Cross-sectional area as a measure of nasal resistance.

The possibility of using cross-sectional area as a measure of nasal resistance was investigated with an equation based on hydraulic principles that link the area of a constriction in an airway to the pressure gradient and flow rate of air passing through it. Experiments with anatomical models of the nasal cavity confirmed the area of the nasal valve could be measured from simple pressure and flow data with a mean error of 3.5 mm2 (SD = 2.2). The software of a clinical rhinomanometer was then modified to incorporate this equation. Initial tests with a series of substitute airway constrictions of known area indicated the rhinomanometer could then use pressure and flow data to derive the area of each constriction with a mean error of 1.4 mm2 (SD = 0.9). Using this modification during rhinomanometry on 18 adults with subjectively clear nasal airways, a mean value for the narrowest area of the combined nasal cavities was found to be 48 mm2 (SD = 13.7) and results from 17 subjects complaining of nasal obstruction produced a mean narrowest area of 27 mm2 (SD = 11.8). Thus, this system can accurately derive area from data normally gathered from rhinomanometry and the value is constant over a range of pressure gradients and flow rates. The advantages of considering nasal obstruction in terms of area are discussed.