Absence of age-related decline in total blood volume in physically active females.

Total blood volume (TBV) is an important determinant of cardiovascular functional capacity and the ability to maintain homeostasis during acute thermal and orthostatic stress. The primary aim of the present study was to test the hypotheses that TBV is 1) decreased with age in healthy, sedentary females, 2) not decreased with age in physically active females, and 3) directly related to maximal aerobic activity [maximal O2 consumption (VO2max)] in women of different ages and physical activity levels. An additional aim was to determine whether the use of hormone-replacement therapy in postmenopausal women is associated with altered TBV. Resting supine plasma volume (modified Evans blue dye technique) was measured in 25 postmenopausal women [12 sedentary (post-S), 13 physically active (post-PA; mean values, respectively, age 60 and 58 yr, and VO2max = 23 and 40 ml.kg-1.min-1)] and 27 premenopausal women [12 sedentary (pre-S), 15 physically active (pre-PA; mean values, respectively, age 29 and 31 yr, and VO2max = 35 and 54 ml.kg-1.min-1)]. TBV was lower in post-S (61 ml/kg) compared with pre-S (73 ml/kg) but not in post-PA (82 ml/kg) compared with pre-PA (87 ml/kg). It was also lower in post-S compared with post-PA. The lower TBV in post-S relative to pre-S and post-PA was related to lower plasma and estimated red blood cell volumes. Volumes did not differ between users and nonusers of hormone replacement. TBV was directly related to VO2max among all subjects (r = 0.65). It is concluded that 1) aging is associated with a decrease in TBV due to reductions in both plasma and erythrocyte cell volumes in healthy, sedentary females; 2) total blood, plasma, and red blood cell volumes are maintained with age in physically active females; 3) TBV is directly related to maximal aerobic capacity in females; and 4) TBV is not different in postmenopausal women using versus not using hormone-replacement therapy.