Importance of blood volume on female cardiac, hemodynamic, and pulmonary responses to endurance exercise

Abstract

Purpose: The fundamental role of BV on cardiorespiratory responses to exercise have been well studied in young males. However, it is unknown whether these responses can be extrapolated in female populations. Therefore, the purpose of this thesis was to investigate the effect of a 10 % blood withdrawal on cardiac, hemodynamic, and pulmonary responses to exercise in females. Methods: Cardiac function was assessed during exercise using transthoracic echocardiography. Hemodynamic variables were measured using a non-invasive blood pressure monitoring system. Pulmonary variables were assessed in supine, left-lateral tilt position within a LBNP chamber to assess VO2max. BV was determined via the CO rebreathing technique. Submaximal workloads were performed at a constant workload of 100 W. Primary outcomes included LVEDV, SV, Q, HR, and VO2. Results: During submaximal exercise, 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). MAP (P < 0.015), SBP (P < 0.005), and DBP (P < 0.038) were reduced while VO2 was unaltered (P = 0.250). During maximal exercise, following blood withdrawal, there was a reduction in LVEDV and SV (≥ 10 % decrements, P ≤ 0.009). Peak Q was proportionally reduced (P < 0.001). Blood withdrawal induced a 10 % decrement in VO2peak (P < 0.001). Conclusion: Moderate blood withdrawal in females results in impairment of cardiac filling and SV with compensatory increases in HR to preserve Q at acute, constant load submaximal exercise. Thus, BV determines the relative exercise intensity at submaximal workloads. At maximal exercise, blood withdrawal impairs cardiac filling, output, and aerobic capacity in precise proportion to the magnitude of hypovolemia.