Institute for Continuing Education

An Overview of Circadian Rhythm

Course Objectives

Upon successful completion of this module, you will be able to:

• Describe the neurobiological basis of circadian rhythms including the suprachiasmatic nucleus as the master pacemaker, molecular clock mechanisms involving clock genes, and the role of environmental zeitgebers (particularly light) in entrainment.
• Explain the physiological processes regulated by circadian rhythms including sleep-wake cycles, core body temperature, melatonin and cortisol secretion, alertness and performance patterns, and metabolic functions.
• Identify the major circadian rhythm sleep-wake disorders including delayed sleep-wake phase disorder, advanced sleep-wake phase disorder, irregular sleep-wake rhythm disorder, non-24-hour sleep-wake rhythm disorder, shift work disorder, and jet lag disorder with their clinical presentations and diagnostic criteria.
• Apply assessment tools and methodologies for circadian rhythm evaluation including sleep logs and diaries, actigraphy monitoring and interpretation, dim light melatonin onset (DLMO) testing, and polysomnographic findings relevant to circadian disorders.
• Recognize treatment approaches for circadian rhythm disorders including timed light therapy (bright light exposure and light avoidance), exogenous melatonin and melatonin agonists, chronotherapy and sleep scheduling interventions, and behavioral strategies for shift workers.
• Evaluate the impact of circadian misalignment on health including metabolic dysfunction, cardiovascular disease risk, mood disorders, cognitive impairment, and increased accident risk, with implications for patient education and risk mitigation.
• Integrate the sleep technologist's role in circadian rhythm assessment including patient education about sleep logs and actigraphy, proper actigraphy device application and data download, recognition of circadian patterns in clinical presentation and polysomnographic data, and collaboration with physicians in diagnosis and treatment monitoring.

Course Information

Circadian rhythm describes the approximately 24-hour cycles that are generated by an organism. Most physiological systems demonstrate circadian variations. The systems with the most prominent variations are the sleep-wake cycle, thermoregulation, and the endocrine system.

Circadian rhythm disturbances can be categorized into 2 main groups:
1. transient disorders (e.g., jet lag; changed sleep schedule due to work, social responsibilities, illness)
2. and chronic disorders.
The most common chronic disorders are delayed sleep-phase syndrome (DSPS), advanced sleep-phase syndrome (ASPS), and irregular sleepwake cycle. Katzenberg et al suggested genetic correlation (i.e., clock polymorphisms) to circadian rhythm patterns.