Surface tension of upper airway mucosal lining liquid in obstructive sleep apnea/hypopnea syndrome

Study Objectives: The obstructive sleep apnea hypopnea syndrome (OSAHS) is a disorder characterized by repetitive closure and reopening of the upper airway during sleep. Upper airway luminal patency is influenced by the surface tension (γ) acting within the liquid layer lining the upper airway. The aim of the present study was to examine the γ of upper airway mucosal lining liquid (UAL) in both healthy subjects and patients with OSAHS before and after sleep. Design: Measurements were performed before (PM) and after (AM) an overnight polysomnographic study. Setting: Sleep laboratory. Participants: We studied 11 healthy adults (5 men, 6 women) and 15 patients with OSAHS (14 men, 1 woman). Interventions: None. Measurements and Results: The γ of UAL ("pull-off" force technique, pooled PM and AM samples) in patients with OSAHS was increased (59.9 [53.8, 58.8] mN/m; mean [95% confidence interval]) compared with healthy subjects (56.3 [57.7, 62.1] mN/m; linear mixed effects models; P = .05). In both groups there was no significant difference between PM (56.6 [53.7, 59.5] mN/m for healthy subjects, 60.1 [57.9, 62.3] mN/m for the patients with OSAHS) and AM (56.1 [51.8, 60.4] mN/m and 59.6 [57.4, 61.8] mN/m, respectively) samples for γ of UAL and salivary flow rate (5 minutes unstimulated collection; PM = 0.53 [0.22, 0.84] mL/minute for healthy subjects, 0.38 [0.22, 0.54] mL/minute for OSAHS; AM = 0.39 [0.23, 0.55] mL/minute and 0.32 [0.2, 0.44] mL/minute). However, the occurrence of nasal breathing during sleep was associated with a fall in γ of UAL overnight (r² = 0.15, P < .05). Conclusion: Patients with OSAHS have normal salivary flow rate but an increased γ of UAL. In both healthy subjects and OSAHS patients, nasal breathing during sleep was associated with an overnight fall in the γ of UAL.