The Effects Of Reduced Blood Volumes On Oxygen Uptake Kinetics In Trained Athletes

Abstract

The Effects of reduced blood volumes on Oxygen Uptake Kinetics PURPOSE: The purpose of this study was to test the hypothesis that a reduced total blood volume will influence the (VO2) on-kinetic response during both moderate (MOD) and heavy (HVY) intensity exercise. METHOD: Following University Institutional ethics approval twelve subjects volunteered and agreed to participate (age, 21 ± 2 yrs; height, 175.2 ± 5.1 cm; weight, 66.4 ± 2.8 kg; VO2max, 53.0 ± 4.1 ml.kg-1·min-1). The subjects completed two exercise trials, un-bled (UBL) and bled (BLL) which were interspersed by a period of 48h. The trials consisted of an initial phase of 4-min of unloaded cycling followed by 2 bouts of 6-min constant load cycling at D 80% base-line VO2 - VO2 at ventilatory threshold (MOD), which were separated by 10-min of recovery unloaded cycling. Following the same recovery phase the subjects completed a third bout of 6-min constant load cycling at D50% ventilatory threshold - VO2max (HVY). Between the two exercise trials the subjects donated 500ml3 of blood. For both the UBL and BL trials VO2 was recorded on a breath-by breath basis using a pre-calibrated metabolic cart, haemodynamic responses were recorded throughout the trials and haematological variables were recorded pre-exercise. For both UBL and BLL trials the VO2 on-kinetic response data were fitted with a 3-component exponential model for analysis of the primary time component and mean response times. RESULTS: There were significant differences between UBL and BLL for Hb g·dl-1 (p< 0.005), HcT % (p< 0.001) and RBC·μl-1 (p< 0.013) with Hb showing a decrease of 9.7% from 14.5 ± 5.5 g·dl-1 to 13.1 ± 14.9 g·dl-1. There were non-significant differences between UBL and BLL for either the time constant or the amplitude of the phase II/III VO2 responses in both the MOD and HVY conditions (p >0.05). However there was a significant increase in the D pulse pressure for phase II between UBL and BLL in both MOD (10.4 ± 24.1mmHg) (p< 0.037) and HVY domains (21.2 ± 4.1mmHg) (p< 0.042). CONCLUSION: The data highlights the capability of the cardiovascular system in compensating for a reduction in the O2 carrying capacity of the blood through central alterations of cardiovascular function suggesting that exercise in the MOD and HVY domains does not appear to be limited by O2 delivery in healthy young individuals.