Projet de recherche BL/C/38 (Action de recherche BL)
1/1/2005-31/12/2007
Context and objectives
Microgravity is a unique environment that challenges human adaptive responses, especially with respect to the cardiovascular system. In microgravity conditions, body fluid hydrostatic pressure gradients will change and as a result blood will pool in the thorax and blood volume will decrease. This will influence venous return and as a result changes in autonomic modulation of the cardiovascular system can be expected. All these symptoms result in cardiovascular deconditioning. One of its manifestations is post-flight orthostatic intolerance and is a current operational problem for all astronauts.
The project aims to evaluate the relative role of the autonomic nervous system in cardiovascular deconditioning during astronaut training and after weightlessness. The goal is to better understand the detailed mechanism leading to cardiovascular deconditioning and especially to orthostatic intolerance, and to evaluate the potential role of autonomic alterations.
Recent evidence implicates post-flight autonomic dysfunction as a contributor to orthostatic intolerance. The autonomic nervous system is studied during specific tests (tilt test, breathing at fixed rate, head flexion) using heart rate variability (HRV) tools, with linear and non-linear methods.
The project should contribute to a better understanding of the cardiovascular impairment in a selected group and induced by weightlessness and study the influence of race and further help to develop new countermeasures.
Methodology
Respiration (an important modulator of HRV) is monitored continuously.
ECG electrodes are applied to the chest wall.
Continuous blood pressure is determined (Portapres) with a non-invasive pulse method at the finger and conversed to brachial blood pressure Modelflow® is be used to derive blood flow from the continuous arterial blood pressure curves. Although this method might not give accurate absolute values of blood flow, it is well-suited for providing relative changes. All analysis will be performed off-line. After peak detection, the RR interval file (tachogram) and a systogram are created that can be processed. Analysis of HRV, BPV and baroreflex will be performed to determine cardiac vagal and sympathetic and vasomotor sympathetic modulation..
