CARDIOVASCULAR RESPONSE TO LOW BODY NEGATIVE PRESSURE ABOARD MIR SPACE STATION
After spaceflight cosmonauts often experiment orthostatic intolerance with tachycardia, hypotension and occasionally syncope in standing position. These are the results of cardiovascular deconditioning. With alterations of heart rate variability and spontaneous baroreflex sensitivity, the autonomic control of cardiovascular system is suspected to be changed by real and simulated weightlessness. However, these alterations could also reflect the changes in heart rate and in blood volume observed during spaceflights. Lower Body Negative Pressure (LBNP) was a common method used for medical checks of the cosmonauts and training for return to gravity aboard Mir space station. LBNP mimics cardiovascular orthostatic adaptation with several levels of stimulation. In this study we hypothesized that long term spaceflight alters the cardiovascular responses to LBNP. Changes of RR-interval (RRI) and systolic blood pressure (SBP) in response to LBNP were mainly observed at low level of stimulation (-25 mmHg). During stimulation by LBNP in flight, RRI tended to decrease significantly (p<005) and SBP tended to increase (p<0.05). These results emphasize the conclusion that weightlessness induces changes of sensitivity to blood volume (low pressure baroreceptors).