ASSESSMENT OF POSTURAL DIFFERENCES IN REGIONAL PULMONARY PERFUSION INMAN BY SINGLE-PHOTON EMISSION COMPUTERIZED-TOMOGRAPHY

1. With the advent of single-photon emission computerized tomography, controversy has arisen with regard to the significance of gravitationa l influences on regional pulmonary perfusion (<(Q)over circle (r)>) in the supine versus prone postures, We investigated the dorsal-ventral distributions of <(Q)over circle (r)> in prone (n = 5) and supine (n = 5) normal subjects, as assessed by single-photon emission computerize d tomography after intravenous injection of technetium-99m-labelled ma croaggregated albumin at end-tidal expiration, Reconstructed serial (o ne pixel thickness) coronal sections were traced on a computer screen, to yield the encompassed radioactive counts and number of pixels per each image, Coronal section data (expressed as mean radioactive counts /pixel) were expressed in a 'profile' and normalized to the maximum co ronal section of each lung (%maximum), 2. Coefficients of variation an d linear regression slopes for the prone versus supine profiles for le ft and right lungs were not statistically different (unpaired Student' s t-test), The coronal section with maximum <(Q)over circle (r)> was i dentified in the more dependent lung regions and, hence, affected by g ravity, 3. We conclude that, in contrast to previous canine models, wh ich have suggested postural differences in dorsal-ventral perfusion gr adients, in normal man gravity primarily determines the non-dependent to dependent distribution of <(Q)over circle (r)>. We speculate that i nterspecies differences in physiology may be teleological and related to the different perfusion demands of the quadruped compared with upri ght man.