Cardiopulmonary Exercise Testing and Pulmonary Function for Assessing Chronic Obstructive Pulmonary Disease

Purpose: To compare the grading concordance between pulmonary function tests (PFTs) and cardiopulmonary exercise testing (CPET) in grading chronic obstructive pulmonary disease (COPD) and to guide the clinical application of CPET in appropriate patient populations. Patients and Methods: A retrospective analysis was conducted on 152 patients with COPD who underwent PFT, CPET, the 6-minute walking test (6MWT), and body composition assessment. COPD was graded using forced expiratory volume in 1 second as a percentage of the predicted value (FEV 1 %pred) and Peak Oxygen Uptake per Kilogram of Body Weight (PeakVO 2 /kg), respectively. Grading discordance between the two systems was assessed, and clinical characteristics of patients with a higher disease severity grade on CPET were analyzed. Results: Agreement between GOLD and peakVO 2 /kg-based CPET grading was slight (linear weighted Kappa = 0.182, 95% CI: 0.087– 0.277; P < 0.001), with exact grade concordance observed in 47 of 152 patients (30.9%). Overall, 92 patients (60.5%) were assigned a more severe grade by peakVO 2 /kg-based CPET grading than by GOLD. Upward reclassification occurred in 49 of 67 patients with GOLD Mild disease (73.1%) and 41 of 62 patients with GOLD Moderate disease (66.1%). Compared with the non-upgraded group, patients in the CPET-upgraded group were older, had higher BMI, body fat percentage, and fat mass, and were more likely to have cardiovascular comorbidity (all P < 0.05). In partial correlation analyses adjusted for age, sex, and height, peakVO 2 /kg was negatively correlated with fat mass (r = − 0.287, P = 0.002), whereas peakVO 2 %pred was not (r = 0.041, P = 0.657), indicating that the observed discordance was partly related to the body-weight normalization inherent to peakVO 2 /kg. Conclusion: Discordance between GOLD and peakVO 2 /kg-based CPET grading was common, particularly in patients with mild-to-moderate airflow obstruction, and was associated with age, adiposity, and cardiovascular comorbidity. CPET may provide physiological information complementary to spirometry; however, because peakVO 2 /kg-based grading is influenced by adiposity, a more severe CPET grade in overweight or obese patients should not necessarily be interpreted as indicating intrinsically greater cardiopulmonary impairment. PeakVO 2 %pred, body composition, and other clinical and physiological findings should be considered alongside peakVO 2 /kg when interpreting CPET results.