ArticlesAmbulatory blood pressure after therapeutic and subtherapeutic nasal continuous positive airway pressure for obstructive sleep apnoea: a randomised parallel trial
Introduction
In more-developed countries, 2–4% of adult men, and about 1% of adult women have detectable obstructive sleep apnoea,1, 2 and up to 1·5% of men in the UK have moderate or severe disease.3 Sleep apnoea is caused by the collapse of the pharynx during sleep, which leads to airway occlusion and transient asphyxia. Asphyxia is reversed when the patient wakes and pharyngeal muscle tone returns to wake levels. These events are repetitive, with severely affected patients having hundreds of obstructive episodes and arousals every night. Both nocturnal and daytime blood pressure are raised in patients with obstructive sleep apnoea. This effect is seen in community-based epidemiological studies4, 5 and hospital clinic populations,6 and is independent of obesity and other risk factors for raised blood pressure that are prevalent in this population.4, 5, 6
The standard treatment for sleep apnoea is nasal continuous positive airway pressure (nCPAP), and if this treatment reduces blood pressure it should also reduce vascular risk, which is high in patients with this disorder.7 Results of observational cohort studies8, 9 and of a small crossover trial controlled by an oral placebo10 suggest that blood pressure falls in patients with sleep apnoea who are given nCPAP. However, existing data11, 12 have been strongly criticised for not being adequately controlled, and vigorous debate about the effect of sleep apnoea treatment on vascular risk has resulted. For example, Phillipson13 has described sleep apnoea as a vascular risk factor that is “as important as diabetes”, whereas in another editorial,14 the argument is that this disorder “may not be a disease at all”. Wright and colleagues11 have emphasised the need for methodologically robust trials to settle this debate, since the large symptomatic placebo effects seen with subtherapeutic nCPAP15 probably change physical activity and diet, and hence blood pressure. We have addressed this uncertainty by comparing changes in ambulatory blood pressure when nCPAP treatment is used for obstructive sleep apnoea with those of the most robust control therapy available, subtherapeutic nCPAP.
Section snippets
Design and setting
We did a parallel, randomised, double-blind trial of patients in the Sleep and Respiratory Trials Units, Oxford Centre for Respiratory Medicine, Oxford, UK. The unit takes patients who have been referred with possible obstructive sleep apnoea from the surrounding region. About a third of patients are from the Oxford area. Referrals are made by general practitioners (36%); ear, nose, and throat surgeons (41%); or other hospital consultants (23%).
Patients
Patients were eligible for the trial if they were
Results
Figure 1 shows the trial profile. Of the 339 eligible patients, 67 had been included in our previous study of sleepiness in obstructive sleep apnoea.15 Blood pressure measurement was added to this previous protocol after it had received ethical approval and after it was established to be manageable within the protocol. Patients who declined to take part did so mainly because of the extra time needed to participate, or the distance to travel. The severity of sleep apnoea was similar between
Discussion
Our results showed a significant fall from baseline of 3·3 mm Hg in mean ambulatory blood pressure in patients with moderate or severe obstructive sleep apnoea when given therapeutic nCPAP compared with patients on subtherapeutic nCPAP. Similar reductions were seen in systolic and diastolic blood pressure during both sleep and wake times. This result directly addresses a deficit in the evidence of the blood pressure response to nCPAP therapy in patients with sleep apnoea; specifically, the
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