Intrapulmonary arteriovenous anastomoses in humans with chronic obstructive pulmonary disease: implications for cryptogenic stroke?

INTRODUCTION: The pulmonary capillaries prevent stroke by filtering venous emboli from the circulation. Intrapulmonary arteriovenous anastomoses are large diameter (≥ 50μm) vascular connections in the lung that may compromise the integrity of the pulmonary capillary filter and have been recently linked to cryptogenic stroke and transient ischemic attack. Prothrombotic populations, such as individuals with chronic obstructive pulmonary disease (COPD) may be at increased risk of stroke and transient ischemic attack facilitated by intrapulmonary arteriovenous anastomoses, but the prevalence and degree of blood flow through intrapulmonary arteriovenous anastomoses in this population has not been fully examined and compared to age matched healthy control subjects. METHODS: We used saline contrast echocardiography to assess blood flow through intrapulmonary arteriovenous anastomoses at rest (n = 29 COPD, 19 control) and during exercise (n = 10 COPD, 10 control) in COPD subjects and age matched healthy control subjects. RESULTS: Blood flow through intrapulmonary arteriovenous anastomoses was detected in 23% of COPD subjects at rest and was significantly higher compared to age matched healthy control subjects. Blood flow through intrapulmonary arteriovenous anastomoses at rest was reduced or eliminated in COPD subjects after breathing hyperoxic gas. Sixty percent of COPD subjects who did not have blood flow through intrapulmonary arteriovenous anastomoses at rest, had blood flow through intrapulmonary arteriovenous anastomoses during exercise. DISCUSSION: The combination of blood flow through intrapulmonary arteriovenous anastomoses and potential for thrombus formation in individuals with COPD may permit venous emboli to pass into the arterial circulation and cause stroke and transient ischemic attack. Breathing supplemental oxygen may reduce this risk in COPD. The link between blood flow through intrapulmonary arteriovenous anastomoses, stroke, and transient ischemic attack is worthy of future investigation in COPD and other populations.

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