T. Kelly1, A. Patrician2, M. Bryant-Ekstrand1, C. Brown2, C. Gasho2, H.G. Caldwell2, R. Lord3, T. Dawkins3, A. Drane3, M. Stembridge3, T. Dragun4, O. Barak5, B. Spajić6, I. Drviš6, J.W. Duke7, G.E. Foster2, P.N. Ainslie2, Ž. Dujić4, and A.T. Lovering1

1University of Oregon, Eugene, OR, 2University of British Columbia, Kelowna, BC, Canada, 3Cardiff Metropolitan University, Cardiff, Wales, UK, 4University of Split School of Medicine, Split, Croatia, 5University of Novi Sad, Novi Sad, Serbia, 6University of Zagreb, Zagreb, Croatia, 7Northern Arizona University, Flagstaff, AZ

Patent Foramen Ovale (PFO) is an intra-atrial tunnel allow for right-to-left intracardiac shunt, allowing blood to bypass the pulmonary circulation. This may be advantageous for apneic diving although the prevalence of PFO in apneic divers has not been previously reported. PURPOSE: To determine the prevalence of PFO in apneic divers compared to non-divers. METHODS: Apnea divers (n = 36, 9 female) were recruited from an international training camp in Cavtat, Croatia and the diving community of Split, Croatia. Control subjects (n = 17, 3 female) were recruited from the general population of Split, Croatia and Eugene, Oregon. Subjects were instrumented with an intravenous catheter and underwent PFO screening utilizing transthoracic saline-contrast echocardiography. The appearance of microbubbles in the left heart within 3 cardiac cycles of bubble injection indicated the presence of PFO. Prevalence of PFO comparison between divers and controls was conducted using a chi-square analysis with the significance set at p <0.05. Anthropometrics were compared using a two-tailed independent Student’s t test with the significance set at p <0.05. RESULTS: Apnea divers had a significantly higher prevalence of PFO (19 of 36, 53%) than Controls (4 of 17, 23%)( X2(1, N = 53) = 4.02, p = .0449). Divers were significantly taller (181.2 ± 7.6 v 176.4 ± 7.0 cm, p = 0.0351), had a lower body mass index (23.5 ± 3.5 v 25.7 ± 3.0 kg/m2, p = .0366), but had comparable lung function to controls. CONCLUSION: We found that apneic divers have a significantly higher prevalence of PFO compared to controls. Apneic divers regularly achieve depths sufficient to induce hyperbaric stress on the pulmonary circuit, as well as significant reduction in lung volume due to compression. This combination may substantially increase pulmonary arterial pressure during a diver, and a buildup of ‘backpressure’ may elevate right-atrial pressure and force open otherwise closed but incompletely endothelialized foramen ovale, resulting in PFO subsequently detectable by ultrasound. Alternately, PFO may function as a ‘pressure relief valve’, reducing the fraction of cardiac output reaching the lungs, thereby limiting the increase in ‘backpressure’ and aiding in the preservation of left-ventricular output.

Supported by Burroughs Welcome Fund grant and Fulbright Scholars Program grant to A.T. Lovering.

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