Heat Strain Index Research Articles

CUMULATIVE HEAT STRAIN INDEX IN EXERCISE-HEAT ACCLIMATION

1268 Exercise-heat stress mutually contribute to the physiological strain. Heat acclimation which is achieved by repetitive exercise-heat exposures results with a reduction in the physiological strain. It is the aim of this study to evaluate the net contribution of heat exposure, during acclimation, on the total strain. It is supposed that physiological strain in terms of physiological cost of heat exposure can be estimated by the difference in the Cumulative Heat Strain Index (CHSI) (Frank et. al., MSSE 26:S125, 1997; MSSE 29:S134, 1997) calculated during exercise in comfortable and warm conditions. Seven healthy volunteers underwent a procedure of acclimation to heat. The subjects were exposed for ten consecutive days to heat (45 °C, 30% rh) while walking on a treadmill (5 km·h-1, 2% grade) for 120 min. Before and after acclimation the same protocol was executed under comfort conditions (21 °C, 60% rh). Physiological cost of exercise in comfortable conditions was not effected by acclimation. The net increase in physiological cost caused by heat was significantly lower after acclimation, than before it(CHSI: 128±103 and 431±236 units respectively, p<0.01). It is therefore concluded that the lowering of heat strain obtained during heat acclimation can be quantitatively evaluated, in a convenient way, by the CHSI.

THE THERMOREGULATORY AND CARDIOVASCULAR STRAINS IN THE ESTIMATION OF HEAT INTOLERANCE 772

The aim of the present study was to examine whether rectal temperature(Tre) by itself is sufficient for the determination of heat intolerance. Sixty nine young (20±2 yrs) subjects underwent heat tolerance test. All subjects were healthy except for a history of heat disorders. The subjects were tested under standardized exercise-heat stress (40°C/ 40%RH, VO2≈1l/min). Exercise consisted of walking on a treadmill (5kmh-1, 2%) for 120 min. Tre and heart rate (HR) were monitored every min, the Cumulative Heat Strain Index (CHSI) (MSSE 26:S125, 1994) was calculated, and blood pressure(BP) was measured every 5 min. Eleven out of the 69 subjects were considered as heat intolerant (HI). Tre exceeded 38.5°C in only six of the HI, while the HR and BP values did not differ from the others. However in all 11 HI the dynamic pattern of HR and Tre changes differed from heat tolerant subjects. This was reflected by the higher values of CHSI. It is therefore suggested that the cumulative combination of thermoregulatory and cardiovascular strains is a better determinator for heat intolerance than Tre or HR by itself.

Methodology of investigation of hot working conditions in the field

The paper describes the methods used by the different teams contributing to the European interlaboratory validation of techniques study for assessing hot environments. It describes the methodology used for assessing the primary parameters (temperature, humidity, radiation, air velocity, metabolic rate and clothing) of the hot environments and the physiological constraints resulting from them (core temperature, sweat rate, heart rate). It draws attention to the practical problems and issues that need to be addressed when selecting a monitoring method (zonal or ambulatory method), when choosing appropriate instruments and also when opting for a specific heat strain index.

Effective heat strain index using pocket computer.

An effective heat strain index (EHSI) using a hand calculator with memory is suggested for on-site evaluation of prevailing hot ambient conditions. The inputs to the programmed calculator include dry-bulb, wet-bulb and globe temperatures, and estimates of metabolism and air movements. The index is based on a program for calculation of the total heat balance and on the efficiency of sweating. The display of information on the ambient conditions EHSI display is one of following: no strain; low strain; high strain; or time limits of exposure.

Thermal responses to intermittent work in selected enironments.

Acclaimed subjects exercised intermittently for 8 hrs in 25 to 50 degrees environments. Thermal and metalobic determinations were made. Results showed the time-weighted WBGT heat strain index for intermittent work needs re-evaluation. For acclimated subjects working steadily at 350 kcal/hr, 30% max, the ULPZ is more than 33% WBGT.