Effects of Blood Withdrawal on Cardiac, Hemodynamic, and Pulmonary Responses to a Moderate Acute Workload in Healthy Middle‐Aged and Older Females

Abstract

Background The fundamental role of blood volume (BV) on cardiorespiratory fitness has been well studied in males during maximal exercise. However, understanding the importance of BV on key physiological responses to a submaximal workload in females has yet to be elucidated. The objective of this study was to investigate the effects of blood withdrawal on cardiac, hemodynamic, and pulmonary responses to submaximal exercise in females. We hypothesized that blood withdrawal would reduce cardiac filling and stroke volume (SV) which would result in a compensatory increase in heart rate (HR) to preserve cardiac output (Q) at a fixed submaximal workload. Methods 30 healthy females (63.8 ± 8.3 yr) were recruited for this study. Transthoracic echocardiography, non-invasive blood pressure monitoring, and a peak oxygen uptake (VO2peak) test were performed at a 100 W submaximal workload prior to and immediately after a 10 % reduction of BV. Primary outcomes included left ventricular end-diastolic volume (LVEDV), SV, Q, HR, and VO2peak. BV was determined using an established carbon monoxide rebreathing technique. Results BV of subjects ranged from 3.8 to 6.6 L, with an average 10 % reduction of 0.5 ± 0.1 L. Following blood withdrawal, both LVEDV (P ≤ 0.030) and SV (P < 0.019) were reduced while Q was unchanged (P = 0.139) due to an augmented HR (P < 0.026). Submaximal hemodynamic variables including MAP (P < 0.015), SBP (P < 0.005), and DBP (P < 0.038) were reduced while VO2peak was unaltered (P = 0.250). Conclusion Blood withdrawal results in marked reductions in cardiac filling with compensatory chronotropic responses that preserve Q at an acute moderate submaximal workload in healthy females. BV thus determines the relative exercise intensity, as typically determined by HR, of submaximal efforts in this population.