Background: Exercise intolerance is an integral component of chronic obstructive pulmonary disease (COPD) and coronary heart disease (CHD) and is caused by several mechanisms that ultimately impact overall functional capacity. We assessed various components of exercise function in patients with CHD and COPD during the course of cardiac and pulmonary rehabilitation to evaluate changes unique to each condition.
Methods: Work efficiency (WEf, defined as delta watts/delta VO2) and peak VO2 were measured and compared at baseline and after 3 months (36 sessions) of outpatient cardiac and pulmonary rehabilitation programs in 25 patients (mean age = 66 +/- 7 years) with severe COPD (mean FEV1.0 = 0.90 +/- 0.35 L) and in 25 patients (mean age = 65 +/- 8 years) with CHD.
Results: At baseline, patients with COPD had significantly reduced values of WEf (2.04 +/- 0.86 versus 3.23 +/- 1.38 watts/mL/kg/min; P = 0.004) and peak VO2 (13.2 +/- 3.9 versus 17.1 +/- 3.9 mL/kg/min; P = 0.005) compared with patients with CHD. After rehabilitation, patients with CHD increased peak VO2 by 12% (17.1 +/- 3.9 to 19.1 +/- 4.9 mL/kg/min; P = 0.01) with no change in WEf (3.23 +/- 1.38 to 3.32 +/- 1.43 watts/mL/kg/min; P = not significant). In contrast, patients with COPD increased peak VO2 by only 5% (13.2 +/- 3.9 to 13.9 +/- 3.8 mL/kg/min; P = 0.0008), but WEf increased by 36% (2.04 +/- 0.86 to 2.78 +/- 0.84 watts/mL/kg/min; P = 0.0002). Subjective measures of functional status improved similarly in both groups.
Conclusions: In contrast to patients with CHD, work inefficiency contributes significantly to exercise intolerance in patients with severe COPD. Outpatient rehabilitation programs enhance functional status in patients with CHD and COPD by differing mechanisms, depending on the underlying disease. These data show the disparate effects of out-patient rehabilitation on peak VO2 and WEf in cardiac and pulmonary patients.