Sunday, July 22, 2012

Sleep and Health: an update

By Narayan Krishnamurthy, MD

The Institute of Medicine estimates that 50 to 70 million adult Americans have a chronic sleep disorder that contributes to poor health. Approximately 1 in 3 adult Americans are sleeping less than recommended 7 hours per night. This manifests with physiological and neurobehavioral deficits leading to chronic medical and psychiatric disorders.

Longer work hours and commute times, shift work, poor sleep hygiene, and a mindset of “If you snooze, you lose” have contributed to the growing sleep deficiency problem. An estimated 20% of the US workforce is exposed to shift work schedules that contribute to chronic disruption of biological “clock”, resulting in higher risk of developing a number of illnesses.

Chronic sleep deficiency defined as a state of inadequate or irregular sleep habit due to any cause, is growing and often underappreciated. Sleep deprivation contributes to a number of changes that play a role in disease development. These changes in response to chronic sleep deficiency has been shown to play a major role in the development and exacerbation of common cardiovascular and metabolic diseases such as hypertension, diabetes, heart failure, heart attacks, and stroke to name a few. It can ultimately lead to shortened lifespan as well as sudden death, particularly when associated with low oxygen level in complex conditions such as sleep apnea with chronic lung or heart disease. A vast body of evidence based on animal, human cross-sectional longitudinal research and interventional studies suggests that sleep disorders, particularly, sleep apnea is associated with significant cardiovascular risk factor. In addition, sleep deprivation results in significant impairments in concentration and motor performance, which increase the risk of motor vehicle accidents and severe injuries at work place.

Poor sleep health is largely accounted for by the high prevalence of primary sleep disorders (e.g., sleep apnea, insomnia, narcolepsy, and restless legs syndrome). Obstructive sleep apnea (OSA) is largely under-recognized and usually undiagnosed until patients start experiencing adverse health effects such as hypertension, daytime sleepiness, uncontrolled diabetes and drowsiness-related accidents. Children with OSA seem may present with irritability, impaired attention and vigilance, emotional instability, and decreased intelligence. This cognitive impairment can cause problematic behavioral manifestations with poor performance in school.

In the Sleep Heart Health Study, subjects sleeping ≤ 5 h/night had a higher frequency of prevalent hypertension. Lack of diminished nocturnal dipping of BP as occurs in OSA is a strong, independent predictor of cardiovascular risk. Accordingly, sleep-related diseases that induce increases in BP such as OSA would be anticipated to substantially affect cardiovascular risk. This association appears to be most significant during middle age.

Approximately 50% of patients with OSA are hypertensive, and an estimated 30% to 40% of patients with hypertension have OSA. More severe the OSA, the higher the risk of hypertension of increasing severity. OSA-induced increases in sympathetic activation contribute to increase in BP. OSA is common in patients with resistant hypertension, which is defined as BP that remains uncontrolled with three or more medications.

OSA, now an established cause of hypertension also worsens the control of cardiovascular diseases such as coronary disease, arrhythmia, pulmonary hypertension, all of which are causes of acute decompensation and admission to the hospital. Atrial fibrillation (AF) is another highly prevalent condition strongly associated with Sleep apnea. A similar relationship with sleep apnea has been reported in patients with heart failure and stroke as well. More recent studies have shown an association between stroke and even mild to moderate OSA. Silent brain infarction has been shown to be increased in patients with OSA. Patients with heart failure have a higher prevalence of OSA than the general population. Recent data indicate that majority of obese patients with type 2 diabetes experience clinically significant OSA which remain undiagnosed. narayan krishnamurthy Hence, there is a strong link between OSA and the metabolic syndrome of obesity, hypertension, and diabetes leading to higher incidence of coronary artery disease.