The Use of Acoustic Rhinometry to Quantitatively Assess Changes after Intranasal Allergen Challenge

Acoustic rhinometry (AR) is a technique of measuring the cross-sectional area (CSA) of the nasal cavity by analyzing reflected sound waves. It allows a quantitative measurement of the changes of the nasal airway diameter after intranasal allergen challenge. In this study, AR is used to quantitate the degree of narrowing of the nasal cavity produced by various amounts of allergen challenge. Intranasal challenges were performed on seven subjects using radioallergosorbent test (RAST) discs of dust mite or ragweed allergens. At the same time, the (modified) mRAST class of the subjects was obtained by performing mRAST in vitro testing. Five subjects had positive mRAST scores to either dust mite or ragweed, and two subjects had negative mRAST scores. AR was performed prior to intranasal challenge to obtain a baseline. Then AR was performed 15, 30, and 45 minutes after the application of one RAST disc to the head of the inferior turbinate on both sides of the nose. The same measurements were taken after the serial application of two, three, and four RAST discs. For each AR measurement, the CSA at 10 locations in the nasal cavity was averaged for both sides. The endpoint is defined as the number of RAST discs required to produce a 50% reduction in the average CSA of the nasal cavity. We found that the endpoint correlates inversely with the mRAST class of the subject (r = –0.89). In the subjects with negative mRAST scores, no end point was found, even after challenge with four discs.