Oscillatory mechanics of the respiratory system in normal rats

Abstract

Respiratory system impedances were measured by a modified forced oscillatory technique in 30 normal male CRD-free Sprague-Dawley rats at frequencies between 20 and 90 Hz. A resonance frequency was found (mean = 39 Hz) below which reactances were negative and above which reactances were positive. Resistances were generally found to be frequency dependent, increasing with increasing frequencies. Frequency dependent behavior in resistance has been ascribed to inhomogeneities in parallel airway pathways and to the effects of airways wall compliance. Optimization techniques were used to estimate the values of parameters in a variety of lumped-parameter mechanical networks incorporating parallel pathways and/or airway wall compliance. The model whose response compared the best with the data and that resulted in the most consistent parameter values was found to be one where the airways are separated into central and peripheral components by a shunt pathway containing an airway wall compliance. The mean values for each of the parameters within the model were central airway resistance (54 cm H 2O/L/sec), peripheral airway resistance (53 cm H 2O/L/sec), central airway inertance (0.058 cm H 2O/L/sec 2), peripheral airway inertance (0.116 cm H 2O/L/sec 2), airway wall compliance (0.182 × 10 −4 L/cm H 2O), and respiratory system compliance (1.267 × 10 −4 L/cm H 2O).