Effect of ventilatory inefficiency over exercise capacity in COPD patients with hyperinflation

Abstract

Background: we demonstrated the influence of Ventilatory inefficiency (increased VE/VCO2) as an independent mechanism in reducing exercise capacity in COPD (Resp Care 2012; 57: 583 – 589) Purpose: to show that Ventilatory inefficiency reduces exercise capacity in COPD patients with hyperinflation, by a different pathophysiological way. Methods: 28 COPD patients with hyperinflation were studied, with a mean of age, FEV1/CVF, FEV1 and DLCO of 64.8, 53.9%, 69.5% and 49.7% respectively. Cardiopulmonary stress tests were performed measuring Power (W), Oxygen consumption (VO2), Ventilatory efficiency (VE/VCO2), reduction on Inspiratory Capacity (ΔIC) and breathing reserve (BR). Influence of VE/VCO2 and ΔIC over VO2 and W were determined by regressions. Also models of multiple regressions between VE/VCO2, ΔIC and DLCO over response variables VO2 and W were calculated. Results: patients ended the test with dyspnea and leg fatigue (mean Borg of 4.9 and 4.6) with reduced VO2, W and BR (mean 72.9%, 66.1% and 15% respectively). Hyperinflation (mean ΔIC of 0.57 L) and Ventilatory inefficiency (VE/VCO2 mean 39.2) were detected. Inverse correlations between Ventilatory inefficiency over VO2 and W were demonstrated (r 0.48 and 0.47 with p 0.021 and 0.032), with no correlation between hyperinflation and them. Multiple regressions with ΔIC, VE/VCO2 and DLCO confirmed the independent influence of Ventilatory inefficiency over VO2 and W (r 0.72 and 0.64 with p 0.023 and 0.018). Conclusions: Ventilatory inefficiency is a different and independent parameter tampered during exercise in COPD patients with hyperinflation, indicating a different pathophysiological way to influence exercise capacity.