Effects of mandibular advancement on respiratory resistance

Mandibular advancing devices are proposed as nonsurgical treatment for cert ain patients with an obstructive sleep apnoea syndrome. Since they act by i ncreasing the upper airway calibre, the aim of the present study was to inv estigate the changes in respiratory resistance (Rrs) resulting from mandibu lar advancement. Rrs was measured at the nose by the forced oscillation technique (4-32 Hz). Ten normal subjects were studied under three conditions: resting mandibula r position, passive mandibular advancement steadied by a wax bite, and volu ntary advancement, in random order. Respiratory resistance was extrapolated to 0 Hz (R0) and estimated at 16 Hz (R16) by linear regression analysis of respiratory resistive impedance versus frequency. R0 (mean+/-SEM=3.5+/-0.2 cmH(2)O .L-1 s in the resting position) decreased significantly with passive advancement (2.9+/-0.2 cmH(2)O .L-1.s, p<0.001), but remained unchanged with voluntary mandibular advancement (3.6+/-0.2 cm H(2)O<bullet>L-1.s). Similar results were obtained for R16. The results of this study demonstrate that the effects of mandibular advanc ement on upper airway resistance differ, depending on whether advancement i s passive or active, and suggest that in order to simulate the actual effec ts of therapeutic devices, mandibular advancement should be passive.