Many children treated with cystic fibrosis transmembrane conductance regulator (CFTR) modulators increase their body mass index (BMI). To extend this observation, we prospectively monitored rates of change for growth, body mass and composition indices and z scores, forearm strength, and FEV1 during ETI therapy for a cohort of 27 children, ages 6-11, assessed potential risk factors for concerning change rates; and documented variability of individual change rates. Body composition was assessed by bioelectrical impedance analysis (BIA). Z score calculations used matched data from US children. Outcomes rates of change were analyzed using a linear mixed effects regression model. At enrollment, median BMI z-score was 0.6, percent body fat was 22.7, and percent predicted (pp) FEV1 was 100. During ETI treatment, mean z scores for annualized change rates of BMI (0.02±0.07), fat mass index (FMI) (0.02±0.08), and fat free mass index (-0.03±0.07) were not different from zero. Percent increase of FMI (mean:12.0±29.0) often exceeded that for skeletal muscle mass index (SMMI)(4.7±4.9). Older children and girls experienced the largest weight gain. Individual body mass and composition index rates of change varied extensively. FEV1 increase was independent of body composition and muscle strength change rates. Preadolescent children, as a group, experienced growth and body composition trajectories expected of US children, adding muscle mass, but preferentially adding fat mass when treated with ETI. Individual outcomes variation suggests potential benefit for body composition monitoring and interventions to promote healthy physical maturation during ETI therapy.

Pulmonary defects are reported in pectus excavatum but the physiological impact on exercise capacity is unclear. To test the hypothesis that pectus deformities are associated with a pulmonary impairment during exercise we performed a retrospective review on pectus patients in our center who completed a symptom questionnaire, cardiopulmonary exercise test, pulmonary function tests (PFT), and chest magnetic resonance imaging. Of 259 patients studied, dyspnea on exertion and chest pain was reported in 64% and 41% respectively. Peak oxygen uptake (VO2) was reduced in 30% and classified as mild in two-thirds. A pulmonary limitation during exercise was identified in less than 3%. Ventilatory limitations on PFT was found in 26% and classified as mild in 85%. Obstruction was the most common abnormal pattern (11%) followed by a nonspecific ventilatory limitation and restrictive pattern (7% each). There were no differences between patients with normal or abnormal PFT patterns for the anatomic degree of pectus malformation, VO2, or percentage reporting dyspnea or chest pain. Scatter plots demonstrated significant inverse relationships between severity of the pectus deformity with lung volumes on PFT and VO2 but no correlation between the severity of the pectus deformity and lung volumes during exercise. We conclude that resting lung volume measurements were associated with the anatomic degree of pectus severity but respiratory limitations during maximal exercise are uncommon and PFT patterns have poor correlation with symptomatology or VO2. These findings suggest non-respiratory causes are more likely for the high rates of dyspnea and reduced aerobic fitness reported in pectus.