Environmental Health, Japan-Objectives: Measuring core body temperature is crucial for preventing heat stress disorders in workers. We developed a method for measuring auditory canal temperatures based on a thermocouple inserted into a sponge-type earplug. We verified that the tip of this thermocouple is positioned safely, allowing the wearer to engage in normal physical tasks; this position averaged 6.6 mm from the tympanic membrane. Methods: To assess this technique, we had six healthy male students repeat three cycles of exercise and rest (20 min of exercise and 15 min of rest) in a temperaturecontrolled chamber with temperatures set at 25, 30, or 35°C, while monitoring the auditory canal, esophageal, rectal, and skin temperatures. Results: We observed differences of a mere 0.30-0.45°C between rectal temperatures and auditory canal temperatures measured with the thermocouple, the smallest such difference reported to date in studies involving auditory canal temperature measurement. Conclusions: We conclude that monitoring temperatures based on a technique involving an auditory canal plug can be used to estimate rectal temperatures accurately, and thereby to avoid conditions leading to heat stress disorders. Although controlling ambient temperatures is the ideal approach to eliminating heat stress disorders, this is often not possible. This makes it especially important to optimize work schedules by reducing hours worked, providing workers with frequent breaks, or having workers work in alternating shifts. Ideal work schedules should be based on evaluations of physiological response, including perspiration rates and heat balance, as defined in the ISO7933 Predicted Heat Strain model 1) . In practice, however, measuring the parameters required for this model poses major difficulties. The indices available for workplace evaluations include various proxies for core temperature (t cr ) measurements, including measurements of skin temperature (t sk ), heart rate (HR), and body weight. Monitoring t cr in vivo is essential to preventing heat disorders.According to ISO 9886 2) , the term "core" refers to all tissue located at depths sufficient to remain unaffected by the temperature gradient existing on surface tissue. Esophageal temperature (t es ), rectal temperature (t re ), intraabdominal temperature (t ab ), oral temperature (t or ), tympanic temperature (t ty ), auditory canal temperature (t ac ) and urine temperature (t ur ) have been proposed as core temperature indices. The transducer of t es is placed in the lower part of the oesophagus, which is in contact over a length of 50 to 70 mm with the front of the left auricle and with the rear surface of the descending aorta. Consequently, t es reflects the temperature of the arterial blood with a very short reaction time. t re is independent of ambient conditions because the rectum is surrounded

Health, Japan-Envisioning a cooling method and aiming at maximum feasibility and simplicity, we designed an experimental intervention-control study based on non-refrigerated water usage, consisting of pouring 2 l of 23.0°C water simultaneously on head and hands for one minute, after every 20 min of exertion. The subjects were 11 fit male individuals between 19 and 26 yr old. Each individual participated in one control and one intervention measurement in a climatic chamber at 35°C and 60% humidity (31.5°C WBGT) on different days. Heart rate, rectal, esophageal, skin and external ear canal temperatures were monitored constantly. Each experiment consisted of 10 min of basal recording followed by 3 intervals of 20 min of cycling and 15 min of rest. Stabilometry and visual reaction time tests were performed before and after each resting period. A questionnaire evaluating equilibrium, concentration, alertness and tiredness was administered at the beginning and at the end of every experiment. Paired t-test analysis revealed significant improvements in subjective parameters (all p<0.05), as well as skin (p<0.05), external ear canal (p<0.01) and esophageal (p<0.05) temperatures during the rest periods. Repeated measurement analysis of variance revealed significant cooling in all the aforementioned temperatures except the esophageal temperature (p=0.28). Other parameters were not significantly different. Our findings indicate that this method has subjective and physiologic positive effects, and thus can be used as a complementary low cost method to cool subjects safely. (J Occup Health 2008; 50: 251-261)

Objectives To examine the thermoregulatory and fluid‐electrolyte responses of firefighters ingesting ice slurry and carbohydrate–electrolyte solutions before and after firefighting operations. Methods Twelve volunteer firefighters put on fireproof clothing and ingested 5 g/kg of beverage in an anteroom at 25°C and 50% relative humidity (RH; pre‐ingestion), and then performed 30 minutes of exercise on a cycle ergometer (at 125 W for 10 minutes and then 75 W for 20 minutes) in a room at 35℃ and 50% RH. The participants then returned to the anteroom, removed their fireproof clothing, ingested 20 g/kg of beverage (post‐ingestion), and rested for 90 minutes. Three combinations of pre‐ingestion and post‐ingestion beverages were provided: a 25℃ carbohydrate–electrolyte solution for both (CH condition); 25℃ water for both (W condition); and a −1.7℃ ice slurry pre‐exercise and 25℃ carbohydrate–electrolyte solution post‐exercise (ICE condition). Results The elevation of body temperature during exercise was lower in the ICE condition than in the other conditions. The sweat volume during exercise was lower in the ICE condition than in the other conditions. The serum sodium concentration and serum osmolality were lower in the W condition than in the CH condition. Conclusions The ingestion of ice slurry while firefighters were wearing fireproof clothing before exercise suppressed the elevation of body temperature during exercise. Moreover, the ingestion of carbohydrate–electrolyte solution by firefighters after exercise was useful for recovery from dehydration.

To test an economically reasonable method to reduce thermal stress, we performed an alternated intervention-control study on 2 groups of 8 male steel workers performing the same jobs, using 2 l of water at ambient temperature (23.5°C ± 1.4), poured on the head and hands. Each group participated for 2 d as control and 2 d as intervention during 4 consecutive summer days in Brazil, 5 h per shift per day. Testing was done by: 1) recording of temperature by thermistors placed on the external ear canal through earplug, skin (chest, upper arm, inner thigh, outer calf) and clothes; 2) recording of heart rate; and 3) Wet Bulb Globe Temperature recording. The intervention was held hourly, when body weight and water intake were evaluated. Symptoms and subjective sensations were evaluated in the beginning and at the end of each shift. No differences were observed in external ear canal and skin temperatures. Subjective thermal sensation (p=0.018), sweat perception (p=0.043), and tiredness (p=0.028) presented positive statistically significant results when comparing intervention to control measurements. In conclusion, our results could not provide evidence that the proposed method cools the analyzed temperatures, although the subjective evaluation suggests a decrease in the head skin temperature, which could be a useful comfort measure.

We examined whether blowing hot air above body temperature under work clothing may suppress core temperature. Nine Japanese men engaged in two 30-min bicycle ergometer sessions at a workload of 40% VO2max at 40 °C and 50% relative humidity. The experiment was conducted without wearing any cooling apparatus (CON), wearing a cooling vest that circulated 10.0 °C water (VEST), and wearing a fan-attached jacket that transferred ambient air underneath the jacket at a rate of 30 L/s (FAN). The VEST and FAN conditions suppressed the increases of rectal temperature (CON, VEST, FAN; 38.01 ± 0.19 °C, 37.72 ± 0.12 °C (p = 0.0076), 37.54 ± 0.19 °C (p = 0.0023), respectively), esophageal temperature (38.22 ± 0.30 °C, 37.55 ± 0.18 °C (p = 0.0039), 37.54 ± 0.21 °C (p = 0.0039), respectively), and heart rate (157.3 ± 9.8 bpm, 136.9 ± 8.9 bpm, (p = 0.0042), 137.5 ± 6.5 bpm (p = 0.0023), respectively). Two conditions also reduced the estimated amount of sweating and improved various subjective evaluations. Even in the 40 °C and 50% relative humidity environment, we may recommend wearing a fan-attached jacket because the heat dissipation through evaporation exceeded the heat convection from the hot ambient air.