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Erschienen in:
26.06.2018 | Original Article
Impact of 60 days of 6° head down tilt bed rest on muscular oxygen uptake and heart rate kinetics: efficacy of a reactive sledge jump countermeasure
Erschienen in: European Journal of Applied Physiology | Ausgabe 9/2018
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Purpose
The effects of 60 days of head down tilt bed rest (HDBR) with and without the application of a reactive jump countermeasure were investigated, using a method which enables to discriminate between pulmonary (\(\dot{\text{V}}\)O2pulm) and muscular (\(\dot{\text{V}}\)O2musc) oxygen uptake kinetics to control for hemodynamic influences.
Methods
22 subjects were randomly allocated to either a group performing a reactive jumps countermeasure (JUMP; n = 11, male, 29 ± 7 years, 23.9 ± 1.3 kg m− 2) or a control group (CTRL; n = 11, male, 29 ± 6 years, 23.3 ± 2.0 kg m− 2). Heart rate (HR) and \(\dot{\text{V}}\)O2pulm were measured in response to repeated changes in work rate between 30 and 80 W before (BDC-9) and two times after HDBR (R+ 2, R+ 13). Kinetic responses of HR, \(\dot{\text{V}}\)O2pulm, and \(\dot{\text{V}}\)O2musc were assessed applying time series analysis. Higher maxima in cross-correlation functions (CCFmax(x)) between work rate and the respective parameter indicate faster kinetics responses. Statistical analysis was performed applying multifactorial analysis of variance.
Results
CCFmax(\(\dot{\text{V}}\)O2musc) and CCFmax(\(\dot{\text{V}}\)O2pulm) were not significantly different before and after HDBR (P > 0.05). CCFmax(HR) decreased following bed rest (JUMP: BDC-9: 0.30 ± 0.09 vs. R+ 2: 0.28 ± 0.06 vs. R+13: 0.28 ± 0.07; CTRL: 0.35 ± 0.09 vs. 0.27 ± 0.06 vs. 0.33 ± 0.07 P = 0.025). No significant differences between the groups were observed (P > 0.05). Significant alterations were found for CCFmax of mean arterial blood pressure (mBP) after HDBR (JUMP: BDC-9: 0.21 ± 0.07 vs. R+ 2: 0.30 ± 0.13 vs. R+ 13: 0.28 ± 0.08; CTRL: 0.25 ± 0.07 vs. 0.38 ± 0.13 vs. 0.28 ± 0.08; P = 0.008).
Conclusions
Despite hemodynamic changes, \(\dot{\text{V}}\)O2 kinetics seem to be preserved for a longer period of HDBR, even without the application of a countermeasure.