Validation of a Non-Invasive Approach to Assess Muscular Oxygen Uptake Kinetics

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Introduction
In the exercise steady-state, pulmonary oxygen uptake (V’O2pulm) reflects the rate of oxygen consumed by the tissues (V’O2musc). However, during non-steady-state the dynamics of V’O2pulm are dissociated from V’O2musc. It is frequently assumed that the V’O2pulm kinetics are simply a time-shifted version of V’O2musc, with an early distortion due to the dynamics of cardiac output (CO) and venous return (cardio-dynamic phase). Therefore, we analyzed a range of V’O2musc, CO, and V’O2pulm kinetics to determine the ability to estimate V’O2musc kinetics from V’O2pulm.
Methods
Twenty simulations for V’O2musc- and CO-kinetics (time constants: 10-70s; 10-55s) were generated as mono-exponential responses to dynamic work rate changes between 30 and 80 W. Two models (Barstow et al. (1990; 5 data sets); Benson et al. (under review; 15 data sets)) were applied to generate computed V'O2pulm kinetics from known V'O2musc and CO dynamics, which account for the dynamics of venous transport and flow-weighted mixing from different vascular beds. Sample-to-sample noise was added to computed V’O2pulm responses, which was sampled at a typical breathing frequency for the exercise transient. Blinded estimation of the time constant for V’O2musc kinetics from V’O2pulm was based on the approach of Hoffmann et al. (2013). SPSS 21 was applied for statistical analysis (Spearman’s rho, Wilcoxon signed-rank test).Results
We found significant correlations between the time constants of actual (known) and predicted V’O2musc (r=0.913; p<0.01; N=20), and between actual V’O2musc and V’O2pulm (r=0.879; p<0.01; N=20). However, a significant difference was observed between the time constants of V’O2pulm (34.2 ± 14.3s) and actual V’O2musc (30.5 ± 15.2s; p<0.05; N=20), but not between actual and predicted V’O2musc (30.6 ± 14.6 s; p=0.709; N=20).DiscussionThe results show that significant differences can occur between muscular and pulmonary V’O2 kinetics during dynamic work rate changes. This is likely due to the influence of CO and venous return dynamics causing a transient non-linear distortion in O2 exchange between muscle and lung. Accounting for these distortions (Hoffmann et al., 2013) allows the time constants for V’O2musc to be recovered from pulmonary measurements with high validity. The study was funded by the DLR (Deutsches Zentrum für Luft- und Raumfahrt), Germany (FKZ 50WB0726); and the Biotechnology and Biological Sciences Research Council, UK (BB/I00162/X).

References
Barstow TJ, Lamarra N, Whipp BJ (1990) Modulation of muscle and pulmonary O2 uptakes by circulatory dynamics during exercise. J Appl Physiol 68:979–989

Benson, AP, Grassi, B, Rossiter, HB. (under review) A validated model of oxygen uptake and circulatory dynamic interactions at exercise onset in humans.

Hoffmann, U, Drescher, U, Benson, AP, Rossiter, HB, Essfeld, D (2013) Skeletal muscle V’O2 kinetics from cardio-pulmonary measurements: assessing distortions through O2 transport by means of stochastic work-rate signals and circulatory modelling. Eur J Appl Physiol DOI10.1007/s00421-013-2598-7
OriginalspracheEnglisch
Titel19th IAA Humans in Space : Linking the challenges of space exploration with medicine on Earth
Erscheinungsdatum09.07.2013
PublikationsstatusVeröffentlicht - 09.07.2013
VeranstaltungIAA Humans in Space - , Deutschland
Dauer: 01.01.1800 → …

ID: 255662

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