Phase-Resolved Functional Lung MRI Evaluation of Dynamic Hyperinflation Induced by Metronome-Paced Tachypnea in Patients with Chronic Obstructive Pulmonary Disease

Hyperinflation in chronic obstructive pulmonary disease (COPD) patients worsens on exertion/exercise when breathing frequency increases. Fast breathing, paced at 40 breaths per minute using a metronome (metronome-paced tachypnea, MPT), induces dynamic hyperinflation (DH) and can be performed during MRI. MPT in combination with phase-resolved functional lung (PREFUL) MRI can be used to assess stress-driven ventilation dynamics globally and regionally. A 90 s time series of one coronal slice centered to the trachea was acquired for PREFUL MRI during 60 s of resting tidal breathing (RTB) and 30 s of MPT at 40 breaths per minute in COPD patients and healthy volunteers. MPT detected DH in 12 out of 15 COPD patients and in 1 out of 15 healthy controls. During MPT, the global fractional ventilation decreased by 20% in healthy subjects (p = 0.01) and by 48% in COPD patients (p < 0.001). The end-expiratory lung area remained stable in healthy subjects and increased significantly by 7% in COPD patients over the course of MPT (p = 0.004). Younger, healthy volunteers adapted to increase breathing frequency by reducing tidal volume (global fractional ventilation), while older healthy volunteers showed less tidal volume reduction (p = 0.036). The MPT-induced change of regional ventilation homogeneity (flow volume loop cross-correlation, FVL-CC<inf>MPT/RTB</inf>) increased with age in healthy volunteers (p = 0.039) likely due to the development of compensatory dystelectasis in younger volunteers leading to reduced homogeneity during MPT. In the future, the MPT test during MR imaging may be used for COPD treatment analysis and disease monitoring.