title: Perfusion through vessels open in zone 1 contributes to gas exchange in rabbit lungs in situ.
abstract: We previously found that up to 15% of the normal cardiac output can flow through lungs that are entirely in zone 1 and that the zone 1 pathway utilizes alveolar corner vessels. Because of the proximity of these vessels to alveoli, we hypothesized that lungs perfused under zone 1 conditions would exchange gas. We used the multiple inert gas elimination technique to assess the ventilation-perfusion (VA/Q) distribution under zones 1 and 2 in six rabbit lungs perfused with tris(hydroxymethyl)aminomethane-buffered Tyrode solution containing 1% albumin, 4% dextran, and papaverine (25 mg/l). High-frequency oscillation (tidal volume = 2.8 ml at 20 Hz, bias flow = 1 l/min) kept alveolar pressure (PA) nearly constant at 10 or 20 cmH2O. Pulmonary arterial pressure was set 2.5 cmH2O below or 5 cmH2O above PA (zones 1 and 2, respectively). Pulmonary venous pressure was kept at 0 cmH2O, with zero reference being the bottom of the lung. At PA of 10 cmH2O, flow was 64 +/- 40 and 5 +/- 3 ml/min (P < 0.05) and the mean VA/Q for perfusion was 1.1 +/- 0.4 and > 5 (P < 0.05) in zones 2 and 1, respectively. At PA of 20 cmH2O, flow was 89 +/- 36 and 22 +/- 13 ml/min (P < 0.05) and the mean VA/Q for perfusion was 0.8 +/- 0.3 and 3.7 +/- 2.4 (P < 0.05) in zones 2 and 1, respectively. Shunt averaged < 5% of total flow in all conditions. Blood flowing through vessels remaining open under zone 1 conditions 1) exchanges gas, 2) does not occur through anatomic or physiological shunts, and 3) may explain the high VA/Q seen with positive end-expiratory pressure.
authors.affiliation: Department of Medicine, University of Washington, Seattle 98104, USA.
authors.forename: W J
authors.initials: WJ
authors.lastname: Lamm
authors.forename: T
authors.initials: T
authors.lastname: Obermiller
authors.forename: M P
authors.initials: MP
authors.lastname: Hlastala
authors.forename: R K
authors.initials: RK
authors.lastname: Albert
mesh_terms: D000418:Albumins / Q000494:pharmacology; D000818:Animals; D003911:Dextrans / Q000494:pharmacology; D008168:Lung / Q000187:drug effects* / Q000502:physiology; D010208:Papaverine / Q000494:pharmacology; D011652:Pulmonary Circulation / Q000187:drug effects / Q000502:physiology*; D011659:Pulmonary Gas Exchange; D011817:Rabbits; D012119:Respiration / Q000187:drug effects*
chemical_list: D000418:Albumins; D003911:Dextrans; D010208:Papaverine