Effect of reduced body weight on muscle aerobic capacity in patients with COPD

Background: Reduced muscle aerobic capacity in COPD patients has been demonstrated in several laboratories by phosphorus magnetic resonance spectroscopy and by analysis of oxygen uptake ((V) over dot o(2)) kinetics, COPD patients are usually elderly, hypoxemic, poorly active with muscle atrophy, and often malnourished Under these conditions there is usually reduction of O-2 deliver to the tissues (bulk O-2 flow), redistribution of fiber type within the muscle, capillary rarefaction, and decreased mitochondrial function, alterations all capable of reducing muscle aerobic capacity, In COPD, the effect of reduced body mass on muscle aerobic capacity has not been investigated (to our knowledge), Methods: We studied 24 patients with stable COPD with moderate-to-severe airway obstruction (68+/-5 [SD] years; FEV1, 39+/-12% predicted; PaO2, 66+/-8 mm Hg; PaCO2, 41+/-3 mm Hg) with poor to normal nutritional status, as indicated by a low-normal percent of ideal body weight (IBW). Each subject first underwent 1-min maximal incremental cycle ergometer exercise for determination of (V) over dot o(2) peak and lactate threshold (LT), Subsequently, they performed a 10-min moderate (80% of LT-(V) over dot o(2)) constant load exercise for determination of oxy-gen deficit (O2DEF) and mean response time (V) over dot o(2) (MRT). (V) over dot o(2), CO2 output ((V) over dot co(2)), and minute ventilation were measured breath by breath, Results: Patients displayed low (V) over dot o(2) peak (1,094+/-47 [SE] mL/min), LT-(V) over dot o(2) (35+/-3% predicted (V) over dot o(2) max), and higher MRT-(V) over dot o(2) (67+/-4 s), Univariate regression analysis showed that percent of IBW correlated with indexes of maximal and submaximal aerobic capacity: vs (V) over dot o(2) peak, R=0.53 (p<0.01); vs MRT R=-0.77 (p<0.001). Using stepwise I egression analysis, MRT correlated (R-2=-0.70) with percent of IBW (p<0.01) and with PaO2 (p<0.05). Conclusions: Reduced body mass has an independent negative effect on muscle aerobic capacity in COPD patients: this effect may explain the variability in exercise tolerance among patients with comparable ventilatory limitation.