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 × 1074 μm particles to 7.5 × 10450 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.
The William S. Middleton Memorial Veterans Hospital, Madison, Wisconsin rconhaim@wisc.edu.|Department of Surgery, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin.
Robert L
RL
Conhaim
Department of Surgery, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin.
Gilad S
GS
Segal
Department of Surgery, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin.
Kal E
KE
Watson
D000818:Animals; D001163:Arteriovenous Anastomosis / Q000187:drug effects* / Q000502:physiology; D004621:Embolization, Therapeutic; D005434:Flow Cytometry / Q000379:methods; D008168:Lung / Q000098:blood supply* / Q000502:physiology; D008297:Male; D008833:Microcirculation / Q000187:drug effects* / Q000502:physiology; D018613:Microscopy, Confocal; D008863:Microspheres; D010477:Perfusion / Q000379:methods*; D011650:Pulmonary Alveoli / Q000098:blood supply; D011651:Pulmonary Artery / Q000187:drug effects* / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
Alveolar capillary; arterio‐venous anastomoses; pulmonary circulation; pulmonary microcirculation; sheet flow