[Evaluation of nasal obstruction with acoustic rhinometry: a simulated study with a nasal model]

The measurement of nasal resistance is important for understanding the pathophysiology of nasal obstruction. However, it is difficult to define the normal range of nasal resistance because of various physiological factors. Several authors have reported that nasal resistance is not correlated with the sensation of nasal obstruction. On the other hand, acoustic rhinometry was introduced by Hilberg et. al. (1989) to determine the geometry of the nasal cavity. The method based on sound reflection analysis provides an estimate of the cross-sectinal area of the nasal cavity as a function of the distance from the nostril. Recently, the measurement by acoustic rhinometry is becoming popular also in our country. However, the assessment by acoustic rhinometry may be different from that by measuring nasal resistance because the cross-sectional area is measured without studying the air flow. The aim of this study was to investigate the benefit of acoustic rhinometry using a nasal model. First, 4 pieces of nasal model LM005 (KOKEN, Co., Japan) made of silicone were coated with resinous putty. Then, the changes in the area-distance curve were measured with an acoustic rhinometer RHIN 2100 (SRE, Co., Denmark) in which this putty was scraped off gradually from anterior to posterior. In the next study, the quality of coated putty was increased at three points of the nasal area: anterior part, middle part, and posterior part. Thereafter the changes in the area-distance curve were observed in the same way. As a result, neither a decrease or an increase in the putty changed the area-distance curve at the posterior part. Therefore, it is suitable that the degree of the changing of nasal mucosa is defined as the change in the nasal volume between the top the I-notch and the end of the C-notch. In conclusion, acoustic rhinometry is useful to investigate nasal obstruction, especially the change in the nasal mucosa. Therefore, further clinical study is required for the different purpose of measuring nasal resistance.