Background: Although comorbidites of cardiovascular disease is common in patients with chronic obstructive pulmonary disease (COPD), the interaction between the heart and lungs in COPD patients has yet to be further elucidated. Synchrogram index is a new parameter that can quantify this interaction and has the potential to apply in COPD patients.
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 respiratory flow signals in patients with chronic obstructive pulmonary disease.
Methods: This is a cross-sectional and a preliminary data from a prospective study, examining 55 COPD patients. K-means clustering analysis was applied to cluster COPD patients based on synchrogram index. Linear regression and multivariable regression analysis were used to determine the correlation between the synchrogram index and the exercise capacity assessed by six-minute walking test (6MWT).
Results: The 55 COPD patients were separated 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 K-means clustering analysis. Synchrogram index was correlated significantly with six minutes walking distance (r=0.42, p=0.001) and distance saturation product (r= 0.41, p=0.001) assessed by 6MWT, and still was an independent variable by multivariable regression analysis.
Conclusion: This is the first result studying the heart-lung interaction in terms of cardiorespiratory coupling in COPD patients by the synchrogram index, and COPD patients are clustered into synchronized and desynchronized groups. Cardiorespiratory coupling is associated with exercise capacity in patients with COPD.