Heat and acute dehydration effects on acceleration response in man

Publisher Website
Google Scholar
Abstract
Though heat and dehydration each impair acceleration tolerance, interactions among these stresses were not previously studied. Seven men were dehydrated in heat by 0, 1, and 3% of body weight before a series of +Gz, gradual-onset centrifuge runs with the capsule first 38.degree. C, then 20.degree. C. Heat alone raised heart rate [HR] by 6.5 beats/min independent of other stresses. Dehydration and acceleration appeared to act synergistically in raising HR. Heat lowered relaxed g tolerance by 0.3 g; dehydration tended to lower g tolerance and increased the variability of response to heat. A high-tolerance subgroup (n = 4) could normally sustain +7 Gz for 60 s with anti-g suit and straining, but 3% dehydration reduced mean time to 35 s. Dehydration was associated with a decrease in the loss of plasma volume at 7 g. Heat-induced tolerance loss appears similar for both gradual- and rapid-onset centrifuge profiles. Dehydration effects are greater in rapid-onset runs, evidence that normal anti-g protective mechanisms can partly counteract the effect of fluid deficit. The results are relevant for crew members of high-performance aircraft, where unexpected diminution of their normally high g tolerance can have disastrous consequences.

This publication has 1 reference indexed in Scilit: