Abstract Introduction Spirometry is the current gold standard for monitoring progression of respiratory weakness and restrictive lung disease among patients with dystrophinopathy, but the forced maneuvers can be difficult for these patients to perform reliably, especially for those with neurodevelopmental disorders or severe respiratory muscle weakness. Oscillometry is a low-effort method of measuring respiratory impedance during tidal breathing. The objective of this study was to compare lung function measured with oscillometry and spirometry between ambulatory and non-ambulatory patients with dystrophinopathy. Methods In this cross-sectional, single-site study, 50 male participants with dystrophinopathy aged 4 years and older completed oscillometry with the Tremoflo c-100 5-37Hz waveform (Thorasys). Impedance-derived metrics included low-frequency resistance (R5, airway obstruction), frequency dependence of resistance (R5-19), and area of reactance (AX, lung stiffness). Forced vital capacity (FVC) and maximal expiratory pressure (MEP) were recorded from clinical spirometry obtained on the same day. One-sample Wilcoxon tests compared impedance metrics to reference mean. Two-sample Wilcoxon tests compared lung function metrics (transformed to height-based z-scores) between ambulatory and non-ambulatory status. Median (IQR) reported. Results Participants were 14.4 (11.4, 18.8) years old; 24 (48%) were ambulatory. Almost twice as many participants successfully completed oscillometry (n = 42, 84.0%) compared to spirometry (n = 22, 44%, p 0.001, McNemar’s test). Median impedance metrics were lower than or not different from the reference population mean (z-score=0), indicating lower airway resistance and reactance during tidal breathing: R5z=-0.939 (-1.56,-0.203; p 0.001); R5-19z=-0.783 (-1.23,-0.453;p0.001). No patients had abnormal (z 1.645) R5 or R5-19; 3 had abnormal AX. 14 (63.6%) of the participants with acceptable spirometry had abnormal FVC (z-1.645), with most patients showing respiratory muscle weakness: FVCz=-3.37 (-4.68,-0.980; p 0.001) and MEP=38.0 (29.5, 49.5) cmH2O. Non-ambulatory patients had lower FVC -3.52 (-4.89,-1.69) vs -0.900 (-1.22,0.180), p = 0.039 and lower MEP 34.5 (28.5,42.5) vs 72.0 (57.0,82.5) cmH2O, p 0.001 compared to ambulatory participants, while there were no statistically significant differences in R5, R5-19, and AX by ambulatory status (Figure). Discussion Despite the severe muscle weakness and restrictive lung function measured by spirometry among non-ambulatory patients with dystrophinopathy, oscillometry metrics were normal or lower than reference mean and did not differ between non-ambulatory and ambulatory patients. This suggests that progression of respiratory muscle weakness, rather than underlying airway obstruction or lung tissue stiffness, drives poor lung function. However, because of its ease of use, oscillometry could be a useful tool to identify andmonitor co-occurring airways disease in this population, especially among patients who cannot perform reliable spirometry. This abstract is funded by: NIH/NCATS Colorado CTSA UM1 TR004399
Mccoy et al. (Fri,) studied this question.