Effects of acute hypoxia on the VO2p kinetics of older adults during exercise

This thesis investigated the effect of hypoxia in determining the rate of adjustment in pulmonary O2 uptake (VO2p) for young and older adults. The pulmonary oxygen uptake (VO2p), heart rate (HR), limb blood flow (LBF), and muscle deoxygenation [HHb] were examined during the on-transient of moderate-intensity exercise in normoxia and hypoxia. Young and older adults exhibited slower VO2p kinetics in hypoxia compared to normoxia. Under hypoxic conditions, older adults showed a great mismatch between O2 delivery and O2 utilization within the muscle, this being responsible for the slower VO2p kinetics. On the other hand, young adults did not show significant differences in the matching of O2 delivery and O2 utilization between normoxia and hypoxia. Thus, factors other than the microvascular O2 delivery (i.e central O2 delivery and/or mithocondrial respiration) are responsible for the slower VO2p kinetics observed for young adults under hypoxic conditions. For older adults, the vasodilatory response to hypoxia was found to depend on the work rate. At very low work rate, older adults were able to counterbalance the hypoxia-induced drop in CaO2 with an increased blood flow, thus preventing the slowing of the VO2p kinetics. At higher work rate however, older adults exhibited a slow VO2p kinetics, with a great mismatch between O2 delivery and O2 utilization within the muscle.