Model of airway narrowing in asthma and chronic obstructive pulmonary disease

Exaggerated airway narrowing in response to a wide variety of nonspecific stimuli is a characteristic feature of asthma and occurs in some patients who have chronic obstructive pulmonary disease. We have developed a computational model of the human bronchial tree which allows us to investigate the effect of volume changes, airway smooth muscle shortening and airway wall thickening on airways resistance. This model is based on Weibel's symmetric lung geometry, pressure-area curves by 1-3 cmH2O. Values of smooth muscle shortening between 20 and 40% were used in the model to generate sigmoidal shaped 'dose' response curves. The analysis shows that moderate amounts of airway wall thickening, which has little effect on baseline resistance, can profoundly effect the airway narrowing caused by smooth muscle shortening - especially if the wall thickening is localized in peripheral airways. The combination of a loss of recoil and airway wall thickening are more than additive in their effect on simulated airway responsiveness. We conclude that airway wall thickening and a loss of lung recoil would explain in part the airway hyperresponsiveness characteristics of patients with chronic obstructive lung disease and asthma.