Pulmonary capillary diameters and recruitment characteristics in subpleural and interior networks

Abstract

In vivo microscopic observations of pulmonary capillaries are limited to subpleural networks that are less dense than interior networks. In addition to the density difference, subpleural and interior capillary diameters may differ, although there are conflicting data on this point. We measured the diameters of subpleural and interior capillaries in rats and dogs. Subpleural diameters were 30% larger in rats and 20% larger in dogs. Because diameter and density differences might cause differences in recruitment between subpleural and interior networks, we measured subpleural and interior recruitment by counting the number of red blood cells per 10 microns of alveolar wall in histological cross sections of rapidly frozen rat lungs. Lung inflation pressures of 4, 12, and 25 cmH2O created a wide range of capillary recruitment in different groups of animals. Red blood cell counts for interior and subpleural capillaries moved in parallel and progressively increased as inflation pressures were reduced. These data demonstrate that recruitment in subpleural capillaries accurately reflect recruitment in interior capillaries and validate the use of in vivo microscopic observations of subpleural capillaries to investigate pulmonary capillary recruitment in general.

Firstin vivomagnetic particle imaging of lung perfusion in rats

“…Note that average human lung capillaries are also roughly 6 µm in diameter, hence a similar principle could be used to design MAA-SPIOs for human studies (Short et al 1996; Townsley 2012). …”

“…99 m Tc-MAA is macroaggregated albumin (MAA) chelated to the radionuclide tracer 99 m Technetium. MAA targets the lung because at a size range of 10−90 µm, it is trapped in the first capillary bed reached after IV injection, i.e., the lungs, which have 6 µm average lumen diameter (Short et al 1996; Townsley 2012). Out of the two scans, perfusion is the more relevant to PE diagnosis because it shows any vascular blockages (e.g., emboli).…”

Lung heparan sulfates modulate Kfc during increased vascular pressure: evidence for glycocalyx-mediated mechanotransduction

“…Fluid flux is dependent on vascular surface area; if step increases in Pla increased recruitment, our measured K fc values may reflect only the increasing surface area and not an actual change in endothelial permeability. Short et al (40) reported that, in rat lungs, recruitment of subpleural capillaries accurately reflected recruitment of interior capillaries; using similar methods, Presson et al (35) showed that lung capillary recruitment was 90% complete when capillary pressure equaled 10 cmH 2 O and was nearly 100% complete when capillary pressure was 12 cmH 2 O. Pulmonary artery pressure is an indicator of downstream resistance and should decrease with increasing vascular recruitment.…”

Bronchial temperature reflects transcapillary heat transport of isolated blood-perfused rabbit lungs

“…This is of particular interest since pulmonary blood flow is heterogeneous and not only increases in dependent lung regions [5] but also has a hilar-to-peripheral gradient [6]. In addition, subpleural capillaries have different diameters when compared to interior capillaries [7], so that it is likely that capillary blood flow and mean transit times on The present results were obtained from isolated rabbit lungs perfused with their own blood. The main advantage of this experimental protocol is the exact and independent control of study conditions, especially of pulmonary blood flow as the major variable for mean transit times.…”