ULTRASTRUCTURE AND TENSILE PROPERTIES OF HUMAN TRACHEAL CARTILAGE

The cartilage of the walls of the trachea and bronchi acts to keep the se airways open despite intrathoracic pressure differences during brea thing that would otherwise collapse them and limit air flow. Changes i n biomechanical properties and composition of airway cartilage may con tribute to altered lung function in obstructive lung diseases. To inve stigate the relationship between collagen organization and equilibrium tensile modulus within the structure of airway cartilage, we used sca nning electron microscopy (SEM), histochemistry and equilibrium tensil e testing to analyze tracheal cartilage from 10 humans aged 17-81 yr. We show that the surfaces of tracheal cartilage matrix are collagen-ri ch and surround a proteoglycan-rich core. Collagen fibrils in the supe rficial zones are oriented in the plane of the cartilage surface. In d eeper layers of the cartilage, collagen fibrils are oriented less regu larly. Equilibrium tensile modulus of 100 mu m thick strips of cartila ge was measured and was found to decrease with depth; from 13.6 +/- 1. 5 MPa for the ablumenal superficial zone to 4.6 +/- 1.7 MPa in the mid dle zone(means +/- S.D., n = 10, p < 0.001). Stress-strain curves were linear for strains up to 10% with minimal residual strain. This is co nsistent with a model in which collagen fibres in the outer layers of the cartilage resist tensile forces, and hydrated proteoglycans in the central zone resist compression forces as the cartilage crescent bend s. (C) 1998 Elsevier Science Ltd. All rights reserved.