Effects of blood withdrawal on cardiac, hemodynamic, and pulmonary responses to a moderate acute workload in healthy middle-aged and older females

Objectives: To investigate the effects of blood withdrawal on cardiac, hemodynamic, and pulmonary responses to submaximal exercise in females. Design and methods: 30 healthy females (63.8 +/- 8.3 years) were recruited for this experimental study. Transtho-racic echocardiography, non-invasive blood pressure monitoring, and oxygen uptake were assessed during a fixed submaximal workload (100 W) prior to (day 1) and immediately after (day 2) a 10% reduction of blood vol-ume. Main measurements included left ventricular end-diastolic volume, stroke volume, cardiac output, mean arterial pressure, systolic blood pressure, diastolic blood pressure, and oxygen uptake. Blood volume was deter-mined via carbon monoxide rebreathing. Results: Participant's blood volume ranged from 3.8 to 6.6 L. Following 10% reduction in blood volume (0.5 +/- 0.1 L), left ventricular end-diastolic volume (p <= 0.030) and stroke volume (p < 0.019) were reduced during submaximal exercise while cardiac output was unchanged (p = 0.139) due to increased heart rate (p < 0.026). Hemodynamic variables including mean arterial pressure (p < 0.015), systolic blood pressure (p < 0.005), and diastolic blood pres -sure (p < 0.038) were reduced while oxygen uptake was unaltered (p = 0.250). Conclusions: Blood withdrawal results in marked reductions in cardiac filling with compensatory chronotropic responses that preserve cardiac output at a moderate submaximal workload in healthy females. Thus, blood volume determines the relative exercise intensity, as typically determined by heart rate, of submaximal efforts in this population. (c) 2021 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.