Non-invasive measurement methods will be used to achieve the cardiovascular key values of the study: stroke volume (SV) and cardiac output determination by pulse contour analysis, impedance cardiography and inert gas rebreathing, beat-to-beat finger blood pressure measurement, heart rate and heart rate variability determination by ECG. All of these methods have proven their accuracy during parabolic flights. Nevertheless pulse contour analysis and impedance cardiography are known to provide only relative SV and CO values. Thus inert gas rebreathing gives us the possibility to calibrate these stroke volumes and cardiac outputs to absolute values. Success of this procedure was shown during former parabolic flights.