In humans, as all organisms studied, the majority of biologic functions, including blood pressure, heart rate, temperature, sleep, and hormonal activity, follow a circadian time structure. These are the so-called biological rhythms. Chronoblology is the branch of science which studies biological rhythms. Medical chronobiology focuses on understanding how biologic rhythms influence the diagnosis, manifestation, and treatment of disease. The biology of human beings is not constant over the 24 h day as is suggested by the concept of homeostasis. Instead, it varies predictably according to defined and inherited bioperiodicities. Taking into account the influence of biologic lime structure with reference to the chronokinetics and chronesthesy of the particular medication, we can use this knowledge to when to conduct diagnostic tests, when symptoms and diseases manifest or worsen, and, finally, when to medicate. Basic concepts in medical chronobiology, circadian aspects in dementia and seasonal affective depression, and circadian rhythm sleep disorders are reviewed In this paper. Presenting characteristics, diagnostic approaches, pathophysiologic models, and treatment strategies are summarized for each disorder. Developments in the understanding of chronobiological physiology offer promise for
important advances in the diagnosis and treatment of these chronobiological disorders.
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