Effect of change in ambient temperature on core temperature during the daytime

Abstract

In this study, the hypothesis is tested that continuous increases in ambient temperature (Ta) during daytime would give elevated core and skin temperatures, and consequently better thermal sensation and comfort. Rectal temperature (Tre), skin temperatures and regional dry heat losses at 7 sites were continuously measured for 10 Japanese male subjects in three thermal conditions: cond. 1, stepwise increases in Ta from 26 °C at 9 h00 to 30 °C at 18 h00; cond. 2, steady Ta at 28 °C from 9 h00 to 18 h00 and cond. 3, stepwise decreases in Ta from 30 °C at 9 h00 to 26 °C at 18 h00. Oxygen consumption was measured and thermal sensation and comfort votes were monitored at 15 min intervals. Body weight loss was measured at 1 h intervals. While Tre increased continuously in the morning period in any condition, it increased to a significantly greater (p<0.05) 36.9±0.3 °C at 18 h00 in cond. 1 relative to 36.7±0.28 °C in Cond. 2 and 36.5±0.37 °C in cond. 3. Better thermal comfort was observed in the afternoon and the evening in Cond.1 as compared with the other 2 conditions. Thus, a progressive and appropriate increase in Ta may induce optimal cycle in core temperature during daytime, particularly for a resting person.

A review of human thermal comfort in the built environment

“…In Thailand, research indicates that in order to maintain and increase productivity, indoor temperatures should be higher in the morning (26-28ºC, warmer thermal condition than PMV-ISO 7730) than in the afternoon and evening (24.5-26ºC) [375]. This finding may be related to the results obtained by Kakitsuba and White [377] in climate chamber experiments in Japan. The authors evaluated the core temperature of the human body (Tc, which is lowest during wake up in the morning and increased during the daytime) -circadian rhythm-and concluded that the best outcomes for thermal comfort and thermal sensation were obtained through daytime temperature variations -with higher air temperatures during the morning and lower temperatures in the afternoon.…”

Human thermal perception and time of day: A review

“…Among the 15 reviewed experimental studies investigating diurnal variations in thermal perception, six found no significant differences in thermal perception [12][13][14][15][16][17]78] six observed significant differences [19,[71][72][73][74]77], two observed significant differences but were conducted only with male subjects [18,75] and the remaining one observed significant differences only for heat-acclimatized subjects [76]. In addition, two out of the six studies finding significant differences observed these differences only in male subjects [19,72].…”

Influence of indentation test factors on the mechanical response of the skin

“…• C] levels [30]) because it depends on an air conditioning system and on the time needed to adjust a room's temperature, the relative humidity is controlled with the air conditioned system [31]. To ensure thermal conditioning, subjects were placed in the study room 15 min before testing.…”

“…were selected carefully to avoid any damage over the volunteer but keeping the experimental changes. For instance, difference of 10 • C in environment temperature can reflect 2 • C on the skin [30], the pressure of the pump is needed to fix the forearm and limit all involuntary movements, and the indentation velocity was estimated between 300 um/s and 3 mm/s, considering that the time of tissue response and load application is extended from 1 to 10 seconds.…”