ANALYSIS OF BEHAVIOR OF THE RESPIRATORY SYSTEM IN ARDS PATIENTS - EFFECTS OF FLOW, VOLUME, AND TIME

The effects of inspiratory flow (V) and inflation volume (DELTA-V) on the mechanical properties of the respiratory system in eight ARDS patients were investigated using the technique of rapid airway occulsion during constant-flow inflation. We measured interrupter resistance (Rint,rs), which in humans represents airway resistance, the additional resistance (DELTA-Rrs) due to viscoelastic pressure dissipations and time constant inequalities, and static (Est,rs) and dynamic (Edyn,rs) elastance. The results were compared with a previous study on 16 normal anesthetized paralyzed humans (D'Angelo et al. J. Appl. Physiol. 67: 2556-2564, 1989). We observed that 1) resistance and elastance were higher in ARDS patients; 2) with increasing V, Rint,rs and Est,rs did not change, DELTA-Rrs decreased progressively, and Edyn,rs increased progressively; 3) with increasing DELTA-V, Rint,rs decreased slightly, DELTA-Rrs increased progressively, and Est,rs and Edyn,rs showed an initial decrease followed by a secondary increase noted only in the ARDS patients. The above findings could be explained in terms of a model incorporating a standard resistance in parallel with a standard elastance and a series spring-and-dashpot body that represents the stress adaptation units within the tissues of the respiratory system.