A number of studies have assessed the effect of CPAP on systemic hypertension. Becker and co-workers found that effective treatment of sleep apnea with nasal CPAP for > 9 weeks lowered both nocturnal and daytime systolic and diastolic BP by approximately 10 mm Hg. Strengths of this study included a longer duration of CPAP treatment and use of a noninvasive BP monitoring device that makes continuous measurements and is less likely to cause arousals. It was limited by a relatively large number of dropouts due to technical issues or changes in BP medications. Other investigations have shown smaller or no effects on daytime BP. These conflicting results may reflect inadequate CPAP treatment (poor adherence), too short a treatment interval, or populations with less severe sleep apnea. In addition, some of the studies included patients who were not hypertensive. Of note, ambulatory BP monitoring can cause arousals from sleep with an associated increase in BP. Despite the somewhat conflicting data on the effects of CPAP on BP, a standard of practice paper of the American Academy of Sleep Medicine on the use of PAP treatment recommended CPAP as an adjunctive treatment for systemic hypertension in patients with sleep apnea.
Patients with OSA also have nocturnal increases in pulmonary arterial pressure secondary to hypoxic vasoconstriction. OSA patients with normal daytime blood gas levels usually have normal or only mildly increased daytime pulmonary arterial pressures. However, studies- have shown that PAP reduces both nocturnal and daytime pulmonary arterial pressure.
Studies have also evaluated the effect of CPAP in patients with OSA and cardiac dysfunction. Kangala and coworkers found that patients with untreated OSA had a higher rate of recurrence of atrial fibrillation after cardioversion. The increased risk of recurrence was eliminated by CPAP treatment. Other studies- have found that CPAP treatment is beneficial in OSA patients with left ventricular failure (improved ejection fraction and symptoms). Another study found that CPAP treatment reduced the frequency of ventricular premature beats in patients with OSA, heart failure, and a ventricular premature beat rate > 10/h. Studies’ have also suggested that PAP treatment may improve brady-arrhythmias (sinus pauses, A-V block) or tachyarrhythmias.
A considerable literature exists about the beneficial effects of CPAP on a number of factors relevant to cardiovascular health, including decreased sympathetic activity, decreased markers of inflammation, and improved endothelial function. Some of these results are summarized in Table 1.