TECHNIQUES FOR MEASURING RESPIRATORY MECHANICS - AN ANALYTIC APPROACHWITH A VISCOELASTIC MODEL

A homogeneous model with stress relaxation that is described by a pure viscoelastic component was recently proposed to describe the mechanic al behavior of the respiratory system during mechanical ventilation (B ates et al. J. Appl. Physiol. 67: 2276-2285, 1989). With the use of th is model, analytic expressions of the pressure in response to typical volume inputs are developed, and the recently published studies relati ng to the influence of the ventilatory pattern on respiratory mechanic s are reviewed and analyzed. The analytic expression of pressure respo nses to rapid airway occlusion following constant-flow inflation and t o sinusoidal volume oscillations allows prediction of most of the repo rted results. The theoretical analysis suggests that in normal subject s the observed flow and volume dependencies of respiratory mechanics a re, in fact, illustrations of the dependence of the viscoelastic resis tance on inspiratory time and respiratory frequency. Thus the homogene ous viscoelastic model appears suitable to describe respiratory system mechanical behavior under mechanical ventilation.