Prevalence of patent foramen ovale and its impact on oxygen desaturation in obstructive sleep apnea

Background: A possible association between patent foramen ovale (PFO) and obstructive sleep apnea has been suggested (OSA), whereby right-to-left shunting may exacerbate the severity of nocturnal oxygen desaturation. However, the interaction between these two conditions has not been well characterised. Methods: A case-control study was conducted to evaluate the epidemiological association between PFO and OSA. Subjects were recruited prospectively from a sleep laboratory population, and 102 OSA subjects (mean age 51.5 ± 13 years) were compared to 50 controls without OSA (mean age 49.9 ± 12.4). The presence and size of right-to-left shunting were determined by contrast transcranial Doppler ultrasonography with Valsalva provocation. Using the 21,749 obstructive breathing events recorded at polysomnography from the OSA group, a mixed-effects linear regression model was developed to evaluate the impact of right-to-left shunting on nocturnal oxygen desaturation (ΔSpO ₂). Results: A higher prevalence of PFO was present in the OSA group compared to the control group (47.1% vs. 26.0%, OR 2.53, CI 1.20 to 5.31, p = 0.014). From the regression model, right-to-left shunt size did not exert a significant influence on the severity of ΔSpO₂ (coefficient 0.85, CI - 0.62 to 2.32, p = 0.254); whereas sleep state, event type, body position, event duration, awake oxygen saturation, apnea-hypopnea index and body mass index were all independent predictors of ΔSpO_2. Conclusion: A higher prevalence of PFO is found in OSA subjects. However, the degree of right-to-left shunting, characterised by Valsalva provocation, is not associated with an increased severity of nocturnal oxygen desaturation.