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Obstructive sleep apnea and resistant hypertension: a case-control study.

BACKGROUND
Obstructive sleep apnea syndrome (OSAS) has been linked to resistant hypertension, but the magnitude of this association and its independence of confounding have not been established.


METHODS
Case patients were 63 patients with resistant hypertension (BP >or= 140/90 mm Hg using at least three BP-lowering drugs, including a diuretic), and control subjects were 63 patients with controlled BP receiving drug treatment. The primary outcome was the frequency of OSAS (apnea-hypopnea index [AHI] >or= 10 episodes per hour) determined with a portable home monitor. The comparison of AHI episodes in patients truly normotensive, truly hypertensive, and in patients with white coat or masked hypertension, based on BP determined at office and by ambulatory BP monitoring (ABPM) was a secondary outcome.


RESULTS
Case patients and control subjects were well matched for confounding factors. OSAS was present in 45 case patients (71%) and in 24 control subjects (38%) [p < 0.001]. In a logistic regression model, OSAS was strongly and independently associated with resistant hypertension (odds ratio, 4.8; 95% confidence interval, 2.0 to 11.7). The AHI of case patients with normal BP in ABPM (white coat hypertension) and control subjects with abnormal BP in ABPM (masked hypertension) was intermediate between the AHI of individuals with normal and abnormal BP measures in both settings (p < 0.001).


CONCLUSIONS
The magnitude and independence of the risk of OSAS for resistant hypertension strengthen the concept that OSAS is a risk factor for resistant hypertension. Comorbid OSAS should be considered in patients with resistant hypertension.