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To the Editor:

I read with interest the article by Gurubhagavatula and colleagues.[1] They prepared two screening methods for severe obstructive sleep apnea syndrome (OSAS) in hypertensive outpatients and recommended a 2-stage model for identifying severe OSAS with satisfactory screening indicators. But before accepting their study outcome, pathophysiology of hypertension should be more precisely evaluated in their study.

Solini and Ruilope presented their perspectives on the management of resistant hypertension, selecting OSAS as one of the modifiable predisposing conditions.[2] They explained the relationship between obstructive sleep apnea and hypertension from several common factors and mechanisms such as obesity, several vascular atherosclerotic factors, and renin-angiotensin-aldosterone activation. Combinations of resistant hypertension and OSAS have been reported, and therapy with continuous positive airway pressure is effective for controlling hypertension.[3, 4]

I have a query for the outcome presented by Gurubhagavatula and colleagues.[1] They selected patients with hypertension and hypertension-associated factors to be included in their analysis, such as the severity of hypertension and the content of treatment.[5] Causalities of hypertension and OSAS are complex, and bidirectional analyses are required. For example, OSAS might contribute to resistant hypertension through sympathetic activation, reduced baroreflex sensitivity, endothelial dysfunction, oxidative stress, inflammation, and arterial stiffness.[2, 6] Conversely, the “excess salt intake” is the main cause of increased circulating blood volume,[7] and increased serum aldosterone might promote accumulation of fluid within the neck, which leads to OSAS.[8, 9]

I appreciate their statistical approach to validate the screening method for severe OSAS, but specification of hypertensive patients should be included in their analysis. For example, the area under the receiver operating characteristic curve should also be estimated after stratification of several characteristics of hypertension. Severity of hypertension would be associated with the status of OSAS, and such analysis would be useful for the primary care physician.

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