Effects of mandibular advancement on upper airway dynamics in awake normal subjects: a pilot study with phrenic nerve stimulation.

Background: Mandibular advancement (MA) can be an alternative to continuous positive airway pressure (CPAP) in the treatment of obstructive sleep apnea syndrome. This study was designed to describe its effects on upper airway mechanics.

Methods: Six awake healthy subjects (four men, 31+/-8 years, body mass index (BMI) 25+/-2kg/m2) were studied supine. Phrenic stimulation was used to measure pressure-flow relationships in response to diaphragm contractions without pre-activation of upper airway dilators during progressive MA.

Results: Phrenic stimulation consistently induced flow limitation (initial peak V'-t1, corresponding to the limiting pressure; reduction to a nadir V'-t2; reincrease to a second peak V'-t3). The upper airway resistances were negatively correlated with MA. Their values at 4mm were significantly lower than at baseline. Further MA reduced resistances.

Conclusions: As with CPAP, MA in normal subjects decreases the propensity of the upper airway to collapse in response to a negative pressure pulse.