Perfusion through vessels open in zone 1 contributes to gas
exchange in rabbit lungs in-situ.
Lamm, W. J. E., T. Obermiller, M. P. Hlastala, R. K. Albert.
Department of Medicine, University of Washington, Seattle,
Washington 98104
APStracts 2:0314A, 1995.
We have 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 these vessels are
in close proximity 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
ratio (A/) distribution under zones 1 and 2 in six rabbit lungs
perfused with Tris-buffered Tyrode's solution containing 1% albumin,
4% dextran, and 25 mg.L-1 papaverine. High frequency oscillation
(tidal volume = 2.8 mL at 20 Hz, bias flow of 1 L.min-1) kept
alveolar pressure nearly constant at 10 or 20 cmH2O. Pulmonary
arterial pressure was set 2.5 cmH2O below, or 5 cmH2O above alveolar
pressure (zones 1 and 2, respectively). Pulmonary venous pressure was
kept at 0 cmH2O with zero reference being the bottom of the lung. At
an alveolar pressure of 10 cmH2O, flow was 64 +/- 40 and 5 +/- 3
mL/min (P < 0.05) and the mean A/ for perfusion was 1.1 +/- 0.4
and > 5 (P < 0.05) in zone 2 and 1, respectively. At an
alveolar pressure of 20 cmH2O, flow was 89 +/- 36 and 22 +/- 13
mL/min (P < 0.05) and the mean A/ 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 anatomical or physiological shunts,
and (3) may explain the high A/ seen with positive end-expiratory
pressure.
Received 17 May 1994; accepted in final form 30 June 1995.
APS Manuscript Number A477-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.