In addition to these major cardiovascular manifestations of coronary insufficiency, certain arrhythmias (atrioventricular junctional and idioventricular rhythms, ventricular premature beats, nonsustained ventricular tachycardia, and the ventricular rates in atrial fibrillation to mention a few) exhibit characteristic circadian variations. Establishing a direct cause-effect relationship between arrhythmic events and myocardial ischemia/necrosis is not always possible, and although many rhythm abnormalities are manifestations of impaired coronary blood supply, the incidence of primary arrhythmias could be modulated by the increased adrenergic tone that characterizes the awakening/rising period.
Additionally, two recent studies using computed tomographic scanning of the brain have demonstrated a circadian pattern of stroke onset similar to that of acute myocardial infarction and sudden cardiac death. These multiple observations underscore the clinical relevance of the complex cardiovascular and hemodynamic changes that take place on awakening/rising that are conducive to a state of increased cardiovascular vulnerability; the hourly incidence of in-hospital cardiac death is virtually identical for each hour of the day. buy asthma inhalers
The presence of an internal biologic clock has been long recognized by physiologists. Multiple hemodynamic and neurohumoral changes occur with predictable and consistent periodicity in the human. The repetitive, cyclic nature of these biorhythms and its relationship with the environment is the subject of study of human chronobiology.
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