A new method for measuring airway resistance in man using a body plethysmograph: values in normal subjects and in patients with respiratory disease.

Satisfactory methods, utilizing measurements of transthoracic or transpulmonary pressure and airflow, are now available for determining "nonelastic" pulmonary resistance. However, the nonelastic pulmonary resistance has two components, tissue resistance and airway resistance, and no valid direct method is available for measuring either of these components separately in man. Since airway resistance is the ratio of alveolar pressure during flow to airflow, airway resistance alone could be measured if there were a method for determining alveolar pressure during flow. This report presents a new method for accomplishing this measurement, and gives data for airway resistance obtained in normal subjects and in patients with respiratory disease. Of previous attempts to measure airway resistance, one of the earliest was the painstaking study by Rohrer (1) who made anatomical measurements on the tracheobronchial tree of a human lung post mortem and calculated the cumulative resistance to airflow of the entire system using Poiseuille's law and turbulence theory. The first important experimental study of pulmonary resistance in the living animal was made by von Neergaard and Wirz who, in 1927 (2), analyzed intrapleural pressure into two major components, "dynamic" (which is essentially resistive) and "static" (which is predominantly elastic in nature). This approach made it possible to obtain values for total pulmonary resistance, though not for airway resistance alone. Bayliss and Robertson (3), reasoning that airway resistance, but not tissue resistance, would vary with the viscosity of the gases breathed, ventilated isolated animal lungs with gases of different density and viscosity;