Spatial pattern of pulmonary blood flow distribution is stable over days

Abstract

Despite the heterogeneous distribution of regional pulmonary perfusion over space, local perfusion remains stable over short time periods (20-100 min). The purpose of this study was to determine whether the spatial distribution of pulmonary perfusion remains stable over longer time periods (1-5 days). Regional blood flow was measured each day for 5 days in five awake standing dogs. Fluorescent microspheres of different colors were injected into a limb vein over 30 s on each day. After the last microsphere injection, the dogs were killed, and lungs were flushed free of blood, excised, dried at total lung capacity, and diced into approximately 2-cm3 pieces (n = 1,296-1,487 per dog). Relative blood flow to each piece on each day was determined by extracting the fluorescent dyes and determining the concentrations of each color. We established that blood flow is spatially heterogeneous with a coefficient of variation of 29.5 +/- 2%. Blood flow to each piece is highly correlated with flow to the same piece on all days (r = 0.930 +/- 0.006). The temporal heterogeneity of regional perfusion as measured by the coefficient of variation is 6.9 +/- 0.7% over the 5 days and is nonrandom. The magnitude of spatial and temporal variation is significantly less than previously reported in a study in which anesthetized and mechanically ventilated dogs were used. We conclude that spatial distribution of pulmonary blood flow remains stable over days and we speculate that in the normal awake dog regional perfusion is determined primarily by a fixed structure such as the geometry of the pulmonary vascular tree rather than by local vasoactive regulators. Anesthesia and/or mechanical ventilation may increase the temporal variability in regional perfusion.

A Class of Flow Bifurcation Models with Lognormal Distribution and Fractal Dispersion

“…To compare the #ow distribution in the branches with the laboratory measurements, we make the assumption that each vessel of generation n serves a same volume or mass of tissue. The experimentally observed D1s for regional blood #ow are around 1.15}1.28 in heart and 1.07}1.15 in lung (van Beek et al, 1989;Glenny et al, 1991).…”

Microsphere maps of regional blood flow and regional ventilation

“…Relative to RMS, FMS labels show only a modest signal overlap with combinations of different labels, and as with RMS, this overlap is readily corrected by a matrix inversion program (51). Properly stored FMS maintain their fluorescent intensity over time and also remain stable over extended periods of time when injected into experimental animals (23). Finally, FMS markers are particularly convenient to use in studies of the lung, because the fluorescence can be completely extracted from dried lung pieces by soaking in a solvent, without requiring tissue digestion, as is necessary for FMS measurements in other organs (18).…”

“…Measurement error also contributes to between-run differences in flow, but the extent of this artifact can be estimated by simultaneous administration of two different RMS or FMS labels (10), with the residual variability attributable to true temporal shifts. For studies of anesthetized dogs and pigs, the contribution of temporal shifts to overall flow heterogeneity has generally ranged between 7 and 17% of the summed heterogeneity (2,23,24). In response to the question of whether any structure could be discerned within these temporal shifts, Glenny et al (24) applied the statistical technique of cluster analysis to regional pulmonary blood flow measurements in anesthetized dogs.…”

“…The size of the units undergoing these spontaneous shifts was larger than the ϳ2-cm 3 piece size, generally in the 20-cm 3 range. Some fraction of the temporal variability observed in anesthetized animals may have been attributable to effects anesthesia or mechanical ventilation, because sequential FMS measurements of regional pulmonary blood flow in awake, standing dogs over 1 wk showed a temporal coefficient of variation of only 7% (23). In this study of awake animals, the lung pieces with the greatest variability still tended to be the low-flow pieces, but the awake animals generally demonstrated less temporal variability than that previously described with anesthetized animals.…”

Direct assessment and distribution of regional portal blood flow in the pig by means of fluorescent microspheres

“…Functional pulmonary blood flow can easily be measured by injecting the MS intravenously (10,29). MS are carried by the venous blood into the right ventricle, where they mix homogeneously with the blood before entering the lung.…”