Effect of combivent on dynamic hyperinflation induced by metronome paced tachypnea in a patients with moderate COPD

Rationale In patients with COPD, dynamic hyperinflation occurs with increased breathing frequency due to increased airway resistance and reduced lung elastic recoil (Weigt SS et al. J COPD 2008; 5(5): 298-304). Bronchodilator therapy alleviates dynamic hyperinflation during exercise and should therefore impact dynamic hyperinflation during metronome paced tachypnea. Methods We recruited 24 patients with moderate COPD (16 men). Their mean (SD) age was 61 (8) years, FEV1/FVC 53 (9) % and FEV1 60 (9) %. Body plethysmography demonstrated resting (static) hyperinflation: TLC 110 (19) %, FRC 129 (30) % and 169 (40) %. Transfer coefficient was mildly reduced at 76 (21) %. Each subject was randomized to receive Combivent or identical placebo inhaler in a crossover study design, necessitating two further visits. Subjects performed baseline measures of inspiratory capacity and breathing pattern followed by metronome paced tachypnea at 30 and 40 /min for 30 seconds. The pacemaker imposed an I:E ration of 1:1 or 1:2, also in random sequence. Inspiratory capacity (IC) was measured every 30 seconds and a fall in IC was judged to represent DH. Results The table shows changes in inspiratory capacity from baseline for each condition of metronome paced tachypnea. Values are in mean (SEM) ml. All changes are highly significant (P<0.0001). (Table presented) Conclusion Metronome paced tachypnea with various controlled breathing patterns consistently elicited dynamic hyperinflation which was greater at higher breathing frequency and with higher I:E ratio (shorter exhalation time). Dynamic hyperinflation was consistently less with Combivent compared to placebo. Although not statistically significant these changes are perhaps clinically meaningful in the context of increased breathing frequency in COPD.