Cardiovascular chronobiology: do you know what time it is?

Cardiovascular indices, such as blood pressure, heart rate, cardiac output, and fibrinolytic factors, vary over a 24-hour period. For example, nocturnal blood pressure may decrease to 30-50 mm Hg and heart rate to 25 beats per minute. In addition, these cardiovascular rhythms interact and may trigger a cardiovascular catastrophe, such as a myocardial infarction, sudden cardiac arrest, or stroke, with the highest risk during the first 6 hours after awakening and arising. Understanding the fluctuations in cardiovascular indices and the rhythmic increase in risk is crucial in assessing patients and developing a protective plan of care. This article discusses the cardiovascular rhythms and the rhythmic increase in risk for cardiovascular catastrophes. A framework demonstrating the interaction of these rhythms provides the basis for the development and exploration of interventions, including modification of activity and medications, and nursing actions to protect patients during periods of high cardiovascular risk.