Comparison between spirometry and computed tomography to evaluate dynamic hyperinflation in COPD patients

Background: Dynamic hyperinflation (DH) is a key mechanism related with dyspnea and exercise intolerance in COPD patients. Quantitative computed tomography (CT) measurements strongly correlate with physiologic measurements of airway obstruction; however nothing is known about its relationship with physiological assessment of DH. Aims: Compare the effects of metronome-paced hyperventilation (MPH) on lung volumes evaluated by spirometry and CT densitovolumetry (CTd) in patients with moderate COPD (50%≤FEV 1 <80%pred). Methods: 16 patients with COPD (60.7±10.7 yr; FEV1= 70±7% pred) after a 1-wk wash-out period using only short acting BD as rescue medication performed spirometry and CTd before and after MPH (respiratory rate twice the baseline rate for 30s). Results: Patients ranged from normal to slightly/moderately hyperinflated at rest (TLC: 109±14; FRC: 121±24; and RV: 125±36 % predicted). After MPH, inspiratory capacity (IC) significantly reduced, indicating DH. Nevertheless, CTd measurements did not change significantly Measurements before and after metronome-paced hyperventilation (MPH). Pre MPH Post MPH Physiological measurement Inspiratory Capacity (IC), L 2.16 ± 0.56 1.66 ± 0.49* CT densitovolumetry Total Lung Volume (TLV), ml 5234±1468 5203±1852 Emphysema Volume (EV), ml 157±303 301±302 Emphysema Index (EI), % 7 ± 7 7 ± 7 Air Trapping (AT), % 58 ± 13 61 ± 9 EV=% of low-attenuation areas≤-950 HU on inspiratory CT; EI=EV/TLV; AT=% of low-attenuation areas≤-856 HU on expiratory CT. * p<0.05 . Conclusions: In the present sample, quantitative CT measurements were insensitive to detect DH in patients with moderate COPD.