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Intrapulmonary Shunt During Normoxic and Hypoxic Exercise in Healthy Humans

  • Andrew T. Lovering
  • Michael K. Stickland
  • Marlowe W. Eldridge
Conference paper
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 588)

Abstract

This review presents evidence for the recruitment of intrapulmonary arteriovenous shunts (IPAVS) during exercise in normal healthy humans. Support for pre-capillary connections between the arterial and venous circulation in lungs of humans and animals have existed for over one-hundred years. Right-to-left physiological shunt has not been detected during exercise with gas exchange-dependent techniques. However, fundamental assumptions of these techniques may not allow for measurement of a small (1–3%) anatomical shunt, the magnitude of which would explain the entire A-aDO2 typically observed during normoxic exercise. Data from contrast echocardiograph studies are presented demonstrating the development of IPAVS with exercise in 90% of subjects tested. Technetium-99m labeled macroaggregated albumin studies also found exercise IPAVS and calculated shunt to be ∼2% at max exercise. These exercise IPAVS appear strongly related to the alveolar to arterial PO2 difference, pulmonary blood flow and mean pulmonary artery pressure. Hypoxic exercise was found to induce IPAVS at lower workloads than during normoxic exercise in 50% of subjects, while all subjects continued to shunt during recovery from hypoxic exercise, but only three subjects demonstrated intrapulmonary shunt during recovery from normoxic exercise. We suggest that these previously under-appreciated intrapulmonary arteriovenous shunts develop during exercise, contributing to the impairment in gas exchange typically observed with exercise. Future work will better define the conditions for shunt recruitment as well as their physiologic consequence.

Key Words

pre-capillary gas exchange hypoxia intrapulmonary anastomoses pulmonary circulation arterial hypoxemia 

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Copyright information

© Springer Science+Business Media, LLC 2006

Authors and Affiliations

  • Andrew T. Lovering
    • 1
  • Michael K. Stickland
    • 1
  • Marlowe W. Eldridge
    • 2
    • 3
  1. 1.The John Rankin Laboratory of Pulmonary Medicine, Department of Population Health SciencesUniversity of WisconsinMadison
  2. 2.The John Rankin Laboratory of Pulmonary Medicine, Department of Population Health SciencesUniversity of WisconsinMadison
  3. 3.Department of Pediatrics and Critical Care MedicineUniversity of Wisconsin School of MedicineMadisonUSA

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