Long-duration Spaceflight Induces Atrophy in the Left Ventricular Papillary Muscles.

Abstract Microgravity exposure induces cardiac deconditioning, primarily due to hypovolemia and inactivity. Animal models suggest microgravity may cause left ventricular (LV) papillary muscle atrophy, but this has not been studied in humans. This study used MRI to assess LV papillary muscle mass and LV morphology and function in nine male cosmonauts before and 6 ± 2 days after long-duration spaceflight (247 ± 90 days). Spaceflight did not affect LV volumes and ejection fraction but increased heart rate (P < 0.001), cardiac output (P = 0.03), and longitudinal strain parameters. There was a 13.6% decrease in LV papillary muscle mass (P = 0.017) with a trend of increase in the LV mass, increased mitral annular diameter (P = 0.004) without mitral leakage, and increased LV sphericity (P = 0.02). These findings suggest LV adapts to space with geometric changes, but microgravity-induced papillary muscle atrophy requires further study for long-term implications.