Circadian rhythms and clinical medicine with applications to hypertension.

Circadian (24-h) rhythms are important to the practice of medicine. The phasing and amplitude of key physiologic and biochemical circadian rhythms contribute to predictable-in-time patterns in the manifestation and exacerbation of most medical conditions. Moreover, body rhythms can significantly affect responses of patients to diagnostic tests and medications. Rhythmicity in the pathophysiology of medical conditions is the rationale for chronotherapeutics--that is purposeful variance of the concentration of medicines in synchrony with biologic rhythm determinants of disease activity--to optimize treatment outcomes. This article discusses the concept of biologic time structure and its relevance to the practice of medicine, with a focus on hypertension and cardiovascular issues.