The Effects of Different Light Intensities during the Daytime on the Forearm Blood Flow and Mean Body Temperature in the Evening.

Aizawa, Seika; Tokura, Hiromi

doi:10.2170/jjphysiol.46.481

Cited by 13 publications

(7 citation statements)

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“…It might have been due to a reduced set-point of core temperature induced by the exposure to 6-h bright light during the morning. A reduced set-point of core temperature under the in¯uence of the bright light has previously been suggested for thermal sensation (Teramoto et al 1996), for rectal (Tokura et al 1994) and tympanic (Aizawa and Tokura 1997) temperatures, for dressing behaviour in the cold (Kim and Tokura 1995) and for the relationship between forearm skin blood¯ow and mean body temperature (Aizawa and Tokura 1996). The reduced set-point of core temperature might have acted to inhibit the increase of rectal temperature via an increase of melatonin concentration (Fig.…”

Section: Discussionmentioning

confidence: 78%

Thermoregulatory responses in humans during exercise after exposure to two different light intensities

Zhang

Tokura

1999

European Journal of Applied Physiology

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The effects after exposure to two different light intensities (dim, 50 lx and bright, 5000 lx) on thermoregulatory responses during exercise in a climatic chamber (27 degrees C, 60% relative humidity) were studied in nine untrained female subjects, aged 19-22 years. The subjects were in either the dim or bright light intensities from 0600 hours to 1200 hours. They were then instructed to exercise on a cycle ergometer at an intensity of 60% maximal oxygen uptake from 1200 hours to 1300 hours in a light intensity of 500 Ix. The main results can be summarized as follows. Firstly, exercise-induced increases of core temperature were significantly smaller, after exposure to the bright than after the dim light intensities, although both tests were performed in the same light intensity. Secondly, body mass loss after exercise was significantly greater after exposure to the bright light intensity. Thirdly, an increase in salivary lactic acid during exercise was significantly lower after the bright intensity. Fourthly although the salivary melatonin level was not different between the two light intensities both before and after the exercise, it increased significantly during exercise only after the bright intensity. These results are discussed in terms of the establishment of a lower set-point in the core temperature after exposure to a bright light intensity.

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Section: Discussionmentioning

confidence: 78%

Thermoregulatory responses in humans during exercise after exposure to two different light intensities

Zhang

Tokura

1999

European Journal of Applied Physiology

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“…Furthermore, we have found that exposure to bright light of 4000 lux from 0930 hours to 1800 hours induced a steeper slope of the regression line between skin blood ow of the forearm and mean body temperature under an external heat load in the evening than after dim light of 100 lux (Aizawa and Tokura 1996). Although all these ®ndings would suggest that bright light exposure during the daytime may modulate thermoregulation in humans and probably reduce the set point of core temperature, it seems necessary that more data be collected under various conditions to draw these conclusions.…”

Section: Introductionmentioning

confidence: 76%

Influence of bright light exposure for several hours during the daytime on cutaneous vasodilatation and local sweating induced by an exercise heat load

Aizawa

Tokura

1998

European Journal of Applied Physiology

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The aim of the present study was to investigate the effect of exposure to differing light intensities for several hours during the daytime on the cutaneous vasodilatation and local forearm sweat rate induced by exercise. Seven healthy female subjects were exposed to bright light of 6000 lux (bright) or dim light of 100 lux (dim) during the daytime between 0900 hours to 1330 hours, followed by exposure to 150 lux until the test was over at 1600 hours. They spent their time in neutral conditions (29 degrees C, 40% relative humidity) from 0900 hours to 1500 hours, and then exercised on a cycle ergometer for 30 min at 50% maximal physical work capacity. Average tympanic temperatures were significantly lower in bright than in dim from 1133 hours to 1430 hours. The onset of cutaneous vasodilatation and local forearm sweating occurred at significantly lower tympanic temperature (Tty) during exercise after bright than after dim. After exercise, the cessation of forearm sweating and the rapid change of skin blood flow occurred at significantly lower Tty after bright than after dim. It was concluded that exposure to bright light over several hours during the daytime could reduce Tty and shift the threshold Tty for cutaneous vasodilatation and forearm sweating to a lower level.

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“…Thus, the effect of bright light exposure on subsequent sleep appears to depend on the effect on body temperature: A stronger decrease is associated with sleep facilitation, whereas an attenuated decrease is associated with a longer sleep latency. It has indeed been shown that bright light exposure during the day causes a stronger release of peripheral vasoconstrictor activity during the subsequent night, resulting in increased skin blood flow and skin temperature and decreased rectal temperature (Aizawa and Tokura 1996). It should be noted that bright light not only temporarily affects temperature, but also can increase the general level of arousal (Badia et al 1991) as well as shift the circadian rhythm and thereby either improve (Campbell et al 1993) or disturb (Cajochen et al 1992) sleep.…”

Section: Effects On Sleep Of Changes In Thermoregulation and Body Andmentioning

confidence: 99%

More Than a Marker: Interaction Between the Circadian Regulation of Temperature and Sleep, Age-Related Changes, and Treatment Possibilities

Someren

2000

Chronobiology International

287

193

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The neurobiological mechanisms of both sleep and circadian regulation have been unraveled partly in the last decades. A network of brain structures, rather than a single locus, is involved in arousal state regulation, whereas the suprachiasmatic nucleus (SCN) has been recognized as a key structure for the regulation of circadian rhythms. Although most models of sleep regulation include a circadian component, the actual mechanism by which the circadian timing system promotes--in addition to homeostatic pressure--transitions between sleep and wakefulness remains to be elucidated. Little more can be stated presently than a probable involvement of neuronal projections and neurohumoral factors originating in the SCN. This paper reviews the relation among body temperature, arousal state, and the circadian timing system and proposes that the circadian temperature rhythm provides an additional signaling pathway for the circadian modulation of sleep and wakefulness. A review of the literature shows that increased brain temperature is associated with a type of neuronal activation typical of sleep in some structures (hypothalamus, basal forebrain), but typical of wakefulness in others (midbrain reticular formation, thalamus). Not only local temperature, but also skin temperature are related to the activation type in these structures. Warming of the skin is associated with an activation type typical of sleep in the midbrain reticular formation, hypothalamus, and cerebral cortex (CC). The decreasing part of the circadian rhythm in core temperature is mainly determined by heat loss from the skin of the extremities, which is associated with strongly increased skin temperature. As such, alterations in core and skin temperature over the day could modulate the neuronal activation state or "preparedness for sleep" in arousal-related brain structures. Body temperature may thus provide a third signaling pathway, in addition to synaptic and neurohumoral pathways, for the circadian modulation of sleep. A proposed model for the effects of body temperature on sleep appears to fit the available data better than previous hypotheses on the relation between temperature and sleep. Moreover, when the effects of age-related thermoregulatory alterations are introduced into the model, it provides an adequate description of age-related changes in sleep, including shallow sleep and awakening closer to the nocturnal core temperature minimum. Finally, the model indicates that appropriately timed direct (passive heating) or indirect (bright light, melatonin, physical activity) manipulation of the nocturnal profile of skin and core temperature may be beneficial to disturbed sleep in the elderly. Although such procedures could be viewed by researchers as merely masking a marker for the endogenous rhythm, they may in fact be crucial for sleep improvement in elderly subjects.

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The Effects of Different Light Intensities during the Daytime on the Forearm Blood Flow and Mean Body Temperature in the Evening.

Abstract: The subjects were exposed to bright or dim light during the daytime. Compared to dim light exposure, bright light exposure induced a steeper slope in the regression line between the skin blood flow of the forearm and mean body temperature under an external heat load in the evening.

Cited by 13 publications

References 0 publications

Thermoregulatory responses in humans during exercise after exposure to two different light intensities

Thermoregulatory responses in humans during exercise after exposure to two different light intensities

Influence of bright light exposure for several hours during the daytime on cutaneous vasodilatation and local sweating induced by an exercise heat load

More Than a Marker: Interaction Between the Circadian Regulation of Temperature and Sleep, Age-Related Changes, and Treatment Possibilities

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