Determinants of dynamic hyperinflation during metronome-paced tachypnea in COPD and normal subjects

•MPT is a simple, reproducible test that elicits dynamic hyperinflation (DH) in COPD.•Expiratory time is the main determinant of DH during MPT in subjects with COPD.•DH can also be induced during MPT in normal subjects but to a lesser degree.•DH in normal subjects correlates with end-tidal CO2, not expiratory time.

In COPD, dynamic hyperinflation (DH) occurs during exercise and during metronome-paced tachypnea (MPT). We investigated the relationship of DH with breathing pattern and ventilation (V˙E) in COPD and normal subjects (NS).In 35 subjects with moderate COPD and 17 younger healthy volunteers we measured inspiratory capacity (IC), breathing frequency (fR), expiratory time (TE), ventilation (V˙E) and end-tidal carbon dioxide tension (PETCO2) at baseline and after 30 s of MPT at 40 breaths/min with metronome-defined I:E ratios of 1:1 and 1:2. A reduction in IC (ΔIC) was taken to indicate DH. In COPD subjects, DH correlated with TE but not with V˙E or PETCO2, and was best predicted by total lung capacity. NS also showed DH (although less than in COPD), which correlated with PETCO2 but not with fR, TE or V˙E.We conclude that MPT evokes DH in both NS and patients with COPD. TE is the most important determinant of DH during MPT in patients with COPD.