Impact of the human circadian system, exercise, and their interaction on cardiovascular function

Abstract

The risk of adverse cardiovascular events peaks in the morning (≈9:00 AM) with a secondary peak in the evening (≈8:00 PM) and a trough at night. This pattern is generally believed to be caused by the day/night distribution of behavioral triggers, but it is unknown whether the endogenous circadian system contributes to these daily fluctuations. Thus, we tested the hypotheses that the circadian system modulates autonomic, hemodynamic, and hemostatic risk markers at rest, and that behavioral stressors have different effects when they occur at different internal circadian phases. Twelve healthy adults were each studied in a 240-h forced desynchrony protocol in dim light while standardized rest and exercise periods were uniformly distributed across the circadian cycle. At rest, there were large circadian variations in plasma cortisol (peak-to-trough ≈85% of mean, peaking at a circadian phase corresponding to ≈9:00 AM) and in circulating catecholamines (epinephrine, ≈70%; norepinephrine, ≈35%, peaking during the biological day). At ≈8:00 PM, there was a circadian peak in blood pressure and a trough in cardiac vagal modulation. Sympathetic variables were consistently lowest and vagal markers highest during the biological night. We detected no simple circadian effect on hemostasis, although platelet aggregability had two peaks: at ≈noon and ≈11:00 PM. There was circadian modulation of the cardiovascular reactivity to exercise, with greatest vagal withdrawal at ≈9:00 AM and peaks in catecholamine reactivity at ≈9:00 AM and ≈9:00 PM. Thus, the circadian system modulates numerous cardiovascular risk markers at rest as well as their reactivity to exercise, with resultant profiles that could potentially contribute to the day/night pattern of adverse cardiovascular events.

Theoretical Identification of Behavioral Risk Factors Among Multiple Risk Factors Causing Morning Onset of Cardiac Events due to Circadian Variations

“…However, several studies have confirmed the occurrence of more events in the morning than in the evening (Atkinson et al, 2010;Mulcahy et al, 1988;Scheer et al, 2010). Two peaks of onset of cardiac events were found: a high frequency of cardiac events in the hours after rising in the morning and in the evening hours (Atkinson et al, 2010;Hjalmarson et al, 1989;Mulcahy et al, 1988;Muller, 1987).…”

“…Key words were as follows: circadian variation, sleep, ischemic episodes, cardiac events, cardiac disease, autonomic nervous system activation, physical stress (abrupt upright posture), mental stress, endothelial response of the coronary blood vessels, morning surge of blood pressure, and blood components (Carnethon et al, 2002;Cooke-Ariel, 1998;Furukawa et al, 1998;Khoury et al, 1992;Scheer et al, 2010;Thrall et al, 2007;White, 2003). By searching the database for these key words, evidence regarding behavioral risks factors triggering morning cardiac events was identified, and preventive patient education strategies to decrease morning onset of cardiac events are proposed.…”

“…Circadian variations of cardiac events exist, although times of onset differ slightly between studies (Atkinson et al, 2010;Muller et al, 1989;Quyyumi, 1990;Scheer et al, 2010;Willich et al, 1987). However, several studies have confirmed the occurrence of more events in the morning than in the evening (Atkinson et al, 2010;Mulcahy et al, 1988;Scheer et al, 2010).…”

“…A specific single factor causing circadian variation in the morning has not been identified. It has been suggested that interactions between multiple factors during transition from the sleep state to the waking stage may occur simultaneously or as a self-sustaining reaction (Atkinson et al, 2010;Scheer et al, 2010).…”

The Association Between Acute Myocardial Infarction with Seasonal Variations and Admission Time

“…Cardiovascular disease is the most common cause of deaths among females and males in the developed countries (4); it is the cause of 12.8% of all the deaths (5), almost 83 million people have cardiovascular diseases in America (6). Cardiovascular diseases are also recognized as the most important causes of death in Iran; the study of death face in 18 cities of Iran showed that 46% of all the deaths were due to such diseases (3).…”