Introduction Spirometry plays an important role in the assessment of possible respiratory failure in children with neuromuscular disorders (NMDs). However, obtaining reliable spirometry results is a major challenge. We studied the relation between Forced Oscillation Technique (FOT) and spirometry results. FOT is an easy, non-invasive method to measure respiratory mechanics, i.e. respiratory resistance R and respiratory reactance X. We hypothesized an increased resistance R and reduced reactance X in patients with more reduced lung function. Methods In this prospective single center study we included all children with NMDs able to perform spirometry. We consecutively measured respiratory resistance R and reactance X at 5, 11 and 19 Hz and (Forced) Vital Capacity, Peak Expiratory Flow. Spearman correlation coefficients were calculated and regression curves were estimated. Results We included 148 patients, with a median age of 13 years (IQR 8-16). All correlation coefficients were statistically significant with p = 0.000. A negative correlation was found between resistance R and spirometry outcomes (spearman correlation coefficient (ρ) between -0.5 and -0.6). A positive correlation was found between reactance X (i.e. less negative outcomes) and spirometry outcomes (ρ between 0.4 and 0.6). Highest correlation was found at lower frequencies. Regression analysis showed a non-linear relation between FOT and spirometry results. Conclusion We found a non-linear relation between FOT and spirometry results with increased resistance R and reduced reactance X in patients with more restrictive lung function decline. Given the difficulties with performing spirometry, FOT may be a promising surrogate measure of lung function.

Introduction Understanding the impact of scoliosis surgery on lung function is important for counseling patients about risks and benefits of surgery. We prospectively compared the trends in lung function test (LFT) results prior to and after scoliosis surgery in children with neuromuscular diseases, or dysmorphic syndromes. We hypothesized a stabilization. Methods We prospectively included children with neuromuscular or syndromic scoliosis able to perform LFTs. We studied (Forced) Vital Capacity ((F)VC), the ratio of Forced Expiratory Volume in 1 second (FEV1) and FVC, and Peak Expiratory Flow (PEF). Preoperative LFT results were compared with results 3-4 months after surgery. The mean monthly change in LFT results up to 2 years after surgery was compared with the preoperative natural history using linear mixed effects models. Results We included 43 patients. No significant change was observed in absolute values of (F)VC, FEV1/FVC and PEF prior to and after surgery. Median standardized VC, FVC and PEF decreased significantly after surgery from 59 to 58%, 60 to 51% and 61 to 53% respectively. The monthly rate of change in FVC was -0.13 % (95% CI -0.42 to 0.17) prior to surgery and -0.20% (95% CI -0.42 to 0.03) after surgery, mean difference -0.07 (95% CI -0.46 to 0.31; p=0.36). Conclusion No stabilization of lung function 3-4 months after scoliosis surgery was observed in children with neuromuscular and syndromic scoliosis with restrictive lung function disease. The effect of surgery on the rate of lung function decline remains inconclusive.

Objective: To verify if the extent of structural lung damage visible on chest CT is correlated with change in ppFEV1 after start of CFTR modulating therapy in CF patients. Methods: In our retrospective observational study, we included patients aged ≥6 years starting ivacaftor or lumacaftor/ivacaftor treatment who were in routine follow up. FEV1 and BMI were recorded every 3 months. From the group of patients who had started lumacaftor/ivacaftor, patients were selected who underwent chest CT within 18 months before or after start of treatment. Patients who had started ivacaftor all underwent chest CT just before the start of treatment. These CT scans were reviewed to determine Brody score. ppFEV1 data was retrieved. To assess correlations, Spearman R and Pearson R tests were applied. Results: Thirty patients met the inclusion criteria, with Brody scores between 0.46-55.30 (median: 19.97, normalized score out of 100) and ppFEV1 before treatment of 19-113 (median: 67). Twenty-three and 7 patients had started lumacaftor/ivacaftor and ivacaftor respectively. Change in ppFEV1 after 6 months of treatment ranged from -19 to +24 (median: +5). For patients using lumacaftor/ivacaftor, the correlation between Brody score and change in ppFEV1 was not significant: Spearman R=-0.213, (p=0.164), but for patients using ivacaftor, there was a significant correlation between Brody score and ppFEV1 change, with a Spearman R=0.679 (p=0.029). Conclusion: The extent of structural damage to the lungs of CF patients is correlated with the response in ppFEV1 to ivacaftor, however this correlation was not demonstrable in patients treated with lumacaftor/ivacaftor.