Transpulmonary passage of 99mTc macroaggregated albumin in healthy humans at rest and during maximal exercise

J Appl Physiol (1985). 2009 Jun;106(6):1986-92. doi: 10.1152/japplphysiol.01357.2007. Epub 2009 Apr 16.


We have demonstrated that 50-mum-diameter arteriovenous pathways exist in isolated, healthy human and baboon lungs, ventilated and perfused under physiological pressures. These findings have been confirmed and extended by demonstrating the passage of 25-microm microspheres through the lungs of exercising dogs, but not at rest. Determination of blood flow through these large-diameter intrapulmonary arteriovenous pathways would be an important first step to establish a physiological role for these vessels. Currently, we sought to estimate blood flow through these arteriovenous pathways using technetium-99m ((99m)Tc)-labeled macroaggregated albumin (MAA) in healthy humans at rest and during maximal treadmill exercise. We hypothesized that the percentage of (99m)Tc MAA able to traverse the pulmonary circulation (%transpulmonary passage) would increase during exercise. Seven male subjects without patent foramen ovale were injected with (99m)Tc MAA at rest on 1 day and during maximal treadmill exercise on a separate day (>6 days). Within 5 min after injection, subjects began whole body imaging in the supine position. Six of the seven subjects showed an increase in transpulmonary passage of MAA with maximal exercise. Using two separate analysis methods, percent transpulmonary passage significantly increased with exercise from baseline to absolute values of 1.2 +/- 0.8% (P = 0.008) and 1.3 +/- 1.0% (P = 0.016), respectively (means +/- SD; paired t-test). We conclude that MAA may be traversing the pulmonary circulation via large-diameter intrapulmonary arteriovenous conduits in healthy humans during exercise. Recruitment of these pathways may divert blood flow away from pulmonary capillaries during exercise and compromise the lung's function as a biological filter.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Echocardiography
  • Exercise / physiology*
  • Exercise Test*
  • Humans
  • Lung / blood supply*
  • Male
  • Pulmonary Circulation / physiology*
  • Pulmonary Gas Exchange / physiology
  • Radiopharmaceuticals*
  • Technetium Tc 99m Aggregated Albumin*
  • Young Adult


  • Radiopharmaceuticals
  • Technetium Tc 99m Aggregated Albumin