Lower transfer factor of the lung for carbon monoxide in women with a patent foramen ovale

What is the central question of this study? Do individuals with a patent foramen ovale (PFO⁺ ) have a lower lung transfer factor for carbon monoxide than those without (PFO^- )? What is the main finding and its importance? We found a lower rate constant for carbon monoxide uptake in PFO⁺ compared with PFO^- women, which was physiologically relevant (≥0.5 z-score difference), but not for PFO⁺ versus PFO^- men. This suggests that factors independent of the PFO are responsible for our findings, possibly inherent structural differences in the lung.

The transfer factor of the lung for carbon monoxide (TL_CO ) measure assumes that all cardiac output flows through the pulmonary circuit. However, right-to-left blood flow through a shunt can result in a lower transfer factor than predicted. A patent foramen ovale (PFO) is a potential source of right-to-left shunt that is present in ∼35% of the population, but the effect of PFO on TL_CO is unknown. We sought to determine the effect of PFO on the TL_CO . We conducted a retrospective analysis of TL_CO data from 239 (101 women) participants. Anthropometrics and lung function, including spirometry, plethysmography and TL_CO , were compiled from our previously published work. Women, but not men, with a PFO had a significantly lower TL_CO and rate constant for carbon monoxide uptake (K_CO ) (percentage of predicted and z-score) than women without a PFO. Women and men with a PFO had normal alveolar volumes that did not differ from those without a PFO. Correcting the data for haemoglobin in a subset of subjects did not change the results (n = 58; 25 women). The lower K_CO in women with versus without a PFO was physiologically relevant (≥0.5 z-score difference). There was no effect of PFO in men. This suggests that factors independent of the PFO are responsible for our findings, possibly inherent structural differences in the lung.