Oxygen uptake kinetics of older humans are slowed with age but are unaffected by hyperoxia

Cross-sectional studies have compared the oxygen uptake ((V)over dot (O2)) kinetics during the on-transient of moderate intensity exercise in older an d younger adults. The slower values in the older adults may have been due t o an age-related reduction in the capacity for O-2 transport or alternative ly a reduced intramuscular oxidative capacity. We studied: (1) the effects of ageing on (V)over dot (O2) kinetics in older adults on two occasions 9 y ears apart, and (2) the effect of hyperoxia on (V)over dot (O2) kinetics at the second test time. After a 9 year period, follow-up testing was underta ken on seven older adults (78 +/- 5 years, mean +/- S.D.). They each perfor med six repeats of 6 min bouts of constant-load cycle exercise from loadles s cycling to 80% of their ventilatory threshold. They breathed one of two g as mixtures (euoxia: inspired O-2 fraction F-I,F-O2, 0.21; hyperoxia: F-I,F -O2, 0.70) on different trials determined on a random basis. Breath-by-brea th (V)over dot (O2) data were time aligned and ensemble averaged. (V)over d ot (O2) kinetics, modelled with a single exponential from phase 2 onset (+2 0 s) to steady state and described by the exponential time constant (tau) w ere compared with data collected from the same adults 9 years earlier. One- way repeated measures analysis of variance revealed that tau was slowed sig nificantly with age (from 30 +/- 8 to 46 +/- 10 s), but was unaffected by h yperoxia (43 +/- 15 s). We concluded that: (1) in older adults studied long itudinally over a 9 year period, the on-transient (V)over dot (O2) kinetics are slowed, in agreement with, but to a greater extent, than from cross-se ctional data; and (2) the phase 2 time constant (tau) for these older adult s was not accelerated by hyperoxic breathing. Thus the expected hyperoxia-i nduced increase in the capacity for 0, transport was not associated with fa ster on-transient (V)over dot (O2) kinetics suggesting either that O-2 tran sport may not limit (V)over dot (O2) kinetics during the 8th decade, or tha t O-2 transport was not improved with hyperoxia.