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

Abstract

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)over dot(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 (f(R)), expiratory time (T-E), ventilation ((V)over dot(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 (Delta IC) was taken to indicate DH. In COPD subjects, DH correlated with T-E but not with (V)over dot(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 f(R), T-E or (V)over dot(E). We conclude that MPT evokes DH in both NS and patients with COPD. T-E is the most important determinant of DH during MPT in patients with COPD.