Effect of aging on thermoregulatory and subjective responses during a 15-minute bath at 41 °C

Abstract

The purpose of this study was to clarify the effects of bathing on thermoregulatory and subjective responses in elderly persons compared to those in young persons. Ten young (20.4 years) and 10 elderly (69.7 years) individuals were asked to bathe for 15 minutes in water at 41 °C. Tympanic temperature (Tty) was measured using a thermometer with a thermistor, sweating rate (SR) was measured by a ventilated capsule method, and skin blood flow (SkBF) was measured by laser Doppler flowmetry to assess thermoregulatory responses. Subjective thermal and comfort sensations were evaluated using a sevenpoint scale. The results showed significant increases in Tty, SR and SkBF in young participants than in elderly participants. In addition, we divided the total bathing period into three time periods and observed later SR and SkBF responses in elderly participants than in young participants. While young participants felt hot and unpleasant during the late time period, elderly participants felt warm and comfortable during the entire duration of bathing. These results demonstrate the thermoregulatory responses due to changes in physical structure and function due to aging during a 15-minute bath at 41 °C in the elderly.

A review of Japanese-style bathing: its demerits and merits

“…Fluctuations in the physiological response vary considerably depending on the hot water temperature, bathing time, room temperature, etc., the age difference in physiological fluctuations while performing JSB was summarized based on the following three experimental studies. The water temperature and immersion time reported by Nagasawa et al [44], Miwa et al [45], and Miwa et al [43] were 40 °C for 10 min, 40 °C for 20 min and 41 °C for 15 min, respectively. The water level of the bath was almost shoulder level in all three experiments.…”

“…In addition, only young people complained of discomfort due to heat when the water temperature was 42 °C. Miwa et al [43] also compared the degree of warmth and discomfort of 10 elderly and 10 young people when they were soaked in hot water at 41 °C up to the chest for 15 min. For young people, while taking a bath, the changed from "slightly hot" or "hot", the elderly reported that it was almost "neutral. "…”

“…In addition, the amount of weight loss in the elderly was significantly small. Recently, Miwa et al [43] compared the thermoregulatory response associated with bathing at a hot water temperature of 41 °C for 15 min between the elderly and young. It was revealed that the increase in tympanic temperature, local sweating (arm), and skin blood flow (forearm) while taking a bath was relatively smaller in the elderly.…”

The importance of body core temperature evaluation in balneotherapy

“…However, limited assessment may be made in line with information shared in hot tub immersion studies monitoring BCT for different purposes. With immersion to nipple level, significant BCT increases compared to basal values were shown in the 15 th minute with tympanic temperature for people with coronary artery disease at 40 °C water temperature (~ 0.6 °C) (Allison et al 1993), in the 9 th minute for esophageal temperature in healthy people (~ 0.5 °C) (Allison and Reger 1992), and in the 15 th minute for tympanic temperature in 41 °C water temperature (in young people ~ 0.5 °C, in the elderly ~ 0.3 °C) (Miwa et al 2020). Another study observed a significant increase in tympanic temperature in the 10 th minute of head-out immersion in healthy people at 39 °C (~ 0.5 °C) (Koska et al 2003).…”

“…Additionally, a study with only 5 min BCT monitoring did not identify a significant variation in tympanic temperature at the end of 5 min with immersion to heart level in 40-41 °C water (Sugawara and Tomoto 2021). In light of this data, temperature measurement frequencies may be determined according to the targeted BCT increase value during balneotherapy practice considering that the proportion of BCT variation may change due to personal differences (Miwa et al 2020).…”