title: Oxygen uptake kinetics of older humans are slowed with age but are unaffected by hyperoxia.
abstract: Cross-sectional studies have compared the oxygen uptake (VO2) kinetics during the on-transient of moderate intensity exercise in older and younger adults. The slower values in the older adults may have been due to an age-related reduction in the capacity for O2 transport or alternatively a reduced intramuscular oxidative capacity. We studied: (1) the effects of ageing on VO2 kinetics in older adults on two occasions 9 years apart, and (2) the effect of hyperoxia on VO2 kinetics at the second test time. After a 9 year period, follow-up testing was undertaken on seven older adults (78 +/- 5 years, mean +/- S.D.). They each performed six repeats of 6 min bouts of constant-load cycle exercise from loadless cycling to 80% of their ventilatory threshold. They breathed one of two gas mixtures (euoxia: inspired O2 fraction, FI,O2, 0.21; hyperoxia: FI,O2, 0.70) on different trials determined on a random basis. Breath-by-breath VO2 data were time aligned and ensemble averaged. VO2 kinetics, modelled with a single exponential from phase 2 onset (+20 s) to steady state and described by the exponential time constant (tau) were compared with data collected from the same adults 9 years earlier. One-way repeated measures analysis of variance revealed that tau was slowed significantly with age (from 30 +/- 8 to 46 +/- 10 s), but was unaffected by hyperoxia (43 +/- 15 s). We concluded that: (1) in older adults studied longitudinally over a 9 year period, the on-transient VO2 kinetics are slowed, in agreement with, but to a greater extent, than from cross-sectional data; and (2) the phase 2 time constant (tau) for these older adults was not accelerated by hyperoxic breathing. Thus the expected hyperoxia-induced increase in the capacity for O2 transport was not associated with faster on-transient VO2 kinetics suggesting either that O2 transport may not limit VO2 kinetics during the 8th decade, or that O2 transport was not improved with hyperoxia.
authors.affiliation: Centre for Activity and Ageing, School of Kinesiology, University of Western Ontario, London, Canada.
authors.forename: C
authors.initials: C
authors.lastname: Bell
authors.forename: D H
authors.initials: DH
authors.lastname: Paterson
authors.forename: J M
authors.initials: JM
authors.lastname: Kowalchuk
authors.forename: D A
authors.initials: DA
authors.lastname: Cunningham
mesh_terms: D000368:Aged; D000375:Aging / Q000502:physiology*; D001642:Bicycling; D005080:Exercise Test; D005260:Female; D006801:Humans; D018496:Hyperoxia / Q000378:metabolism*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*
chemical_list: D010100:Oxygen