Effects of hemodynamic edema formation on peripheral vs. central airway mechanics

The mechanisms governing increased central (Rc) and peripheral airway resistance (Rp) during hemodynamic edema formation were studied in anesthetized dogs. Rc and Rp were measured by forced oscillation at 1 Hz by use of a retrograde catheter to partition resistance and a pleural capsule to detect alveolar pressure. After elevation of left atrial pressure to 30 cmH₂O by inflation of the left atrial balloon, Rc gradually increased an average of 60% above control in ~100min. Vagotomy had a small influence on the change. On the other hand, Rp with vagus nerves intact increased triphasically: first, it increased transiently by 160% above the control value within 15-20 min before returning to near base line. It then increased gradually for ~40 min and finally rose sharply up to five times the control value after ~100 min. With vagi cut, the initial phase disappeared, but the second gradual and final rapid phases were not affected. Several sequential mechanisms of increased Rp can be proposed: transient bronchoconstriction mediated by vagal reflex; gradual formation of peribronchial edema; and a sharp increase in airway fluid and formation of bronchial froth. In addition, narrowing of the airways by vascular engorgement may have contributed to the increase of Rp throughout all stages.