Short paper EVect of high versus low ambient humidity on the severity of obstructive sleep apnoea

Background—Surface tension forces appear to make a significant contribution to upper airway closure in patients with obstructive sleep apnoea (OSA). It is possible that drying of the upper airway mucosa at night might contribute to these surface tension forces and the severity of OSA might therefore change with alteration of the ambient humidity. Methods—A randomised single blind crossover study of high ambient relative humidity (HRH) versus low ambient relative humidity (LRH) was performed in 12 men of mean (SD) age 49 (9) years with mild OSA (apnoea/hypopnoea index (AHI) 14 (5.2)). On one night patients slept in continuous HRH (85 (4)%, range 80–93%) and on the other in LRH (16 (4)%, range 11–22%). Results—The AHI was similar on the HRH and LRH nights (mean diVerence 3; 95% CI –2 to 9, p = 0.20) and no statistically significant diVerences in AHI were observed on the two nights after standardising for body position and sleep stage. Sleep stage distribution and the proportion of time spent in the supine position were similar on the HRH and LRH nights. The number of nonrespiratory arousals was also similar on the two nights. Conclusion—Altering ambient humidity alone has no significant impact on the severity of OSA. (Thorax 1999;54:711–713)