Thoracotomy increases peripheral airway tone and reactivity

Our goal was to investigate the extent to which thoracotomy for chronic vascular instrumentation alters peripheral airway tone and reactivity. Using the wedged bronchoscope technique to measure peripheral airway resistance (R(P)), pentobarbital-fentanyl anesthetized, ventilated dogs were studied before and (16 ± 2 d) after a left thoracotomy for chronic implantation of instrumentation to measure the left pulmonary vascular pressure-flow relationship. A map of the airways was constructed as bronchoscopes were advanced and wedged in the middle lobes of both the left and right lung. This allowed us to measure Rp in the same sublobar region of the left and right lung both pre- and postoperatively. At the time of postoperative experimentation, all dogs appeared fully recovered from the surgical procedure. Compared with preoperative values, baseline R(P) (cm H₂O · ml^{- 1} · s^-1) was selectively increased (p < 0.03) postoperatively in the left (0.41 ± 0.07 versus 1.27 ± 0.36) but not in the right (0.29 ± 0.06 versus 0.35 ± 0.07) lung. Peripheral airway responses to acetylcholine, histamine, hypocapnia, and dry air challenges were all increased (p < 0.05) in both magnitude and duration in the left but not the right lung postoperatively. Total lung volume (helium dilution technique) was decreased (p < 0.01) by 10 ± 3% postoperatively. However, similar reductions in lung volume were observed in the left and right lung. These results indicate that left thoracotomy for chronic instrumentation selectively increases left lung peripheral airway tone and reactivity, but has no effect on the right lung. These changes cannot be explained by the concomitant postoperative decrease in lung volume.