| Autor: |
Love LK; Canadian Centre for Activity and Aging, The University of Western Ontario, London, Ontario, Canada.; School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada.; Department of Kinesiology and Physical Education, Redeemer University, Ancaster, Ontario, Canada., Hodgson MD; Canadian Centre for Activity and Aging, The University of Western Ontario, London, Ontario, Canada.; School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada., Keir DA; Canadian Centre for Activity and Aging, The University of Western Ontario, London, Ontario, Canada.; School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada.; Toronto General Research Institute, Toronto General Hospital, Toronto, Ontario, Canada., Kowalchuk JM; Canadian Centre for Activity and Aging, The University of Western Ontario, London, Ontario, Canada.; School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada.; Department of Kinesiology and Physical Education, Redeemer University, Ancaster, Ontario, Canada. |
| Abstrakt: |
A step-transition in external work rate (WR) increases pulmonary O 2 uptake (V̇o 2p ) in a monoexponential fashion. Although the rate of this increase, quantified by the time constant (τ), has frequently been shown to be similar between multiple different WR amplitudes (ΔWR), the adjustment of O 2 delivery to the muscle (via blood flow; BF), a potential regulator of V̇o 2p kinetics, has not been extensively studied. To investigate the role of BF on V̇o 2p kinetics, 10 participants performed step-transitions on a knee-extension ergometer from a common baseline WR (3 W) to: 24, 33, 45, 54, and 66 W. Each transition lasted 8 min and was repeated four to six times. Volume turbinometry and mass spectrometry, Doppler ultrasound, and near-infrared spectroscopy were used to measure V̇o 2p , BF, and muscle deoxygenation (deoxy[Hb + Mb]), respectively. Similar transitions were ensemble-averaged, and phase II V̇o 2p , BF, and deoxy[Hb + Mb] were fit with a monoexponential nonlinear least squares regression equation. With increasing ΔWR, τV̇o 2p became larger at the higher ΔWRs ( P < 0.05), while τBF did not change significantly, and the mean response time (MRT) of deoxy[Hb + Mb] became smaller. These findings that V̇o 2p kinetics become slower with increasing ΔWR, while BF kinetics are not influenced by ΔWR, suggest that O 2 delivery could not limit V̇o 2p in this situation. However, the speeding of deoxy[Hb + Mb] kinetics with increasing ΔWR does imply that the O 2 delivery-to-O 2 utilization of the microvasculature decreases at higher ΔWRs. This suggests that the contribution of O 2 delivery and O 2 extraction to V̇O 2 in the muscle changes with increasing ΔWR. NEW & NOTEWORTHY A step increase in work rate produces a monoexponential increase in V̇o 2p and blood flow to a new steady-state. We found that step transitions from a common metabolic baseline to increasing work rate amplitudes produced a slowing of V̇o 2p kinetics, no change in blood flow kinetics, and a speeding of muscle deoxygenation kinetics. As work rate amplitude increased, the ratio of blood flow to V̇o 2p became smaller, while the amplitude of muscle deoxygenation became greater. The gain in vascular conductance became smaller, while kinetics tended to become slower at higher work rate amplitudes. |
