Influence of lung volume hysteresis on collateral resistance in intact dogs

Collateral resistance (Rcoll) is highly lung volume dependent. We studied 12 dogs in an attempt to evaluate the influence of hysteresis on this volume dependency. Rcoll measurements were obtained at baseline and at different lung volumes as modified by the application of negative or positive extrathoracic pressure (ETP) in an iron lung. ETP was modified in 5 cmH2O steps from +20 to -25 cmH2O) and back to +20 cmH2O on the first day (cycle 1), and, in 4 of these dogs, from -25 to +20 cmH2O and back to -25 cmH2O on a second day (cycle 2). The behavior of Rcoll for both cycles was the same in all dogs, varying inversely with the changes in end-expiratory lung volume (EELV). All dogs presented a similar pattern: during cycle 1, for a same lung volume, Rcoll was much higher during the deflation limb than during the inflation limb. For cycle 2, Rcoll at a given lung volume was similar whether measured during the inflation or deflation limb. Changes in EELV were higher for any given negative ETP during the deflation than during the inflation limb of the pressure cycles (e.g., for the 4 dogs who had both cycles, at -15 cmH2O ETP of cycle 2 the increase in EELV was 1167 +/- 121 ml during deflation and 525 +/- 102 ml during the subsequent inflation [mean +/- SEM]). In conclusion, the effects of hysteresis on Rcoll and on lung volumes are similar, except at low lung volumes during the deflation limb of cycle 2.(ABSTRACT TRUNCATED AT 250 WORDS)