Circadian and Cyclic Environmental Determinants of Blood Pressure Patterning and Implications for Therapeutic Interventions

Blood pressure (BP) exhibits significant 24 h variation; in most normotensive and uncomplicated hypertensive persons, BP declines during the first half of nighttime sleep by 10–20 % from its daytime mean level, starts rising in the second half of sleep, further increases with commencement of diurnal activity, and peaks in the afternoon or early evening. Environmental 24 h cycles of temperature and noise; behavior-driven nyctohemeral patterning of food, liquid, and stimulant consumption, posture, mental and emotional stress, and physical activity; plus innate circadian rhythms in wake/sleep, autonomic nervous, hypothalamic–pituitary–adrenal, renal hemodynamic, opioid, renin–angiotensin–aldosterone, endothelial, and vasoactive peptide systems constitute the key determinants of the BP day/night variation. The current perspective is that the environmental and behavioral cycles are far more influential than the innate circadian ones in determining the BP nyctohemeral profile. Yet, the facts that the: (1) BP 24 h pattern of secondary hypertension, e.g., diabetes and other endocrine disorders, renal disease, heart failure, is different—BP fails to decline as expected during nighttime sleep typically due to pathological alteration of autonomic nervous system and other influential circadian rhythms, and (2) scheduling of conventional long-acting medications at bedtime, rather than in the morning, results in much better hypertension control and vascular risk reduction, presumably because highest drug concentration coincides closely with the peak of most key circadian determinants of the BP 24 h profile, indicates the endogenous rhythmic influences are of much greater importance than previously appreciated.