Cardiorespiratory regulation in response to exercise - First results from HERA C4

摘要

Cardiorespiratory kinetics are slowed in astronauts, returning from six month missions on-board the International Space Station (ISS). Many factors influence cardiorespiratory kinetics on-board the ISS. Some of these factors were controlled inside the Human Exploration Research Analog (HERA) facility: The effects of 45 d of confinement in combination with restrictions for sleep and physical training on muscular oxygen uptake (V'O_(2musc)) kinetics and cardiovascular regulation during exercise were investigated. To date, ten healthy individuals (3 females, 7 males, 38±7 y, 24±4 kg.m~(-2)) were analysed 8 d before the mission (MD-8), on mission day 22 (MD22), mission day 42 (MD42) and 4 d after (MD+4) a simulated mission to an asteroid. At all test days a cycle exercise test with changing work rates (WR) of 30 and 80 W was completed. On MD-8 and MD+4 a step protocol to assess peak oxygen uptake (V'O_(2peak)) was added. Heart rate (HR) and mean arterial blood pressure (MAP) were measured beat-to-beat and pulmonary oxygen uptake (V'O_(2pulm)) breath-by-breath. V'O_(2musc) was estimated from HR and V'O_(2pulm). Kinetics responses were calculated using time series analysis: Higher maxima of the cross correlation function (CCF_(max)) between WR and the respective parameter indicate faster kinetics. During the mission, exercise training sessions were restricted to every second day with a HR below 85% of the age-related maximum. Sleep was restricted to 5h per weekday and 8h at the weekends. Statistical analyses of the kinetics parameters (V'O_(2musc), V'O2pulm) were performed by means of repeated measures ANOVA (MD-8, MD22, MD42, MD+4) and the Friedman-test (MAP, HR). V'O_(2peak) was compared using a t-test. HR kinetics did not change significantly throughout the mission (MD-8 vs. MD22 vs. MD42 vs. MD+4; mean ± standard deviation [a.u.]: 0.31±0.14 vs. 0.34+0.07 vs. 0.38+0.13 vs. 0.31+0.07; p=0.373) just as V'O_(2pulm) (0.35+0.14 vs. 0.33+0.08 vs. 0.31+0.07 vs. 0.30+0.04;