Body cooling effects of immersion of the forearms in high-concentration artificial carbonic acid water at 25°C.

BACKGROUND: This study examined the effects of immersion in stirred, high-concentration, artificial carbonic acid water on body cooling. METHODS: Seven healthy male students (23 ± 2 years old) participated in the experiment. Signed informed consent was obtained from all subjects before the experiment. The subjects changed into shorts and T-shirts and entered an experimental room (with room temperature controlled at 30 °C and relative humidity maintained at 70%) at least 30 min before starting the experiment. After starting the experiment, the subjects were asked to rest on an exercise bike for 5 min and then pedal for 20 min. The exercise load was set to reach 50% of each subject's presumed maximum oxygen intake at 5 min after starting exercise. Subjects then continued pedaling for 1 min to cool down. After this exercise, subjects sat on a chair and immersed forearms in tap water or artificial carbonic acid water (CO2 water) at 25 °C for 20 min. During immersion, tap water or CO2 water was stirred slowly with a pump. After immersion, subjects rested for 10 min. Skin temperature and skin blood flow (left forearm), as well as heart rate and ear canal temperature, were measured continuously. Thermal sensation and thermal comfort were measured intermittently. RESULTS: Skin blood flow of the immersed forearms was higher in CO2 water than in tap water during immersion. The blood flow in the last 5 min (average at rest was 100%) was significantly higher in CO2 water (290.85 ± 84.81%) than in tap water (104.80 ± 21.99%). Thermal sensation and thermal comfort were not different between conditions. Ear canal temperature significantly declined more in CO2 water (- 0.56 ± 0.31 °C) than in tap water (- 0.48 ± 0.30 °C) during immersion. CONCLUSIONS: Our study suggests that immersion of the forearms in slowly stirred CO2 water at 25 °C reduces core temperature elevated by heat stress or exercise more effectively than does tap water at the same temperature. Immersion of the forearms in stirred CO2 water at 25 °C could be useful as a preventive measure against heat stroke from summer work or exercise.

Differences in reported linguistic thermal sensation between Bangla and Japanese speakers.

BACKGROUND: Thermal sensation is a fundamental variable used to determine thermal comfort and is most frequently evaluated through the use of subjective reports in the field of environmental physiology. However, there has been little study of the relationship between the semantics of the words used to describe thermal sensation and the climatic background. The present study investigates the linguistic differences in thermal reports from native speakers of Bangla and Japanese. METHODS: A total of 1141 university students (932 in Bangladesh and 209 in Japan) responded to a questionnaire survey consisting of 20 questions. Group differences between Bangladeshi and Japanese respondents were then tested with a chi-square test in a crosstab analysis using SPSS (version 21). RESULTS: For the Bangla-speaking respondents, the closest feeling of thermal comfort was "neutral" (66.6%) followed by "slightly cool" (10.2%), "slightly cold" (6.0%), "slightly hot" (4.1%), and "cold" (3.8%). For the Japanese respondents, the closest feeling of thermal comfort was "cool" (38.3%) followed by "slightly cool" (20.4%), "neutral" (14.6%), "slightly warm" (13.1%), and "warm" (10.7%). Of the Bangladeshi respondents, 37.7% reported that they were sensitive to cold weather and 18.1% reported that they were sensitive to hot weather. Of the Japanese respondents, 20.6% reported that they were sensitive to cold weather and 29.2% reported that they were sensitive to hot weather. Of the Bangladeshi respondents, 51.4% chose "higher than 29 °C" as hot weather and 38.7% of the Japanese respondents chose "higher than 32 °C" as hot weather. In the case of cold weather, 43.1% of the Bangladeshi respondents selected "lower than 15 °C" as cold weather and 53.4% of the Japanese respondents selected "lower than 10 °C" as cold weather. CONCLUSIONS: Most of the Bangla-speaking respondents chose "neutral" as the most comfortable temperature, and most of the Japanese respondents chose "cool." Most of the Bangladeshi respondents reported that they were sensitive to "cold temperatures," but most of the Japanese respondents reported that they were sensitive to "hot temperatures."

Cold-induced vasodilation comparison between Bangladeshi and Japanese natives.

BACKGROUND: The human thermoregulation system responds to changes in environmental temperature, so humans can self-adapt to a wide range of climates. People from tropical and temperate areas have different cold tolerance. This study compared the tolerance of Bangladeshi (tropical) and Japanese (temperate) people to local cold exposure on cold-induced vasodilation (CIVD). METHODS: Eight Bangladeshi males (now residing in Japan) and 14 Japanese males (residing in Japan) participated in this study. All are sedentary, regular university students. The Bangladeshi subject's duration of stay in Japan was 2.50 ± 2.52 years. The subject's left hand middle finger was immersed in 5 °C water for 20 min to assess their CIVD response (the experiment was conducted in an artificial climate chamber controlled at 25 °C with 50% RH). RESULTS: Compared with the Bangladeshi (BD) group, the Japanese (JP) group displayed some differences. There were significant differences between the BD and JP groups in temperature before immersion (TBI), which were 33.04 ± 1.98 and 34.62 ± 0.94 °C, and time of temperature rise (TTR), which were 5.35 ± 0.82 and 3.72 ± 0.68 min, respectively. There was also a significant difference in the time of sensation rise (TSR) of 8.69 ± 6.49 and 3.26 ± 0.97 min between the BD and JP groups, respectively (P < 0.05). Moreover, the JP group showed a quick TTR after finishing immersion. CONCLUSIONS: The Japanese group (temperate) has a higher tolerance to local cold exposure than the Bangladeshi group (tropical) evaluated by the CIVD test.

µ-Crystallin controls muscle function through thyroid hormone action.

µ-Crystallin (Crym), a thyroid hormone-binding protein, is abnormally up-regulated in the muscles of patients with facioscapulohumeral muscular dystrophy, a dominantly inherited progressive myopathy. However, the physiologic function of Crym in skeletal muscle remains to be elucidated. In this study, Crym was preferentially expressed in skeletal muscle throughout the body. Crym-knockout mice exhibited a significant hypertrophy of fast-twitch glycolytic type IIb fibers, causing an increase in grip strength and high intensity running ability in Crym-null mice. Genetic inactivation of Crym or blockade of Crym by siRNA-mediated knockdown up-regulated the gene expression of fast-glycolytic contractile fibers in satellite cell-derived myotubes in vitro These alterations in Crym-inactivated muscle were rescued by inhibition of thyroid hormone, even though Crym is a positive regulator of thyroid hormone action in nonmuscle cells. The results demonstrated that Crym is a crucial regulator of muscle plasticity, controlling metabolic and contractile properties of myofibers, and thus the selective inactivation of Crym may be a potential therapeutic target for muscle-wasting diseases, such as muscular dystrophies and age-related sarcopenia.-Seko, D., Ogawa, S., Li, T.-S., Taimura, A., Ono, Y. µ-Crystallin controls muscle function through thyroid hormone action.