ESTIMATION OF RESISTANCE AND ELASTANCE OF THE LUNGS IN THE PRESENCE OF ALINEARITIES - A MODEL STUDY

The reliability of dynamic elastance, E dyn and resistance, R dyn, as expressions of the mechanical properties of the respiratory system is evaluated by means of a model mimicking the various alinearities met in lungs and airways in vivo, and demonstrating a non-sinusoidal breathing pattern. E dyn and R dyn are compared with other, more sophisticated expressions of elastance and resistance, unaffected by alinearities and by the presence of harmonics in the pattern of breathing. The study shows that: (1) under realistic conditions, E dyn and R dyn are satisfactory estimates of the 'true' elastance and resistance, (2) because of the complexity of the respiratory system and the asymmetrical diameter-transmural pressure relationship of the bronchi the resistance during breathing is larger than that measured in steady state conditions, (3) the frequency-dependence of E dyn and R dyn is but minimally affected by alinearities or by the asymmetry in bronchial dichotomy and (4) bronchial instability may be expected to enhance the alinear behavior of the system. The predictions of the model are corroborated by measurements obtained in healthy subjects.