Functional localization of pulmonary stretch receptors in the airways of the cat.

During a respiratory effort against a closed airway the afferent activity of vagal fibres from pulmonary stretch receptors does not appreciably increase during the inspiratory phase because the lung is prevented from expanding. The possibility to perform occlusions at different levels of the airways allows the localization of pulmonary stretch receptors in the tracheo-bronchial tree. 100 fibres from pulmonary stretch receptors of the left and right sides of the tracheo-bronchial tree have been studied in 3 cats and their localization found as follows: 10% in the higher half of the intrathoracic trachea, 22% in the lower half of the intrathoracic trachea and the carina, 7% in the main bronchus and 61% in the intrapulmonary airways. Knowing the surface area of the tracheo-bronchial tree at different levels and assuming total of 1200 stretch receptors from each side their average concentration resulted as follows: 50.0 receptors/cm2 in the higher half of the intrathoracic trachea, 108.0/cm2 in the lower half of the intrathoracic trachea and the carina, 213.0/cm2 in the main bronchus and 1.3/cm2 in the intrapulmonary airways.