PURPOSE: Patients with COPD are at increased risk for neurological sequelae such as transient ischemic attack and stroke but the reasons for this are unknown. We have recently demonstrated in healthy humans the existence of large diameter intrapulmonary arteriovenous anastomoses that are closed when breathing room air but open in subjects breathing hypoxic gas mixtures. These hypoxia-inducible, large diameter intrapulmonary arteriovenous anastomoses may allow emboli to bypass the pulmonary microcirculation and enter into the systemic circulation resulting in embolic injury. However, it is unknown if these vessels are patent in COPD subjects who have arterial hypoxemia. We hypothesized that COPD subjects with arterial hypoxemia would have patent intrapulmonary arteriovenous anastomoses that would close when subjects breathed supplemental oxygen.
METHODS: To detect intrapulmonary arteriovenous anastomoses, we performed agitated saline contrast echocardiography in 13 subjects with COPD (7 Female), GOLD stage I-III, reclined in the left lateral decubitus position. Bubble scores ranging from 0 to 5 (no bubbles to many bubbles, homogenously distributed) were assigned and arterial oxygen saturations off and on supplemental oxygen were recorded. All subjects were screened for patent foramen ovale (PFO) with and without the release of a Valsalva maneuver.
RESULTS: Four subjects had a PFO and were excluded from further study. Six of the remaining 9 COPD subjects (FEV1% pred = 56.89±20.55) demonstrated patent intrapulmonary arteriovenous anastomoses at rest while breathing room air as evidenced by bubble scores ranging from 1 to 2, with saturations ranging from 94-97. Subsequently, subjects breathed 100% O2 (6 L/min via a facemask) and all bubble scores were reduced to 0 or 1 with saturations at 100%.
CONCLUSIONS: These data suggest that intrapulmonary arteriovenous anastomoses can be open in COPD patients with arterial hypoxemia but that this is reversible with supplemental oxygen.
CLINICAL IMPLICATIONS: Thus, patent intrapulmonary arteriovenous anastomoses may allow for emboli to bypass the pulmonary microcirculation providing an explanation for the increased incidence of neurological sequelae in COPD patients. Our data suggest keeping saturation greater than 97% in subjects with COPD.
DISCLOSURE: The following authors have nothing to disclose: Andrew Lovering, Kara Beasley, Henry Norris, Jonathan Elliott, Steven Laurie, Robert Carolan
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