Lobar blood flow, blood volume and water content in atelectasis

In nine intact supine anesthetized dogs we measured pulmonary blood flow distribution, lobar hemoglobin content, and lobar wet wt/dry wt during left lower lobe collapse. The animals breathed a mixture of 88% O2/12% N2 and atelectasis was induced by occluding the left lower lobe bronchus. Lobar volume was assessed by measuring lobar N2 concentrations. Using the radioactive microsphere technique, perfusion distribution was measured at lobar volumes of 50% FRC and 18-25% FRC. Hemoglobin content and wet wt/dry wt were measured at the latter volume. At 50% FRC lobar blood flow was unchanged though lobar pressure was negative. At the lower volume lobar blood flow averaged 72% of that at FRC, and lobar hemoglobin content was similar to that of the right lower lobe, indicating that lobar blood volume was unchanged. Wet wt/dry wt was significantly less in collapsed left lower lobes than in control right lower lobes, perhaps indicating that pressure in fluid-exchanging vessels was less than interstitial pressure during atelectasis.