Indirect assessment of lung compliance in chronic lung diseases.

The slope of the flow volume curves was analysed in 20 normal subjects 28 patients with irreversible chronic airway obstruction, 24 patients with bronchial asthma, 8 patients with diffuse interstitial fibrosis and 7 patients with extensive bronchiectasis. Time constant of the system was taken as the slope of the curve between 50 and 25% of the vital capacity. When considered along with plethysmographically obtained airway resistance, an indirect estimate of the lung compliance was obtained. Significant differences in the estimated lung compliance in the normal subjects, patients with obstructive lung disease or diffuse interstitial fibrosis were demonstrated.