Regional Pulmonary Blood Flow in Humans and Dogs by 4D Computed Tomography1

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: sQ_t), 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 sQ_t 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.

Key Words: Pulmonary circulation, image processing, computer assisted