Authors: Greg Atkinson Helen Jones Philip N Ainslie
Publish Date: 2009/10/14
Volume: 108, Issue: 1, Pages: 15-29
Abstract
Sudden cardiac and cerebral events are most common in the morning A fundamental question is whether these events are triggered by the increase in physical activity after waking and/or a result of circadian variation in the responses of circulatory function to exercise Although signaling pathways from the master circadian clock in the suprachiasmatic nuclei to sites of circulatory control are not yet understood it is known that cerebral blood flow autoregulation and cerebrovascular reactivity to changes in CO2 are impaired in the morning and therefore could explain the increased risk of cerebrovascular events Blood pressure BP and the rate pressure product RPP show marked ‘morning surges’ when people are studied in freeliving conditions making the rupture of a fragile atherosclerotic plaque and sudden cardiac event more likely Since cerebral autoregulation is reduced in the morning this surge in BP may also exacerbate the risk of hemorrhagic and ischemic strokes in the presence of other acute and chronic risk factors Increased sympathetic activity decreased endothelial function and increased platelet aggregability could also be important in explaining the morning peak in cardiac and cerebral events but how these factors respond to exercise at different times of day is unclear Evidence is emerging that the exerciserelated responses of BP and RPP are increased in the morning when prior sleep is controlled We recommend that such ‘semiconstant routine’ protocols are employed to examine the relative influence of the body clock and exogenous factors on the 24h variation in other circulatory factorsG Atkinson leads the project “Shiftwork and Health optimal timing of meals and physical activity” which is funded by the National Prevention Research Initiative http//wwwnpriorguk with support from the following organisations British Heart Foundation Cancer Research UK Chief Scientist Office Scottish Government Health Directorate Department of Health Diabetes UK Economic and Social Research Council Health and Social Care Research and Development Office for Northern Ireland Medical Research Council Welsh Assembly Government and World Cancer Research Fund
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