Patent Foramen ovale and high-altitude pulmonary edema

Context Individuals susceptible to high-altitude pulmonary edema ( HAPE) are characterized by exaggerated pulmonary hypertension and arterial hypoxemia at high altitude, but the underlying mechanism is incompletely understood. Anecdotal evidence suggests that shunting across a patent foramen ovale (PFO) may exacerbate hypoxemia in HAPE. Objective We hypothesized that PFO is more frequent in HAPE-susceptible individuals and may contribute to more severe arterial hypoxemia at high altitude. Design, Setting, and Participants Case-control study of 16 HAPE-susceptible participants and 19 mountaineers resistant to this condition ( repeated climbing to peaks above 4000 m and no symptoms of HAPE). Main Outcome Measures Presence of PFO determined by transesophageal echocardiography, estimated pulmonary artery pressure by Doppler echocardiography, and arterial oxygen saturation measured by pulse oximetry in HAPE-susceptible and HAPE-resistant participants at low ( 550 m) and high altitude ( 4559 m). Results The frequency of PFO was more than 4 times higher in HAPE-susceptible than in HAPE-resistant participants, both at low altitude (56% vs 11%, P=.004; odds ratio [ OR], 10.9 [95% confidence interval {CI}, 1.9-64.0]) and high altitude (69% vs 16%, P=. 001; OR, 11.7 [ 95% CI, 2.3-59.5]). At high altitude, mean (SD) arterial oxygen saturation prior to the onset of pulmonary edema was significantly lower in HAPE-susceptible participants than in the control group (73% [10%] vs 83% [7%], P=. 001). Moreover, in the HAPE-susceptible group, participants with a large PFO had more severe arterial hypoxemia (65% [6%] vs 77% [8%], P=. 02) than those with smaller or no PFO. Conclusions Patent foramen ovale was roughly 4 times more frequent in HAPE-susceptible mountaineers than in participants resistant to this condition. At high altitude, HAPE-susceptible participants with a large PFO had more severe hypoxemia. We speculate that at high altitude, a large PFO may contribute to exaggerated arterial hypoxemia and facilitate HAPE.