Influence of phase I duration on phase II VO2 kinetics parameter estimates in older and young adults.

School of Kinesiology, University of Western Ontario, London, Ontario, Canada N6A 3K7.
AJP Regulatory Integrative and Comparative Physiology (Impact Factor: 3.53). 04/2011; 301(1):R218-24. DOI: 10.1152/ajpregu.00060.2011
Source: PubMed

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.

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    • "LBF and HR were fit from the first data point after the start of the exercise transient until the end of the exercise bout. On the other hand, the initial 20 s of VO 2p data was excluded to avoid inclusion of data points from Phase 1 VO 2p in the fitting of Phase 2 VO 2p (Murias et al. 2011b). Moreover, the TD was allowed to vary freely to optimize the accuracy of the estimated parameters. "
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    • "In the present study, the MRT values for Q cap were close to the t values for VO 2p in children and adults and suggest that O 2 delivery was a determinant of VO 2p adjustment. These data bear similarity to a recent study by Murias et al. (2011) indicating that adaptation of VO 2p kinetics may be constrained by O 2 availability. "
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