The role of phenotype on ventilation and exercise capacity in patients affected by COPD: a retrospective study

BACKGROUND: The idea of phenotype in chronic obstructive pulmonary disease (COPD) has evolved in the last decades, and the importance of peculiar treatment strategies has now been acknowledged. Although dyspnea and exercise limitation are hallmarks of COPD, this aspect has never been fully explored in literature in terms of disease phenotype. The aim of the present study was to explore the relevance of clinical COPD phenotypes on exercise ventilation and maximal capacity. METHODS: In this observational cohort retrospective study we analyzed the data of 50 COPD patients who underwent cardiopulmonary exercise test, categorized as emphysematous (n=29), and non-emphysematous (n=21) according to a previously validated model. RESULTS: We found a significant difference in terms of VE/VCO(2) slope (median values 32.4 vs 28.0, p=0.015) and VE/VCO(2) ratio at nadir (median values 37 vs. 33, p=0.004), which resulted higher in emphysematous patients, who also presented lower P(ET)CO(2) values (median values 32.6 vs 35.6, p=0.008). In a subgroup of 31 tests which met the maximality criteria, emphysematous patients presented a significantly lower work rate at peak (median value 51 vs 72% predicted, p=0.016), and showed a lower peak oxygen consumption, although at the limit of significance (median values of 63 vs 85 % predicted, p=0.051). CONCLUSIONS: This study extends our knowledge about the characterization of the COPD phenotypical expression of disease, showing that patients affected by emphysema are more prone to ventilatory inefficiency during exercise, and that this is likely to be an important cause of their overall reduced exercise capacity.