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Biomedical subjects

J Foret

Publications and source records attributed to J Foret.

At least 19 recordsLinked to original sources
PubMed1996

Detrimental influence of bright light exposure on alertness, performance, and mood in the early morning.

The aim of this study was to assess the effects of exposure for one night to moderate bright light (BL) on subjective and objective measures of alertness, performance, and mood. Eight subjects were exposed to either BL or dim light (DL) during one night. During the previous day, they were exposed to bright light in both experimental conditions. Nocturnal BL suppressed melatonin secretion and increased body temperature. The ability to stay awake during the night, as measured by the power density in the alpha band, was significantly improved by BL exposure. BL also improved subjective alertness and performance during the first part of the night. However, improvements in the last two variables were followed by marked disruption in early morning patterns, with deterioration of mood and motivation.

Adult↗
PubMed1996

The effect on body temperature and melatonin of a 39-h constant routine with two different light levels at nighttime.

Eight healthy subjects were studied during 39-h spans (from 07:00 on one day until 22:00 the second) in which they remained awake. During one experiment, subjects were exposed to 100 lux of light between 18:00 and 8:00, and during a second experiment, they were exposed to 1000 lux during the same time span. Throughout the daytime period, they were exposed to normal daylight (1500 lux or more). The nighttime 1000-lux light treatment suppressed the melatonin metabolite aMT6s, while the 100 lux treatment did not. On the treatment day, the 1000 lux, in comparison to the 100 lux, light treatment resulted in both an elevated temperature minimum and a delay in its clock-time occurrence overnight. No real circadian phase shift in the temperature, urinary melatonin, or cortisol rhythms was detected after light treatment. This study confirmed that nocturnal exposure to lower light intensities is capable of modifying circadian variables more than previously estimated. The immediate effects of all-night light treatment are essentially not different from those of evening light. This may be important if bright light is used to improve alertness of night workers. Whether subsequent daytime alertness and sleep recovery are affected by the protocol used in our study remains to be determined.

Adult↗
PubMed1994

Irregularity of working hours in railway workers and types of complaints.

Seventy-three permanent morning workers, 33 three-shift workers and 43 workers with irregular working schedules (roster) filled out a questionnaire on sleep, well-being and health complaints. The frequency of sick leave tended to be smaller in workers in the roster group. However, in this group health was rated "poor" more often; digestive, respiratory, osteoarticular and nervous symptoms as well as sleep difficulties were more frequently reported. In the day work and shift group, ratings of sleep quality were higher on days of rest than on working days but not in the roster group. This suggests that a worker does not at present get enough non-work days for a complete short-term recovery. In contrast, the length of sleep reported did not differ among groups. The gap between the subjective assessment of health and the actual frequency of sick leave corresponded with the irregularity of the working schedule.

Absenteeism↗
PubMed1993

Temperature drop and sleep: testing the contribution of SWS in keeping cool.

Sleep and body temperature characteristics were studied in man in baseline (B), 24 h-constant routine (CR) and recovery (R) after the CR. The sleep advanced and deepened the trough of the minimum temperature when compared with CR. No relevant difference in minimum body temperature, or in the slope of temperature decrease was found, however, between B and R sleeping nights. No correlation was found between the amount of slow wave sleep and body cooling. The results do not support a homeostatic role of slow wave sleep in brain and/or body cooling.

Adult↗
PubMed1993

Effect of morning bright light on body temperature, plasma cortisol and wrist motility measured during 24 hour of constant conditions.

Using 24 h constant conditions, time course of body temperature, plasma cortisol and wrist motility was measured in response to a 3 day morning 2 h bright light pulse. This protocol demonstrated that a 2000 lux illumination was sufficient to elicit a shift of about 2 h of temperature minimum and cortisol peak. In reference session, actimetric recordings showed a circadian time course, closely in relation with core temperature. Bright light pulse resulted in a decrease of amplitude and a disappearance of circadian pattern of actimetry.

Adult↗
PubMed1993

Bright light affects alertness and performance rhythms during a 24-h constant routine.

The aim of the present study was to assess the stimulating effects of bright light (BL) on subjective and objective alertness. Eight subjects were exposed to either bright light or dim light (DL) during a 24-h constant routine (0900-0900). Bright light failed to modify either the 24-h course or the level of body temperature. Compared to DL, BL delayed the circadian trough of motor activity by 2 h. During the night, relative to the dim-light condition, BL significantly increased subjective and objective (EEG test) alertness and improved performances. Thus, BL exposure partly counteracted the effects of sleep deprivation and/or the circadian trough on alertness and performances. During the day, BL only improved the mood and motivation levels. However, the time course of mood and motivation was not affected by the BL exposure, a nocturnal circadian trough occurring at 0630 in both light conditions.

Arousal↗
PubMed1992

Effects of a two-hour early awakening and of bright light exposure on plasma patterns of cortisol, melatonin, prolactin and testosterone in man.

Bright light is a synchronizing agent that entrains human circadian rhythms and modifies various endocrine and neuroendocrine functions. The aim of the present study was to determine whether and how the exposure to a bright light stimulus during the 2 h following a 2 h earlier awakening could modify the disturbance induced by the the sleep deprivation on the plasma patterns of hormones whose secretion is sensitive to light and/or sleep, namely melatonin, prolactin, cortisol and testosterone. Six healthy and synchronized (lights on: 07.00-23.00) male students (22.5 +/- 1.1 years) with normal psychological profiles volunteered for the study in winter. The protocol consisted of a baseline control night (customary sleep schedule) followed by three shortened nights with a rising at 05.00 and a 2 h exposure to either dim light (50 lux; one week) or bright light (2000 lux; other week). Our study showed a phase advance of the circadian rhythm of plasma cortisol without significant modifications of the hormone mean or peak concentration. Plasma melatonin concentration decreased following bright light exposure, whereas no obvious modifications of plasma testosterone or prolactin patterns could be observed in this protocol.

Adult↗
PubMed1990

Modifications of sleep structure by brief forced awakenings at different times of the night.

Four subjects were awakened once a night for 10 min at either 01.30, 03.30 or 05.30 h. During the waking intervals, they performed a mental task while remaining in bed. The awakenings did not significantly modify the amount of different stages during subsequent sleep with no effect of time of occurrence in the night. In contrast, the timing of the awakening within the cycle had a significant influence on REM cycle structure. If awakening occurred during a REM episode or shortly thereafter, the following inter-REM interval was shortened; if it occurred late in the cycle, that is shortly before a REM episode, it increased the inter-REM interval beyond the reference length of the corresponding uninterrupted cycle. An explanation based on a model of sleep which implies the simultaneous activity of REM-on and REM-off neurones is proposed.

Adult↗
PubMed1990

Psychophysiological effects of early morning bright light exposure in young adults.

The effects of bright light on circadian rhythms in man are well documented. Nevertheless the theoretical basis and the rules for the practical utilization of light exposure as therapy need still to be better defined. The present study determined to what extent a 2-hr bright light exposure (0500-0700 h) improved the adjustment to an early rising in normal adults. Phase changes were assessed in subjective alertness, performance in several search tasks, time estimation, and a visual discrimination task, as well as in body motility, plasma cortisol concentrations, and body temperature. In comparison with a dim light exposure, the bright light resulted in increased motor activity during waking, in earlier peak of subjective alertness, and an improvement in performance speed in three out of five tasks in the morning. Cortisol and body temperature also were phase-advanced. In summary, light applied to a portion of the circadian cycle sensitive to phase advance shifts influenced rhythms with strong endogenous components (temperature and cortisol), while other rhythms with strong exogenous components were more sensitive to sleep deprivation caused by the early rising time.

Adult↗
PubMed1990

The Multiple Sleep Latency Test: individual variability and time of day effect in normal young adults.

The influence of individual characteristics on diurnal physiological sleep tendency was investigated in young good sleepers. Fifty-five subjects underwent a Multiple Sleep Latency Test (MSLT) procedure. Among them 11 also participated in Repeated Test Sustained Wakefulness (RTSW) procedure. The MSLT results were analyzed as a function of both the number of sleep onsets per day and the time of day. Diurnal sleepiness seemed to be better appreciated by sleep onset (SO) frequency than by the traditional criteria of sleep latency. SO frequency, unlike latency, was influenced by factors such as usual sleep duration, morning/evening score, and RTSW procedure. Time of day effect was characterized by a decrease in sleep tendency at the beginning and at the end of the day (decrease in SO frequency and increase in SO latencies); between these two points a peak of sleepiness around 1400 was observed. The morning and evening periods of high alertness could represent important anchor points for the coupling of the sleep/wake and temperature rhythms.

Adult↗
PubMed1990

Daytime wakefulness following a bedtime oral dose of zolpidem 20 mg, flunitrazepam 2 mg and placebo.

1. The effects of zolpidem 20 mg, flunitrazepam 2 mg and placebo, administered at bed time, were studied in 12 healthy young male volunteers. 2. The assessments included, at awakening, subjective ratings of overnight sleep, cognitive function, psychomotor performance (digit symbol substitution, choice reaction time, flicker fusion threshold), subjective ratings of alertness, and plasma assay of residual drug concentration. Daytime sleep propensity during the day after dosing was evaluated with the multiple sleep latency test. 3. Compared with placebo, both active drugs improved subjective assessment of the ease of getting to sleep. At awakening, under flunitrazepam treatment, the reduction of performance, on memory and psychomotor tests, paralleled an increased subjective rating of sleepiness, but zolpidem treatment left subjects unimpaired compared with placebo. Similarly, daytime sleep propensity was enhanced throughout the following day under flunitrazepam treatment, but not under zolpidem treatment. Plasma assay for residual drug concentration at awakening found significant amounts of flunitrazepam and marginal amounts of zolpidem. 4. Results indicate that zolpidem 20 mg is devoid of residual effects in a range of tasks that were sensitive enough to demonstrate a prolonged wakefulness impairment following flunitrzepam 2 mg in healthy volunteers.

Administration, Oral↗
PubMed1988

[Circadian regulation of the sleep-wake cycle].

A review of the studies considering the sleep/wake alternation as a biological circadian cycle is presented. The methods designed to evaluate respectively the role of both the endogenous component and the external synchronizers of isolation (free-running protocols). There are mutual relations between wake/sleep cycle and some other circadian rhythms, particularly body temperature rhythm. When sleep is subjected to any time manipulation, the homeostatic regulation of some sleep characteristics (REM-sleep amount, sleep onset probability, sleep length) remains very strong. Alertness appears to be linked both to sleep characteristics and to internal temperature evolution. In addition, it proved to present some degree of independence of the two afore mentioned factors, specially when motivation and/or other psychological factors are involved. The afternoon nap, far from being simply after lunch reaction, is a normal manifestation of circadian rhythmicity.

Attention↗
PubMed1987

Early rising or delayed bedtime: which is better for a short night's sleep?

The present study compares the effects on sleep and the subsequent period of wakefulness of delaying bedtime of 2 h or advancing rising time by 2 h in subjects clearly differentiated by morningness or eveningness in their circadian rhythms. Twelve young healthy good sleepers, six morning types (MT) and six evening types (ET), were selected. The data obtained from the second 24 h (night and day) with delayed bedtime (DB) and advanced rising time (AR) were compared with those obtained in the reference condition (R) with normal sleep schedules. Sleep was recorded polygraphically and rectal temperature was continuously monitored during the nights and during the day following the second night of each condition. Subjective estimations of alertness, performance tasks and urinary steroids were analysed. Early rising appeared to be more disturbing than a late bedtime. The second shortened night showed fewer characteristics of recovery sleep in AR than in DB. The decrease in self rated alertness was a function both of the type of condition (DB or AR) and of the morning-evening typology of the subject. The largest decrease was observed in AR and in the ET subjects. AR also resulted in the most pronounced decrease in performance tasks and in an increase in urinary 17 ketosteroids without changes in the 17 hydroxy-corticosteroids. The effects on rectal temperature were limited to short periods after bedtime in DB and rising time in AR.

17-Hydroxycorticosteroids↗
PubMed1986

Diurnal variation in subjective and objective measures of sleepiness: the effects of sleep reduction and circadian type.

In young, good sleepers the diurnal evolution of alertness was studied as a function of degree of morningness: (1) during habitual sleep routine and (2) in a 2-hr sleep reduction protocol. During habitual sleep routine, alertness was assessed using both the subjective evaluation based on Thayer's Activation Deactivation Adjective Checklist (43 subjects) and the objective measurement of sleep latency (Multiple Sleep Latency Test, MSLT). Self-alertness scored highest around midday. Later it showed a dip, then stayed on a plateau until about 2200 hr. On average, 77% of the subjects fell asleep at the 1400 hr MSLT session while only 35.5% did at 1000 hr and 25.8% at 2000 hr. Morning-types (MT) and evening-types (ET) differed only during the morning: ET fell asleep more frequently at 1000 hr and 1200 hr and rated lower self-alertness on arising than did MT. Twelve subjects were given the protocol of a 2-hr sleep reduction (both in delayed bedtime and advanced rising time conditions). At 0700 hr, MT rated their alertness lower when they had only just gotten up (delayed bedtime condition) than when they had been awake for 2 hr (advanced rising time condition). In contrast, ET had the same low level of alertness at 0800 hr, independent of the time elapsed since arising. On average the advanced rising time condition affected the general pattern of alertness more than did delayed bedtime.

Adult↗
PubMed1985

Sleep and body temperature in "morning" and "evening" people.

Three groups of young, normal sleepers were selected as morning types (MTs), evening types (ETs), and neither types (NTs) as determined by the Horne and Ostberg questionnaire. Sleep and rectal temperatures were recorded under three conditions: baseline nights (Cond. 1), sleep on the recovery day after 1 night of sleep deprivation (Cond. 2), and sleep on the recovery night after 1 night and 1 day of sleep deprivation (Cond. 3). During Conds. 1 and 3, when sleep schedules were self-determined, sleep structure and body temperature were similar in MTs, and ETs, and NTs. During Cond. 2, however, MTs had poorer sleep, i.e., a smaller percentage of REM sleep and more awakenings, than ETs. This difference can be related to the evolution of temperature during Cond. 2; i.e., a temperature increase in the MT and NT and a decrease in the ET.

Adult↗