Lung function and exercise capacity in single ventricle patients post Fontan palliation and potential role of diaphragm ultrasound imaging

AIMS: Patients with Fontan circulation have reduced functional capacity, due to a reduced cardiac output, but also to an abnormal lung function and respiratory muscle weakness. This study aimed to assess lung function and exercise capacity in a cohort of patients with Fontan circulation and evaluate the prognostic impact of restrictive lung function (RLF). In addition, diaphragmatic ultrasound (DUS) investigated diaphragmatic function in a subgroup of patients. METHODS: Patients with Fontan palliation who underwent lung function evaluation were included. A subgroup of patients additionally underwent DUS to assess diaphragmatic function. RESULTS: The study population consisted of 53 post-Fontan patients (mean age 25 ± 10 years). Exercise capacity was reduced, with a median peak VO₂ of 18.4 mL/kg/min (IQR 14.7-22.6). Oxygen pulse was reduced and flattened, and ventilatory efficiency was impaired (mean VE/VCO₂ slope 36 ± 7), without evidence of mechanical ventilatory limitation. Spirometry revealed RLF in 48% of patients. RLF was associated with lower peripheral oxygen saturation, diuretic therapy use, and lower engagement in regular physical activity. Moreover, RLF was significantly associated with adverse events at follow-up (χ²: 6.8, p = 0.004). Diaphragm ultrasound (DUS), performed in 10 patients, showed abnormal function of at least one hemidiaphragm in most cases. CONCLUSIONS: Patients with Fontan circulation exhibit a markedly reduced exercise functional capacity resulting from a complex interplay between cardiac, pulmonary, and peripheral factors. Restrictive lung function was associated with increased need for diuretic therapy and lower levels of physical activity. Abnormal diaphragmatic function was frequently observed and may represent a potentially modifiable contributor to functional limitation warranting further investigation.