Blood pressure regulation and sleep apnea

Many patients with obstructive sleep apnea (OSA) have elevated blood pressure, and many patients with essential hypertension have sleep-disordered breathing. Indeed, epidemiologic studies have confirmed a high prevalence of hypertension among patients presenting with OSA. Other studies demonstrate that OSA or milder forms of sleep-disordered breathing are very common among unselected patients with hypertension. Increased activity of the sympathetic nervous system as indicated by levels of circulating catecholamines, excretion of catecholamine metabolites in the urine, or directly measured sympathetic activity in peripheral nerves has been recognized as a consistent feature of untreated OSA. Furthermore, symptomatic treatment with tracheostomy or more recently with nasal continuous positive airway pressure (CPAP) reduces blood pressure and sympathetic neural activity in many patients with OSA. These observations have prompted the question whether OSA causes hypertension and whether this form of hypertension may be mediated by the sympathetic nervous system.