Correlation between cardiorespiratory coupling and six-minute walking tests in patients with chronic obstructive pulmonary disease

Background: Cardiovascular disease is a common comorbidity and cause of mortality among patients with chronic obstructive pulmonary disease (COPD). However, the interaction between the heart and lungs in COPD patients has yet to be fully elucidated. Aim: Our objective in this study was to characterize cardiorespiratory interactions in terms of cardiorespiratory coupling (CRC) using the synchrogram index of the heart rate and respiration flow signals. Methods: This prospective study examined 10 normal subjects and 55 COPD patients. Linear regression and forward stepwise regression were used to determine the correlation between the synchrogram index and the six-minute walking test. Results: K-means clustering analysis was used to separate the 55 COPD patients into a synchronized group (median 0.89 (0.64-0.97), n=43) and a desynchronized group (median 0.23 (0.02-0.51), n=12) based on the synchrogram index. In this study, the synchrogram index was significantly correlated with the six-minute walking distance (r2=0.3, sigma T=0.02) and the distance saturation product (r2=0.3, sigma T =0.03). Note that age was a significant confounding factor. Conclusion: The synchrogram index shows clinical potential for the stratification of COPD patients for treatment.