Clinical significance of airway resistance curve by the body plethysmograph

Abstract

Background: Airway resistance (Raw) is measured with the body plethysmograph by displaying the relationship between airflow and alveolar pressure (V/P(A)). If the resistance curve on V/P(A) tracing is curved or looped, the estimation of Raw is difficult. This study was designed to examine whether there is any correlation between the shape of resistance curve and the clinical status and the pulmonary function of patients. Methods: The 146 pulmonary disease patients with increased Raw were included in this study. The shapes of resistance curves on V/P(A) tracing with body plethysmograph during quiet breathing were analyzed and compared with pulmonary function. Results: The results were as follows; 1) The shapes of resistance curves were summarized in 5 categories; type 1: linear, type 2: ovoid, type 3: sigmoid, type 4: scoop, type 5: paisley. The type 3 except 1 case, type 4 and type 5 were found to have loop mainly in expiratory phase. 2) Although the shapes of resistance curves were not typical for specific disease, the resistance curves of acute disease tended to belong to type 1 or 2 and those of chronic airflow obstruction tended to belong to type 3, 4 or 5. But resistance curves of bronchial asthma and destructive lung with tuberculosis showed all types in proportion to degree of airflow obstruction or destruction of parenchyme. 3) In the cases of resistance curves going to type 5 rather than type 1 and those with looping, airflow obstruction tended to be severe and airway resistance and residual volume tended to increase. Conclusions: Analysis of resistance curve on V/P(A) tracing measuring airway resistance is helpful for judging degree of airflow obstruction and air trapping. Although the shape of resistance curve is not typical for specific disease, there is a close association between looping and airway obstruction.