Obstructive sleep apnea (OSA) has been identified as a significant cause of and/or contributor to cardiovascular disease. OSA has been shown to increase the risk for hypertension, pulmonary vascular disease, ischemic heart disease, stroke, congestive heart failure, and arrhythmias. The true relationship remains controversial despite the growing body of evidence that links OSA to the development of cardiovascular disease. Many risk factors for OSA are also known risk factors for cardiovascular disease, such as age, male gender, obesity, diabetes mellitus and hypertension. Therefore, it is difficult to prove whether OSA independently causes cardiovascular disease.
Episodes of sleep-disordered breathing cause blood vessel changes that can cause and contribute to cardiovascular disease. The adverse effects that OSA imposes on cardiovascular function are thought to arise from recurrent cycles of not breathing, intermittent hypoxia and the resulting arousals. This cycle of nocturnal desaturation results in an increase in sympathetic tone, impaired nitric oxide synthesis, endothelial dysfunction and ultimately leads to vascular and cardiac dysfunction, atherosclerosis and hypertension.
The 2004 American College of Chest Physicians (ACCP) consensus panel found that pulmonary hypertension occurred in 17 percent to 53 percent of individuals with OSA, whereas a review from Johns Hopkins found that 82 percent of patients with pulmonary arterial hypertension had underlying sleep-disordered breathing. The nocturnal drop in oxygen impairs nitric oxide synthesis and causes vascular remodeling which can lead to the development of pulmonary vascular disease. However, whether OSA independently causes clinically significant pulmonary hypertension remains controversial. Thus, the current ACCP guidelines do not recommend evaluating patients with OSA for pulmonary hypertension unless it is clinically suspected. However, patients with pulmonary arterial hypertension should be evaluated for OSA.
CPAP (continuous positive airway pressure) has been shown to be effective in patients with heart failure. Controlled trials have shown that treatment of OSA with CPAP is associated with significant improvements in cardiac function, sympathetic activity and quality of life. In the Canadian Positive Airway Pressure study, CPAP improved nocturnal oxygenation, increased left ventricular function, lowered norepinephrine levels and improved functional capacity among patients with sleep apnea and heart failure. Several recent studies have shown reductions in pulmonary artery pressure in patients with OSA after nocturnal CPAP treatment.