Cardiovascular aspects of obstructive sleep apnoea and their relevance to the assessment of the efficacy of nasal continuous positive airway pressure therapy

Wright et al 1 set out to assess the “health effects” of obstructive sleep apnoea (OSA) and the evidence for the efficacy of continuous positive airway pressure (CPAP) in this disorder. In their assessment they concentrated particularly on whether or not OSA causes cardiovascular disease. The review included more than 70 papers examining cardiovascular end points and less than 30 pertaining to daytime sleepiness and quality of life. It was structured to emphasise these cardiovascular issues and appeared to imply that these factors are the important reasons for the treatment of sleep apnoea. In fact this is incorrect. Patients with sleep apnoea are treated primarily to control disabling daytime sleepiness and to improve quality of life. Heated debates about possible links with cardiovascular disease continue but these are not primarily relevant to the efficacy of CPAP treatment. By getting this balance wrong, the review by Wright et al 1 was seriously flawed; by asking the wrong question it inevitably produced a misleading answer. Wright et al 1 first dealt with “health effects” and then separately with “CPAP efficacy” and the present discussion is structured similarly. Most of the available cardiovascular evidence relates to systemic arterial blood pressure and hence this dominates what follows. The discussion of arterial blood pressure deals first with blood pressure at night in patients with OSA and then separately with daytime awake blood pressure, since the patterns and mechanisms of any blood pressure changes are different in these two states. Figure 1 shows the disturbance of blood pressure and cardiac output which occurs during obstructive apnoeas. The blood pressure trace shows repeated falls during apnoea followed by a sharp rise in the period following the apnoea which is coincident with arousal on the electroencephalogram. The magnitude of the rise in blood pressure following apnoea can be …