LARGE ARTERY FUNCTION AND VENTRICULAR ARTERIAL COUPLING FOLLOWING CARDIOVASCULAR UNLOADING RELATED TO PROLONGED BED REST IN YOUNG HEALTHY SUBJECTS: PP.31.218

Abstract

Background: prolonged head-down tilt bed rest (HDTBR) is followed by a decrease in circulating volume possibly affecting large artery structure and function. Aim of the study was to investigate common carotid artery (CCA) remodelling and ventricular-arterial (VA) coupling after HDTBR. Methods: ten healthy male volunteers (age 23 ± 2) were studied before and after a 35-day HDTBR. Ultrasound (Esaote MyLab30) was used to estimate LV volumes, transmitral and aortic flow velocity (FV), CCA diameter and FV, high resolution IMT (Q-IMT). Applanation tonometry (PulsePen, DiaTecne), was used to explore large artery dynamics and wave reflection (WR). Carotid-femoral pulse wave velocity (PWV) was also estimated (Complior, Alam). Results: no changes were observed for central BP vs baseline, while LV volumes and stroke volume significantly decreased and HR increased (from 58 ± 2 to 73 ± 6, p < 0.05). Myocardial performance index (MPI), a Doppler derived index of global LV function [isovolumic contraction time+isovolumic relaxation time)/LV ejection time], increased after HDTBR (0.71 ± 0.12 vs 0.52 ± 0.06, p < 0.005), as well as arterial elastance (Ea = end systolic pressure/stroke volume) and LV elastance [Elv = end systolic pressure (ESP)/end systolic volume (ESV)] (for Ea: 1.08 ± 0.198 vs 1.31 ± 0.21, p = 0.01; for Elv 1.478 ± 0.32 vs 1.765 ± 0.42, p = 0.04), with unchanged Ea/Elv (0.74 ± 0.09 vs 0.76 ± 0.1). PWV, CCA diameter, systolic FV and QIMT did not change, while diastolic and mean FV significantly increased (p < 0.05: FVd from 25 ± 4 to 29 ± 4 cm/s, FVm from 42 ± 8 to 52 ± 11 cm/s). Pulsatility index [PI = (peak systolic velocity-diastolic velocity)/Mean velocity] decreased from 2.3 ± 0.3 to 1.9 ± 0.2, p < 0.02). Applanation tonometry showed no significant changes for Augmentation Index (AIx) and time to WR, while PPI (Pulse Pressure Index: PP/MBP) decreased from 0.55 ± 0.14 to 0.45 ± 0.09, p < 0.05). Conclusions: after prolonged HDTBR, a reduction in LV pump function is observed with unchanged VA coupling. No significant changes are found in intrinsic arterial stiffness, CCA remodelling and WR, while changes in arterial dynamics indicate a reduction in the pulsatile component and an increase in the steady component of BP, possibly associated with reduced circulating volume and increased peripheral vasodilation.