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BMJ No 7104 Volume 315 Letters Saturday 9 August 1997 Obstructive sleep apnoeaSuperficial analysis ignores evidence on efficacy of treatmentEditor,The conclusions of John Wright and colleagues have the potential to jeopardise public health as well as patients' care; their systematic review lacks the necessary depth and understanding of the issues.(1) The authors note that sleep apnoea is currently viewed as a public health concern because it is prevalent and thought to be associated with morbidity and mortality. The collective evidence from the studies included in the review supports this view; the authors' conclusions that evidence for the health effects of sleep apnoea is 'weak or contradictory' and that 'the relevance of sleep apnoea to public health has been exaggerated' are disturbing. The authors seem to have misinterpreted the findings of some studies. In their assessment of nine studies of hypertension judged to be methodologically adequate, the authors dismiss seven studies that show an independent association between sleep apnoea and hypertension. The authors choose to base their conclusion solely on the two studies that found no association. The studies that found an association were rejected because associations were found only for blood pressure measured in the morning, or because of failure to control for use of antihypertensive drugs, smoking, or use of alcohol. Acute spikes in blood pressure are known to follow episodes of apnoea and hypopnoea; therefore, it is not unreasonable to expect a stronger effect in the morning. If the effect on blood pressure later in the day is less, the small sample sizes of these studies may have precluded detection. Not controlling for antihypertensive drugs would only serve to reduce a true association. Smoking and alcohol use are unlikely to be strong enough risk factors to cause significant confounding.
Wright and colleagues' review of evidence on treatment with continuous positive airways pressure is also unbalanced. While we support the call for a large randomised clinical trial - the next logical step in this field - there is already evidence for the efficacy of continuous positive airways pressure as evaluated by short term neurobehavioural measures and quality of life assessments. We are concerned that the superficial analysis and conclusions of Wright and colleagues will lead to many patients being denied access to this treatment, which is associated with minimal risks. Wright and colleagues should be alerted that well designed longitudinal studies on sleep apnoea are under way. We hope that the authors will conduct a more informed review of forthcoming reports. Allan I Pack
Center for Sleep and Respiratory Neurobiology,
Terry Young
Department of Preventive Medicine, References 1 Wright J, Johns R, Watt I, Melville A, Sheldon T. Health effects of obstructive sleep apnoea and the effectiveness of continuous positive airways pressure: a systematic review of the research evidence. BMJ 1997;314:851-60. (22 March.)
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