Mechanics in rats by end-inflation occlusion and single-breath methods

In six mechanically ventilated anesthetized (pentobarbital sodium, 30 mg/kg) paralyzed rats (187-253 g body wt) volume, airflow, and tracheal, esophageal, and transpulmonary pressures were measured. Respiratory system elastic and resistive properties were partitioned into their lung and chest wall components after end-inflation occlusion of the airways subsequent to constant-flow inspirations and during relaxed expiration ensuing release of occlusion. The values provided by both methods were similar. Mean respiratory system, lung, and chest wall elastances amounted to, respectively, 5.536, 3.440, and 2.097 cmH2O.ml-1. Mean values of intrinsic respiratory system, pulmonary, and chest wall resistances (at flows of 3.5 ml.s-1) were 0.235, 0.144, and 0.091 cmH2O.ml-1.s, respectively. Resistive pressure-flow relationships for the respiratory system, lung, and chest wall were also determined during the entire tidal expiration. A linear relationship was found for the former, whereas power functions best described the others: the pulmonary pressure-flow relationship exhibited an upward concavity and that for the chest wall presented an upward convexity.