Estimation of Nasal Cross-sectional Areas, Using Oral Versus Nasal Pressure Measurements

Abstract

This study examines calculations of model nasal cross-sectional area, using nasal versus oral pressure measurements. The results indicate that greater accuracy of nasal cross-sectional area estimation is achieved by using nasal rather than oral pressures. Nasal pressures measured in the anterior model nose more closely reflect nasopharyn-geal pressures under a wide range of nasal constriction sizes and airflow rates. KEY WORDS: nasal area, nasal air pressure, oral air pressure. Warren recently described a quantitative technique for evaluating nasal airway impairment. This technique was recommended over the use of radiographs, given the latter's " two-dimensional superimposition of shadows of structures " as well as over the use of nasal airway resistance measurements, given their flow dependence. Specifically, the technique pro— vides calculations of the cross-sectional area of the nasal airway from measurements of trans-nasal pressure .and airflow rate, using the formula: Na Vlk(2[AP/d])1/2, where Na is the cross-sectional area of the nose, V is airflow rate through the nose, AP is pressure drop across the nose, d is density of air, and k is a correction factor, or constant (Warren, 1984). In this method, pressure drop across the nose is measured by means of a catheter inserted into the mouth, and nasal airflow rate is measured from both nostrils by means of a nose mask. It is suggested that pressure measured orally represents nasopharyngeal pressure (Warren, 1984). 199 pressure measurements obtained by this method may, in part, reflect the contribution of the velopharyngeal region, especially at higher flow rates (Kumlien and Schiratzki, 1979; Warren and DuBois, 1964). Therefore, nasal cross—sectional areas calculated from oral pressures may be less accurate at high flow rates than those made using pressures that more closely reflect pressures in the nasopharynx. Results of our recent modeling studies suggest that pressure measured in the anterior portion of the nose provides a more accurate estimation of nasopharyngeal pressure. It follows that use of such measurements may lead to more accurate estimates of nasal cross-sectional area than use of oral pressure measurements. This study compares nasal cross-sectional area measurements made using oral versus nasal pressures under controlled conditions in which various degrees of nasal constriction were simu— lated, using a model of the upper respiratory tract. MATERIALS AND METHODS Modeling Apparatus The model of the upper respiratory tract used to simulate nasal obstruction in this study is similar to that described by Warren (1984). This plastic model has been used in previous breathing research (Warren, 1984; Warren, Lehman, and Hinton, 1984). The model approximates the oral and pharyngeal dimensions of the adult vocal tract, and the cross—sectional