Medical Implications of Circadian Rhythmicity Prominent circadian variations have been reported in the incidence of acute myocardial infarction, sudden cardiac death, and stroke, the leading causes of death in the United States. Platelet aggregability is increased after arising in the early morning hours, coincident with the peak incidence of these cardiovascular events. A better understanding of the possible role of circadian rhythmicity in the acute destabilization of a chronic condition such as atherosclerotic disease could improve the understanding of the pathophysiology. Diagnostic and therapeutic procedures may also be affected by the time of day at which data are collected. Examples include. | Chapter 028. Sleep Disorders Part 15 Medical Implications of Circadian Rhythmicity Prominent circadian variations have been reported in the incidence of acute myocardial infarction sudden cardiac death and stroke the leading causes of death in the United States. Platelet aggregability is increased after arising in the early morning hours coincident with the peak incidence of these cardiovascular events. A better understanding of the possible role of circadian rhythmicity in the acute destabilization of a chronic condition such as atherosclerotic disease could improve the understanding of the pathophysiology. Diagnostic and therapeutic procedures may also be affected by the time of day at which data are collected. Examples include blood pressure body temperature the dexamethasone suppression test and plasma cortisol levels. The timing of chemotherapy administration has been reported to have an effect on the outcome of treatment. Few physicians realize the extent to which routine measures are affected by the time or sleep wake state when the measurement is made. In addition both the toxicity and effectiveness of drugs can vary during the day. For example more than a fivefold difference has been observed in mortality rates following administration of toxic agents to experimental animals at different times of day. Anesthetic agents are particularly sensitive to time-of-day effects. Finally the physician must be increasingly aware of the public health risks associated with the ever-increasing demands made by the duty-rest-recreation schedules in our round-the-clock society. Further Readings Flemons WW Clinical practice. Obstructive sleep apnea. N Engl J Med 347 498 2002 PMID 12181405 Pack AI et al Risk factors for excessive sleepiness in older adults. Ann Neurol 59 893 2006 PMID 16718691 Scammell TE The neurobiology diagnosis and treatment of narcolepsy. Ann Neurol 53 154 2003 PMID 12557281 Silber MH Clinical practice. Chronic insomnia. N Engl J Med 353 803 2005 PMID .
