Changes in instantaneous complex dynamics during exercise in Chronic Mountain Sickness

The combination of persistent polycythemia with decreased physical and cognitive performances while living in high-altitude is defined as `Chronic Mountain Sickness´ (CMS). To date, the role of the autonomic nervous system in CMS is still unknown. In this study, we analyze instantaneous tracking of cardiovascular complexity in order to increase the knowledge on CMS physio-pathology. To this extent, we processed heartbeat dynamics gathered from 13 CMS males and 7 high-altitude male dwellers, taken as healthy controls (HC), during semi-supine bicycle tasks performed at 25W, 50W, and 100W, along with a recovery session. Instantaneous Dominant Lyapunov exponents (IDLE), as estimated through point-process nonlinear models with Laguerre and Volterra expansions, were evaluated from such series. Results showed that instantaneous heartbeat complex dynamics was significantly altered in CMS. In particular, IDLE increases were associated to CMS, with respect to HC, during the 25W and 50W exercise sessions (p <; 0.01). Conversely, no statistical differences were found when analyzing the 100W session, and first recovery after exercise.