Effect of mouth leak on effectiveness of nasal bilevel ventilatory assistance and sleep architecture

Mouth leak is common during nasal ventilatory assistance, but its effects on ventilatory support and on sleep architecture are unknown. The acute effect of sealing the mouth on sleep architecture and transcutaneous carbon dioxide tension (Ptc,CO2) was tested in 9 patients (7 hypercapnic) on longterm nasal bilevel ventilation with symptomatic mouth leak. Patients slept with nasal bilevel ventilation at their usual settings on two nights in random order. On one night, the mouth was taped closed. Leak was measured with a pneumotachograph. Median leak fell from 0.35+/-0.07 (mean +/- SEM) L x s(-1) untaped to 0.06+/-0.03 L x s(-1) taped. Ptc,CO2 fell in 8/9, including all hypercapnic patients. Across all patients, the mean Ptc,CO2 fell by 1.02+/-0.28 kPa (7.7+/-2.1 mm Hg) with taping (p = 0.007). Arousal index fell in every patient. Mean arousal index fell from 35.0+/-3.0 to 13.9+/-1.2 h(-1) (p<0.0001), and rapid eye movement (REM) sleep increased from 12.9+/-1.5% to 21.1+/-1.8% sleep time (p = 0.0016). Slow wave sleep changed inconsistently, from a mean of 13.1+/-1.6% to 19.5+/-2.2% of sleep (p = 0.09). Sleep latency and efficiency were unchanged. In four healthy volunteers ventilator-induced awake hypopharyngeal pressure swing during timed bilevel ventilation fell by 35+/-5% L(-1) x s(-1) of voluntary mouth leak (p<0.0001). Mouth leak reduces effective nasal bilevel ventilatory support, increases transcutaneous carbon dioxide tension, and disrupts sleep architecture.