Biomedical subjects

G Brandenberger

Publications and source records attributed to G Brandenberger.

At least 19 recordsLinked to original sources

PubMed2006

Relationship between very high physical activity energy expenditure, heart rate variability and self-estimate of health status in middle-aged individuals.

In middle-aged persons, moderate physical activity energy expenditure (PAEE) has been shown to be associated with increased vagal-related heart rate variability (HRV) indexes and better health status. The purpose of this study was to determine whether a very high PAEE has greater effect on vagal-related HRV indexes and self-estimates of well-being in middle-aged subjects having distinct long-term physical activity profiles. Forty-four subjects were divided into three groups on the basis of the sport score of the Modified Baecke Questionnaire for Older Adults: sedentary (SED, n = 15), moderately-trained (MT, n = 16), and highly-trained subjects (HT, n = 13). PAEE was estimated by triaxial accelerometry during one week. Time and frequency domain HRV indexes were determined during quiet periods in the morning on 5-min R-R interval segments under controlled breathing. Quality of life was evaluated using the SF-36 health survey questionnaire. PAEE was significantly different for each group (374.5 +/- 13.8, 616.8 +/- 22.4, and 1086.6 +/- 43.2 kcal . day (-1) for SED, MT, and HT, respectively, p < 0.001). MT presented significantly higher vagal-related HRV indexes than SED and HT (p < 0.05). None of the HRV indexes was significantly greater in HT than in SED. MT and HT had similar health status scores, which were significantly higher than for SED. These results indicate that in middle-aged subjects, habitual moderate PAEE is associated with greater vagal tone and self-estimates of well-being compared to low PAEE. In contrast, very high PAEE is associated with similar vagal-related indexes as low PAEE, despite better overall health status.

Aging↗

PubMed2004

Effects of increased training load on vagal-related indexes of heart rate variability: a novel sleep approach.

There is little doubt that moderate training improves cardiac vagal activity and thus has a cardioprotective effect against lethal arrhythmias. Our purpose was to learn whether a higher training load would further increase this beneficial effect. Cardiac autonomic control was inferred from heart rate variability (HRV) and analyzed in three groups of young subjects (24.5 +/- 3.0 yr) with different training states in a period free of stressful stimuli or overload. HRV was analyzed in 5-min segments during slow-wave sleep (SWS, a parasympathetic state that offers high electrocardiographic stationarity) and compared with data collected during quiet waking periods in the morning. Sleep parameters, fatigue, and stress levels checked by questionnaire were identical for all three groups with no signs of overtraining in the highly trained (HT) participants. During SWS, a significant (P <0.05) increase in absolute and normalized vagal-related HRV indexes was observed in moderately trained (MT) individuals compared with sedentary (Sed) subjects; this increase did not persist in HT athletes. During waking periods, most of the absolute HRV indexes indistinctly increased in MT individuals compared with controls (P < 0.05) but did not increase in HT athletes. Normalized spectral HRV indexes did not change significantly among the three groups. Heart rate was similar for MT and Sed subjects but was significantly (P <0.05) lower in HT athletes under both recording conditions. These results indicate that SWS discriminates the state of sympathovagal balance better than waking periods. A moderate training load is sufficient to increase vagal-related HRV indexes. However, in HT individuals, despite lower heart rate, vagal-related HRV indexes return to Sed values even in the absence of competition, fatigue, or overload.

Adult↗

PubMed2004

Sympathovagal response to orthostatism in overt and in subclinical hyperthyroidism.

Heart rate variability (HRV) is a measure of the physiological variation of R-R intervals, reflecting the sympathovagal balance. In both overt and subclinical hyperthyroidism, a relative increase in sympathetic activity has been demonstrated, mainly due to a decrease in vagal activity. The modifications of HRV during orthostatism in normal subjects resemble those seen in hyperthyroidism. We have studied the response of 19 patients with overt hyperthyroidism and 12 with subclinical hyperthyroidism during orthostatism using HRV and compared the results to those of 32 healthy controls. In the three groups, the R-R intervals decreased in the same proportion after orthostatism. The low frequency power (LF)/[LF + high frequency power (HF)] ratio, which reflects the sympathetic tone, also increased in the same proportion in the three groups. However, the mechanisms of the modulation of the sympathovagal balance during orthostatism were different among the three groups. In controls, the relative increase of sympathetic tone after orthostatism was due principally to a decrease in vagal tone (reflected by decreased power in the HF band), while in overt hyperthyroidism, where the power in the HF band was already minimal in the lying position, there was a clear increase in the LF band power during orthostatism. The results were intermediate in the subclinical hyperthyroidism group, reflecting a continuum of effects of the thyroid hormone excess on the autonomic nervous system. Our study shows that despite an apparent normal cardiovascular adaptation to orthostatism in hyperthyroidism, the modulation of the autonomic nervous system is profoundly modified.

Adult↗

PubMed2004

Abnormal heart rate variability in a subject with second degree atrioventricular blocks during sleep.

OBJECTIVE: We compare the profiles of heart rate variability (HRV) during sleep stages in 9 healthy controls and one subject with second degree atrioventricular blocks (AVB), investigating the role of sympathovagal balance in such pathology. METHOD: Sleep and cardiac records were taken for one night in 9 male subjects from 21:00 to 07:00 h and for two nights in a male subject with AVB. Time and frequency domain indexes of HRV were calculated over 5 min-periods. RESULTS: In one subject without any daytime heart disease, 253 and 318 AVB of type 2 (Mobitz 2) were observed during the two experimental nights, predominantly during rapid eye movement (REM) sleep and the surrounding sleep stage 2 in the second half of the night. In the 9 control subjects, absolute HRV indexes and low frequency (LF)/(LF+high frequency, HF) (where LF and HF are low frequency and high frequency power) were low during slow wave sleep, and significantly increased during REM sleep and the preceding sleep stage 2. In the subject with AVB, these HRV indexes were abnormally low during all sleep stages, with a predominant increase in parasympathetic activity as inferred from low LF/(LF+HF). During wake, however, LF/(LF+HF) normally increased, and the tachycardia observed with the arousal that terminates SWS was preserved in the subject with AVB. CONCLUSION: These results suggest that in the subject with second degree atrioventricular blocks, sleep processes, particularly during REM sleep, create a specific neurological background that prevents an increase in sympathetic tone and triggers cardiac pauses.

Adult↗

PubMed2004

Effect of acute hypoxia on heart rate variability at rest and during exercise.

The purpose of this study was to investigate sympathovagal balance as inferred from heart rate variability (HRV) responses to acute hypoxia at rest and during exercise. HRV was evaluated in 12 healthy subjects during a standardized hypoxic tolerance test which consists of four periods alternating rest and moderate exercise (50 % V.O (2)max) in normoxic and hypoxic conditions. Ventilatory responses were determined and HRV indexes were calculated for the last 5 min of each period. In well-tolerant subjects, hypoxia at rest induced a decrease of root-mean-square of successive normal R-R interval differences (RMSSD) (p < 0.05) and of absolute high frequency (HF) power (p < 0.001). All absolute HRV indexes were strongly reduced during exercise (p < 0.001) with no further changes under the additional stimulus of hypoxia. A significant increase (p < 0.05) in the HF/(LF+HF) ratio (where LF is low frequency power) was found during exercise in hypoxia compared to exercise in normoxia, associated with similar mean changes in ventilation and tidal volume. These results indicate a vagal control withdrawal under hypoxia at rest. During exercise at 50 % V.O (2)max, HRV indexes cannot adequately represent cardiac autonomic adaptation to acute hypoxia, or possibly to other additional stimuli, due to the dominant effect of exercise and the eventual influence of confounding factors.

Adaptation, Physiological↗

PubMed2003

Mechanisms of renal hyporesponsiveness to ANP in heart failure.

The atrial natriuretic peptide (ANP) plays an important role in chronic heart failure (CHF), delaying the progression of the disease. However, despite high ANP levels, natriuresis falls when CHF progresses from a compensated to a decompensated state, suggesting emergence of renal resistance to ANP. Several mechanisms have been proposed to explain renal hyporesponsiveness, including decreased renal ANP availability, down-regulation of natriuretic peptide receptors and altered ANP intracellular transduction signal. It has been demonstrated that the activity of neutral endopeptidase (NEP) is increased in CHF, and that its inhibition enhances renal cGMP production and renal sodium excretion. In vitro as well as in vivo studies have provided strong evidence of an increased degradation of intracellular cGMP by phosphodiesterase in CHF. In experimental models, ANP-dependent natriuresis is improved by phosphodiesterase inhibitors, which may arise as new therapeutic agents in CHF. Sodium-retaining systems likely contribute to renal hyporesponsiveness to ANP through different mechanisms. Among these systems, the renin-angiotensin-aldosterone system has received particular attention, as angiotensin II and ANP have renal actions at the same sites and inhibition of angiotensin-converting enzyme and angiotensin-receptor blockade improve ANP hyporesponsiveness. Less is known about the interactions between the sympathetic nervous system, endothelin or vasopressin and ANP, which may also blunt ANP-induced natriuresis. To summarize, renal hyporesponsiveness to ANP is probably multifactorial. New treatments designed to restore renal ANP efficiency should limit sodium retention in CHF patients and thus delay the progression to overt heart failure.

Arginine Vasopressin↗

PubMed2003

[The ultradian rhythm of sleep: diverse relations with pituitary and adrenal hormones].

We evaluated the relationship between the ultradian rhythm of sleep and the secretory episodes of pituitary-adrenal hormones. Prolactin (PRL) and TSH exhibited opposite phase relationships with delta waves, PRL increasing and TSH decreasing when delta waves developed. Delta waves never increased together with an increase in cortisol secretion. They oscillated independently from each other throughout the 24 hour period, but when they were present at the same time, they oscillated in opposing phases. Concerning growth hormone (GH), its major peak which occurred shortly after sleep onset in association with the first slow wave sleep episode was blunted during sleep deprivation. However, this blunting was compensated during the day, so that the amount of GH secreted during a 24-hr period was similar whether or not a person had slept during the night. The physiological significance and the clinical implications of the various relationships of the endocrine systems with sleep are poorly known.

Adult↗

PubMed2002

The start of the quiescent period of cortisol remains phase locked to the melatonin onset despite circadian phase alterations in humans working the night schedule.

Using a 10-min blood sampling procedure, we established 24-h plasma melatonin and cortisol rhythms in 11 night workers and determined whether the extent in the shift of the melatonin onset, highly variable among night workers, was reflected in the shift of the markers of the cortisol rhythm, i.e. the quiescent period of secretion and the acrophase. In all day-active subjects, the melatonin onset occurred during low cortisol secretion, with a time lag between the start of the quiescent period and the melatonin onset of 1 h 28+or-27 min. In night workers, whatever the shift of the melatonin surge, the start of the quiescent period of cortisol secretion remained phase locked to the melatonin onset with a similar time lag (1 h 25+or-27 min). There was a significant correlation between the timing of the melatonin onset and the timing of the start of the quiescent period (r=0.88; P=0.0072). No preserved time lag was found between the melatonin onset and the other cortisol phase markers, either with the end of the quiescent period or with the acrophase. These results settle the start of the quiescent period of cortisol and the melatonin onset as two coordinate markers, and suggest that each of them are reliable to assess circadian phase in humans.

Adaptation, Physiological↗

PubMed2002

Time-courses in renin and blood pressure during sleep in humans.

We previously described a strong concordance between nocturnal oscillations in plasma renin activity (PRA) and the rapid eye movement (REM) and non-REM (NREM) sleep cycles, but the mechanisms inducing PRA oscillations remain to be identified. This study was designed to examine whether they are linked to sleep stage-related changes in arterial blood pressure (ABP). Analysis of sleep electroencephalographic (EEG) activity in the delta frequency band, intra-arterial pressure, and PRA measured every 10 min was performed in eight healthy subjects. Simultaneously, the ratio of low frequency power to low frequency power + high frequency power [LF/(LF + HF)] was calculated using spectral analysis of R--R intervals. The cascade of physiological events that led to increased renin release during NREM sleep could be characterized. First, the LF/(LF + HF) ratio significantly (P < 10(-4) decreased, indicating a reduction in sympathetic tone, concomitantly to a significant (P < 10(- 3) decrease in mean arterial pressure (MAP). Delta wave activity increased (P < 10(-4) 10-20 min later and was associated with a lag of 0-10 min with a significant rise in PRA (P < 10(-4) . Rapid eye movement sleep was characterized by a significant increase (P < 10(-4) in the LF/(LF + HF) ratio and a decrease (P < 10(-4) in delta wave activity and PRA, whereas MAP levels were highly variable. Overnight cross-correlation analysis revealed that MAP was inversely correlated with delta wave activity and with PRA (P < 0.01 in all subjects but one). These results suggest that pressure-dependent mechanisms elicit the nocturnal PRA oscillations rather than common central processes controlling both the generation of slow waves and the release of renin from the kidney.

Adult↗

PubMed2001

Inverse coupling between ultradian oscillations in delta wave activity and heart rate variability during sleep.

OBJECTIVE: We investigate the relationship between changes in heart rate variability and electroencephalographic (EEG) activity during sleep. METHOD: Nine male subjects with regular non-rapid-eye movement-rapid-eye movement (NREM-REM) sleep cycles were included in the study. They underwent EEG and cardiac recordings during one experimental night. Heart rate variability was determined over 5-min periods by the ratio of low frequency to low frequency plus high frequency power [LF/(LF+HF)] calculated using spectral analysis of R-R intervals. EEG spectra were analyzed using a fast Fourier transform algorithm. RESULTS: We found an ultradian 80-120 min rhythm in the LF/(LF+HF) ratio, with high levels during rapid eye movement (REM) sleep and low levels during slow wave sleep (SWS). During sleep stage 2 there was a progressive decrease in the transition from REM sleep to SWS, and an abrupt increase from SWS to REM sleep. These oscillations were significantly coupled in a 'mirror-image' to the overnight oscillations in delta wave activity, which reflect sleep deepening and lightening. Cardiac changes preceded EEG changes by about 5 min. CONCLUSIONS: These findings demonstrate the existence of an inverse coupling between oscillations in delta wave activity and heart rate variability. They indicate a non-uniformity in sleep stage 2 that underlies ultradian sleep regulation.

Activity Cycles↗

PubMed2001

Sleep deprivation blunts the night time increase in aldosterone release in humans.

The aim of this study was to determine the effect of sleep deprivation on the 24-h profile of aldosterone and its consequences on renal function. Aldosterone and its main hormonal regulatory factors, ACTH (evaluated by cortisol measurement) and the renin-angiotensin system [RAS, evaluated by plasma renin activity (PRA) measurement] were determined every 10 min for 24 h in eight healthy subjects in the supine position, once with nocturnal sleep and once during total 24-h sleep deprivation. Plasma Na(+) and K(+) were measured every 10 min in four of these subjects. In an additional group of 13 subjects under enteral nutrition, diuresis, natriuresis and kaliuresis were measured once during the sleep period (23.00--07.00 h) and once during a 23.00--07.00 hours sleep deprivation period. During sleep deprivation, aldosterone displayed lower plasma levels and pulse amplitude in the 23.00--07.00-hour period than during sleep. Similarly, PRA showed reduced levels and lower pulse frequency and amplitude. Plasma cortisol levels were slightly enhanced during sleep deprivation. Overnight profiles of plasma K(+) and Na(+) were not affected. Diuresis and kaliuresis were not influenced by sleep deprivation. In contrast, natriuresis significantly increased during sleep deprivation. This study demonstrates that sleep deprivation modifies the 24-h aldosterone profile by preventing the nocturnal increase in aldosterone release and leads to altered overnight hydromineral balance.

Adrenocorticotropic Hormone↗

PubMed2001

Hypothalamo-pituitary-adrenal axis activity is related to the level of central arousal: effect of sleep deprivation on the association of high-frequency waking electroencephalogram with cortisol release.

The temporal and quantitative interrelationships between the hypothalamo-pituitary-adrenal (HPA) axis activity and the level of central arousal were studied in 10 healthy young men during daytime wakefulness. Two experimental sessions were conducted randomly between 09.00 and 18.00 h, once after nocturnal sleep and once after a night of total sleep deprivation. Spectral analysis of serial waking electroencephalography (EEG) from a short target fixation task repeated every 10 min was undertaken, along with an estimation of cortisol secretory profiles by deconvolution of plasma radioimmunoassay measures obtained from continuous blood withdrawal with regular sampling at a 10-min interval. Following nocturnal sleep, a temporal association between the HPA axis activity and the waking EEG activity was found, cortisol secretory rate following changes in frontal gamma (20-45 Hz) band power by 10 min (average R = 0.458, p < 0.001). Although it remained significant (average R = 0.276, p < 0.05), the association strength decreased significantly following total sleep deprivation (p < 0.05, Wilcoxon test). Cortisol plasma level, secretory rate and pulse amplitude were increased as well as waking EEG power in the delta (0.5-5.5 Hz), theta (5.5-8.5 Hz) and gamma frequency bands (all p values <0.05, Student t tests). The sleep deprivation-related increases in cortisol secretory rate and waking EEG gamma activity were quantitatively associated (R = 0.504, p < 0.05). These results support the existence of a common ultradian regulatory mechanism, co-ordinating HPA axis activity to the level of central arousal in man, which seems involved in the sleep deprivation-induced hyper-arousal.

Adrenal Glands↗

PubMed2000

Effect of sleep deprivation on overall 24 h growth-hormone secretion.

After sleep deprivation, the blunting of the normal sleep-related growth-hormone (GH) pulse is compensated during the day. Consequently, the amount of GH secreted during a 24 h period is similar whether or not a person has slept during the night. These results argue against the belief that sleep disorders in children can inhibit growth through a daily GH deficit.

Adult↗

PubMed2000

High frequency waking EEG: reflection of a slow ultradian rhythm in daytime arousal.

The ultradian dynamics of the human waking EEG was studied using a short visual fixation task repeated every 10 min throughout the daytime. The EEG spectra obtained from the tasks were assessed for time effect and ultradian periodicity. Fronto-central EEG high frequency powers (22.5-44.5 Hz) decreased at the time of the midafternoon vigilance dip (14.00-17.00 h) along with slight concomitant increases in parietal alpha (7.5-13.5 Hz) and delta (1-3 Hz) powers. A slow ultradian rhythm with a 3-4 h periodicity strongly modulated EEG power in all frequency bands between 1 and 44.5 Hz. The high frequency waking EEG may well reflect the activity of a brain arousal process underlying maintenance of the waking state probably throughout the 24 h cycle.

Activity Cycles↗

PubMed2000

Head-down tilt bed rest and immune responses.

Head-down tilt bed rest (HDT) is used as a model for studying the physiological changes occurring in weightlessness during spaceflight. In the present study, eight volunteers were subjected to a strict HDT of -6 degrees for 42 days. Blood samples were obtained 37 and 13 days before, at days 13, 34, and 41 during, and 12, 33, and 47 days after HDT. FACScan analysis was used to determine cell subpopulations. Plasma was used to quantify various circulating hormone levels. Whole blood and reconstituted blood were stimulated with various activators such as phytohaemagglutinin-P (PHA), PHA combined with phorbol-12-myristate 13-acetate (PMA), anti-CD2, anti-CD3, and lipopolysaccharide. Supernatants were collected and analysed for the interleukins IL-1beta, IL-2, IL-6, and IL-10, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha). The total number of T lymphocytes and monocytes did not change significantly, whereas the number of polymorphonuclear cells increased during HDT. The percentage of CD2+ and CD3+ cells was increased at day 35 of HDT. The percentage and total number of natural killer cells (CD2+/CD3-/CD56+) was increased 12 days before and 14 days after HDT. TNF-alpha secretion did not change significantly during HDT. IL-2, IL-10 and IFN-gamma were increased at day 34 of HDT. IL-1beta levels were increased before and during HDT compared to post-HDT measurements. No significant changes were observed in plasma immunoglobulin, complement factors and other factors of the inflammatory system. Prolactin levels increased slightly but significantly at day 35 of HDT, thyreotropin and growth hormone levels remained virtually unchanged. Cortisol decreased slightly but significantly over the entire duration of the study. The changes observed during HDT do not indicate that the immune system is blunted, and these changes do not seem to correlate with the duration of HDT. Taken together these results show that a HDT does not reproduce the changes in immune responses observed after spaceflight.

Bed Rest↗

PubMed2000

Alpha activity and cardiac correlates: three types of relationships during nocturnal sleep.

OBJECTIVE: We examined simultaneously alpha activity and cardiac changes during nocturnal sleep, in order to differentiate non-rapid eye movement (NREM) sleep, REM sleep, and intra-sleep awakening. METHODS: Ten male subjects displaying occasionally spontaneous intra-sleep awakenings underwent EEG and cardiac recordings during one experimental night. The heart rate and heart rate variability were calculated over 5 min periods. Heart rate variability was estimated: (1) by the ratio of low frequency (LF) to high frequency (HF) power calculated from spectral analysis of R-R intervals; and (2) by the interbeat autocorrelation coefficient of R-R intervals (rRR). EEG spectral analysis was performed using a fast Fourier transform algorithm. RESULTS: Three types of relationships between alpha waves (8-13 Hz) and cardiac correlates could be distinguished. During NREM sleep, alpha activity and cardiac correlates showed opposite variations, with high levels of alpha power associated with decreased heart rate, rRR and LF/HF ratio, indicating low sympathetic activity. Conversely, during REM sleep, alpha activity was low whereas heart rate, rRR, and the LF/HF ratio peaked, indicating high sympathetic activity. During intra-sleep awakenings, alpha activity and cardiac correlates both increased. No difference in time-course between alpha 1 (8-10 Hz) and alpha 2 (10-13 Hz) activity could be shown. Alpha waves occurred in fronto-central areas during slow wave sleep (SWS), migrated to posterior areas during REM sleep, and were localized in occipital areas during intra-sleep awakenings. CONCLUSIONS: These results suggest that alpha waves are not simply a sign of arousal, as is commonly thought. Fronto-central alpha waves, associated with decreased heart rate, possibly reflect sleep-maintaining processes.

Adult↗

PubMed2000

Twenty-four-hour rhythms of plasma glucose and insulin secretion rate in regular night workers.

To determine whether the ultradian and circadian rhythms of glucose and insulin secretion rate (ISR) are adapted to their permanent nocturnal schedule, eight night workers were studied during their usual 24-h cycle with continuous enteral nutrition and a 10-min blood sampling procedure and were compared with 8 day-active subjects studied once with nocturnal sleep and once with an acute 8-h-shifted sleep. The mean 24-h glucose and ISR levels were similar in the three experiments. The duration and the number of the ultradian oscillations were influenced neither by the time of day nor by the sleep condition or its shift, but their mean amplitude increased during sleep whenever it occurred. In day-active subjects, glucose and ISR levels were high during nighttime sleep and then decreased to a minimum in the afternoon. After the acute sleep shift, the glucose and ISR rhythms were split in a biphasic pattern with a slight increase during the night of deprivation and another during daytime sleep. In night workers, the glucose and ISR peak levels exhibited an 8-h shift in accordance with the sleep shift, but the onset of the glucose rise underwent a shift of only 6 h and the sleep-related amplification of the glucose and ISR oscillations did not occur simultaneously. These results demonstrate that despite a predominant influence of sleep, the 24-h glucose and ISR rhythms are only partially adapted in permanent night workers.

Activity Cycles↗

PubMed1999

[Biologic rhythms: their changes in night-shift workers].

ENVIRONMENTAL STRESS: Environmental cycles, such as the light-dark cycle, provide information used by the biological clock in the hypothalamus to synchronize the biological systems and maintain the organism's internal cohesion. In persons whose work schedules include night hours (approximately 20% of the working population in France) the sleep-wake cycles are not in phase with these environmental cycles. BIOLOGICAL RHYTHMS: What effect does the conflicting information perceived by night-shift workers have on their biological rhythms? Indices of the processes going on in the cerebral clock, these biological rhythms are the only tool available in man to determine possible dysfunction of the clock. Several studies have identified these rhythms in night-shift workers but results have been contradictory. PARTIAL ADAPTATION: Recently we made repeated measurements every 10 min over a 24 hour period in night-shift workers to determine the precise melatonin, cortisol, and thyrotropin (TSH) patterns, which reflect the endogenous clock, and prolactin (PRL) and growth hormone (GH) patterns which are influenced by sleep but also have a circadian component. This study demonstrated that there is some, but partial, adaptation of the biological rhythms in these persons. The shift in the melatonin pattern is quite variable from one individual to another. Night work causes a distortion in the cortisol and TSH rhythms. This partial adaptation is also seen in the GH and PRL curves, mainly related to sleep, but whose endogenous component previously described in other experimental situations is found in night workers with a distribution incompletely adapted to the secretory episodes. RESEARCH PERSPECTIVES: Both daytime sleep and night-time work are associated with perturbed endocrine functions which could explain certain health problems and sleep disorders observed (or avowed) after several years of night-shift work. These problems require further research into factors susceptible of resynchronizing the biological clock.

Adaptation, Physiological↗