Excess ventilation in COPD: Implications for dyspnoea and tolerance to interval exercise

Abstract

Interval exercise delays critical mechanical-ventilatory constraints with positive consequences on Dyspnoea and exercise tolerance in COPD. We hypothesized that those advantages of interval exercise would be partially off-set in patients showing excessive ventilation (V˙E) to metabolic demand (V˙CO2). Sixteen men (FEV1 = 42.3 ± 8.9%) performed, on different days, 30 s and 60 s bouts at 100% peak (on) interspersed by moderate exercise at 40% (off). Nine patients did not sustain exercise for 30 min irrespective of on duration. They presented with higher V˙E/V˙CO2 nadir (35 ± 3 vs. 30 ± 5) and dead space/tidal volume (0.39 ± 0.05 vs. 0.34 ± 0.06) compared to their counterparts (p < 0.05). [Lactate], operating lung volumes and symptom burden (dyspnoea and leg effort) were also higher (p < 0.05). Unloading off decreased the metabolic-ventilatory demands, thereby allowing 7/9 patients to exercise for 30 min. Increased wasted ventilation accelerates the rate at which critical mechanical constraints and limiting dyspnoea are reached during interval exercise in patients with COPD.