Acoustic rhinometry measurements in stepped-tube models of the nasal cavity.

Stepped-tube models with a constriction in the anterior section were used to evaluate the effects that nasal valve passage area and nasal cavity shape have on acoustic rhinometry (AR) measurements. The AR-determined cross-sectional areas beyond a constriction of small passage area were consistently underestimated, and the corresponding area-distance curves showed pronounced oscillations. Also, the AR technique did not accurately reproduce abrupt changes in passage area. The results suggest that, regardless of the particular shape of the nasal cavity model, AR does not provide reliable information about cross-sectional areas posterior to a severe constriction. The experimental results are discussed in terms of theoretically calculated acoustic input impedance for the models studied, the physical limitations of AR, and assumptions made in AR algorithms. The study demonstrated that energy losses and sound wave attenuation due to air viscosity do not significantly affect AR measurements. It was also shown that passage area beyond a severe constriction is underestimated because the barrier created by the constriction reflects most of the incident sound power. The results also indicate that the oscillations in area-distance curves are due to low-frequency acoustic resonances in the nasal cavity model.