The influence of patent foramen ovale on oxygen desaturation in obstructive sleep apnoea.

Obstructive sleep apnoea (OSA) is associated with oxygen desaturation to a varying degree. A patent foramen ovale (PFO) may allow interatrial right-to-left shunting. The hypothesis of the current study was that oxygen desaturation will occur more often, in proportion to the frequency of respiratory disturbances, in OSA subjects with PFO than in those without. In a group of 209 subjects diagnosed with OSA, the proportion of desaturation to respiratory events was calculated as the ratio of oxygen desaturation index (ODI)/apnoea-hypopnoea index (AHI). A total of 15 cases with high proportional desaturation (ODI/AHI >or=0.66) were individually matched with 15 controls with low proportional desaturation (ODI/AHI <or=0.33), all without pulmonary disease. PFO was assessed with contrast transoesophageal echocardiography and considered large when >or=20 bubbles passed over from the right to the left atrium after a single injection. The prevalence of large PFO was nine out of 15 (60%) in the high proportional desaturation group versus two out of 15 (13%) in the low proportional desaturation group. The median number of passing bubbles was positively correlated to minimum oxygen saturation among those with PFO. In conclusion, oxygen desaturation occurs more often, in proportion to the frequency of respiratory disturbances, in obstructive sleep apnoea subjects with a patent foramen ovale than in those without.