Respiratory mechanics in anesthetized paralyzed humans: effects of flow, volume, and time

The effects of inspiratory flow rate and inflation volume on the resistive properties of the total respiratory system were investigated in 16 anesthetized paralyzed humans by using the technique of rapid airway occlusion during constant flow inflation. This allowed measurement of the intrinsic resistance (Rmin,rs) and of the effective additional resistance (ΔRrs) as the results of viscoelastic pressure dissipations within the pulmonary and chest wall tissues. We observed that 1) at fixed inflation volume, Rmin,rs increased linearly with increasing flow although ΔRrs decreased according to an exponential function; 2) at fixed inflation flow, Rmin,rs decreased with increasing inflation volume although there was a concomitant increase in ΔRrs. This behavior could be explained in terms of a spring-and-dashpot model incorporating 1) the standard resistance and elastance and 2) a spring-and-dashpot in parallel with standard elastance, reflecting the stress adaptation units within the thoracic tissues.