Physiological biochemical, and performance responses to a 24-hour crash diet.

Twelve overweight male subjects were evaluated on both a normal diet and a 24-h crash diet. During approximately 2 1/4-h complex performance tests subjects breathed an O2/N2 mixture equivalent to 3810 m. (12,500 ft). There were no significant findings due to diet for heart rate, blood pressure, serum electrolytes, subjective fatigue and urinary excretion of K+, epinephrine and norepinephrine. body temperatures were lower (p less than 0.05) for the crash diet than for the normal diet. Serum glucose levels increased during the normal diet and decreased during the crash diet. Hematocrit increased more for the crash diet (p less than 0.05) than for the normal diet. Urinary excretion of 17-ketogenic steroids was less (p less than 0.001) during sleep for the crash diet than for the normal diet. Complex performance showed no significant differences when subjects were tested under low workloads. Performance was enhanced during the crash diet when subjects were tested under the medium and high workload conditions.

Effects of altitude and two decongestant-antihistamine preparations on physiological functions and performance.

Fourteen men were studied to determine the combined effects of two altitudes--388 and 3,810 m or 1,274 and 12,500 ft--and three preparations--lactose placebo, Compound A (Actified, and Compound B (Dristan). Subjects reported least attentiveness with A and greatest with placebo. Fatigue increased significantly with time while energy, interest, and attentiveness decreased. The Multiple Task Performance Battery (MTPB) showed no effects of altitude, drugs, or time on overall performance; however, performance declined with time in several tasks, while problem solving improved. Subjects enjoyed the problem-solving tasks and may have given them preference as levels of interest declined. Though the MTPB overall composite scores did not change significantly, physiological parameters and subjective evaluations indicate that type of compound and time after ingestion are important. Declines in energy and attentiveness 2.5 h after ingestion could result in neglect of important--although routine--tasks. Hypoxia might enhance this effect and consequences might be worse in subjects whose medical conditions require these drugs.

Transient and permanent effects of hyperthermia in dogs: a study of a simulated air transport environmental stress.

Heat-induced hyperthermia can be a major problem in dogs shipped during summer months. Dogs shipped by air transport can encounter temperatures as high as 54.4 C. Usually, little concern is given to effects produced by hyperthermia. To assess the heat stress problem, 20 dogs were exposed to a temperature of 54.4 C for 30 minutes--10 dogs at 15% relative humidity and 10 dogs at 35%. Dogs did not die as a result of exposure, but certain transient and permanent changes occurred. All dogs had increased heart rate, rectal temperature, blood pH, hemoglobin concentration, packed cell volume, and erythrocyte count. Body weight and PVCO2, decreased. Differences also were shown between the 2 humidity group for blood PH PVCO2, rectal temperature, and weight loss. The major tissue changes attributed to hyperthermia were fragmentation of the myocardium, acute cortical necrosis in kidney, and marked degenerative changes in the cerebellum and cerebral cortex. Changes in the cerebellum and cerebral cortex were considered severe and permanent.

Protection of airline flight attendants from hypoxia following rapid decompression.

To determine the maximum time for working flight attendants to effectively initiate airline passenger mask donning after onset of a rapid, severe decompression, we exposed 10 subjects in two series of tests to a decompression from 6,500 to 34,000 ft (2,000 to 10,400 m) in 26 s, followed by descent at 5,000 ft/min (1,500 m/min) while subjects performed a light-to-moderate workload. Supplemental oxygen was provided in one series from a compressed oxygen system, and in the other series from a chemical oxygen generator system. With delays to mask doning of 10 and 15 s, no hypoxic effects occurred. With delays of 20 and 25 s, increasing hypoxic effects, similar in frequency for the two systems, occurred. Some technical problems in mask donning contributed to losses of consciousness with the latter two delays.

Effect of physical activity of airline flight attendants on their time of useful consciousness in a rapid decompression.

To determine the effect of physical activity on the "time of useful consciousness" (TUC) of airline flight attendants in a rapid, severe decompression, 10 male and 10 female subjects were exposed to a decompression profile while at rest and performing light-to-moderate work. Decompression from 6,500 to 34,000 ft (2,000 to 10,400 m) was followed by descent at 5,000 ft/min (1,500 m/min). The average TUC for the males decreased from 54 s (omega 7.1) at rest to 34 s (omega 4.4) while performing work. The average TUC for the females decreased from 54 s (omega 8.1) at rest to 32 s (omega 4.0) while performing work. Supplemental oxygen had a marked paradoxical effect when the subjects were performing work.