Medical chronobiology: concepts and applications.

Chronobiology is the study of biologic rhythms and biologic time structure. Medical chronobiology, in particular, is concerned with circadian (24-h) and other bioperiodic influences on human diseases such as (1) their occurrence or variation in severity over the 24-h or other time scale, (2) response of patients to diagnostic procedures and tests and, (3) the effect of medical treatments. The symptoms of chronic diseases--allergic rhinitis, regular and variant type angina, rheumatoid and osteoarthritis, asthma, epilepsy, hypertension and ulcer disease, for example, commonly exhibit circadian, menstrual cycle (in women), and seasonal patterns. The life-threatening events of myocardial and cerebral infarction and cerebral hemorrhage also exhibit predictable-in-time patterns over 24 h and the year. In the clinic, bioperiodicities strongly influence the results of blood pressure assessment, cutaneous antigen testing and spirometric evaluation, to mention but a few. Bodily rhythms also affect the pharmacokinetics and dynamics of medications. A major goal of medical chronobiology is chronotherapeutics, the optimization of pharmacotherapies, taking into consideration rhythm-dependencies in the kinetics and dynamics of medications plus predictable-in-time variability in the manifestation and severity of human disease. The concepts of medical chronobiology are discussed in detail herein. Examples have been chosen for their relevance to clinical allergy and chest medicine.