There are no equivalent experiment setups to create comparable changes of gravitation such as during parabolic flights. To determine the initial orthostatic responses of the cardiovascular system under the gravitational conditions of mars and moon is an essential step for a better understanding of 1) the fundamental functions of the human cardiovascular system (basic research) 2) specific impact of partial-g on the human heart, lungs and vessels in a spaceflight-context 3) approaches for countermeasure development against orthostatic intolerance on moon and mars (applied research).

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.

Inclusion Criteria:

• Healthy volunteers (men or women)
• Aged from 18 to 55
• Affiliated to a Social Security System
• Who accepted to take part in the study
• Who have given their written stated consent
• Who already participated in parabolic flights or performed a centrifuge run up to 4 G with head movements without occurrence of serious nausea or vomiting or cardiovascular discomfort.
• Who has passed a medical examination similar to a standard aviation medical examination for private pilot aptitude (JAR FCL3 Class 2 medical examination). There will be no additional test performed for subject selection.

Exclusion Criteria:

• Person who took part in a previous biomedical research protocol, of which exclusion period is not terminated
• Pregnant women
• Medication with beta blockers, ACE inhibitors, calcium channel blockers or diuretics.