Mitral and aortic flow adaptation to 58-days head-down bed-rest assessed by PC-MRI, and effectiveness of high-intensity jump training countermeasure

Abstract

Aims: Prolonged immobilization generates cardiac deconditioning, a cardiovascular disease risk factor, and efficient countermeasures (CM) are needed to prevent it. We aimed to assess by Phase-Contrast (PC) MRI the effects of long-term strict head-down (-6 degrees) bed-rest (BR) deconditioning and the effectiveness of high-intensity jump training CM on aortic and mitral flow. Methods: 23 males (29±6 years, 181±6 cm, 77±7 kg) were enrolled. The experiment was conducted at Envihab research facility as part of the European Space Agency BR studies. Participants were randomly allocated to the jump training group (JUMP, n=12) or to the control group (CTRL, n=11). A typical training session consisted of 4x10 countermovement jumps and 2x10 hops in a horizontal sledge jump system, with 5–6 sessions/week. PC-MRI images (3T Biograph mMR) with interleaved 3-directional velocity encoding (VENC: x and y: 80 cm/s; z: 150 cm/s) were obtained (spatial resolution 1.4x1.4 mm2) at the level of the aortic root, and of the mitral plane, before (PRE) and after 58-days (HDT58) of BR. The resulting planar magnitude data and 3-directional velocity images were semi-automatically analysed with previously validated custom software to compute the following parameters: cardiac output (CO), stroke volume (SV), flow rate (Qpeak), systolic duration (Sys) and heart beat duration (RR), rapid filling (Efill) and inflow rate (Epeak). Results: In CTRL, compared to baseline values, at HDT58 a significant (p<.05, paired t-test) RR (14%) and systolic (10%) shortening, with a decrease in CO (8%), SV (22%), Qpeak (12%), Efilling (26%), Epeak (26%) were observed. In CM, only RR was shortened (8%), together with a decrease in SV (12%), Qpeak (7.5%), Efilling (11%), Epeak (15%).