Simulation of tissue properties in irreversible diffuse obstructive pulmonary syndromes. Enzyme digestion

The length-tension properties of alveolar wall from normal cats were studied before and after exposure to enzymes naturally found in mammals (elastase, trypsin, collagenase, hyaluronidase). Hyaluronidase effected little change while all the proteolytic enzymes altered the mechanical properties of lung tissue. Collagenase removed the "mechanical stop" and the alveolar walls fractured at low forces. The properties of wall exposed to trypsin resembled those of elastase-treated tissue. Elastase increased the extension necessary to reach a given force and increased the maximum length (L(max)) and resting length (L(o)). Maximum extensibility (lambda(max)), the ratio of L(max) to L(o), fell with both elastase and trypsin digestion. A reduction in lambda(max) simulates the changes in alveolar wall properties seen in the lungs of the aged and in those with an irreversible diffuse obstructive pulmonary syndrome (DOPS(I)). Unlike these states, however, the energy loss in stretching alveolar wall increased with elastolysis. Furthermore, the changes in L(o) necessary to effect a change in lambda(max) of alveolar wall comparable to that seen in DOPS(I) were excessive. The altered tissue properties that occur in man with obstructive pulmonary syndromes could not be produced with these proteolytic enzymes or with hyaluronidase.