Head-temperature effects on physiology, comfort, and performance during hyperthermia.

This study assessed the effects of head temperature on subjects under hyperthermic conditions. Six volunteers were trained to plateau on a manikin task that tested cognitive performance and reaction time. A subject's core temperature was driven with a full-length, liquid-conditioned garment perfused with water at 30 degrees or 43 degrees C, and head temperature was controlled by a cap with an inlet temperature of 8 degrees or 43 degrees C. Heavy insulation was worn overall; ambient temperature was 30 degrees C. Subjects were heated and cooled twice during each experiment to include all possible cap/suit temperature combinations. Each subject did one control and four stress experiments. Comfort and performance were measured as the subject's esophageal temperature (Tes) rose and fell through the range 37.5-39.0 degrees C. Cap temperature did not affect rectal temperature (Tre) but significantly altered the Tes rate of change; a cool head sometimes truncated the peak Tes value. Although the cap covered only 3-4% of the body surface, the head was a major determinant of subjective comfort. Body heating tended to shorten reaction time and diminish performance accuracy, while head cooling largely reversed these trends. Possible mechanisms include 1) change in overall heat balance; 2) countercurrent exchanges in the neck, and 3) change in sensory output. Head cooling deserves serious consideration for machinery operators where whole-body thermoneutrality is impractical.

Head acceleration and psychomotor performance.

Concussion resulting from head acceleration could explain the poor survival rates in some types of accidents. Experiments have been conducted on a decelerator using a tracking task to determine whether high head acceleration could affect psychomotor performance. Human subjects were exposed to impact acceleration of O (sham), 5, 10 and 12 -Gx facing forwards. Measurements were made of the linear and angular accelerations experienced at the head and a step tracking task was used to examine psychomotor performance. Electroencephalographs were also recorded. Both the linear and angular accelerations at the head were increased at the higher levels of impact acceleration. At -5Gx there were no significant differences in psychomotor performance when compared with controls, but at -10Gx, and especially -12Gx, significant differences were found. The EEG activity did not vary significantly and no concussive effects were observed in any subject. These results suggest that impairment of psychomotor performance severe enough to jeopardise survival could be produced by high accelerations of the head, though neither linear nor angular acceleration appear to have special significance.

Joint Committee on Aviation Pathology: III. Some influences of restraint harness design on accident pathology.

Careful investigation of restraint harness function can reveal the mechanism of failure and, by rectification, prevent repetition of such failures. The investigation can also lead to alteration in the specification for restraint harnesses, and so eliminate weaknesses in future design. The aviation pathologist can play an important part in the assessment of the efficiency of a restraint system in use. His assessment can sometimes be more revealing than laboratory tests, as the unforeseen event often reveals unknown weaknesses.