Ventilatory adaptation to eccentric cycling in moderate to severe COPD patients

Abstract

Backgroung In moderate to severe COPD patients, ventilation adaptation to metabolic demand during concentric exercise (CONC) is often limited by dynamic hyperinflation that impedes tidal volume (Vt) to increase. According to its low metabolic cost, eccentric exercise (ECC) could be an alternative to CONC with these patients.

Aims and objectives To compare ventilatory adaptation during CONC and EXC cycling in moderate to severe COPD patients.

Methods On 5 separate days, 13 patients (FEV1: 42±9% pred) performed a symptom-limited incremental CONC cycle exercise test followed by four 30-min sessions of constant-load ECC cycling. Load of ECC exercise was increased by 50% at each session. Vt, breath frequency (BF) and several physiologic parameters were compared at the maximal common minute ventilation (V'E) observed during CONC and ECC (iso-V'E).

Results Iso-V'E was 24.9±7.9 L.min^-1 duringECC and 24.9±7.8 L.min^-1 during CONC (61±21% of maximal estimated ventilation). The power outputs at isoV'E were 37±16 W and 104±18 W for CONC and ECC, respectively. At iso-V'E, Vt was 22% lower in ECC than in CONC (890±220 vs. 1080±320 mL; p=0.005) and BF was 24% higher (28.3±5.6 vs. 22.8±3.1 min^-1; p<0.001). However, heart rate (HR), oxygen consumption (V'O₂) and Borg dyspnoea score were similar in both conditions (HR: 95.4±13.1 vs. 95.4±12.5 min^-1; V'O₂: 0.74±0.23 vs. 0.77±0.26 L; Borg: 2.4±2.4 vs. 1.7±0.9 in ECC and CONC, respectively; p>0.05).

Conclusion At an identical V'E of about 60% of maximal estimated ventilation, patients with moderate to severe COPD have a 24% higher breathing frequency during ECC compared with CONC cycling. The mechanisms and consequences of this hyperpnoea deserve further studies.