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.
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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. "
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; DOI:10.1007/s00421-013-2599-6 · 2.30 Impact Factor
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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. "
ABSTRACT: This study aimed to examine if the faster pulmonary oxygen uptake (VO(2p) ) phase 2 in children could be explained by increased O (2) availability or extraction at the muscle level. For that purpose, O (2) availability and extraction were assessed using deoxyhemoglobin (HHb) estimated by near-infrared spectroscopy during moderate-intensity constant load cycling exercise in children and young adults. Eleven prepubertal boys and 12 men volunteered to participate in the study. They performed one maximal graded exercise to determine the power associated with the gas exchange threshold (GET) and four constant load exercises at 90% of GET. VO(2p) and HHb were continuously monitored. VO(2p) , HHb, and estimated capillary blood flow ( Q ˙ cap ) kinetics were modelled after a time delay and characterized by the time to achieve 63% of the amplitude (τ) and by mean response time (MRT: time delay + τ), respectively. Mean values of τ for VO(2p) (P < 0.001), of MRT for HHb (P < 0.01) and of MRT for Q ˙ cap (P < 0.001) were significantly shorter in children. Faster VO(2p) kinetics have been shown in children; these appear due to both faster O (2) extraction and delivery kinetics as indicated by faster HHb and Q ˙ cap kinetics, respectively.Scandinavian Journal of Medicine and Science in Sports 02/2012; 23(6). DOI:10.1111/j.1600-0838.2012.01446.x · 3.17 Impact Factor
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ABSTRACT: To investigate the association between oxygen uptake ((Equation is included in full-text article.)O2) kinetics and demographic, behavioral, and clinical factors among patients with peripheral artery disease (PAD). A total of 85 PAD patients with intermittent claudication performed a constant load treadmill test, and breath-by-breath (Equation is included in full-text article.)O2 was obtained to assess (Equation is included in full-text article.)O2 kinetics. Demographic information, anthropometry, cardiovascular risk factors, and comorbid conditions were recorded. Using univariate analyses, higher values of tau ([τ], ie, slowed (Equation is included in full-text article.)O2 kinetics) were associated with female gender, non-Caucasian race, hypertension, dyslipidemia, and age ≤66 years. Smoking, diabetes, obesity, metabolic syndrome, height, and ankle brachial index were not significantly related to (Equation is included in full-text article.)O2 kinetics. Using multiple regression procedures, the identified predictors of slowed (Equation is included in full-text article.)O2 kinetics were female gender (4.76 [95% CI: 1.49-8.03] seconds; P = .0049), non-Caucasian race (4.70 [95% CI: 1.29-8.12] seconds; P = .0075), hypertension (12.06 [95% CI: 8.83-15.28] seconds; P < .0001), and age ≤66 years (4.97 [95% CI: 1.95-7.99] seconds; P = .0015). In PAD patients, slowed (Equation is included in full-text article.)O2 kinetics are associated with demographic and clinical factors. The clinical significance is that female, non-Caucasian, and hypertensive PAD patients present central and/or peripheral limitations that may partially account for their walking impairment.Journal of cardiopulmonary rehabilitation and prevention 01/2013; 33(6):411-8. DOI:10.1097/HCR.0000000000000025 · 1.68 Impact Factor