title: Influence of phase I duration on phase II VO2 kinetics parameter estimates in older and young adults.
abstract: Older adults (O) may have a longer phase I pulmonary O(2) uptake kinetics (Vo(2)(p)) than young adults (Y); this may affect parameter estimates of phase II Vo(2)(p). Therefore, we sought to: 1) experimentally estimate the duration of phase I Vo(2)(p) (EE phase I) in O and Y subjects during moderate-intensity exercise transitions; 2) examine the effects of selected phase I durations (i.e., different start times for modeling phase II) on parameter estimates of the phase II Vo(2)(p) response; and 3) thereby determine whether slower phase II kinetics in O subjects represent a physiological difference or a by-product of fitting strategy. Vo(2)(p) was measured breath-by-breath in 19 O (68 ± 6 yr; mean ± SD) and 19 Y (24 ± 5 yr) using a volume turbine and mass spectrometer. Phase I Vo(2)(p) was longer in O (31 ± 4 s) than Y (20 ± 7 s) (P < 0.05). In O, phase II τVo(2)(p) was larger (P < 0.05) when fitting started at 15 s (49 ± 12 s) compared with fits starting at the individual EE phase I (43 ± 12 s), 25 s (42 ± 10 s), 35 s (42 ± 12 s), and 45 s (45 ± 15 s). In Y, τVo(2)(p) was not affected by the time at which phase II Vo(2)(p) fitting started (τVo(2)(p) = 31 ± 7 s, 29 ± 9 s, 30 ± 10 s, 32 ± 11 s, and 30 ± 8 s for fittings starting at 15 s, 25 s, 35 s, 45 s, and EE phase I, respectively). Fitting from EE phase I, 25 s, or 35 s resulted in the smallest CI τVo(2)(p) in both O and Y. Thus, fitting phase II Vo(2)(p) from (but not constrained to) 25 s or 35 s provides consistent estimates of Vo(2)(p) kinetics parameters in Y and O, despite the longer phase I Vo(2)(p) in O.
authors.affiliation: School of Kinesiology, University of Western Ontario, London, Ontario, Canada N6A 3K7.
authors.forename: Juan M
authors.initials: JM
authors.lastname: Murias
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Spencer
authors.forename: John M
authors.initials: JM
authors.lastname: Kowalchuk
authors.forename: Donald H
authors.initials: DH
authors.lastname: Paterson
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008168:Lung / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange; D015656:Respiratory Mechanics / Q000502:physiology*; D013997:Time Factors
chemical_list: D010100:Oxygen