Sympathovagal Imbalance in Drug-Naïve Chronic Obstructive Pulmonary Disease Patients: A Physiological Mechanism to Cope With the Severity of Airway Obstruction in an Observational Study.

INTRODUCTION: In the modern world, chronic obstructive pulmonary disease (COPD) is known to affect a large subset of the middle-aged and elderly adult population, primarily due to the increasing prevalence of smoking addiction, indoor air pollution, and poor air quality index in metropolitan cities. We hypothesize that, in an attempt to cope with this respiratory distress, the body reacts with an overdriven sympathetic discharge, which helps maintain pulmonary airway patency and causes sympathovagal imbalance. Heart rate variability (HRV) is a neurophysiological test used to assess sympathovagal balance. A higher HRV signifies normal parasympathetic dominance. The low-frequency-to-high-frequency (LF/HF) ratio is a parameter of HRV that is directly correlated with sympathovagal balance and inversely correlated with HRV. The objective of our study was to compare the sympathovagal balance between COPD patients (cases) and healthy subjects (controls) and find a correlation between sympathovagal balance and spirometry parameters in both cases and controls. METHODOLOGY: A group of 72 drug-naïve COPD patients (diagnosed according to GOLD criteria) were included as cases, and 72 age- and sex-matched, apparently healthy individuals were enrolled as controls in this case-control study. Their spirometry was performed, and the percentage of expected forced expiratory volume in the first second (% FEV1), percentage of expected forced vital capacity (% FVC), and percentage of expected forced expiratory volume in the first second-to-forced vital capacity ratio (% FEV1/FVC ratio) were determined and recorded. Their sympathovagal balance was assessed using the low-frequency-to-high-frequency (LF/HF) ratio of the frequency domain of HRV. Data analysis was performed using SPSS, version 26 (IBM Corp., Armonk, NY). Metric data were represented as numerical values and analyzed as mean ± standard deviation. Student's t-test was used to compare the LF/HF ratio between the two groups, and Pearson's correlation coefficient was used to correlate the LF/HF ratio with spirometry data. A P-value <0.05 was considered statistically significant. RESULTS: Cases had a significantly higher LF/HF ratio than controls (1.34 ± 0.45 vs 1.048 ± 0.56; t = 3.38, P = 0.0007). Among cases, the LF/HF ratio showed a statistically significant inverse correlation with % FEV1 (r = -0.772, P < 0.0001) and % FVC (r = -0.583, P < 0.0001). However, its correlation with % FEV1/FVC was not statistically significant (r = -0.133, P = 0.268). Among controls, the LF/HF ratio showed a statistically significant inverse correlation with % FEV1 (r = -0.499, P < 0.0001), % FVC (r = -0.462, P < 0.0001), and % FEV1/FVC (r = -0.354, P = 0.0023). CONCLUSIONS: Drug-naïve COPD patients have significantly higher sympathovagal dominance in comparison to the apparently healthy control population. Their sympathovagal dominance is inversely correlated with their spirometry parameters. In the control population, sympathovagal dominance is also inversely correlated with spirometry parameters; however, to a lesser extent. This implies that greater sympathovagal dominance is produced to combat an increasing degree of airway obstruction.