Acoustic rhinometry in nasal allergen challenge study: which dimensional measures are meaningful?

Acoustic rhinometry (AR) is commonly used as a quantitative assessment of nasal response to nasal allergen challenge (NAC). However, sources of error and physical limitations of various AR area-distance measurements have not been adequately evaluated.

To investigate the clinical value of AR measurements, and the relationship between subjective sensation and objective AR measurements in the NAC study.

Nasal challenge using increasing concentrations of crude Blomia tropicalis (Bt) extracts (0.6, 6, and 60 microg/mL) was performed in 15 adult patients (eight males and seven females) with ongoing persistent allergic rhinitis. Subjective symptom scores of nasal obstruction were recorded together with the objective AR measurements of the minimum cross-sectional area (MCA), distance to MCA and cross-sectional area (CSA) at 3.3, 4.0 and 6.4 cm from the nostril, during the 7 h after the last challenge.

The dose-response increase in nasal obstruction score was significantly (P<0.001 for all) associated with decreases in mean MCA (r=0.75), mean CSA3.3 (r=0.54), mean CSA4.0 (r=0.53) and mean CSA6.4 (r=0.20). The mean MCA (+/-SD) for each subjective symptom score 0, 1, 2 and 3 was found to be 0.73 (+/-0.22) cm2, 0.63 (+/-0.29) cm2, 0.33 (+/-0.17) cm2 and 0.21 (+/-0.14) cm2, respectively. When the MCA (left and right separately) reached an area <0.2 cm2, measurements of CSA3.3 and CSA4.0 were significantly reduced by 60-70%.

This study demonstrates that AR is a useful and objective investigational tool, which correlates well with the sensation of nasal obstruction. MCA, CSA3.3 and CSA4.0 are more reliable measurements than CSA6.4 due to physical limitations. It is important to note that when the MCA is smaller than 0.2 cm2, a common condition in the early-phase reaction, area-distance measurements beyond this point can be misinterpreted and should be considered with caution.