Validation by fluid volume of acoustic rhinometry before and after decongestant in normal subjects

To validate the measurement of nasal volume by acoustic rhinometry, acoustic rhinometry (AR) measures before and after decongestion were compared to a reference volume measurement in 10 healthy volunteers over 3 visits each. The reference method was hydraulic infusion with manometry, involving slow constant-rate infusion of isotonic saline into each nasal cavity while the subject was appropriately positioned. Consecutive 10 mm nasal segments were measured, and hydraulic volume derived. AR volume and hydraulic volume measures were compared. Within subject reproducibility of hydraulic volume and AR volume measures over 3 study days was better than 16% and 11%, respectively. Pre-decongestant, highly significant correlations between AR volume and hydraulic volume in the 20-40 mm segment were found. The mean ratios of AR volume/hydraulic volume ranged from 1.01-1.14. Post decongestant, significant correlations were found in the 30-50 mm segments. The mean AR volume/hydraulic volume ratios were significantly lower (0.88-1.03). Hence, the magnitude of the AR volume change after decongestant was less than the hydraulic volume change (ratio range 0.8 to 1.01), but there were still significant correlations between hydraulic volume and AR volume in the 20-50 mm segments of the cavity. Since hydraulic volume is expected to be similar to anatomical nasal volume, we conclude that changes in AR volume before and after vasoconstriction are similar to anatomical changes in nasal vasculature. AR volume measurements provide a sensitive, reliable and accurate assessment of vasoactive drugs in the nasal cavity.