Respiratory Function of Fontan Pediatric Patients with Hypoplastic Left Heart Syndrome and Other Morphologies of Functionally Single Ventricle—A Pilot Study

<b>Background/Objectives</b>: Management of complex congenital heart defects with functionally single ventricle remains one of the greatest challenges of pediatric cardiology. The multistage surgical treatment completed with Fontan procedure is related to multiple complications. Due to non-pulsatile continuous pulmonary flow and chronic hypoxia, Fontan circulation may induce pulmonary endothelial dysfunction. However, the impact of Fontan physiology on respiratory system function is not well studied. The aim of the research was to assess respiratory function in Fontan pediatric patients with hypoplastic left heart syndrome (HLHS) and other morphologies of functionally single ventricle. The article presents the preliminary results drawn from the pilot study, focusing on Fontan patients, without a healthy children control group. <b>Methods</b>: A cross-sectional study involved Fontan patients hospitalized in the Pediatric Cardiology Clinic of the Medical University of Silesia in Katowice between August 2023 and November 2024. The exclusion criteria were lack of parental and/or patient's consent, age < 6 years old, decompensated heart failure, asthma, atopy, respiratory infection within two weeks before the hospitalization, or significant psychomotor disability. Respiratory function assessment involved spirometry and fractional exhaled nitric oxide (FeNO) measurement. <b>Results</b>: A total of 32 patients who met inclusion criteria performed respiratory measurements. The mean age was 12.9 years old; there were 12 females. A total of 12 patients had HLHS and 20 patients had other morphologies of univentricular heart. FeNO values were relatively high with a mean of 30 ppb. Spirometry showed restrictive or mixed restrictive and obstructive ventilatory pattern. The mean forced vital capacity (FVC) levels were 79.2 ± 12.3% of predicted value (%pv) and forced expiratory volume in the first second (FEV1) 77.3 ± 13.8%pv. Children with HLHS presented statistically significantly lower percentages of predicted value of FEV1. There were statistically significant negative correlations between NT-proBNP concentrations and FEV1, FEV1%pv, MEF25-75 and MEF25-75%pv. <b>Conclusions</b>: Fontan pediatric patients present a restrictive or mixed restrictive and obstructive ventilatory pattern and relatively high FeNO levels. Patients with HLHS have worse pulmonary function than patients with other univentricular heart morphologies. This may be related to worse ventricular function in patients with HLHS.