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1 Pediatrics and Population Health Sciences, Rankin Laboratory of Pulmonary Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States
2 Population Health Sciences, Rankin Laboratory of Pulmonary Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States
* To whom correspondence should be addressed. E-mail: atlovering{at}wisc.edu.
Postmortem microsphere studies in adult human lungs have demonstrated the existence of intrapulmonary arteriovenous pathways using non-physiologic conditions. The aim of the current study was to determine if large diameter (>25 and 50 µm) intrapulmonary arteriovenous pathways are functional in human and baboon lungs under physiologic perfusion and ventilation pressures. We used fresh healthy human donor lungs obtained for transplantion, and fresh lungs from baboons (Papio c. anubis). Lungs were ventilated with room air using a peak inflation pressure of 15 cm H2O and a positive end expiratory pressure of 5 cm H2O. Lungs were perfused between 10 and 20 cm H2O using a phosphate buffered saline solution with 5 % albumin. We infused a mixture of 25 and 50 µm microspheres (0.5 and 1 million total for baboons and human studies, respectively) into the pulmonary artery and collected the entire pulmonary venous outflow. Under these conditions, evidence of intrapulmonary arteriovenous anastomoses were found in baboon (n=3/4) and human (n=4/6) lungs. In those lungs showing evidence of arteriovenous pathways, 50 µm microspheres were always able to traverse the pulmonary circulation and the fraction of transpulmonary passage ranged from 0.0003 to 0.42%. These data show that intrapulmonary arteriovenous pathways greater than 50 µm in diameter are functional under physiologic ventilation and perfusion pressures in the isolated lung. These pathways provide an alternative conduit for pulmonary blood flow that likely bypasses the areas of gas exchange at the capillary-alveolar interface, that could compromise both gas exchange and the lung's ability to filter out microemboli.
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