heart rate (p < 0.001) but the two groups maintained similar indexed left ventricular (LV) stroke volume (SV) and cardiac output. Indexed LV end-diastolic (LVDVI) and end-systolic volumes (LVSVI) were smaller in females (p < 0.001 and p < 0.01, respectively), but filling time (FT) was shorter (p < 0.001) and they had higher early diastolic (E) velocity (p = 0.004), E/E (m) (myocardial E velocity) (p < 0.001) and global longitudinal strain rate atrial velocity (GLSRa') (p = 0.02), compared to males. In males, workload (p < 0.01), LVDVI (p < 0.01), LVSVI (p < 0.05), SVI (p < 0.001) directly but LV myocardial isovolumic relaxation time (IVRTm) (p < 0.01) inversely correlated with pVO(2). In females, mitral E velocity (p < 0.01), GLSRs' (p < 0.05) positively and LVFT negatively (p < 0.05) correlated with pVO(2). In a multivariable analysis SVI in males (p < 0.01) and GLSRs' in females (p < 0.01) were the strongest predictors for pVO(2). Thus, normal exercise capacity as determined by pVO(2) is related to the indexed stroke volume in males and left atrial pressure in females. These native normal differences between genders may explain the known vulnerability of women to endurance exercise compared to men.