High Prevalence of Patent Foramen Ovale in Recreational to Elite Breath-Hold Divers
Authors: Tyler Kelly, Alexander Patrician, Mohini Bryant-Ekstrand, Courtney Brown, Christopher Gasho, Hannah G. Caldwell, Rachel N. Lord, Tony Dawkins, Aimee Drane, Michael Stembridge, Tanja Dragun, Otto Barak, Boris Spajić, Ivan Drviš, Joseph W. Duke, Glen E. Foster, Philip N. Ainslie, Željko Dujić, Andrew T. Lovering
DOI / Source: https://doi.org/10.1016/j.jsams.2022.03.014
Date: 23 March 2022
Reading level: Intermediate
Why This Matters for Freedivers
A PFO is a common “flap” between the heart’s upper chambers that can allow blood (and sometimes bubbles) to pass from the right side to the left side. This paper found PFOs were much more common in breath-hold divers than in non-divers. That’s interesting because a PFO might be a double-edged sword: it could potentially reduce extreme pressure load on the lungs and help maintain cardiac output during deep/hypoxic dives, but it could also provide a pathway for neurological problems in some decompression scenarios.
Synopsis
A patent foramen ovale (PFO) is a leftover opening from fetal life that normally seals after birth, but stays “patent” (openable) in a significant portion of adults. Most people never notice it. The key detail is that a PFO can sometimes allow blood to move from the right atrium to the left atrium when right-sided heart pressures rise—such as during a Valsalva maneuver or when pulmonary pressures are elevated. In scuba diving, PFO has a known association with neurological decompression illness because it can allow venous gas bubbles to bypass the lung filter and enter the arterial circulation.
This study asked a question nobody had properly published before: how common is PFO in freedivers? The researchers recruited 36 apnea divers (recreational through elite) from Croatia (Split and a training camp in Cavtat) and compared them to 36 controls from Split and Eugene, Oregon who had no meaningful breath-hold diving history. Everyone underwent a saline contrast “bubble study” using transthoracic echocardiography. If bubbles appeared in the left heart within three cardiac cycles after appearing on the right side, that was considered evidence of a PFO. Spirometry was also measured.
The result was striking: PFO prevalence was 53% in apnea divers (19 out of 36) compared with 25% in controls (9 out of 36), a statistically significant difference. Divers were also taller and had larger lung volumes (higher FVC and FEV1), which fits with the typical “selection + training” picture in freediving.
The authors then discuss why this might happen. One hypothesis is “self-selection”: people with a PFO might tolerate deep/hypoxic dives better because a PFO can act as a pressure relief valve when pulmonary pressures rise during central blood shift and lung compression—especially during ascent when hypoxia can trigger hypoxic pulmonary vasoconstriction. Another possibility is that repeated exposure to high right-heart pressures in apnea diving could make a partially sealed foramen ovale easier to open or detect. They also note the uncertain risk side: although venous bubble loads in breath-hold diving are often low, there are reports of decompression sickness and brain white-matter lesions in repetitive breath-hold divers, so a PFO could still matter for some profiles.
Abstract
Objectives: During apnea diving, a patent foramen ovale may function as a pressure relief valve under conditions of high pulmonary pressure, preserving left-ventricular output. Patent foramen ovale prevalence in apneic divers has not been previously reported. We aimed to determine the prevalence of patent foramen ovale in apneic divers compared to non-divers.
Design: Cross sectional.
Methods: Apnea divers were recruited from a training camp in Cavtat, Croatia and the diving community of Split, Croatia. Controls were recruited from the population of Split, Croatia and Eugene, Oregon, USA. Participants were instrumented with an intravenous catheter and underwent patent foramen ovale screening utilizing transthoracic saline contrast echocardiography. Appearance of microbubbles in the left heart within 3 cardiac cycles indicated the presence of patent foramen ovale. Lung function was measured with spirometry. Comparison of patent foramen ovale prevalence was conducted using chi-square analysis, p < .05.
Results: Apnea divers had a significantly higher prevalence of patent foramen ovale (19 of 36, 53%) compared to controls (9 of 36, 25%).
Conclusions: 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.