[Long-term G loads (+Gz) and the prediction of their tolerance]

The impacts of comparatively low (1.5-3 G) though prolonged (up to 40 min) "head-pelvis" (+Gz) accelerations at the final and most challenging stage of space flight, i.e. the approach to landing site, are numbered among the extreme factors discomforting the flights on board advanced spacecraft. Specificity of the effects of prolonged g-loads and the ways to predict their tolerance are still little known. 52 flyers aged 24-42 were centrifuged at 3.0 g for 15 min with rise gradient 0.2 g/s. 23.3% of test-subjects developed a set of deadaptive disorders including a critical decrease of arterial pressure in the ear lobe leading to precollapsing state (9.6%), stable relative bradycardia with concurrent manifestations of autonomous nervous reactions (5.8%), apparent (up to 170 beats/min) sine tachycardia (7.9%). This syndrome was generally exhibited by subjects with autonomous-vascular instability. All members of the group of healthy subjects showed good tolerance of prolonged (15 min) accelerations. In addition to centrifuge runs, 52 subjects were exposed to the lower body negative pressure test (-50 mm Hg, up to 15 min) in the sitting position. Similar to g-load test, the worst decompression tolerance was observed in flyers with autonomous-vascular instability. The mean tolerance time in these subjects made 7.9 +/- 0.7 min, while in healthy subject it amounted to 14.0 +/- 0.6 min (p < 0.01). The most convincing correlation between decompression tolerance and prolonged g-loads was established at 10 min of decompression (Pearson factor Ra = 0.51).(ABSTRACT TRUNCATED AT 250 WORDS)