Expiratory phase lung mechanics in late-onset Pompe disease: a multicenter study using oscillometry to identify specific breathing abnormalities.

INTRODUCTION: In late-onset Pompe disease (LOPD), muscle weakness causes restrictive lung impairment. In murine models, glycogen deposition in lung parenchyma suggests additional causes for restriction that remain poorly understood. We investigated whether oscillometry detects respiratory abnormalities not identified by spirometry and evaluated changes after air-stacking manoeuvres. METHODS: We prospectively evaluated 16 adults with LOPD from three Italian centres. Alongside spirometry, oscillometry (at 5, 11, and 19 Hz) was performed to assess resistance (R) and reactance (X) across the breathing cycle and by respiratory phase. Measurements were repeated 5 min after an air-stacking manoeuvre. RESULTS: Participants (7 men, 9 women; 51.6 ± 12.5 years) had moderate-to-severe restriction (FVC 53.3 ± 19.6% predicted) with preserved FEV1/FVC. Two oscillometric patterns emerged. The first one (seven patients) was characterised by an abnormal increase in expiratory resistance within breaths ([R5exp - R5insp] > 0.70 cmH2O·s/L), associated or not with abnormal whole-breath R and intrabreath X changes. The second pattern (nine patients) consisted of normal R and X changes in the breathing cycle. Air-stacking increased FVC (53.3 ± 19.6 to 71.3 ± 19.2% predicted, p < 0.001) without normalising reactance. CONCLUSION: In LOPD, oscillometry detects distinct mechanical patterns not identified by spirometry. Air-stacking increases lung volumes without improving respiratory mechanics.