Lung reflexes and receptor activity in a rabbit model of pulmonary fibrosis

Our objective was to see if activity of individual slowly and rapidly adapting pulmonary receptors was changed by pulmonary fibrosis. Diffuse interstitial lung fibrosis of several weeks' standing was induced in 8 rabbits. They displayed changes in lung mechanics and patterns of breathing, when compared to control rabbits, similar to those seen in patients who develop pulmonary fibrosis. Lung reflexes in the fibrotic rabbits were more profoundly changed than eupneic breathing in a way that could be interpreted as slowly adapting receptor activity, which was increased, being overpowered by a prepotent input from pulmonary rapidly adapting receptors. An increase in number of active rapidly adapting receptors was found in the fibrotic rabbits during direct vagal recording. We have demonstrated that pulmonary receptor activity is changed by lung fibrosis. It may be that these changes in receptor activity produce conflicting respiratory drives that could result in the sensation of dyspnea.