Long-term nasal CPAP does not ameliorate obstructive sleep apnoea

Fifty-seven patients with obstructive sleep apnoea (OSA) were treated for at least six months with nasal continuous positive airway pressure (CPAP). At follow-up, sleep studies were performed in which CPAP was not used for the first half of the night. We compared the severity of OSA at follow-up without CPAP to the severity of OSA during the patient's initial diagnostic study. Apnoea and hypopnoea index (AHI) fell from 41.4 +/- 7.5 (mean +/- 95% CI) to 34.8 +/- 7.9 (p = 0.06 by Wilcoxon test) and minimum oxygen saturation rose from 71.6 +/- 3.2 to 78.5 +/- 2.6 (p less than 0.001). Some of this change may have been due to reduced REM sleep in the follow-up study (10.5 +/- 2.1% Total Sleep Time vs 7.4 +/- 2.4% TST, p less than 0.05). Long-term nasal CPAP was not associated with any reduction of obesity (BMI before CPAP 31.9 +/- 1.0, after CPAP 31.7 +/- 1.0 (p = 0.39). Systolic arterial pressure fell (before CPAP 143.0 +/- 4.5 mmHg, after CPAP 136.3 +/- 4.6, p less than 0.05) but diastolic pressure did not (before CPAP 88.5 +/- 3.0 mmHg, after CPAP 85.6 +/- 2.9 mmHg, p = 0.11). We concluded that the effect of CPAP treatment for six or more months was a small fall in AHI and a small rise in minimum SaO2, but that this would be of marginal clinical significance, and may be artefactual.