Abstract

Most cardiovascular functions exhibit circadian changes. On one hand, predictable-in-time differences in the physiological status of the cardiovascular system give rise to rhythmic variations in the susceptibility to morbid and mortal events. On the other, the pathological mechanisms of cardiovascular disease exhibit temporal changes in both their manifestation and severity, leading to predictable-in-time differences in the ability to precipitate the overt expression of disease. It is known that the occurrence of cardiovascular events shows temporal patterns that vary with time. The incidence of potentially life-threatening cardiovascular events, e.g. acute myocardial ischemia and infarction, sudden cardiac death, ischemic and hemorrhagic stroke, and rupture or dissection of aortic aneurysms, displays a diurnal pattern, tending to be higher in the morning. On arousal and the start of daily activities, blood pressure (BP) shows a surge that may last 4- 6 h. Morning BP surge, together with circadian variations in biochemical and physiological parameters, may be potential triggers for acute cardiovascular events. This may open up potential for applications in medical therapy. It is possible that antihypertensive medication given once daily in the morning may not protect against this surge if its duration of action is too short. Thus, the timing of drug administration or specific drug delivery systems that lead to a greater effect at night and/or mitigate the early morning BP surge may provide protection against cardiovascular events.

Keywords: Blood pressure, morning blood pressure surge, chronobiology, circadian rhythm, myocardial infarction, stroke, pulmonary embolism, aneurysm dissection, risk factors, cardiovascular diseases