Auxiliary cooling: comparison of air-cooled vs. water-cooled vests in hot-dry and hot-wet environments.

Water-cooled, air-cooled, and ambient air-ventilated auxiliary cooling vests were evaluated in a hot-wet climate (HW) (35 degrees C, 75% R.H.) and a hot-dry environment (HD) with additional infrared radiation (Ta = 49 degrees C, 20% R.H., 68 degrees C black globe temperature). Twelve subjects dressed in full chemical warfare combat uniforms underwent 120 min of heat exposure in each combination of climate and cooling vest, except for the hot-dry environment and ambient-air vest. During each exposure, total exercise time was 20 min and rest time 100 min. This resulted in a mean time weighted metabolic rate of 180 W. Both water-cooled and air-cooled vests were sufficient for cooling in the HW climate: heat storage (delta S) was 13 and 7 W, final rectal temperature (Tre) 37.4 and 37.3 degrees C, and heart rate (HR) 124 and 112 b . min-1, respectively. While using the ambient-air vest, all variables were significantly (p less than 0.05) higher (delta S, 25 W; Tre, 37.7 degrees C; HR, 139 b . min-1; respectively). In the HD climate, both water and air-cooled vests were insufficient with a delta S of 46 and 48 W, final Tre of 38.4 and 38.3 degrees C, and final HR of 151 and 147 b . min-1. However, both cooling vests improved the subjects' physiological status compared to these predicted variables without auxiliary cooling. No significant differences were found between the air or the water-cooled vests in either the HD or HW climates. It was concluded that an air-cooled vest can be used with the same efficiency as a water-cooled vest. In contrast, the ambient-air vest was shown to have a low effectiveness in HW and to be dangerous in a HD climate.

Study of measurement and experimental design problems associated with the step test.

The Harvard Step Test (HST) scoring formula is inadequate when individuals do not complete the prescribed duration. Insull, et al., (1955) proposed a formula with a quadratic function which rendered scores independent of the duration of stepping. Using Insull's data, a linear function was fit to the relationship between the HST score and the duration of stepping, and a new simpler scoring formula was developed. The new scoring formula was evaluated empirically to help an investigator make a choice among different HST scoring formulas. Three maximum stepping durations were administered to 12 subjects previous to and subsequent to running two miles each day for nine days. Compared to the rapid HST scoring formula, the classical HST formula was not consistently more sensitive to the changes produced by the physical conditioning. Both the classical and rapid formulas were less sensitive than the new versions of the two formulas. It was concluded that the controversial nature of the HST is, in part, a result of inconsistent empirical results produced by the original formulas. It was also concluded that the new formulas should always be used in preference to the original formulas, since the new formulas are more sensitive to the changes produced by physical conditioning, and they produce scores which are comparable to the standard HST scores regardless of the duration of stepping. Finally, concurring with past investigators, it was concluded that the extra two pulse counts employed by the classical formula are redundant, thus rendering the rapid formula preferable since it requires less testing time.