Regional pulmonary blood flow in humans and dogs by 4D computed tomography.

Rationale And Objectives: Pulmonary vascular control mechanisms are complex and likely to differ between species. We wish to quantify regional perfusion and the effects of gravity using computed tomography.

Materials And Methods: Sequential density measurements following the administration of a bolus of iodinated contrast medium were acquired from four healthy human subjects and four dogs.

Results: In humans, perfusion (Q) was linear throughout most of the range of vertical height, with an overall gradient of -2.6% cm(-1). However, when perfusion was normalized to "tissue" density (blood plus tissue: sQt), maximum perfusion occurred around the mid-range of vertical height, being 9% (range 1-22%) greater than either the dorsal or ventral extreme. Within discrete transverse axial sections, concentric zones of perfusion centered on blood vessels were demonstrated. The relationship between sQt and vertical height in dogs was distinctly linear, with a gradient of -7.2% cm(-1). In dogs, the median gradient of Q was -13.6% cm(-1) (range -9.7 to -17.1%).

Conclusions: Differences in regional pulmonary perfusion, particularly the vertical gradient observed in humans and dogs, may in part reflect anatomic differences between the symmetric dichotomous branching structure of the human pulmonary vasculature and the more asymmetrical structure found in dogs.