Lung tissue volume (Vt) and pulmonary capillary blood flow (Qc) were measured with an acetylene rebreathing technique in intact and isolated perfused dog lungs. Qc (1.73 +/- 0.17 l/min) was consistently greater than pump flow (0.87 +/- 0.10 l/min) in isolated perfused lungs because acetylene disappearance from the lung was increased by diffusion across the pleura into the room. In spite of the increased acetylene loss, Vt can be measured in isolated lungs with reproducibility similar to that in intact animals (Vt intact = 207 +/- 63 ml, Vt isolated perfused = 208 +/- 61 ml).
