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1 National Heart and Lung Institute, Imperial College School of Medicine, Sleep and Ventilation Unit, Royal Brompton Hospital, London, UK. 2 Middleton Veterans Administration (VA) Hospital and the University of Wisconsin, Madison, WI and 3 Detroit VA Medical Centre, Wayne State University, Detroit, MI, USA
CORRESPONDENCE: M.J. Morrell, Sleep and Ventilation Unit, Royal Brompton Hospital, London, SW3 6NP, UK. Fax: 44 2073518911. E-mail: m.morrell@ic.ac.uk
Keywords: apnoea, breathing, human, sleep, surfactant
Received: August 17, 2001
Accepted March 15, 2002
This study was supported by the Veterans Adminisration Medical Research Services and National Heart, Lung and Blood Institute. M.J. Morrell is supported by a Wellcome Trust Career Development Fellowship
Instillation of surfactant into the pharyngeal lumen reduces the pressure required to reopen an occluded airway, and decreases the apnoea/hypopnoea index (AHI). The authors hypothesised that surfactant also reduces the sleep-related increase in pharyngeal resistance. To test this hypothesis two single blind, crossover, placebo-controlled studies were performed.
In protocol A seven male, asymptomatic snoring subjects were studied during sleep. Inspiratory pharyngeal resistance was calculated from plots of airflow versus supraglottic pressure (seven breaths) before and after surfactant or saline instillation. In protocol B, in a different group of seven male subjects with sleep apnoea (AHI 15.2 (12) events·h–1) the effect of surfactant or saline on sleep disordered breathing was measured, for 1 h immediately before and after surfactant or saline instillation.
Surfactant decreased pharyngeal resistance calculated at peak pressure (group mean (sd): pre versus post 83.7 (76.4) versus 49.4 (71.1) cmH2O·L–1·s–1) and significantly reduced the respiratory disturbance index (RDI pre versus post 79.7 (58.7) versus 59.6 (56.9) events·h–1). Saline did not decrease resistance (pre versus post 58.6 (31.1) versus 72.5 (73.4) cmH2O·L–1·s–1) or RDI (pre versus post 75.3 (42.4) versus 79.9 (46.1) events·h–1).
Surfactant reduced the collapsibility of the pharynx and led to a modest reduction in respiratory disturbance index. The authors speculate that surfactant may delay occlusion by reducing the liquid "bridging" within the folded pharyngeal lining.
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