Distribution of ventilation and frequency-dependence of dynamic lung compliance

Abstract

Lung components were analysed and dynamic pulmonary compliance was determined in 10 young healthy female subjects and seven adult male patients with bronchial obstruction. In normal subjects with a single ventilatory component (by multiple breath nitrogen washout method) a change of respiratory frequency did not affect dynamic lung compliance. Other normal subjects had two ventilatory components; in them and in the patients with bronchial obstruction, an increase of respiratory frequency decreased dynamic pulmonary compliance. A change of respiratory rate caused a greater change of dynamic lung compliance in the patients with bronchial obstruction than in normal subjects with two-component lungs. The results indicate that frequency-dependence of compliance and non-uniform distribution of inspired gas are caused by a similar mechanism. Inequality of regional time constants may be an important factor in this mechanism. The data also show that a decrease of dynamic lung compliance by more than 20% at a respiratory rate of 80 to 100 breaths/minute may be indicative of lung disease with obstruction.