Comparison of Respiratory and Circulatory Responses to 1-Leg, 2-Leg Knee Extension Exercise and Cycling in Patients with COPD

Background: The mass-specific work rates at which peripheral circulatory blood flow (BF) may become compromised in COPD due to a “respiratory steal” phenomenon was examined using one leg (1-leg KE), two-leg knee extension (2-leg KE) and cycling. Methods: Eleven COPD patients (age: 66 yr ± 8; FEV1= 45% predicted ± 14) did three steady states of cycling, 1-leg KE and 2-leg KE at 20, 40 and 65% of peak power (SS20%; SS40%; SS65%). Ventilation, VO2, arterial blood gas and dye dilution cardiac output were measured at rest and during exercise. Inspiratory capacity (IC) was used to monitor operating lung volume responses and determine dynamic hyperinflation. Results: Preliminary data show higher VO2 (L•min-1) during cycling than 1-leg KE and 2-leg KE (SS65% 1.0 ± 0.2 vs 0.5 ± 0.1 vs 0.6 ± 0.1). Despite the smaller muscle mass involvement of 1-leg KE, breathing frequency during SS65% was not different from that of cycling at SS65% (27 ± 5 vs 28 ± 5). During 1-leg KE, a plateau in tidal volume (0.8L ± 0.1) was achieved at SS20% while during cycling, tidal volume increased up to 1.4L ± 0.3 at SS65%. Similar falls in pH from baseline and similar PCO2 measures were seen with cycling (baseline: pH 7.43 ± 0.02; PaCO2 mmHg 39 ± 2 to SS65%: 7.38 ± 0.03; 40 ± 3) and 1-leg KE (baseline: pH 7.41 ± 0.03; PaCO2 mmHg 39 ± 2 to SS65%: 7.39 ± 0.02; 40 ± 3) although SaO2 was maintained with 1-leg KE, but not with cycling or 2-leg KE (95 to 93% at SS65%). IC (in % total lung capacity) was similarly reduced from baseline in 1-leg KE (30 ± 2 to 23 ± 3) and during cycling (30 ± 2 to 24 ± 3). Conclusion: These data suggest that ventilatory and gas exchange responses depend on the relative symptom-limited exercise intensity and not exercise modality.