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.
- SourceAvailable from: Livio Zerbini[show abstract] [hide abstract]
ABSTRACT: The present study was designed to investigate whether absolute work rate (WR) affects Phase I pulmonary oxygen uptake (VO2p) duration during moderate-intensity (Mod) exercise, and to compare two methods for estimating Phase I VO2p duration (PI-Dur). Fourteen males (24±5 yrs) each completed 4-8 repetitions of Mod transitions from 20W to 50, 70, 90, 110 and 130W. PI-Dur was identified by: (1) a marked decrease in both respiratory exchange ratio and end-tidal partial pressure of O2 following exercise onset (i.e., visual inspection of 3 independent reviewers, and the average (Avg) of the two most similar values); or (2) the intersection (TD) of the first and second components in a bi-exponential non-linear regression of the entire VO2p response from exercise onset. PI-Dur did not differ amongst WRs (p>0.05), regardless of the estimation method used. No differences were detected between Avg and TD (time in s) at any of the five WRs (50W, 21±6 vs. 23±10; 70W, 23±9 vs. 23±7; 90W, 24±3 vs. 22±5; 110W, 23±6 vs. 22±6; 130W, 21±6 vs. 21±7 s; p>0.05 for Avg and TD, respectively). Broad limits of agreement within Bland-Altman plots revealed relatively weak agreement amongst reviewers for individual estimation of PI-Dur. A non-significant correlation coefficient (r=0.13) and broad limits of agreement suggest disparity between individual Avg and TD estimates of PI-Dur. The present data do not support a role for Mod WR in determining PI-Dur per se. Further, this study illustrated a poor agreement of PI-Dur estimates derived from two different, but accepted methods.AJP Regulatory Integrative and Comparative Physiology 12/2012; · 3.28 Impact Factor
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ABSTRACT: The adjustment of pulmonary oxygen uptake (VO2p), heart rate (HR), limb blood flow (LBF), and muscle deoxygenation [HHb] were examined during the transition to moderate-intensity, knee-extension exercise in six older adults (70 ± 4 years) under 2 conditions: normoxia (FIO2=20.9%) and hypoxia (FIO2=15%). The subjects performed repeated step transitions from an active baseline (3 W) to an absolute work rate (21 W) in both conditions. Phase 2 VO2p, HR, LBF, and [HHb] data were fit with an exponential model. Under hypoxic conditions, no change was observed in HR kinetics, on the other hand, LBF kinetics was faster (Norm, 34±3 sec; Hypo 28±2), whereas the overall [HHb] adjustment ( ) was slower (Norm, 28±2; Hypo 33±4 sec). Phase 2 VO2p kinetics were unchanged (p<0.05). The faster LBF kinetics and slower [HHb] kinetics reflect an improved matching between O2 delivery and O2 utilization at the microvascular level, preventing the phase 2 VO2p kinetics from become slower in hypoxia. Moreover the absolute blood flow values were higher in hypoxia (1.17 ± 0.2 l*min-1) compared to normoxia (0.96 ± 0.2 l*min-1) during the steady state exercise at 21 watts. These findings support the idea that, for older adults exercising at a low work rate, an increase of limb blood flow offsets the drop in arterial oxygen content (CaO2) caused by breathing an hypoxic mixture.Arbeitsphysiologie 01/2013; · 2.66 Impact Factor
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ABSTRACT: This study systematically examined the role of work rate (WR) increment on the kinetics of pulmonary oxygen uptake (VO(2p)) and near-infrared spectroscopy (NIRS)-derived muscle deoxygenation (Δ[HHb]) during moderate-intensity (Mod) cycling. Fourteen males (24 ± 5 years) each completed four to eight repetitions of Mod transitions from 20 to 50, 70, 90, 110 and 130 W. VO(2p) and Δ[HHb] responses were modelled as a mono-exponential; responses were then scaled to a relative % of the respective response (0-100 %). The Δ[HHb]/VO(2) ratio was calculated as the average Δ[HHb]/VO(2) during the 20-120 s period of the on-transient. When considered as a single group, neither the phase II VO(2p) time constant (τVO(2p); 27 ± 9, 26 ± 11, 25 ± 10, 27 ± 14, 29 ± 13 s for 50-130 W transitions, respectively) nor the Δ[HHb]/VO(2) ratio (1.04 ± 0.13, 1.10 ± 0.13, 1.08 ± 0.07, 1.09 ± 0.11, 1.09 ± 0.09, respectively) was affected by WR (p > 0.05); yet, the VO(2) functional gain (G; ΔVO(2)/ΔWR) increased with increasing WR transitions (8.6 ± 1.3, 9.1 ± 1.2, 9.5 ± 1.0, 9.5 ± 1.0, 9.9 ± 1.0 mL min(-1) W(-1); p < 0.05). When subjects were stratified into two groups [Fast (n = 6), τVO(2p130W) < 25 s < τVO(2p130W), Slower (n = 8)], a group by WR interaction was observed for τVO(2p). The increasing functional G persisted (p < 0.05) and did not differ between groups (p > 0.05). The Δ[HHb]/VO(2) ratio was smaller (p < 0.05) in the Fast than Slower group, but was unaffected by WR. In conclusion, the present study demonstrated (1) a non-uniform effect of Mod WR increment on τVO(2p); (2) that τVO(2p) in the Slower group is likely determined by an O(2) delivery limitation; and (3) that increasing Mod WR increments elicits an increased functional G, regardless of the τVO(2p) response.Arbeitsphysiologie 07/2012; · 2.66 Impact Factor