Acoustic rhinometry: accuracy and ability to detect changes in passage area at different locations in the nasal cavity.

OBJECTIVES To evaluate the accuracy of acoustic rhinometry (AR) measurements, and to assess how well AR detects obstructions of various sizes at specific sites in the nasal cavity, we created a cast model from an adult cadaver nasal cavity. METHODS The actual cross-sectional areas of the cast model nasal passage were determined by computed tomography and compared with the corresponding areas measured by AR. To assess how nasal obstruction affects the AR results, we placed small wax spheres of different diameters at specific sites in the model (nasal valve, head of the inferior turbinate, head of the middle turbinate, middle of the middle turbinate, choana, and nasopharynx). RESULTS The AR-derived cross-sectional areas in the first 6.5 cm of the cast model nasal cavity were very close to the corresponding areas calculated from computed tomographic sections perpendicular to the presumed acoustic axis. However, AR overestimated the passage areas at locations posterior to the 6.5-cm point. Acoustic rhinometry gave an accurate indication of the passage area of the nasal valve and its distance from the nostril. The nasal valve and the choana were indicated by significant dips on the AR area-distance curve, whereas the curve was smooth throughout the region that included the head of the inferior turbinate, the head of the middle turbinate, the middle of the middle turbinate, and the nasopharynx. In other words, AR did not discretely identify these latter sites. Acoustic rhinometry detected the different-sized inserts (obstructions) more accurately at the nasal valve than at sites posterior to this location. CONCLUSIONS The results of the study show that AR is a valuable method for assessing the anterior nasal cavity. This technique is sensitive for detecting changes in passage area at the nasal valve region; however, the sensitivity is lower at sites posterior to this. The findings suggest that when there is substantial narrowing of the nasal valve, AR will not identify an obstruction at any location posterior to the nasal valve. In such situations, AR measurements beyond the abnormal nasal valve may easily lead to misinterpretation of the patient's nasal anatomy or condition.