Quantification of spatial blood flow distribution in isolated canine lung

Single photon emission computed tomography (SPECT) in intact dogs and humans suggests that blood flow in the lung (Qr) is distributed so that at isogravity a large gradient in Qr exists between the core and the periphery. To confirm such findings, we injected (IV) six anesthetized healthy dogs (approximately 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 degrees 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, 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 Qr in the vertical (direction of gravity) and horizontal direction (isogravity) were comparable.(ABSTRACT TRUNCATED AT 250 WORDS)