Poor growth is common in children with pulmonary hypertension; however, skeletal muscle deficits have not been described and the association between muscle deficits and functional status is unknown.

Patients aged 8–18 years with pulmonary hypertension (diagnostic Groups 1, 2, or 3) and World Health Organization functional class I or II underwent dual-energy absorptiometry to measure leg lean mass Z-score (a surrogate for skeletal muscle). Muscle strength was assessed using dynamometry. Physical activity questionnaires were administered. Clinical data, including 6-minute walk distance, were reviewed. Relationships between skeletal muscle, physical activity score, and 6-minute walk distance were assessed by correlations and linear regression.

Sixteen patients (12.1 ± 3.2 years, 50% female, 56% Group 1, 56% functional class II) were enrolled. Leg lean mass Z-score was significantly less than reference data (−1.40 ± 1.12 versus 0.0 ± 0.9, p < 0.001) and worse in those with functional class II versus I (−2.10 ± 0.83 versus −0.50 ± 0.73, p < 0.01). Leg lean mass Z-score was positively associated with right ventricular systolic function by tricuspid annular plane systolic Z-score (r = 0.54, p = 0.03) and negatively associated with indexed pulmonary vascular resistance (r = −0.78, p < 0.001). Leg lean mass Z-score and forearm strength were positively associated with physical activity score. When physical activity score was held constant, leg lean mass Z-score independently predicted 6-minute walk distance (R2 = 0.39, p = 0.03).

Youth with pulmonary hypertension demonstrate marked skeletal muscle deficits in association with exercise intolerance. Future studies should investigate whether low leg lean mass is a marker of disease severity or an independent target that can be improved.