Phenotyping Cardiopulmonary Exercise Limitations in Chronic Obstructive Pulmonary Disease

BackgroundExercise limitation in chronic obstructive pulmonary disease (COPD) is commonly attributed to abnormal ventilatory mechanics and/or skeletal muscle function, while cardiovascular contributions remain relatively understudied. To date, the integrative exercise responses associated with different cardiopulmonary exercise limitation phenotypes in COPD have not been explored but may provide novel therapeutic utility. This study determined the ventilatory, cardiovascular, and metabolic responses to incremental exercise in patients with COPD with different exercise limitation phenotypes. MethodsPatients with COPD (n = 95, FEV1:23-113%pred) performed a pulmonary function test and incremental cardiopulmonary exercise test. Exercise limitation phenotypes were classified as: ventilatory [peak ventilation (V-Epeak)/maximal ventilatory capacity (MVC) >= 85% or MVC-V-Epeak <= 11 L/min, and peak heart rate (HRpeak) < 90%pred], cardiovascular (V-Epeak/MVC < 85% or MVC-V-Epeak > 11 L/min, and HRpeak >= 90%pred), or combined (V-Epeak/MVC >= 85% or MVC-V-Epeak <= 11 L/min, and HRpeak >= 90%pred). ResultsFEV(1) varied within phenotype: ventilatory (23-75%pred), combined (28-90%pred), and cardiovascular (68-113%pred). The cardiovascular phenotype had less static hyperinflation, a lower end-expiratory lung volume and larger tidal volume at peak exercise compared to both other phenotypes (p < 0.01 for all). The cardiovascular phenotype reached a higher V-Epeak (60.8 +/- 11.5 L/min vs. 45.3 +/- 15.5 L/min, p = 0.002), cardiopulmonary fitness (VO2peak: 20.6 +/- 4.0 ml/kg/min vs. 15.2 +/- 3.3 ml/kg/min, p < 0.001), and maximum workload (103 +/- 34 W vs. 72 +/- 27 W, p < 0.01) vs. the ventilatory phenotype, but was similar to the combined phenotype. ConclusionDistinct exercise limitation phenotypes were identified in COPD that were not solely dependent upon airflow limitation severity. Approximately 50% of patients reached maximal heart rate, indicating that peak cardiac output and convective O-2 delivery contributed to exercise limitation. Categorizing patients with COPD phenotypically may aid in optimizing exercise prescription for rehabilitative purposes.

Automated summary

This study investigated the integrative exercise responses associated with different exercise limitation phenotypes in COPD patients. The results showed that the cardiovascular phenotype had less static hyperinflation, lower end-expiratory lung volume, and larger tidal volume during exercise compared to other phenotypes. The cardiovascular phenotype also showed higher peak ventilation, cardiopulmonary fitness, and maximum workload compared to the ventilatory phenotype. Categorizing COPD patients phenotypically may aid in optimizing exercise prescription for rehabilitation purposes.