Kazuyo Tsuzuki

Effects of season on sleep and skin temperature in the elderly

The effects of season on sleep and skin temperature (Tsk) in 19 healthy, elderly volunteers were investigated. Measurements were obtained in summer, winter, and fall, and activity levels were monitored using a wrist actigraph system for five consecutive days. The temperature and humidity of the bedrooms of the subjects’ homes were measured continuously for five days. During actigraphic measurement, Tsk during sleep was measured for two nights. The bedroom temperature and humidity significantly increased in summer compared to winter and fall. In summer, the total sleep time decreased (mean ± SE min; summer, 350.8 ± 15.7; winter, 426.5 ± 14.2; fall, 403.2 ± 16.4) and wakefulness increased (P < 0.003) compared to those in fall or winter. The sleep efficiency index that was derived from wrist actigraphy was significantly decreased (P < 0.001) in summer (81.4 ± 2.9%) compared with winter (91.6 ± 1.3%) or fall (90.2 ± 1.2%). The forehead Tsk significantly increased, while the chest and thigh Tsks were decreased in summer compared to those in fall or winter. These results suggest that, in the elderly, sleep is disturbed in summer more than in other seasons, and that this disturbance is related to fluctuations in Tsk.

Effects of partial humid heat exposure during different segments of sleep on human sleep stages and body temperature.

The effects of partial humid heat exposure applied at different segments of sleep on sleep stages and body temperature were examined. In the first experiment, eight male subjects slept under 26 degrees C 50% (26) and 26 degrees C for the first 3 h and 45 min followed by a 30-min transition to the conditions of 32 degrees C 80%, which was maintained for the final 3 h and 45 min (26-32). Wakefulness increased significantly over the last 4 h under 26-32 compared to 26. Mean skin temperature and clothing microclimate temperature (Tcm) were significantly higher during the last 3 h and 45 min, while rectal temperature (Tre) was higher during the last 3 h under 26-32 than in 26. In the second experiment, eight male subjects slept under 26 degrees C 50% (26) and 32 degrees C 80% for the first 3 h and 45 min followed by a 30-min transition to 26, which was then maintained for the last 3 h and 45 min (32-26). Wakefulness increased both in first and during the last 4 h, and slow wave sleep (SWS) decreased in the first 4 h under 32-26 compared to 26. Mean Tsk was significantly higher during the first 4:15 h. Tcm decreased in 32-26 compared to 26 just after the 30-min transition due to cooling effects. Tre was higher during the first 5 h under 32-26 compared to 26. These results suggest that humid heat exposure during the initial segment of sleep may be more disruptive to sleep stage distribution, Tre decline, and maintenance of Tcm than the same exposure during the later sleep segments.

Effects of an electric blanket on sleep stages and body temperature in young men

The aim of this study was to investigate any effects of electric blanket on sleep stages and body temperature. Nine male subjects slept under two conditions: using the electric blanket (HB); and not using the electric blanket (C). The ambient condition was controlled at 3°C relative humidity 50 – 80%. Electroencephalography, electrooculography (EOG) and electromyography, rectal temperature, skin temperature and microclimate temperature and humidity were recorded continuously through the night. Body weight was measured before and after sleep. The amount of stage 1 and number of stage 1 and rapid eye movement sleep decreased in HB compared to C. No significant difference was observed in other sleep stages. Rectal temperature was higher in HB compared to C. The thigh, leg and foot skin temperature was higher in HB than C. The microclimate temperature of the foot area was higher in HB compared to C. No significant difference was observed in whole body sweat loss between the conditions. These results suggest that use of an electric blanket under low ambient temperature may decrease cold stress to support sleep stability and thermoregulation during sleep.

Development of a Computational Thermal Manikin Applicable in a Non-Uniform Thermal Environment—Part 2: Coupled Simulation Using Sakoi's Human Thermal Physiological Model

In order to develop a computational thermal manikin to enable the prediction of the thermal sensation of an occupant in a non-uniform environment, in a previous paper (Zhu et al. 2007) we proposed and examined a simulation method combining Smiths human thermal physiological model with convective and radiant simulation by applying the proposed method to calculate the sensible heat transfer over the body surface of an occupant located in several radiant environments with an air temperature of 28°C. However, the simulation results greatly underestimated the skin temperatures at the limbs, even in uniform conditions, due to the improper modeling of the Arteriovenous Anastomose phenomenon in Smiths model. Accordingly, a new human thermal physiological model, Sakois model (Sakoi et al. 2005a, 2006a), was developed with a three-dimensional body configuration similar to Smiths model and a thermo-regulatory mechanism by Yokoyama (1993). In this paper, Sakois model is coupled in the simulation of convection, radiation, and moisture transport to calculate the total (sensible and latent) heat transfer from a seated human body in uniform and front-back asymmetric radiant environments, which were introduced in the previous paper (Zhu et al. 2007). The comparison to the corresponding results of the subject experiments and the coupled simulation using Smiths model in terms of skin temperatures indicates that the prediction accuracy of the numerical simulation is greatly improved as a whole, especially at the limbs; however, it deteriorates around the face and body parts facing cold panels when using Sakois model.

Comparison of thermal responses with and without cold protective clothing in a warm environment after severe cold exposures

Abstract 1. 1. Ten male students remained in a severely cold room (-25°C) for 20 min. thereafter, they transferred in a warm room (25°C) for 20 min. 2. 2. This pattern was repeated three times, total cold exposure time amounting to 60 min. 3. 3. In the warm room, the subjects removed their cold-protective jackets, or wore them continously. 4. 4. Rectal temperature, skin temperatures, manual performance and thermal comfort were measured during the experiment. 5. 5. Removing cold-protective jackets after severe cold exposure increased peripheral skin temperatures and reduced the discomfort in the warm room. 6. 6. However, these results were accompanied by a greater decrease in rectal temperature and manual performance. 7. 7. It is recommended that workers continue to wear cold-protective clothing in the warm areas outside of the cold storage to prevent decreases in deep body temperature and work efficiency caused by repated cold exposures.

Can a short nap and bright light function as implicit learning and visual search enhancers

The present study examined effects of a short nap (20 min) and/or bright light (2000 lux) on visual search and implicit learning in a contextual cueing task. Fifteen participants performed a contextual cueing task twice a day (1200–1330 h and 1430–1600 h) and scored subjective sleepiness before and after a short afternoon nap or a break period. Participants served a total of four experimental conditions (control, short nap, bright light and short nap with bright light). During the second task, bright light treatment (BLT) was applied in the two of the four conditions. Participants performed both tasks in a dimly lit environment except during the light treatment. Results showed that a short nap reduced subjective sleepiness and improved visual search time, but it did not affect implicit learning. Bright light reduced subjective sleepiness. A short nap in the afternoon could be a countermeasure against sleepiness and an enhancer for visual search. Practitioner Summary: The study examined effects of a short afternoon nap (20 min) and/or bright light (2000 lux) on visual search and implicit learning. A short nap is a powerful countermeasure against sleepiness compared to bright light exposure in the afternoon.

The effects of wind and thermal radiation on thermal responses during rest and exercise in a cold environment

Abstract 1. 1. The purpose of this study was to investigate the effects of thermal radiation and wind on thermal responses at rest and during exercise in a cold environment. 2. 2. The experimental conditions were radiation and wind (R + W), no radiation and wind (W), radiation and no wind (R), no radiation and no wind (C). 3. 3. The air temperature was −5°C. Thermal radiation was 360 W/m 2 . Air velocities were 0.76, 1.73 and 2.8 m/s. Rectal and skin temperatures, heart rate and oxygen consumption were recorded. Thermal and comfort sensations were questioned. 4. 4. There are no significant effects of thermal radiation and wind on the physiological responses except the mean skin temperature. There are significant effects on the mean skin temperature ( P P

Indoor thermal environment of bedroom during sleep in Malaysia

This study was conducted to investigate the indoor thermal environment and sleep of occupants in bedrooms where air conditioners (ACs) are preferentially installed. Field measurements and questionnaires were conducted for 22 houses, with a total of 28 occupants, located in the suburbs of Kuala Lumpur. The participants were requested to wear a wrist actigraphy on the non-dominant hand for three consecutive days, except while bathing or washing hands in order to evaluate sleep by the activity of the actigraphy. The average air temperatures in the bedrooms were 22.6–28.9 °C and 28.1–32.2 °C with and without AC, respectively. The observed lowest air temperature was below 21 °C in a bedroom with AC. Such low air temperatures are not considered appropriate in terms of energy consumption and the occupants’ physiological condition during sleep. The wind velocity of fresh air coming through the open window was found as well as when the use of a fan. From the relations among the factors of thermal environment, incr...

Sleep quality and air conditioner use

Airflow is an effective way to increase heat loss - an ongoing process during sleep and wakefulness in daily life. In a previous study, alleviation of heat by increased isothermal airflow reduced wakefulness, skin temperature, rectal temperature, and sweating during sleep at 32 °C with 80% relative humidity [1]. In this study, experiments were conducted to determine the effect on sleep of varying airflow velocity from air conditioners, using 10 healthy young men (age 23.0 +/- 3.6 years; height 170.9 +/- 3.6cm; mass 62.2 +/- 6.8kg) as subjects.