Objective: Normobaric (NH) and hypobaric hypoxia (HH) are associated with acute mountain sickness (AMS) and cognitive dysfunction. Only few variables, like heart-rate-variability, are correlated with AMS. However, prediction of AMS remains difficult. We therefore designed an expedition-study with healthy volunteers in NH/HH to investigate additional non-invasive hemodynamic variables associated with AMS.Methods: Eleven healthy subjects were examined in NH (FiO(2) 13.1%;equivalent of 3.883m a.s.l;duration 4h) and HH (3.883ma.s.l.;duration 24h) before and after an exercise of 120min. Changes in parameters of electrical cardiometry (cardiac index (CI), left-ventricular ejection time (LVET), stroke volume (SV), index of contractility (ICON)), near-infrared spectroscopy (cerebral oxygenation, rScO(2)), Lake-Louise-Score (LLS) and cognitive function tests were assessed. One-Way-ANOVA, Wilcoxon matched-pairs test, Spearman's-correlation-analysis and Student's t-test were performed.Results: HH increased heart rate (HR), mean arterial pressure (MAP) and CI and decreased LVET, SV and ICON, whereas NH increased HR and decreased LVET. In both NH and HH cerebral oxygenation decreased and LLS increased significantly. After 24h in HH, 6 of 11 subjects (54.6%) developed AMS. LLS remained increased until 24h in HH, whereas cognitive function remained unaltered. In HH, HR and LLS were inversely correlated (r=-0.692;p<0.05). More importantly, the rScO2-decrease after exercise in NH significantly correlated with LLS after 24h in HH (r=-0.971;p<0.01) and rScO2 correlated significantly with HR (r=0.802;p<0.01), CI (r=0.682;p<0.05) and SV (r=0.709;p<0.05) after exercise in HH.Conclusion: sBoth acute NH and HH altered hemodynamic and cerebral oxygenation and induced AMS. Subjects, who adapted their CI had higher rScO2 and lower LLS. Furthermore, rScO2 after exercise under normobaric conditions was associated with AMS at high altitudes.