Analysis of temporal and disortive dissociations between muscle and pulmonary oxygen uptake kinetics during dynamic exercise: theoretical considerations and practical applications

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Oxygen uptake (_O2) is a key parameter representing the performance of the aerobic metabolism. The analysis of the _O2 kinetics can be described with the help of a holistic approach that includes various aspects of physiological performance, its description and regulation for given internal (e.g., muscular fitness) and external (e.g., ambient temperature) factors.
However, the approaches used to infer muscle _O2 (_O2musc) kinetics derived using pulmonary _O2 (_O2pulm) measurements at the mouth should be taken with caution (e.g., STEP approach). Due to the time-delaying and distortive impacts of the circulatorysystem(e.g.,venousreturn,cardiacoutput[ ]dynamics),itisoftenunclear in which way _O2pulm kinetics is distorted. It is therefore necessary to adequately consider the temporal and distorting effects of venous return and dynamics between the _O2musc and _O2pulm kinetics by showing these influences on the resulting _O2pulm. This is possible for instance by the theoretical (in silico) and practical (in vivo) application of circulation models with dynamic work rate (WR) protocols (PRBS approach).
The aim of the present work is to (a) evaluate the theoretical effect of venous return and dynamics on the dissociation between _O2musc and _O2pulm kinetics, (b) examine the practical application of _O2 kinetics analysis in the field of exercise physiology, sports science, and medicine, and (c) to provide an overview of additional and potential relevant fields of application. The results can be summarized as follows, which have already been published:
(1) In silico and in vivo studies, such as re-analyses have been performed to illustrate the apparent distortion and temporal dissociation between _O2musc and _O2pulm kinetics.
(2) It was shown that _O2pulm kinetics is affected by venous return alterations based on different body positions (75°, 45°, -6°). In addition, it was demonstrated that the assessment of _O2musc and the measurement of heart rate kinetics are not influenced by different body positions.
(3) Comparing the more-common STEP approach with the novel PRBS approach to infer _O2musc kinetics results in no significant differences, but high deviations were observed. This impairs the predictability between the approaches.
(4) It was confirmed that the kinetic responses of _O2pulm and _O2musc are not significantly different when applying two different PRBS WR amplitudes with the same baseline WR in the moderate exercise intensity domain.

(5) The evaluation of upper- and lower-body exercise tolerance illustrated that significant differences should be assumed for _O2musc kinetics between the exercise modalities, which are lost in the _O2pulm kinetic response. In addition, at maximum isokinetic (concentric-eccentric) loads between upper-body (arm) and lower-body (leg) exercise, the time points of the highest arteriovenous oxygen concentration differences (avDO2) could be shown to differ significantly between arm and leg in the recovery phases.
(6) Exercise interventions (six weeks), comprising continuous and interval endurance training, showed no advantage for the speeding of the cardiorespiratory kinetics. However, a tendency for an interaction effect could be identified, assuming that interval training may speed _O2musc kinetics.
(7) Exposure at different acute ambient temperatures (15°C, 25°C, and 35°C), applied in a climatic chamber, demonstrated no impact on _O2pulm and _O2musc kinetics.
(8) Before and after prolonged weightlessness exposure on the International Space Station, _O2musc kinetics slow, accompanied by significant reductions in peak _O2, illustrating a certain coupling of the capacitive and regulatory systems of the cardiorespiratory system.
The differentiation between _O2musc and _O2pulm kinetics demonstrates that venous return and dynamics have, to a great extent, an unpredictable impact on the resultant _O2pulm. This in turn, reinforces the temporal and distortive dissociation between _O2musc and _O2pulm kinetics, which may lead to a variety interpretations, if _O2pulm is assumed, as an entire or partial response, to be a direct substitute for _O2musc kinetics. Consequently, and venous return should in general be considered whenever _O2 kinetics is analyzed or discussed.
For the future, the opportunity for other potential applications is great, and can be beneficial for the interpretation of other (physiological) variables. For instance, understanding arterial blood pressure dynamics is of interest with regards to those suffering from arterial hypertension. Additionally, application during a potential Moon or Mars mission could be a future possible use of the PRBS approach. This application could include the PRBS WR protocol, which can be used as an interval training method to maintain and improve cardiorespiratory and mental performance in long-term weightlessness exposures.
Original languageGerman
Place of PublicationKöln
PublisherDeutsche Sporthochschule Köln
Number of pages47
Publication statusPublished - 2018

ID: 5268016

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