A quantitative technique for assessing nasal airway impairment.

The controversy concerning the effects of impaired nasal respiration on dentofacial development stems largely from the lack of a reliable method to assess airway impairment. The purpose of this study was to develop and validate a quantitative technique to estimate nasal airway dimensions so that normal and impaired nasorespiratory function could be defined. The method involves a modification of the theoretical hydraulic principle and utilizes the following equation to estimate cross-sectional area of the nose (NA): NA = V/K [2(delta P)/d] 1/2 (where d = density of air). Pressure drop (delta P) across the nose is measured simultaneously with airflow (V) through the nose during breathing, using appropriate transducers and a PDP 11/34 computer. An analog model of the upper airway was used to determine the discharge coefficient (k) and estimate measurement error. Model studies demonstrate a measurement error of less than 5% for nasal cross-sectional areas of 0.02 to 1.2 cm2. Studies involving eighteen adult subjects and twenty-six children 8 to 11 years of age revealed mean smallest cross-sectional nasal areas of 0.62 cm2 +/- 0.17 and 0.43 cm2 +/- 0.076, respectively. The results indicate that the technique should enable clinicians to (1) estimate size of the airway during breathing, (2) distinguish between normal and impaired nasal respiratory function, and (3) determine quantitatively the effects of surgical and/or orthodontic treatment for improving nasal respiration.