Observations with SPECT on the normal regional distribution of pulmonary blood flow in gravity independent planes.

While the effect of gravity on the pulmonary circulation is well documented, the distribution of pulmonary flow under gravity independent conditions is not as well understood. Single photon emission computed tomography was applied to the study of regional pulmonary blood flow in slices where the effect of gravity was constant. Lung tomography, after the injection of [99mTc]MAA, was carried out in six normal volunteers and in the fully inflated and isolated lungs from six dogs that had been killed. Our tomographic results suggest that pulmonary perfusion in isogravitational planes is inherently nonuniform with preferential flow centrally and reduced circulation more peripherally. Planar imaging of the dissected isogravitational slices from the animals further confirmed the uneven perfusion noted on the tomographic slices.