Restrictive lung function defined by body plethysmography is common in children with Fontan palliation and functionally relevant

Background Pulmonary dysfunction is common in single ventricle (SV) patients with Fontan circulation, yet the prevalence and clinical relevance of true restrictive lung disease remain poorly characterized as most studies relied on spirometry alone. This study comprehensively assessed lung function using spirometry and body plethysmography, examined its relationship with cardiac magnetic resonance (CMR)-derived lung volumes, evaluated its impact on exercise capacity, and identified clinical correlates of restrictive physiology. Methods In this prospective, single-centre study, 31 children and adolescents with Fontan circulation underwent spirometry, body plethysmography, cardiopulmonary exercise testing (CPET), and CMR. Restrictive lung function was defined by reduced (<LLN) total lung capacity (TLC). Lung function, CMR findings, exercise performance, and clinical characteristics were compared between patients with and without restrictive physiology. Results Restrictive lung function was identified in n = 8 (26%) participants. TLC correlated strongly with CMR-derived total lung volume (r = 0.889, p < 0.001). Patients with restrictive physiology demonstrated significantly reduced exercise capacity, including lower peak oxygen uptake, tidal volume, and minute ventilation, with reduced breathing reserve and higher peak respiratory rate, indicating clinically relevant ventilatory limitation. Restrictive physiology was associated with lower ventricular ejection fraction and impaired global circumferential strain. In multivariable analysis, TLC was the strongest predictor of peak oxygen uptake. Conclusions Restrictive lung physiology confirmed by body plethysmography is common in children and adolescents with Fontan circulation and associates with impaired exercise performance and reduced ventricular function. Comprehensive pulmonary function testing including body plethysmography may be considered in routine follow-up to identify patients at increased risk of adverse outcomes.