The effects of patent foramen ovale (PFO) on pulmonary gas exchange during incremental exercise

Abstract

The prevalence of a probe‐patent foramen ovale (PFO) reported in autopsy studies vary between 20 and 35%. We hypothesized that individuals with a PFO (PFO+) would have greater pulmonary gas exchange inefficiency during exercise than subjects without a PFO (PFO−) because a PFO could act as a right‐to‐left shunt. PFO+ (n=8) and PFO− (n=8) performed two incremental cycle ergometer exercise tests to max, separated by one hour, while breathing either room air or hypoxic gas (FIO2=0.12). Using saline contrast echocardiography, both PFO− and PFO+ demonstrated significant intrapulmonary shunt (bubbles appearing in the left atrium (LA) after 5 heart beats) during both exercise conditions. However, at rest and during both exercise conditions in PFO+, contrast bubbles were also observed traveling through the foramen ovale as small, intermittent boluses entering directly into the LA within 3 heart beats. These findings suggest, qualitatively, a very small intracardiac shunt at rest and during exercise in PFO+. Consequently, the alveolar‐to‐arterial oxygen difference was not significantly different between PFO+ and PFO− at either peak normoxic (24.2 ± 7.8 vs. 17.5 ± 10.8 mm Hg, p= 0.18) or hypoxic (22.7 ± 2.9 vs. 20.2 ± 4.9 mm Hg, p= 0.25) exercise. We conclude that a PFO does not further exacerbate pulmonary gas exchange inefficiency occurring during exercise in healthy humans. Support: HL‐15469 & T32 HL07654; AHA 0550176Z.