Obstructive sleep apnea and hypertension: from correlative to causative relationship

Abstract

Sleep-disordered breathing, manifested by repetitive episodes of partial or complete cessation of breathing during sleep associated with brief arousal and autonomic activation, is estimated to affect as many as 4% of adult men and 2% of adult women. Studies conducted during the 1980s revealed a strong association between sleep-disordered breathing and hypertension. The results of these early studies, which relied on relatively small samples of patients, have been confirmed in recent years by large-scale epidemiologic studies that are controlled for all possible confounding factors. This paper reviews the evidence suggesting a causative relationship between hypertension and disordered breathing in sleep. The authors discuss the possible underlying mechanisms of the two entities and address the clinical implications of this relationship. They conclude by recommending a proactive approach to the diagnosis of breathing disorders in sleep, in order to prevent the cardiovascular sequelae of this syndrome.

Figure 1

Relationship between severity of breathing disorders in sleep, as indicated by the respiratory disturbance index (RDI)—the total number of apneic plus hypopneic events divided by the total sleep time in hours—and self‐reported hypertension. Data of 10,000 patients diagnosed in the Technion Sleep Medicine Center in Israel during 1990–2000 are presented.

Figure 2

Relationship between self‐reported hypertension and the degree of overweight based on the World Health Organization classification of body mass index (normal, 18.5–24.9 kg/m²; overweight, 25.0–29.9 kg/m²; obesity class 1, 30.0–34.9 kg/m²; class 2, 35.0–39.9 kg/m²; class 3, >40 kg/m²). Data of 10,000 patients diagnosed in the Technion Sleep Medicine Center in Israel during 1990–2000 are presented.

Figure 3

Comparison between the percentage of patients with breathing disorders in sleep who reported on hypertension or used antihypertensive medications and the percentage of patients who were found to have blood pressures >140/90 mm Hg either during morning or evening measurements. Data of 2677 adult patients diagnosed in St. Michael's Hospital Sleep Laboratory in Toronto are presented.