Influence of simulated microgravity by head-down-bed-resting on QT/RR dynamics

There are evidences suggesting that spaceflight may be associated with increased susceptibility to ventricular dysrhythmias. To explore this hypothesis, five days -6° head-down bed rest (HDBR) was performed with the aim at testing the changes in QT/RR dynamics. Electrocardiogram signals (ECG) was acquired in 22 males during tilt-tests performed before and after HDBR. The dynamics of QT interval adaptation in response to upward and downward heart rate (HR) changes during the tilt test was evaluated modeling QT dependence on a history of previous RR intervals. The adaptation time of QT to abrupt changes in RR (t₉₀) was found reduced after HDBR, with no changes in the optimum regression residuum (r_opt) of the QT/RR dynamics. However, a dependence of the results to the width of the memory window considered was found. HDBR seems to induce variations in the phenomena by shortening the memory lag in QT/RR dependecy.