$\dot{V}$O₂ and HR kinetics before and after International Space Station missions

Abstract

Purpose

Heart rate (HR), pulmonary and muscle oxygen uptake ($\dot{V}$O₂pulm, $\dot{V}$O₂musc) kinetics after changes of work rate (WR) indicate regulatory characteristics related to aerobic metabolism. We analysed whether the kinetics of HR, $\dot{V}$O₂pulm and $\dot{V}$O₂musc are slowed after missions to the International Space Station (ISS). The changes of the kinetics were correlated with $\dot{V}$O₂peak data.

Methods

10 astronauts [4 females, 6 males, age: 48.0 ± 3.8 years, height: 176 ± 7 cm, mass: 74.5 ± 15.9 kg (mean ± SD)] performed an incremental test to determine $\dot{V}$O₂peak (before missions on L-110 days, after return on R+1/+10/+36 days), and a cardio-respiratory kinetics test (CRKT) with randomized 30–80 W WR changes to determine HR, $\dot{V}$O₂pulm and $\dot{V}$O₂musc kinetics by time-series analysis (L-236/-73, R+6/+21). Kinetics were summarized by maximum and related lag of cross-correlation function (CCF_max, CCF_lag) of WR with the analysed parameter.

Results

Statistically, significant changes were also found for CCF_max($\dot{V}$O₂musc) between L-236 and R+6 (P = 0.010), L-236 and R+21 (P = 0.030), L-72 and R+6 (P = 0.043). Between pre-to-post mission change in $\dot{V}$O₂peak and CCF_max(HR), a correlation was shown (r _SP = 0.67, P = 0.017).

Conclusion

The $\dot{V}$O₂musc kinetics changes indicate aerobic detraining effects which are present up to 21 days following space flight. The correlations between changes in $\dot{V}$O₂peak and HR kinetics illustrate the key role of cardiovascular regulation in $\dot{V}$O₂peak. The addition of CRKT to ISS flight is recommended to obtain information regarding the potential muscular and cardiovascular deconditioning. This allows a reduction in the frequency of higher intensity testing during flight.