Circadian Rhythm Sleep-Wake Disorders

OBJECTIVE

This article provides an overview of advances in the understanding of circadian rhythms and the health implications of circadian disruption.

LATEST DEVELOPMENTS

Circadian medicine is a relatively new concept, with widespread overlap with many other areas of medicine. Circadian clocks rely on feedback loops that control the expression of many genes. Functional circadian oscillators exist at multiple physiologic levels and facilitate a multimodal clock mechanism. The suprachiasmatic nucleus is the central circadian pacemaker. Peripheral tissues can be entrained by other stimuli (such as food intake) and can uncouple from the suprachiasmatic nucleus pacemaker; this discovery may provide new therapeutic options for circadian rhythm disorders. Numerous modern developments have altered our circadian clocks and these changes are associated with poor health outcomes.

ESSENTIAL POINTS

Circadian clocks are ubiquitous throughout our body and regulate multiple body functions. Several studies have highlighted that circadian disruption can result in significant negative mental and physical health consequences. A deeper understanding of the effects of misalignment between our circadian clocks and the external environment may ultimately have therapeutic implications for our health.

Chronic Insomnia Disorder

PURPOSE OF REVIEW

Neurologists, along with all health care providers, commonly encounter patients with insomnia, which is a condition that impacts patients' underlying neurologic conditions in a bidirectional manner. While chronic insomnia is one of the most common sleep disturbances, only a small proportion of individuals with this condition discuss their sleep problems with their providers. When insomnia is described, it is more often in relationship to another medical problem, as opposed to an independent condition. In neurology practice, multiple factors including pain, movement disorders, sleep apnea, and medications that act on the central nervous system often contribute to insomnia. An all-inclusive approach is necessary when evaluating sleep problems in patients with insomnia.

RECENT FINDINGS

The US Food and Drug Administration (FDA) has approved several medications for the treatment of insomnia that target specific receptor systems in the brain and incorporate several unique pharmacodynamic and pharmacokinetic profiles that can represent customized therapy for specific insomnia phenotypes. FDA-approved medications for insomnia include γ-aminobutyric acid (GABA)-modulating benzodiazepine receptor agonists, a melatonin receptor agonist, a histamine receptor antagonist, and the newest approved option, a hypocretin (orexin) receptor antagonist.

SUMMARY

This article provides an evidence-based multidisciplinary approach to the treatment of insomnia, highlighting the rationale and utility of cognitive-behavioral therapy and pharmacologic interventions. Neurologists should be proactive in assessing the impact of underlying comorbidities on insomnia, particularly in the setting of psychiatric conditions such as depression, sleep disorders such as circadian rhythm disorders, and medical problems such as nocturia.

Is a SIMPLe smartphone application capable of improving biological rhythms in bipolar disorder?

BACKGROUND

Biological rhythms (BR) disturbance has been suggested as a potential mediator of mood episodes in Bipolar Disorder (BD). The Biological Rhythms Interview of Assessment in Neuropsychiatry (BRIAN) was designed as an assessment tool to evaluate BR domains comprehensively. In the context of a trial evaluating a smartphone application delivering personalized psychoeducational contents for BD (SIMPLe 1.0), the main aim of this study is to evaluate the potential impact of SIMPLe 1.0 in BR regulation using the BRIAN scale.

METHODS

51 remitted BD patients were asked to use the application for 3 months. Paired t-test analyses were employed to compare baseline and follow-up BRIAN´s total and domains scores. The sample was divided into completers and non-completers of the study to evaluate differences between groups regarding BRIAN scores using ANCOVA analyses.

RESULTS

The BRIAN's mean total score of the whole sample significantly decreased from baseline to post-intervention (35.89 (SD 6.64) vs. 31.18 (SD 6.33), t = 4.29, p = 0.001). At post-intervention, there was a significant difference between groups regarding the total BRIAN mean score (29.47 (SD 6.21) completers vs. 35.92 (SD 3.90) non-completers, t = 2.50, p = 0.02). This difference was maintained after conducting a one-way ANCOVA controlling for pre-intervention BRIAN scores, F (1, 46) = 10.545, p=0.002.

LIMITATIONS

A limited sample, pre-post measures, and a short study timeframe could have affected the results. Additional factors affecting BR, such as medication, could not be ruled out.

CONCLUSION

Our results suggest that there are potential positive effects of a psychoeducational smartphone application as an adjunctive to treatment as usual on BD patients' BR.

White Adipose Tissue and Circadian Rhythm Dysfunctions in Obesity: Pathogenesis and Available Therapies

A combined neuroendocrine, metabolic, and chronobiological view can help to better understand the multiple and complex mechanisms involved in obesity development and maintenance, as well as to provide new effective approaches for its control and treatment. Indeed, we have currently updated data on the whole adipogenic process involved in white adipose tissue (WAT) mass expansion, namely due to a mechanism whereby WAT cells become hypertrophic, thus inducing a serious local (WAT) inflammatory condition that in turn, will impair not only the cross-talk between the hypothalamus and the WAT, but also favoring the development of deep and widespread neuroendocrine-metabolic dysfunction. Moreover, we also have revisited the circadian clock genes involved in dysfunctional WAT mass expansion and the mechanisms that may lead to obesity development, including early metabolic dysfunctions, enhanced oxidative stress and distorted energy homeostasis. The epigenetic changes of clock genes driving metabolic disease and obesity development have also been included in this review. Finally, we have also underlined the relevance of metabolic homeostasis regulation by central and peripheral organ clocks, sleep disturbances, nutrients, and feeding time, as key factors in obesity development as well as both, classical and chronotherapeutic approaches for its prevention and treatment.

Psychiatric disorders and sleep issues

Sleep issues are common in people with psychiatric disorders, and the interaction is complex. Sleep disorders, particularly insomnia, can precede and predispose to psychiatric disorders, can be comorbid with and exacerbate psychiatric disorders, and can occur as part of psychiatric disorders. Sleep disorders can mimic psychiatric disorders or result from medication given for psychiatric disorders. Impairment of sleep and of mental health may be different manifestations of the same underlying neurobiological processes. For the primary care physician, key tools include recognition of potential sleep effects of psychiatric medications and familiarity with treatment approaches for insomnia in depression and anxiety.

Optimal schedules of light exposure for rapidly correcting circadian misalignment

Jet lag arises from a misalignment of circadian biological timing with the timing of human activity, and is caused by rapid transmeridian travel. Jet lag's symptoms, such as depressed cognitive alertness, also arise from work and social schedules misaligned with the timing of the circadian clock. Using experimentally validated mathematical models, we develop a new methodology to find mathematically optimal schedules of light exposure and avoidance for rapidly re-entraining the human circadian system. In simulations, our schedules are found to significantly outperform other recently proposed schedules. Moreover, our schedules appear to be significantly more robust to both noise in light and to inter-individual variations in endogenous circadian period than other proposed schedules. By comparing the optimal schedules for thousands of different situations, and by using general mathematical arguments, we are also able to translate our findings into general principles of optimal circadian re-entrainment. These principles include: 1) a class of schedules where circadian amplitude is only slightly perturbed, optimal for dim light and for small shifts 2) another class of schedules where shifting occurs along the shortest path in phase-space, optimal for bright light and for large shifts 3) the determination that short light pulses are less effective than sustained light if the goal is to re-entrain quickly, and 4) the determination that length of daytime should be significantly shorter when delaying the clock than when advancing it.

When our body's internal timekeeping system becomes misaligned with the time of day in the outside world, many negative effects can be felt, including decreased performance, improper sleep, and jet lag. When misalignment is prolonged, it can also lead to serious medical conditions, including cancer, cardiovascular disease, and possibly even late-onset diabetes. Rapid readjustment of our internal daily (circadian) clock by properly timed exposure to light, which is the strongest signal to our internal circadian clock, is therefore important to the large proportion of the population which suffers from misalignment, including transmeridian travelers, shift workers, and individuals with circadian disorders. Here we develop a methodology to determine schedules of light exposure which may shift the human circadian clock in the minimum time. By calculating thousands of schedules, we show how the human circadian pacemaker is predicted to be capable of shifting much more rapidly than previously thought, simply by adjusting the timing of the beginning and end of each day. Schedules are summarized into general principles of optimal shifting, which can be applied without knowledge of the schedules themselves.

Pediatric insomnia: clinical, diagnosis, and treatment

Pediatric insomnia is an extrinsic sleep disorder subdivided into two categories: behavioral insomnia and insomnia related to medical, neurological, and psychiatric diseases. This review will cover several types of insomnia, comorbidities and specific pediatric therapies according to clinical characteristics and age. Behavioral insomnia should be differentiated from pediatric insomnia due to medical conditions, mostly occurring during the first year of life. Multiple night awakenings and diurnal hypersomnolence are strong indicators of insomnia due to medical conditions. Insomnia during adolescence and pediatric insomnia associated with psychiatric comorbidity, cognitive disabilities and epilepsy, will be discussed in terms of diagnosis, clinical features and implications for treatment.

Neurobiology, pathophysiology, and treatment of melatonin deficiency and dysfunction

Melatonin is a highly pleiotropic signaling molecule, which is released as a hormone of the pineal gland predominantly during night. Melatonin secretion decreases during aging. Reduced melatonin levels are also observed in various diseases, such as types of dementia, some mood disorders, severe pain, cancer, and diabetes type 2. Melatonin dysfunction is frequently related to deviations in amplitudes, phasing, and coupling of circadian rhythms. Gene polymorphisms of melatonin receptors and circadian oscillator proteins bear risks for several of the diseases mentioned. A common symptom of insufficient melatonin signaling is sleep disturbances. It is necessary to distinguish between symptoms that are curable by short melatonergic actions and others that require extended actions during night. Melatonin immediate release is already effective, at moderate doses, for reducing difficulties of falling asleep or improving symptoms associated with poorly coupled circadian rhythms, including seasonal affective and bipolar disorders. For purposes of a replacement therapy based on longer-lasting melatonergic actions, melatonin prolonged release and synthetic agonists have been developed. Therapies with melatonin or synthetic melatonergic drugs have to consider that these agents do not only act on the SCN, but also on numerous organs and cells in which melatonin receptors are also expressed.

Postoperative circadian disturbances

An increasing number of studies have shown that circadian variation in the excretion of hormones, the sleep wake circle, the core body temperature rhythm, the tone of the autonomic nervous system and the activity rhythm are important both in health and in disease processes. An increasing attention has also been directed towards the circadian variation in endogenous rhythms in relation to surgery. The attention has been directed to the question whether the circadian variation in endogenous rhythms can affect postoperative recovery, morbidity and mortality. Based on the lack of studies where these endogenous rhythms have been investigated in relation to surgery we performed a series of studies exploring different endogenous rhythms and factors affecting these rhythms. We also wanted to examine whether the disturbances in the postoperative circadian rhythms could be correlated to postoperative recovery parameters, and if pharmacological administration of chronobiotics could improve postoperative recovery. Circadian rhythm disturbances were found in all the examined endogenous rhythms. A delay was found in the endogenous rhythm of plasma melatonin and excretion of the metabolite of melatonin (AMT6s) in urine the first night after both minor and major surgery. This delay after major surgery was correlated to the duration of surgery. The amplitude in the melatonin rhythm was unchanged the first night but increased in the second night after major surgery. The amplitude in AMT6s was reduced the first night after minimally invasive surgery. The core body temperature rhythm was disturbed after both major and minor surgery. There was a change in the sleep wake cycle with a significantly increased duration of REM-sleep in the day and evening time after major surgery compared with preoperatively. There was also a shift in the autonomic nervous balance after major surgery with a significantly increased number of myocardial ischaemic episodes during the nighttime period. The circadian activity rhythm was also disturbed after both minor and major surgery. The daytime AMT6s excretion in urine after major surgery was increased on the fourth day after surgery and the total excretion of AMT6s in urine was correlated to sleep efficiency and wake time after sleep onset, but was not correlated to the occurrence of postoperative cognitive dysfunction. We could only prove an effect of melatonin substitution in patients with lower than median pain levels for a three days period after laparoscopic cholecystectomy. In the series of studies included in this thesis we have systematically shown that circadian disturbances are found in the secretion of hormones, the sleep-wake cycle, core body temperature rhythm, autonomic nervous system tone, myocardial ischaemia and activity rhythm after surgery. Correlation exists between circadian rhythm parameters and measures of postoperative sleep quality and recovery. However, oral melatonin treatment in the first three nights after surgery, cannot yet be generally recommended for improvement of sleep quality or other recovery parameters based on the available results. It may be indicated in subgroups or if other perioperative treatment algorithms were used, but this has to be investigated in future trials.

[Sleep disorders in Parkinson's disease: insomnia and sleep fragmentation, daytime hypersomnia, alterations to the circadian rhythm and sleep apnea syndrome]

INTRODUCTION

Sleep disorders in Parkinson's disease are present in 60-98% of patients and reduce their quality of life.

AIMS

To review the pathophysiology, diagnostic approach and management of the different sleep disorders.

DEVELOPMENT

We describe the pathophysiology associated with neurodegeneration, due to symptoms (motor and nonmotor) and drug therapies. This article reviews insomnia, excessive daytime sleepiness, circadian sleep disorders and sleep apnea.

CONCLUSIONS

Subjective or objective sleepiness assessment should routinely be performed by physicians looking after Parkinson's disease patients. Management is difficult and should be targeted to the specific sleep disorder and its likely cause.

Illuminating rationale and uses for light therapy

Light therapy is increasingly applied in a variety of sleep medicine and psychiatric conditions including circadian rhythm sleep disorders, seasonal affective disorder, and dementia. This article reviews the neural underpinnings of circadian neurobiology crucial for understanding the influence of light therapy on brain function, common mood and sleep disorders in which light therapy may be effectively used, and applications of light therapy in clinical practice.

[Circadian rhythm disorders]

The field of circadian rhythm disorders gains recognition within the sleep medicine, although it is true to say that this field is neither well understood nor fully utilised. The example for the later is the field of chronopharmacology, which promises to improve treatment outcome for a number of disorders, including those difficult to treat such as cancer. Another example of successful implementation of findings from the field of circadian rhythms is that of delayed morning school time endorsed by a number of school boards, which often results in improved rate of absenteeism and in the better academic achievements. At the level of a medical profession, better understanding of fundamental principles of circadian rhythms can lead to better and more efficient treatment, with the shift of a therapeutic approach from medications to implementation of cognitive-behavioural measures, and to, ultimately, better rapport with these patients. The article deals with some fundamental issues in respect to chronobiology, circadian rhythms and circadian rhythm disorders.

The phenomenology of bipolar disorder: what drives the high rate of medical burden and determines long-term prognosis?

Bipolar disorder (BD) has been classically described as one of episodic mood disturbances. New evidence suggests that a chronic course and multisystem involvement is the rule, rather than the exception, and that together with disturbances of circadian rhythms, mood instability, cognitive impairment, a high rate of medical burden is often observed. The current diagnostic approach for BD neither describes the multisystem involvement that the recent literature has highlighted nor points toward potential predictors of long- term outcome. In light of the new evidence that the long-term course of BD is associated with a high prevalence of psychiatric comorbidity and an increased mortality from medical disease, we propose a multidimensional approach that includes several symptom domains, namely affective instability, circadian rhythm dysregulation, and cognitive and executive dysfunction, presenting in various combinations that give shape to each individual presentation, and offers potential indicators of overall long-term prognosis.

Light exposure, melatonin secretion, and menstrual cycle parameters: an integrative review

Dysfunction in menstrual physiology has pronounced effects on quality of life, involving mood changes, body image, infertility, and pregnancy complications. Light exposure may affect menstrual cycles and symptoms through the influence of melatonin secretion. The purpose of this systematic review is to determine the current state of knowledge about the effects of light and melatonin secretion on menstrual phase and cycle alterations. A brief overview of the influence of melatonin on human physiology is included. There is evidence of a relationship between light exposure and melatonin secretion and irregular menstrual cycles, menstrual cycle symptoms, and disordered ovarian function. In women with a psychopathology such as bipolar disorder or an endocrinopathy such as polycystic ovary syndrome, there seems to be greater vulnerability to the influence of light-dark exposure. Research on the complex role of light-dark exposure in menstrual physiology has implications for treatment of menstrual-associated disorders.

Circadian phase delay induced by phototherapeutic devices

INTRODUCTION

The Canadian Forces has initiated a multiple study project to optimize circadian phase changes using appropriately timed phototherapy and/or ingestion of melatonin for those personnel on long-range deployments and shift workers. The work reported here compared four phototherapeutic devices for efficacy in effecting circadian phase delays.

METHODS

In a partially counterbalanced treatment order, 14 subjects (7 men and 7 women), ages 18-51 yr, participated in 5 weekly experimental sessions of phototherapy with 4 different phototherapy devices (light tower, light visor, Litebook, LED spectacles) and a no-phototherapy control. Phototherapy was applied from 24:00 to 02:00 on night. (1) Dim light melatonin onset (DLMO) was assessed on night 1 and night. (2) Subjects were tested for psychomotor performance (serial reaction time, logical reasoning, and serial subtraction tasks) and completed the Stanford Sleepiness Scale on night 1 at 19:00, 23:00, 01:00, 02:00, and 03:00. After phototherapy, subjects completed a phototherapy side-effects questionnaire.

RESULTS

All phototherapy devices produced melatonin suppression and significant phase delays. Sleepiness was significantly decreased with the light tower, the light visor, and the Litebook. Task performance was only slightly improved with phototherapy. The LED spectacles and light visor caused greater subjective performance impairment, more difficulty viewing the computer monitor and reading printed text than the light tower or the Litebook. The light visor, the Litebook, and the LED spectacles caused more eye discomfort than the light tower.

CONCLUSIONS

The light tower was the best device, producing melatonin suppression and circadian phase change while relatively free of side effects.

Theoretical models for chronotherapy: periodic perturbations in funnel chaos type

In this work, the Rössler system is used as a model for chrono therapy. We applied a periodic perturbation to the y variable to take the Rössler system from a chaotic behavior to a simple periodic one, varying the period and amplitude of forcing. Two types of chaos were considered, spiral and funnel chaos. As a result, the periodical windows reduced their areas as the funnel chaos character increased in the system. Funnel chaos, in this chrono therapy model, could be considered as a later state of a dynamical disease, more irregular and difficult to suppress.

Sundowning and circadian rhythm disorders in dementia

Sleep disorders and disruptive nocturnal behaviours are commonly reported in people with senile dementia and present both a significant clinical problem and a cause of increased stress for caregivers. Neuronal degeneration of cholinergic Nucleus basalis Meynert (NBM) neurons promote rest-activity disturbance and Sundowning in Alzheimer's disease. NBM neurons modulate the activity of the mainly cholinergic suprachiasmatic nucleus (SCN) and the induction of NONREM sleep. Sundowning might be explained as a syndrome occurring when arousal is to be processed while the neocortex is already turned "off" to (NONREM) sleep. The therapeutic measures should thus primarily be aimed at the stimulation of the circadian system and enforcing "external Zeitgebers". Pharmacologically, application of cholinergic enhancers i.e. cholinesterase inhibitors and melatonin supports and should stabilize the weakened structures.

Tinnitus as an Alarm Bell: Stress Reaction Tinnitus Model

Stress is a significant factor influencing the clinical course of tinnitus. Auditory system is particularly sensitive to the effects of different stress factors (chemical, oxidative, emotional, etc.). Different stages of reaction (alarm, resistance, exhaustion) lead to different characteristics of tinnitus and different therapeutic approaches. Individual characteristics of stress reaction may explain different aspects of tinnitus in various patients with different responses to treatment, despite similar audiological and etiological factors. A model based on individual reactions to stress factors (stress reaction tinnitus model) could explain tinnitus as an alarm signal, just like an 'alarm bell', informing the patient that something potentially dangerous for subject homeostasis is happening. Tinnitus could become a disabling symptom when the subject is chronically exposed to a stress factor and is unable to switch off the alarm. Stress signals, specific for each patient, have to be identified during the 'alarm' phase in order to prevent an evolution toward the 'resistance' and 'exhaustion' phases. In these phases, identification of stressor is no more sufficient, due to the organization of a 'paradoxical auditory memory' and a 'pathologically shifted attention to tinnitus'. Identification of stress reaction phase requires accurate otolaryngology and anamnesis combined with audiological matching tests (Feldman Masking Test, for example) and psychometric questionnaires (Tinnitus Reaction and Tinnitus Cognitive Questionnaires).

[Chronobiology, chronotherapy and vascular risk]

The importance of rhythmic activities in humans, and their influence on the diseases are underscored. Clinical chronology is fundamental in order to interpret the physiopathological basis of temporary variations. Knowing the variability of the biological processes also makes it possible improving the effect of drugs utilized and minimize their adverse effects. This is the objective of Chronotherapy. We apply chronology and Chronotherapy in cardiovascular diseases, since many of them adjust their prevalence for specific rhythms. One thinks about the mechanisms or factors that favor cardiovascular diseases, especially those related to the circadian variations of blood pressure. We also review the variations in the pharmacokinetics of the drugs used in the treatment of cardiovascular diseases, delving further into the analysis of its effects according to their administration schedule. We can conclude that the use of those drugs according to the chronological knowledge makes possible to achieve better results in the control of cardiovascular diseases, and a greater safety in its use.

Increased light exposure consolidates sleep and strengthens circadian rhythms in severe Alzheimer's disease patients

Sleep in the nursing home environment is extremely fragmented, possibly in part as a result of decreased light exposure. This study examined the effect of light on sleep and circadian activity rhythms in patients with probable or possible Alzheimer's disease. Results showed that both morning and evening bright light resulted in more consolidated sleep at night, as measured with wrist actigraphy. Evening light also increased the quality of the circadian activity rhythm, as measured by a 5-parameter extended cosine model (amplitude, acrophase, nadir, slope of the curve, and relative width of the peak and trough). Increasing light exposure throughout the day and evening is likely to have the most beneficial effect on sleep and on circadian rhythms in patients with dementia. It would behoove nursing homes to consider increasing ambient light in multipurpose rooms where patients often spend much of their days.

Behavioral sleep medicine: a historical perspective

Behavioral sleep medicine (BSM) has recently emerged as a subspecialty area within the broader field of sleep medicine. Certain commonly used treatment approaches in BSM were first pioneered in the 1930s, and this article traces the developments within BSM to current practice. Important innovations include the expansion of BSM beyond the treatment of insomnia to include treatment of pediatric sleep disorders, circadian rhythm disorders, parasomnias, as well as desensitization procedures for patients undergoing treatment with nasal continuous positive airway pressure (CPAP).

Introducción general a la cronobiología clínica y a la manipulación terapéutica de los ritmos biológicos

In humans, most clinical variables follow biological rhythms approaching to a mathematical function defined by the cosmic-climatic rhythm. Chronophysiology, chronopathology, chronopharmacology, chronotherapy and phototherapy have common elements frequently studied in a disperse manner, thus making it difficult a global understanding of clinical chronobiology as a unitary and well-characterized discipline. This review focuses on medical chronobiology, which is much more technical since it only gathers those directives of clinical chronobiology having a health-care impact on daily practice.

Light therapy for behavioural and psychological symptoms of dementia

OBJECTIVES

To review literature concerning the efficacy, clinical practicability and safety of light treatment for behavioural and psychological symptoms of dementia (BPSD).

METHOD

Data collection included computer literature searches (MEDLINE, PsycINFO and Cochrane) and checks of references, covering the period of January 1980-September 2003. Trials were searched for evidence for treatment efficacy and for their consideration of the treatment's clinical practicability and evidence of adverse effects.

RESULTS

Results from randomised controlled trials (RCT) indicated some evidence of improvement in aspects of sleep disturbances and circadian activity rhythmicity. One RCT study indicated better response in patients with vascular dementia compared to Alzheimer's disease. By and large, non-RCT studies reported improvement in BPSD including sleep disturbances, agitation and activity rhythm disturbances. Few studies commented on the treatment's practicability and safety.

CONCLUSION

Although there is some evidence for influence of light therapy on sleep and circadian activity rhythmicity, it is not possible to draw any conclusion about efficacy of light therapy for BPSD, or about practicability in clinical settings and safety. There are still too few well designed studies. Suggestions for further research are presented.

Circadian variation in ventricular tachycardia and atrial fibrillation in a medical-cardiological ICU

OBJECTIVE

To assess the diurnal distribution of ventricular tachycardia (VT) and atrial fibrillation (AF) in critically ill patients.

DESIGN AND SETTING

Prospective observational study (episode-based design) in an eight-bed medical/cardiological ICU at a university hospital that also admits postoperative patients.

PATIENTS

98 consecutive patients with AF ( n=55) or ventricular tachycardia ( n=43).

MEASUREMENTS AND RESULTS

There were a total of 218 arrhythmia episodes (83 AF, 136 VT). The time of arrhythmia onset was not evenly distributed. Circadian variation in VT but not AF onset was well represented by a sine wave function. Both VT and AF fibrillation showed a trough during the night. The distribution of VT and AF episodes did not differ significantly with or without analgosedation.

CONCLUSIONS

In critically ill patients the onset of VT and AF over 24-h is nonuniformly distributed. In VT this circadian pattern of occurrence is well modeled by a sine wave function peaking between noon and 2 p.m. The circadian pattern is less clear for AF. The circadian variation is seen irrespective of the presence of absence of analgosedation for both arrhythmias.

Optimization of light and melatonin to phase-shift human circadian rhythms

Both light and melatonin, appropriately timed, have been shown to phase-shift human circadian rhythms. In addition, both light and melatonin have acute physiological and behavioural effects. Depending on the dose, melatonin can reduce core body temperature and induce sleepiness. Conversely, light at night increases body temperature and enhances alertness and performance. The acute and phase-shifting effects of light and melatonin have justified their investigation and use in the treatment of circadian rhythm sleep disorders. Melatonin is the treatment of choice for blind people with non-24 h sleep/wake disorder. Current research is directed towards optimizing these therapies with respect to time of administration, dose and formulation of melatonin, intensity, duration and spectral composition of light. Our studies in totally blind people with non-24 h sleep/wake disorder have shown that, in addition to improving sleep, daily administration of melatonin can entrain their free-running circadian rhythms. The ability of melatonin to entrain free-running rhythms depends, in part, on the time of melatonin administration relative to the subject's circadian phase. Subjects who were entrained by melatonin began their treatment in the phase advance portion (CT 6-18) of the published melatonin phase-response curves (PRCs), whereas those who failed to entrain began their melatonin treatment in the delay portion of the PRC. Whether the effect of light on the human circadian axis can be optimized by altering its spectral composition has been investigated. Recently, it was demonstrated that light-induced melatonin suppression in humans is sensitive to short wavelength light (420-480 nm; lambda(max) approximately 460 nm), a response very different to the classical scotopic and photopic visual systems. Whether other nonvisual light responses (e.g. circadian phase resetting) show a similar spectral sensitivity is currently being studied.

Circadian rhythms and circadian rhythm disorders in children and adolescents

A clinically applicable review of circadian rhythm physiology is presented, including a detailed examination of the interaction of circadian and homeostatic systems and the maturation of the circadian system from preconception through adolescence. Emphasis is placed on the clinical evaluation gathering information through the history, sleep log, and if necessary, actigraphy and polysomnography. Circadian disorders, including advanced sleep phase syndrome, circadian disorders seen in blind children, delayed sleep phase syndrome, and non-24-hour sleep phase are described. Case descriptions of each are provided. Treatment and interventions for these disorders are described, including the importance of education, light therapy, sleep-wake schedule adjustments, and the occasional use of medications, such as sedative hypnotics and melatonin.

Efficacy of bright light and sleep/darkness scheduling in alleviating circadian maladaptation to night work

We tested the hypothesis that circadian adaptation to night work is best achieved by combining bright light during the night shift and scheduled sleep in darkness. Fifty-four subjects participated in a shift work simulation of 4 day and 3 night shifts followed by a 38-h constant routine (CR). Subjects received 2,500 lux (Bright Light) or 150 lux (Room Light) during night shifts and were scheduled to sleep (at home in darkened bedrooms) from 0800 to 1600 (Fixed Sleep) or ad libitum (Free Sleep). Dim light melatonin onset (DLMO) was measured before and after the night shifts. Both Fixed Sleep and Bright Light conditions significantly phase delayed DLMO. Treatments combined additively, with light leading to larger phase shifts. Free Sleep subjects who spontaneously adopted consistent sleep schedules adapted better than those who did not. Neither properly timed bright light nor fixed sleep schedules were consistently sufficient to shift the melatonin rhythm completely into the sleep episode. Scheduling of sleep/darkness should play a major role in prescriptions for overcoming shift work-related phase misalignment.

Mechanisms and clinical significance of circadian rhythms in children

Circadian rhythms are endogenously generated rhythms with a period length of about 24 hours. A biologic clock in the hypothalamic suprachiasmatic nuclei is responsible for the generation of circadian rhythms. Notable examples of the circadian rhythms include the sleep-wake cycle and rhythms in hormone production. Abnormalities of the circadian system include biologic clock lesions that result in arrhythmic behavior and irregular sleep patterns. Abnormalities of the circadian system also occur when there is desynchronization of clock phase with that of the outside world, resulting in conditions such as "jet-lag." Numerous aspects of human physiology are greatly influenced by the time of day, as is the pathogenesis of illness. During development, the circadian system becomes functional at early stages and is regulated by photic information. With the continued elucidation of circadian system influences on human physiology and illness, it is anticipated that circadian biology will have an increasingly important impact on the clinical care of children.