Abstract
Background: Cardiovascular diseases associated with chronic obstructive pulmonary disease (COPD) account for 50% of COPD deaths. Autonomic dysfunction and poor pulmonary function increase the cardiovascular risk in COPD patients. Severity of COPD can be assessed by forced expiratory volume in 1 s. Autonomic balance can be assessed by heart rate variability (HRV). There are variations in the reports of COPD patients regarding the level or onset of dysfunction is a sympathetic or parasympathetic system in them.

Aims and Objectives: In our study, we intended to assess HRV parameters such as, total power (TP), high frequency normalized units (HFnu), low frequency normalized units (LFnu), LF/HF ratio, mean HR, root mean square of the successive differences (RMSSD), NN50, and pNN50 among different stages of COPD and also to identify the association of these HRV parameters with disease severity.

Materials and Methods: It is a cross-sectional study done on (n = 130) male stable COPD patients. Anthropometric parameters, HRV parameters, and pulmonary function test were assessed. Later, based on the Global Initiative for Chronic Obstructive Lung Disease stage criteria (mild, moderate, severe, and very severe), they were divided into four subgroups. Data were analyzed by SPSS 19.0 version software. Kruskal–Wallis test was used to find a statistical difference between the groups. Correlations between the variables were done using Spearman correlation test.

Results: LF/HF ratio (2 ± 0.5) was increased when compared to reference value reported by the previous studies. TP, HFnu, and RMSSD levels were significantly decreased in very severe, severe, and moderate COPD patients when compared to mild COPD patients. The mean HR, LFnu, and LF/HF ratio levels were significantly increased in very severe, severe, and moderate COPD patients when compared to mild COPD patients. TP, HFnu, and RMSSD levels negatively correlated with disease severity and mean HR, LFnu, and LF/HF ratio positively correlated with disease severity.

Conclusion: We have noted that cardiac autonomic dysfunction in the form of increased sympathetic and reduced parasympathetic activity occurs in COPD patients and the association was more prominent when the disease severity increased.

Key words: Chronic Obstructive Pulmonary Disease; Cardiovascular Risk; Forced Expiratory Volume in 1 s; Heart Rate Variability; Sympathovagal Balance