Enlarged pulmonary arteriovenous vessels in COPD. Another possible mechanism of hypoxemia.

Among 27 patients with moderate-to-severe chronic obstructive lung disease, 22 had anatomic intrapulmonary shunting greater than that seen in normal subjects. The shunted blood passed through enlarged pulmonary vessels, as demonstrated with particles 10-90 microns in diameter. The shunt magnitude was correlated with the decrement in lung diffusing capacity. It did not correlate well with pulmonary mechanical abnormalities such as air flows and volumes or resting blood gas data. Nevertheless, shunting through enlarged pulmonary vessels may play a role in the hypoxemia seen in COPD patients, especially at exercise.