Cornelis K. van der Ent

Introduction Spirometry plays an important role in the assessment of possible respiratory failure in children with neuromuscular diseases (NMDs). However, obtaining reliable spirometry results is a major challenge. We studied the relation between oscillometry and spirometry results. Oscillometry is an easy, noninvasive method to measure respiratory resistance R and reactance X . We hypothesized an increased R and reduced 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 R and X at 5, 11, and 19 Hz and (forced) vital capacity, peak expiratory flow. Spearman correlation coefficients and positive and negative predictive values were calculated. Regression curves were estimated. Results We included 148 patients, median age 13 years (interquartile range: 8–16). A negative correlation was found between R and spirometry outcomes (Spearman correlation coefficient [ ρ ]: −0.5 to −0.6, p < 0.001). A positive correlation was found between X (i.e., less negative outcomes) and spirometry outcomes ( ρ : 0.4–0.6, p < 0.001). Highest correlation was found at lower frequencies. Regression analysis showed a nonlinear relation. Measurement of inspiratory and expiratory R and X did not provide added value. Positive predictive values of 80%–85% were found for z ‐scores of R measured at 5 Hz versus (F)VC ≤ 60%. Conclusion We found a nonlinear relation between oscillometry and spirometry results with increased R and reduced X in patients with more restrictive lung function decline. Given the difficulties with performing spirometry, oscillometry may be a promising substitute.