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Biomedical subjects

Koh Mizuno

Publications and source records attributed to Koh Mizuno.

14 recordsLinked to original sources
PubMed2006

Effects of acute simulated microgravity on nocturnal sleep, daytime vigilance, and psychomotor performance: comparison of horizontal and 6 degrees head-down bed rest.

This study examined the effect of acute simulated microgravity on nocturnal sleep, daytime vigilance, and psychomotor performance. Each of 7 volunteers were maintained for 3 days of head-down and horizontal bed rest in a counter-balanced design. Assessment measures were polysomnographic recordings on the first night and performance on psychophysiological tasks on the second day involving subjective and objective vigilance, P300, simple reaction time tasks, and dual performance tasks. No clear difference in sleep structure was observed between the head-down and horizontal conditions, except for a slight decrease in Stage 4 for head-down. Both subjective and objective daytime vigilance, P300, and the simple RT task showed no statistical difference, although tracking performance on the dual task showed deterioration at 10:00 for the head-down condition. These results suggest that nocturnal sleep, daytime vigilance, and psychophysiological functions were not disturbed in head-down sleep conditions, although there was a mild deterioration of higher attentional function in the morning.

Adult↗
PubMed2005

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 degrees 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.

Adult↗
PubMed2005

Heart rate variability under acute simulated microgravity during daytime waking state and nocturnal sleep: comparison of horizontal and 6 degrees head-down bed rest.

This study examined the acute effect of cephalad fluid shift under simulated microgravity on heart rate variability (HRV) during both daytime waking state and nocturnal sleep. Seven healthy male volunteers (21-31 years) underwent a series of experiments involving 6 degrees head-down bed rest (HD) for 3 days. A control experiment on the same subjects was conducted under horizontal bed rest (HZ) in the same series. HRV from electrocardiogram signals was periodically calculated by the MemCalc method during daytime on the first and second days of both conditions. Nocturnal sleep on the first night of bed rest was monitored by polysomnography. HRV during stage 2 sleep and REM sleep were assessed in the former and latter halves of the sleep period time. Nocturnal sleep architecture under both conditions was normal, but a slight decrease in stage 4 sleep and an increase in the number of arousals occurred under HD. On both the first and second days, HRV during the daytime did not differ between HZ and HD. In contrast, high frequency components in HRV during sleep stage 2 were significantly higher in the latter half of sleep under HD than under HZ, although there were no differences in the ratio of low frequency to high frequency components during both stage 2 and the REM stage between the conditions. These results suggest that the acute effect of the cephalad fluid shift on cardiac autonomic nervous activity might be affected by the sleep/wake state modulating the dominance between sympathetic and parasympathetic nervous activity.

Adult↗
PubMed2005

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.

Adult↗
PubMed2005

Consecutive monitoring of sleep disturbance for four nights at the top of Mt Fuji (3776 m).

The purpose of the present study was to conduct consecutive monitoring of sleep from the second to the fifth night at altitude. Three healthy male subjects climbed the top of Mt Fuji (3776 m) and stayed there for 6 days. Polysomnographic recordings were performed during this period and control recordings were made at sea level 1 month after the mountaineering. Disturbed sleep characterized by an increased number of arousals and/or long wake time was observed to persist through the fifth night in all subjects. These results suggest that sleep disturbance might persist during initial days at altitude despite cumulating sleep pressure due to poor night's sleep.

Adult↗
PubMed2004

Effects of humid heat exposure in later sleep segments on sleep stages and body temperature in humans.

This study sought to investigate the effects of humid heat exposure in later sleep segments on sleep stages and body temperature in humans. The subjects were eight healthy males, from whom informed consent had been obtained. The experiments were carried out under three different sets of conditions: a control climate [air temperature (Ta)=26 degrees C, relative humidity (RH)=50%] (C); a humid heat climate (Ta=32 degrees C, RH=80%) (H); and a humid heat exposure in later sleep segments (C for the first 3 h 45 min, followed by a 30-min transition to H, which was then maintained for the last 3 h 45 min) (C-H). Electroencephalogram, EOG, and mental electromyogram, rectal temperature (Tre), and skin temperature (Tsk) were continuously measured. The total amount of wakefulness was significantly increased in H compared to C-H or C. Compared to C, wakefulness in C-H and H was significantly increased during later sleep segments. Tre and mean Tsk were significantly higher in H than in C-H or C. In C-H, Tsk and Tre increased to levels equal to those observed in H after Ta and RH increase. Whole body sweat loss was significantly lower in C-H and C than in H. These results suggest that humid heat exposure in the later sleep segment reduces thermal load as compared to full-night humid heat exposure. In daily life, the use of air conditioning in the initial sleep hours can protect sleep and thermoregulation.

Adult↗
PubMed2004

Intravenous pamidronate prevents femoral bone loss and renal stone formation during 90-day bed rest.

UNLABELLED: Long-term bed rest has potential risks of bone loss and renal stone formation. We examined the effects of resistive exercise and intravenous pamidronate on BMD, bone turnover, urinary calcium, and renal stone formation in 25 healthy males during 90-day bed rest. Pamidronate prevented femoral bone loss and renal stone formation, but resistive exercise showed little effects. INTRODUCTION: Long-term bed rest increases the risks of bone loss and urinary stone formation. Resistive exercise increases bone formation, and bisphosphonates reduce bone resorption. However, the effects of muscle exercise and bisphosphonates have not been examined side-by-side. The objectives of this study are to compare the effects of pamidronate with resistive exercise on BMD and renal stone formation during prolonged bed rest. MATERIALS AND METHODS: Twenty-five male white volunteers, 26-45 years of age, were randomly assigned to the control (n = 9), exercise (n = 9), and pamidronate (n = 7) groups and underwent 90-day 6 degrees head-down tilt bed rest. Exercise group performed squats and heel raises on a flywheel device for 30 minutes every 3 days. Pamidronate (60 mg) was administered intravenously 14 days before bed rest. BMD of the head, forearm, lumbar spine, and proximal femur; biochemical bone markers; calcium (Ca) metabolism; and abdominal radiographs were examined during 90 days of bed rest and 360 days of reloading. RESULTS: In controls, proximal femoral BMD decreased, and bone resorption markers and urinary Ca increased during bed rest, along with development of renal stones in two of nine subjects. Resistive exercise increased bone formation but was unable to prevent femoral BMD decrease and increases in bone resorption and urinary Ca during bed rest, with formation of renal stones in four of nine subjects. Pamidronate maintained femoral BMD, reduced bone resorption and urinary Ca, and completely prevented renal stone formation. CONCLUSIONS: Resistive exercise increased bone formation but could not reduce bone resorption and the risk of renal stones. In contrast, inhibition of bone resorption by pamidronate could preserve bone mineral and reduce the risk of renal stone formation during prolonged bed rest.

Adult↗
PubMed2003

Effects of head cooling on human sleep stages and body temperature.

The purpose of this study was to confirm the effect of head cooling on human sleep stages and body temperature. Nine healthy male volunteers with a mean age of 25 +/- 3.77 years served as subjects. The experiments were carried out under three different sets of conditions: 26 degrees C, relative humidity (RH) 50% (26/50); 32 degrees C, RH 80% (32/80); and 32 degrees C RH 80% with the use of a cooling pillow (32/80 HC). The subjects slept from 2300 hours to 0700 hours with a cotton blanket, wearing short-sleeved pyjamas and shorts on a bed, which was covered with a sheet. Electroencephalograms, electro-ouclogram, and mental electromyelograms were recorded through the night. Rectal temperature (Tre) and skin temperature (Tsk) were measured continuously. Whole-body sweat and the tympanic temperature (Tty) were measured before and after sleep. Wakefulness significantly increased at 32/80 than at 26/50; however, no significant difference was observed between 32/80 HC and 26/50. Tre and mean Tsk were higher both at 32/80 and 32/80 HC than at 26/50. The whole-body sweat loss was significantly greater and Tty in the morning was higher at 32/80 than 32/80 HC and 26/50. These results suggest that head cooling during sleep may help to decrease the whole-body sweat rate during sleep under humid heat conditions.

Adult↗
PubMed2002

Psychological changes and group dynamics during confinement in an isolated environment.

PURPOSE: Cultural and personal traits will become important as the number of short-duration spaceflights of international crews supporting the International Space Station (ISS) increases and more people begin staying aboard ISS for longer durations. This project investigated the interpersonal and personal changes of Japanese subjects during a 1-wk stay in the Japanese Experiment Module. The Giebetaen Test (GT) was used to determine if the cultural background and personality traits of the subjects become more explicit and stronger during isolation. METHODS: Six males and two females aged 22-28 yr participated in the study. They stayed 7 d in the isolation chamber at the National Space Development Agency of Japan (NASDA). The GT was chosen as an individual and group diagnostic instrument; it was administrated four times during, and one time after, isolation. RESULTS: According to the GT-self-picture, subjects exhibited a change toward negative social resonance and social withdrawal. Subgroups formed but caused no isolation or tension. The GT-foreign-pictures showed that the judgment of other subjects changed toward hedonic and permeability directions. The common interpersonal relationships of the Japanese subjects influenced the group dynamics. These relationships tend to be integrative and tend to support the network and value systems, emphasizing connectedness and minimizing differences. CONCLUSION: The cultural background became more explicit and stronger during isolation. Based on this, isolation studies with international crews and intercultural training will be necessary for international crews performing both short- and long-duration missions.

Adaptation, Psychological↗
PubMed2002

Physiological changes, sleep, and morning mood in an isolated environment.

BACKGROUND: Previous isolation studies have shown increased 24-h urine volumes and body weight gains in subjects. This project examined those and other physiological variables in relationship to sleep motor activity, subjective sleep quality, mood, and complaints during confinement. METHODS: Six male and two female subjects lived for 7 d in the National Space Development Agency of Japan's isolation chamber, which simulates the interior of the Japanese Experiment Module. Each 24-h period included 6 h of sleep, 3 meals, and 20 min of exercise. Each morning, subjects completed Sleep Sensation and Complaint Index questionnaires. Catecholamine and creatinine excretion, urine volume, and body weight were measured on the 2 d before and 2 d after confinement, and sleep motor activity was measured during confinement. RESULTS: Confinement produced no significant change in body weight, urine volume, or questionnaire results. In contrast, epinephrine, norepinephrine, and sleep motor activity exhibited significant differences during confinement (p < 0.05). Higher nocturnal norepinephrine excretion correlated with higher sleep motor activity. CONCLUSION: The 24-h epinephrine values were slightly higher than normal throughout the experiment, but lower than for subjects working under time-stress. High sympathetic activity (as indicated by norepinephrine) may have interfered with sleep.

Adult↗