Changes in the autonomic reactivity pattern to psychological load under long-term microgravity--twelve men during...

A complex psychophysiological test battery was applied to twelve subjects during long-term spaceflights. This experiment was designed to assess the psychophysiological reactivity to acute psychological stressors. A set of noninvasive physiological measurements (electrocardiogram, electromyogram, blood pressure, skin conductance, peripheral skin temperature) was used to describe the reactivity of the autonomic nervous system and the cardiovascular system to an induced series of changes between mental activity load and quiet relaxation. It could be shown that under space conditions the subjects react differently than on earth. On the basis of significantly lower heart rates we concluded that an extended parasympathetic cardial influence is present during later periods of long-term space flights. The peripheral skin conductance reactivity, however, indicated a tendency to higher peripheral sympathetic tonus under microgravity. Assuming individually different pathways of sympathetic-parasympathetic traffic under psychological stress, the whole set of data could be classified into autonomic outlet types (AOT) based on clinical reference data. Most of the subjects changed their AOT during flight. After flight the subjects eventually fell back into their pre-flight patterns, but seven of twelve subjects showed a significantly different autonomic system reactivity at least once after landing that was similar to that of hypertensive patients, indicating an extended sympathetic overshoot directly post-flight. In conclusion it is assumed that sympathetic effects in one measurement do not exclude less sympathetic or even parasympathetic effects in others during adaptation to extreme environments.