Spinal muscular atrophy (SMA) causes respiratory compromise that is difficult to assess in young children. The forced oscillation technique (FOT) is commercially available for children as young as 2 years of age and is nonvolitional. The aim of this study was to assess the usefulness of FOT in young children with SMA.
Children with SMA aged < 10 years were recruited. FOT was performed every 3 months for 12 months (five visits). Spirometry and assisted and unassisted peak cough flow (PCF) were performed where possible. Polysomnography was performed on children with type 2 SMA. Clinical information included SMA type, chest infections, Cobb angle, medications, and mobility. Regression analysis assessed relationships between FOT and FVC, PCF, and apnea/hypopnea index (AHI). Analysis of variance sought relationships to clinical characteristics.
Twelve children (seven male) were recruited; mean age was 6.26 (± 2.59) years. Respiratory reactance at 8 Hz (Xrs8) (mean z score, +1.41; SD, 1.90; P < .03) and respiratory resistance at 8 Hz (Rrs8) (mean z score, +0.66; SD, 1.34; P = .12) were abnormal. Four children performed spirometry. Linear relationships to Xrs8 exist: FVC (R2, 0.54), unassisted PCF (R2, 0.33), assisted PCF (R2, 0.43), and AHI (R2, 0.32). Over 12 months, Xrs8z score worsened (rate of change of +1.08, P < .001) and Rrs8z score worsened (rate of change +0.51, P < .001). No relationship (P > .05) was found between clinical characteristics and FOT values.
FOT is feasible in young children with SMA, with abnormal values of reactance and resistance on grouped data, worsening over 12 months. Xrs8 is related to respiratory tests used to monitor progress in SMA (FVC, PCF, AHI). Further research on the value of FOT in managing individuals is warranted.