Heart rate and blood pressure consequences of an afternoon SIESTA (Snooze-Induced Excitation of Sympathetic Triggered Activity)

Abstract

With the increased interest shown in the area of arcadian variations in physiologic parameters and cardiovascular disease processes in recent years, it has been demonstrated that there are distinct circadian rhythms in cardiovascular events, with a surge in ischemia, 1 onset of acute myocardial infarction 2 and sudden cardiac death 3 in the morning waking hours, and a trough in such events at night. Such peaks in ischemia and onset of acute myocardial infarction are particularly related to actual time of waking and commencing activities. Because there are surges in heart rate (HR) and systolic blood pressure (BP) in the morning waking hours, 4 and because β-adrenergic blocking agents blunt the morning peaks in HR, 5 in addition to those of ischemia, 5 onset of acute myocardial infarction 2 and sudden cardiac death, 6 it has been suggested that activation of the sympathetic adrenergic system may play an important role in the increased cardiovascular event rate in the period soon after waking and commencing activities. We have assessed HR and BP responses before, during and after an afternoon siesta in apparently normal subjects, and compared the changes with those recorded on waking and commencing activities in the morning to establish whether the morning waking hours are particularly associated with increases in the determinants of myocardial oxygen demand, or whether this response is reproducible after any period of “sleep”.