Evaluation of changes in T-wave alternans induced by 60-days of immobilization by head-down bed-rest

Prolonged exposure to weightlessness is known to induce cardiovascular deconditioning. The aim of this work was to assess changes in T-wave alternans (TWA) induced by 60 days exposure to simulated microgravity using the -6° head-down bed-rest model (HDBR) and the potential effectiveness of a jump training countermeasure. We hypothesized that TWA could be able to reflect these changes, if they exist. Twenty-four healthy men were recruited at the German Aerospace Center (12 in control group, 12 with applied countermeasure), from which ECG signals were acquired before (PRE), at day 21 of HDBR (HDT21), before the end of HDBR (HDT57), and the day after its conclusion (POST). The index of average alternans (IAA), quantifying the average TWA amplitude, was computed using a fully automated algorithm based on periodic component analysis and the Laplacian likelihood ratio method. A significant increase in HR was found at HDT57 and POST compared to PRE. The IAA showed an increasing trend at POST (median (25th;75th percentile): 0.467(0.381;0.574) μV) compared to PRE (0.337(0.204;0.437) μV, p=0.18) only in the control group, although no significant differences along HDBR were found. In conclusion, long-term exposure to simulated microgravity did not induce significant alterations in electrical instability measured in terms of nocturnal TWA.