Schön, Patrick; Department of Health Sciences and Technology, Zurich, Switzerland.
Boyle, Kyle G P J M; Beltrami, Fernando G;

International journal of cardiology. Congenital heart disease,2026 Aug 27

• Introduction: A decreased peripheral oxygen saturation (SpO₂ ) is common in Fontan patients. We aimed to determine whether these patients experience greater nocturnal desaturation (ΔSpO_2,noct ), and to which extent this may impact sleep quality and exercise performance, compared to healthy controls.
• Methods: 16 adult Fontan patients and 16 healthy, individually matched controls completed questionnaires on quality of life, sleep quality, and daytime sleepiness, performed measurements of lung function and diffusion capacity (DLCO), and cycled in a cardiopulmonary exercise test to volitional exhaustion. Sleep quality was assessed with a wrist-worn actigraph and nocturnal SpO₂ was measured with a pulse oximeter during six nights.
• Results: Fontan patients experienced greater ΔSpO_2,noct (-3.4 ± 0.8%-points, n = 14) compared to their controls (-2.5 ± 0.6%-points, n = 14, p = 0.001). In patients, ΔSpO_2,noct correlated with baseline SpO₂, DLCO, and exercise performance. Fontan patients had a longer sleep onset latency (22.8 ± 9.6 vs. 10.8 ± 6.0 min, p < 0.001) and lower self-perceived physical functioning (91 ± 7 vs. 100 ± 0 points, p < 0.001), but similar subjective sleep quality (4.2 ± 1.5 vs. 3.4 ± 1.4 points, p = 0.121) and daytime sleepiness (6.1 ± 4.3 vs. 6.3 ± 2.8 points, p = 0.884) compared to controls. In patients, daytime sleepiness correlated with the total number of desaturation events (r = 0.74, p = 0.003).
• Conclusion: Indices of nocturnal SpO₂ were related to daytime sleepiness and reduced exercise performance, and may therefore be a contributing factor to exercise limitation in adult Fontan patients. Enhancing nocturnal SpO₂ may thus be a promising target to improve daytime sleepiness and exercise performance in adult Fontan patients.