© 2004 American Thoracic Society
Rebuttal from Dr. StradlingDr. Lavie equates association with causality. All eight cross-sectional studies to which he refers have, by definition, failed to control for unknown confounding variables: just as must have occurred in the hormone replacement and antioxidant cross-sectional studies referred to in my original exposition. The Toronto dog model referred to is very compelling (1), and sudden-onset severe obstructive sleep apnea clearly raises blood pressure over a short time frame. This is not like human obstructive sleep apnea, developing gradually over years and allowing compensatory mechanisms to occur. Recurrent nocturnal hypoxia also raises diurnal blood pressure in rats, but only in certain strains (2); humans may not behave like dogs. Dr. Lavie quotes our work on falls in blood pressure after nasal continuous positive airway pressure therapy (3). The falls, however, were small, only seen at the severer end of the spectrum, and there is no evidence that they equate to changes in long-term cardiovascular morbidity.The elegant mechanisms proposed for how obstructive sleep apnea might cause cardiovascular disease are almost as impressive as those advanced for how extra antioxidants might protect against cardiovascular disease (4). Despite the plausibility of these latter mechanisms, when the randomized controlled trials of antioxidants were done, there was no benefit and therefore the mechanisms were clearly flights of fancy. Until there are interventional trials, these mechanisms remain hypotheses, not facts. Dr. Lavie also describes the early onset of cardiovascular disease in these patients. But, on average, these patients already have high cardiovascular risk profiles. Indeed, a study using brain magnetic resonance imaging, comparing obstructive sleep apnea patients with carefully matched control subjects, found similar high prevalences of subclinical ischemic damage: there being no evidence of extra lesions in those with obstructive sleep apnea, despite their higher blood pressures (5). Thus, I still maintain that there is no evidence that obstructive sleep apnea causes cardiovascular disease, only that it causes some diurnal hypertension. Therefore, there is no evidence yet to treat patients with obstructive sleep apnea in the hope that cardiovascular risk will be reduced over subsequent years. REFERENCES
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