INHERENT COUPLING OF ELASTIC AND DISSIPATIVE BEHAVIOR OF THE LUNG THROUGH A VISCOELASTIC TIME CONSTANT

The simple model best able to describe the viscoelastic behavior of lu ng tissues contains a Kelvin body. Some facets of the viscoelastic beh avior of the model can be characterized by a time constant. We have pe rformed a series of experiments to demonstrate this viscoelastic time constant in open-chest mechanically ventilated puppies by recording th e stress recovery after midexpiratory flow interruption. In 19 8- to 1 0-wk-old puppies, the mean time constant was 0.64 +/- 0.01 (SE) s. Thi s time constant remained unchanged after inhalation challenge with his tamine, methacholine, or hypertonic saline, despite marked changes in tissue mechanics (resistance and elastance) and in hysteresivity. The constancy of the viscoelastic time constant demonstrates a tight coupl ing of the parameters of the Kelvin body model, effectively reducing t he viscoelastic parameters to a single degree of freedom, and may expl ain the coupling between the dynamic elastic and resistive properties of the lung tissues previously demonstrated.