Changes in Instantaneous Complex Dynamics during Exercise in Chronic Mountain Sickness

The combination of persistent polycythemia with de- creased physical and cognitive performances while living in high-altitude is defined as ‘Chronic Mountain Sickness’ (CMS). To date, the role of the autonomic nervous sys- tem in CMS is still unknown. In this study, we analyze instantaneous tracking of cardiovascular complexity in or- der 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 re- covery session. Instantaneous Dominant Lyapunov expo- nents (IDLE), as estimated through point-process nonlin- ear models with Laguerre and Volterra expansions, were evaluated from such series. Results showed that instan- taneous heartbeat complex dynamics was significantly al- tered in CMS. In particular, IDLE increases were associ- ated 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.