High prevalence of patent foramen ovale in recreational to elite breath hold divers

Why patent foramen ovale prevalence is greater in apnea divers remains unknown, though hyperbaria during an apnea dive results in a translocation of blood volume centrally with a concomitant reduction in lung volume and alveolar hypoxia during ascent results in hypoxic pulmonary vasoconstriction. These conditions increase pulmonary arterial pressure, increasing right-atrial pressure allowing for right-to-left blood flow through a patent foramen ovale which may be beneficial for preserving cardiac output and reducing capillary hydrostatic forces.