Correlation of cardiopulmonary exercise testing parameters with quality of life in stable COPD patients

It has been estimated that the burden of chronic obstructive pulmonary disease (COPD) is increasing and it is likely to be the third global leading cause of death by 2030 (1,2). In addition to impact on survival, it is also well recognized that along with increasing severity, COPD has progressive adverse effects on daily symptoms, functional capacity, and health-related quality of life (3,4). Considering these unquestionable aspects of COPD, the patient reported daily symptoms and function status in assessment of the disease has been included in the new Global Initiative on Obstructive Lung Disease (GOLD) classification (5). Although more difficult to use than other tools such as COPD Assessment Test (CAT) or COPD Clinical Questionnaire (CCQ) during routine daily practice (6), the St. George’s Respiratory Questionnaire (SGRQ) is one of the most widely used self-complete measures in research for assessing patients’ symptoms, activities and quality of life (7,8). Along with this subjective measurement, functional capacity in COPD could be measured by objective tools such as cardio-pulmonary exercise testing (CPET) or 6-min walk distance (6MWD) (9-11). Considering the fact that at rest physiologic variable such as pulmonary diffusing capacity for carbon monoxide (DLCO), body mass index (BMI) or even forced expiratory volume in one second (FEV1) could not solely predict exercise intolerance, CPET has been proposed as the gold standard for evaluating the exercise intolerance in patients with pulmonary diseases, including COPD (12). But the precise head to head comparisons of CPET variable with patients’ daily symptoms/activities and the disease social/emotional impact are less well defined. In one study among 129 COPD subjects with GOLD stage II and III, there was at best a weak correlation between Peak-V’O2 (maximum oxygen uptake) % predicted and some sub-domains of health status (13). While in another study Peak-V’O2 was to some extent a predictor of physical function (r2 increased by 0.109) and health-related quality-of-life (r2 increased by 0.044) (14)