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RESPIRATORY MECHANICS AND OXYGEN UPTAKE (VO2) DURING EXERCISE IN PATIENTS WITH COPD AND CONTROL POPULATION: CHANGES OVER TIME

Caritas St. Elizabeth’s Medical Center, Boston, MA

PURPOSE: Exercise in patients with COPD can be limited by ventilatory and/or peripheral muscle dysfunction. Whether these limitations progress synchronously over time and how they compare to a control group is not known.

METHODS: We evaluated 30 COPD patients (FEV1 = 36(9)% predicted) and 50 controls (FEV1 = 94(16)% predicted) of similar ages, 63 (7) and 64(5) years, with spirometry, lung volumes and identical symptom limited cardio pulmonary exercise test (CPET) protocols on 3 different occasions over 3 years. CPET consisted of resting measurements, a 3 minute warm-up and an increasing load of 16 watts per minute. We measured dynamic hyperinflation using IC as a function of respiratory mechanics, dyspnea (visual analog scale) during exercise and O2 uptake (VO2) as an expression of peripheral muscle function. Paired t-test was used to compare the results between baseline and year three.

RESULTS: Over time, the patients’ static lung mechanics remained unchanged. In the COPD population: FEV1: 36(9)% predicted vs. 41(11)% predicted, p=0.09, TLC: 7.37(2.14)L vs. 7.37(1.69)L, p=0.98 and FRC: 5.35(1.85)L vs. 5.16(1.33)L, p=0.58. Similar changes were also noticed in the control group. There was no change in dynamic hyperinflation at isotime (3 min) in the 2 groups over three years: COPD: 1.67(0.46)L vs. 1.64(0.63)L, p=0.67), Control group: 2.60(0.9)L vs. 2.60(0.8)L, p=0.91.There was however a significant reduction in VO2 over the study period: COPD: 0.7469 (0.1729)L/min vs. 0.644 (0.1538)L/min, p= 0.006), Control group: 0.905 (0.2)L/min vs. 0.725(0.16)L/min, p<0.001).

CONCLUSION: This study demonstrates that the decline in peripheral muscle function during exercise is dissociated from the change in lung mechanics in patients with COPD over a three-year period.

CLINICAL IMPLICATIONS: Although the mechanism by which this occurs remains to be explored, our results suggest that therapy aimed at improving peripheral muscle function may improve patients, independent of changes in lung function.

DISCLOSURE: Harpreet Toor, None.