Richard R. Gonzalez

An Environmental Stress Index (ESI) as a Substitute for the Wet Bulb Globe Temperature (WBGT)

Abstract The purpose of this study was to develop a new environmental stress index (ESI) based on different parameters relating to heat stress. Meteorological measurements were taken in three climatic zones (hot/wet, hot/dry, and extremely hot/dry) for 60 days, and a new stress index based on these databases was developed as follows: ESI=0.63 T a − 0.03RH+0.002SR+0.0054( T a · RH) − 0.073(0.1+SR) −1 , where Ta is the ambient temperature (°C), RH the relative humidity (%), and SR the solar radiation (W·m−1). The correlation coefficients between ESI and wet bulb globe temperature (WBGT) were very high (R2>0.981). Therefore, we conclude that ESI, based on fast response and the more commonly used accurate climatic microsensors (Ta, RH, SR) which can be combined in a small portable device, has the potential to be a practical alternative to the WBGT.

Physiologic tolerance to uncompensable heat : intermittent exercise, field vs laboratory

PURPOSE This study determined whether exercise (30 min)-rest (10 min) cycles alter physiologic tolerance to uncompensable heat stress (UCHS) when outdoors in the desert. In addition, the relationship between core temperature and exhaustion from heat strain previously established in laboratory studies was compared with field studies. METHODS Twelve men completed four trials: moderate intensity continuous exercise (MC), moderate intensity exercise with intermittent rest (MI), hard intensity continuous exercise (HC), and hard intensity exercise with intermittent rest (HI). UCHS was achieved by wearing protective clothing and exercising (estimated at 420 W or 610 W) outdoors in desert heat. RESULTS Heat Stress Index values were 200%, 181%, 417%, and 283% for MC, MI, HC, and HI, respectively. Exhaustion from heat strain occurred in 36 of 48 trials. Core temperatures at exhaustion averaged 38.6 +/- 0.5 degrees, 38.9 +/- 0.6 degrees, 38.9 +/- 0.7 degrees, and 39.0 +/- 0.7 degrees C for MC, MI, HC, and HI, respectively. Core temperature at exhaustion was not altered (P > 0.05) by exercise intensity or exercise-rest cycles and 50% of subjects incurred exhaustion at core temperature of 39.4 degrees C. These field data were compared with laboratory and field data collected over the past 35 years. Aggregate data for 747 laboratory and 131 field trials indicated that 50% of subjects incurred exhaustion at core temperatures of 38.6 degrees and 39.5 degrees C, respectively. When heat intolerant subjects (exhaustion < 38.3 degrees C core temperature) were removed from the analysis, subjects from laboratory studies (who underwent short-term acclimation) still demonstrated less (0.8 degrees C) physiological tolerance than those from field studies (who underwent long-term acclimatization). CONCLUSION Exercise-rest cycles did not alter physiologic tolerance to UCHS. In addition, subjects from field studies demonstrate greater physiologic tolerance than subjects from laboratory studies.

Prediction modeling of physiological responses and human performance in the heat

Over the last two decades, our laboratory has been establishing the data base and developing a series of predictive equations for deep body temperature, heart rate and sweat loss responses of clothed soldiers performing physical work at various environmental extremes. Individual predictive equations for rectal temperature, heart rate and sweat loss as a function of the physical work intensity, environmental conditions and particular clothing ensemble have been published in the open literature. In addition, important modifying factors such as energy expenditure, state of heat acclimation and solar heat load have been evaluated and appropriate predictive equations developed. Currently, we have developed a comprehensive model which is programmed on a Hewlett-Packard 41 CV hand held calculator. The primary physiological inputs are deep body (rectal) temperature and sweat loss while the predicted outputs are the expected physical work--rest cycle, the maximum single physical work time if appropriate, and the associated water requirements. This paper presents the mathematical basis employed in the development of the various individual predictive equations of our heat stress model. In addition, our current heat stress prediction model as programmed on the HP 41 CV is discussed from the standpoint of propriety in meeting the Armys needs and therefore assisting in military mission accomplishment.

A mechanistic computer simulation of human work in heat that accounts for physical and physiological effects of clothing, aerobic fitness, and progressive dehydration

Abstract 1. 1. This paper describes a computer model (SCENARIO) specifically designed to simulate the time course of heat strain observed during athletic, industrial, and military settings. 2. 2. The simulations generated by the model dependably reproduce the time course of body temperature shifts, thermoeffector responses, central and peripheral circulatory changes in persons exercising in warm and hot environments. 3. 3. The model takes into consideration different clothing ensembles, varied levels of aerobic fitness in a population, and effects of progressive dehydration and deconditioning (extended bed rest).

Expanded prediction equations of human sweat loss and water needs

The Institute of Medicine expressed a need for improved sweating rate (msw) prediction models that calculate hourly and daily water needs based on metabolic rate, clothing, and environment. More than 25 years ago, the original Shapiro prediction equation (OSE) was formulated as msw (g.m(-2).h(-1))=27.9.Ereq.(Emax)(-0.455), where Ereq is required evaporative heat loss and Emax is maximum evaporative power of the environment; OSE was developed for a limited set of environments, exposures times, and clothing systems. Recent evidence shows that OSE often overpredicts fluid needs. Our study developed a corrected OSE and a new msw prediction equation by using independent data sets from a wide range of environmental conditions, metabolic rates (rest to <or=450 W/m2), and variable exercise durations. Whole body sweat losses were carefully measured in 101 volunteers (80 males and 21 females; >500 observations) by using a variety of metabolic rates over a range of environmental conditions (ambient temperature, 15-46 degrees C; water vapor pressure, 0.27-4.45 kPa; wind speed, 0.4-2.5 m/s), clothing, and equipment combinations and durations (2-8 h). Data are expressed as grams per square meter per hour and were analyzed using fuzzy piecewise regression. OSE overpredicted sweating rates (P<0.003) compared with observed msw. Both the correction equation (OSEC), msw=147.exp (0.0012.OSE), and a new piecewise (PW) equation, msw=147+1.527.Ereq-0.87.Emax were derived, compared with OSE, and then cross-validated against independent data (21 males and 9 females; >200 observations). OSEC and PW were more accurate predictors of sweating rate (58 and 65% more accurate, P<0.01) and produced minimal error (standard error estimate<100 g.m(-2).h(-1)) for conditions both within and outside the original OSE domain of validity. The new equations provide for more accurate sweat predictions over a broader range of conditions with applications to public health, military, occupational, and sports medicine settings.

Evaluation of the environmental stress index for physiological variables

Abstract A new environmental stress index (ESI), based on ambient temperature ( T a ), relative humidity (RH) and solar radiation (SR), was recently suggested as a potential substitute for the wet-bulb globe temperature (WBGT) index. The purpose of this study was to evaluate and validate ESI for three different physiological variables including rectal temperature ( T re ), heart rate (HR), and sweat rate ( m sw ). A database was taken from a previous study where 12 young men (21±1 y) served as subjects exposed to 120 min of 12 different combinations consisting of three metabolic rates (rest and treadmill walking at 5 km·h −1 at 0% and 5% grades), two clothing ensembles (BDU and protective MOPP gear) and two outdoor solar radiation levels (shade and open sky). ESI was calculated as follows: ESI=0.63 T a -0.03RH+0.002SR+0.0054( T a RH)-0.073(0.1+SR) −1 . Significant differences of about 2 units ( p p m sw , HR and T re when measured in the sun and in the shade during all the exercise exposures. Thus, very high correlations ( R 2 >0.838) were found between ESI and T re , HR, or m sw . These results indicate that ESI is strongly correlated to the physiological strain, whereby higher stress is reflected in higher strain. Therefore, evaluating heat stress by ESI, which uses the more common, fast response and accurate climatic measures, becomes more predominant.

Circadian variations in plasma renin activity, catecholamines and aldosterone during exercise in women.

SummaryFour women were studied at 0400 h and 1600 h to determine if their hormonal and hemodynamic responses to exercise varied with the circadian cycle. Esophageal temperature was measured during rest and exercise (60% peak

Sweat Rate Prediction Equations for Outdoor Exercise with Transient Solar Radiation

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