Eliminating paranasal sinus resonance and its effects on acoustic properties of the nasal tract.

The significance of nasal resonance and anti-resonance to voice production is a classical issue in vocal pedagogy and voice research. The complex structure of the nasal tract produces a complex frequency response. This complexity must be heavily influenced by the morphology of the paranasal cavities, but their contributions are far from being entirely understood. Detailed analyses of these cavities are difficult because of their limited accessibility. Here we test different methods aiming at documenting the acoustical properties of the paranasal tract. The first set of experiments was performed under in vivo conditions, where the middle meatus was occluded by means of targeted application of a maltodextrin mass under endoscopic control. The efficiency of this occlusion method was verified by measuring the nasal nitric oxide (NO) output during humming. In another experiment the frequency responses to sine sweep excitation of an epoxy mould of a nasal cavity were measured, with and without elimination of paranasal sinuses. The third experiment was conducted in a cadaveric situs, with and without maltodextrin occlusion of the middle meatus and the sphenoidal ostia. The results show that some nasal tract resonances were unaffected by the manipulation of the paranasal cavities. Providing access to a maxillary sinus resulted in marked dips in the response curve while access to the sphenoidal ostium caused only minor effects.