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(Circulation. 2004;109:e9047-e9048.)
© 2004 American Heart Association, Inc.

Cardiovascular News

Ruth SoRelle, MPH

Circulation Newswriter

An extract of the first 250 words of the full text is provided, because this article has no abstract.

Why the Morning?

The preference of myocardial infarction, sudden death, and stroke for morning hours is an epidemiological fact, but the biological mechanism is not well understood. In this week’s issue of the journal Circulation (Circulation. 2004;109:2507–2510), researchers from the Mayo Clinic Foundation in Rochester, Minn, found that brachial artery flow–mediated endothelium-dependent vasodilation is blunted in the early morning, which may explain why adverse cardiac events occur at that time of day.

In this study led by Maria E. Otto, MD, PhD, of the Mayo Clinic, 19 men and 11 women, all healthy and without sleep disorder, underwent measurement for brachial artery flow–mediated endothelium-dependent vasodilation and endothelium-independent dilation at 3 different times: before they went to sleep at about 9:00 PM, on waking the next day at 6:00 AM, and at 11:00 AM, 5 hours after waking. All subjects slept well.

Brachial artery flow–mediated endothelium-dependent vasodilation decreased markedly in the early morning after waking compared with the measurement made before the subjects went to sleep. The measurement had recovered by late morning. Endothelium-independent dilation was similar at the 3 periods of observation.

The authors noted, "We have noted a significant reduction in morning levels of endothelium-mediated vasodilation in healthy subjects. This morning decrease in flow-mediated vasodilation needs to be recognized in clinical studies of endothelial function so that comparisons of measurements are performed at approximately the same time of day. The morning-related attenuation of endothelial function may also have implications for our understanding of the morning peak . . . [Full Text of this Article]