Quantification of Spatial Blood Flow Distribution in Isolated Canine Lung

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Abstract
Single photon emission computed tomography (SPECT) in intact dogs and humans suggests that blood flow in the lung (.ovrhdot.Qr) is distributed so that is distributed so that at isogravity a large gradient in .ovrhdot.Qr exists between the core and the periphery. To confirm such findings, we injected (IV) six anesthetized healthy dogs (.apprx. 30 kg) with 20 mCi technetium-99m (Tc-99m)-labeled albumin macroaggregates. At injection, the dogs were in the supine position and breathing spontaneously. Injections were given at end expiration. The animals were killed and their chests opened; their lungs were removed and dissected free of other tissue, and the blood was drained. The lungs were inflated to full capacity, and warm (50.degree. C) air was blown into them for about 18 hours to dry them. The fully inflated and dry lungs were placed supine, and SPECT was performed to determine the 3-D distribution of activity. After SPECT was completed, either a coronal slice or a sagittal slice (1 cm thick) was cut and imaged directly by placing it against the gamma camera collimator for 6 minutes. The tomographic images of flow distribution in coronal slices (isogravity) revealed that independent of gravity, .ovrhdot.Qr in the central region of the lungs was greater than that in the periphery. Furthermore, the central-peripheral gradient was discernible within the individual lobes. The direct images of slice confirmed these findings. Tomographic images of sagittal slices showed that heterogeneities in .ovrhdot.Qr in the vertical (direction of gravity) and horizontal direction (isogravity) were comparable. These results suggest that in the intact supine condition, factors other than gravity play an important role in the distribution of pulmonary blood flow. These factors may be related to the conductance of the vascular pathways that lead to different regions in the lungs.