Arterio-venous anastomoses in isolated, perfused rat lungs.
Several studies have suggested that large-diameter (>25 μm) arterio-venous shunt pathways exist in the lungs of rats, dogs, and humans. We investigated the nature of these pathways by infusing specific-diameter fluorescent latex particles (4, 7, 15, 30, or 50 μm) into isolated, ventilated rat lungs perfused at constant pressure. All lungs received the same mass of latex (5 mg), which resulted in infused particle numbers that ranged from 1.7 × 107 4 μm particles to 7.5 × 104 50 μm particles. Particles were infused over 2 min. We used a flow cytometer to count particle appearances in venous effluent samples collected every 0.5 min for 12 min from the start of particle infusion. Cumulative percentages of infused particles that appeared in the samples averaged 3.17 ± 2.46% for 4 μm diameter particles, but ranged from 0.01% to 0.17% for larger particles. Appearances of 4 μm particles followed a rapid upslope beginning at 30 sec followed by a more gradual downslope that lasted for up to 12 min. All other particle diameters also began to appear at 30 sec, but followed highly irregular time courses. Infusion of 7 and 15 μm particles caused transient but significant perfusate flow reductions, while infusion of all other diameters caused insignificant reductions in flow. We conclude that small numbers of bypass vessels exist that can accommodate particle diameters of 7-to-50 μm. We further conclude that our 4 μm particle data are consistent with a well-developed network of serial and parallel perfusion pathways at the acinar level.
['Conhaim|Robert L|RL|', 'Segal|Gilad S|GS|', 'Watson|Kal E|KE|']
D000818:Animals D001163:Arteriovenous Anastomosis D004621:Embolization, Therapeutic D005434:Flow Cytometry D008168:Lung D008297:Male D008833:Microcirculation D018613:Microscopy, Confocal D008863:Microspheres D010477:Perfusion D011650:Pulmonary Alveoli D011651:Pulmonary Artery D011652:Pulmonary Circulation D051381:Rats D017207:Rats, Sprague-Dawley
Alveolar capillary arterio‐venous anastomoses pulmonary circulation pulmonary microcirculation sheet flow