Findings cannot be applied to general public

EDITOR—The study by Lavie et al is the first to provide evidence that sleep apnoea is an independent risk factor for hypertension.1 We think, however, that the clinical implications put forward are limited by the chosen population and study design.

The findings of this study cannot be applied to the general population for the following reasons. Firstly, all the study population consists of patients referred to a sleep clinic and is therefore highly selected. Furthermore, we believe that patients' risk of comorbidity is significantly greater than that of the general population; for example, 22.8% of the control group were hypertensive. Associations in highly selected populations are open to bias,2 a factor not addressed by the authors.

We question whether patients should have been diagnosed as hypertensive on the basis of readings taken over a 24 hour period. Standard practice is to make a diagnosis on the basis of measurements taken on three separate occasions, eliminating influencing factors, in particular environmental stresses.

We agree with Locke that many of these problems could be overcome by adopting a new study design.3 We think, however, that a prospective cohort study is more suitable. Non-apnoeic patients from the general population would be matched and compared with patients with varying degrees of sleep apnoea and …