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Dr. Loube is Director, Sleep Disorders Center, Virginia Mason Medical Center.
Correspondence to: Daniel Loube, MD, FCCP, Virginia Mason Medical Center, Sleep Disorders Center (H-10), 925 Seneca St, Seattle, WA 98111; e-mail: sdcdil{at}vmmc.org
Recently, two well-designed studies by researchers from the University of Wisconsin1 and the Sleep Heart Health Study Group2 documented that untreated obstructive sleep apnea (OSA) increases the risk for hypertension in American adults. In both studies, the risk for hypertension increased in a dose-response association with the frequency of obstructive respiratory events during the night, independently of confounding factors such as age, gender, and weight. It is expected that these and other studies evaluating large patient cohorts will determine whether this increased risk for hypertension results in added morbidity and mortality from ischemic heart disease and other cardiovascular diseases. It may well be that the increased risk of cardiovascular disease sequelae from OSA will warrant widespread efforts at early detection and treatment, much as is the current clinical practice for hyperlipidemia.
Sleep apnea is typically characterized as a disease of obese,
middle-aged men.3
4
This stereotype is a result of older
studies completed in the United States, Europe, and Australia that
found that 60 to 90% of all OSA patients are obese,5
as
defined by a body mass index (BMI) of 
28
kg/m2. A landmark study by Young et
al6
determined that 2 to 4% of Wisconsin factory workers
had OSA, and that the risk for OSA increased in close association with
measures of truncal obesity, such as neck size. The study by Ip et al
in this issue of CHEST (see page 62) indicates that OSA may
occur with a similar prevalence in a cohort of nonobese subjects, as
the mean BMI for this study cohort was only 23.9
kg/m2. Of great importance is the fact that the
study cohort was 784 Chinese office workers in Hong Kong.
There are a paucity of data characterizing the epidemiology of OSA in populations other than middle-aged or older white men, and few studies have focused on young adults, women, or patients of African or Asian descent. Recent investigations on the epidemiology of ischemic heart disease indicate that the clinical recognition and management of this disease varies markedly in cohorts of women7 or of nonwhite patients, compared with that of white men.8 The scenario may be much the same for the epidemiology of OSA.
The study by Ip et al suggests, in a preliminary fashion, that the demographics and even possibly the pathogenesis of OSA may be different for Asians in comparison with whites. Along these lines, a recent study by Li et al9 documented that Asian patients with OSA were less obese but had more severe symptoms than whites presenting over the same 1-year study interval. The authors attempted to attribute these differences to various facial characteristics derived by radiographic measurements that vary between Asians and whites. However, demonstrating an association does not indicate a causal relationship.
A crucial conclusion from these studies is that predictive equations for the presence of OSA developed from populations of obese, white men and based on weight or facial measurements are unlikely to be accurate in Asian men or, indeed, in many other groups. Such predictive equations are often promoted as less-costly recognition strategies for OSA than conventional 12-channel polysomnography. Their use is almost certain to gain broader application if earlier and widespread diagnosis of OSA becomes a public-health issue similar in significance to hyperlipidemia as a risk factor for increased cardiovascular morbidity and mortality.
The study by Ip et al is an important first step in illustrating that fundamental differences may occur in various ethnic populations of OSA patients. Recently, O’Connor et al10 showed that important differences also exist between populations of women and men with OSA. It is obvious that more studies are necessary to facilitate and allow for the accurate diagnosis and appropriate treatment of OSA in those other than middle-aged, white men.
References
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