Effects of exercise countermeasure on myocardial contractility measured by 4D speckle tracking during a 21-day head-down bed rest

Objective: To evaluate functional myocardial contractility after 21 days of head-down bed rest (HDBR) in sedentary control (CON) or with a resistive vibration exercise (RVE) countermeasure (CM) applied, by using 4D echocardiographic (4D echo) imaging and speckle tracking strain quantification.

Methods: Twelve volunteers were enrolled in a crossover HDBR design, and 4D echo was performed in supine position (REST) at BDC-2 and at R + 2, and in - 6° HDT at day 18, and during the first and the last minute of the 80° head-up step of tilt test performed at both BDC-2 and R + 2. Radial (Rad-Str), longitudinal (Lg-Str) and twist (Tw-Str) strains were measured by 4D speckle tracking, as well as left ventricle diastolic volume (LVDV) and mass (LVmass).

Results: On HDT 18: in the CON group, LVDV and LVmass were reduced (p < 0.05), the Rad-Str decreased (p < 0.05) and Tw-Str showed a tendency to increase (p < 0.11), with no changes in Lg-Str. In RVE group, LVDV and LV mass, as well as all the strain parameters remained unchanged. On R + 2: in the CON group, LVDV and LVmass were not recovered in all subjects compared to pre-HDBR (p < 0.08) and Rad-Str was still decreased (p < 0.05), while Tw-Str tended to increase (p < 0.09). These parameters remained unchanged in the RVE group. Tilt 80°: Rad-Str and Lg-Str values at 80° tilt were similar post-HDT in both groups.

Conclusion: The 4D echo and speckle tracking analysis showed that in the CON group, Rad-Str decreased concomitant with LVmass and LVDV with HDBR, but this observation did not allow concluding if HDBR induced a real remodeling or a muscle atrophy. RVE was able to preserve LVmass, LVDV and contractility during HDBR, thus proving its effectiveness to this aim. Nevertheless, the significant HDBR-induced changes observed in the CON group had only a limited effect on the cardiac contractile response as observed during post-HDBR tilt test. The level of contractility at 80° Tilt position was not affected either by HDBR or by RVE CM.