Correlation between heart rate variability and polysomnography‐derived scores of severities for obstructive sleep apnea

Abstract

Obstructive sleep apnea (OSA) is one of the most common sleep disorders and affects nearly a billion people worldwide. Furthermore, it is estimated that many patients with OSA are underdiagnosed, which contributes to the development of comorbidities, such as cardiac autonomic imbalance, leading to high cardiac risk. Heart rate variability (HRV) is a non‐invasive, widely used approach to evaluate neural control of the heart. This study aims to seek the relationship between HRV indices and the presence and severity of OSA. Polysomnography (PSG) exams of 157 patients were classified into four groups: OSA‐free (N=26), mild (N=39), moderate (N=37), and severe OSA (N=55). The electrocardiogram was extracted from the PSG, and a 15‐min beat‐by‐beat series of RR intervals was generated every hour during the first 6 h of sleep. Linear and nonlinear HRV approaches were employed to calculate a variety of indices of HRV. Specifically, time‐ and frequency‐domain, symbolic analysis, entropy measures, heart rate fragmentation, acceleration and deceleration capacities, asymmetry measures, and fractal analysis (detrended fluctuation analysis). Results with indices of sympathovagal balance reinforced previous findings that patients with OSA have sympathetic overactivity. Nonlinear indices showed that these patients suffer from a loss of physiologic complexity, contributing to their higher risk of development of cardiovascular disease. Moreover, as shown in the table below, many HRV indices presented statistically significant correlation with PSG's clinical scores: apnea/hypopnea index (AHI), microarousal index (MI), percentage of the total sleep time that the patient was with oxygen saturation below 90% (T90), and oxygen saturation nadir during sleep (SatMin). Therefore, a complete set of HRV indices, especially the nonlinear ones, can bring valuable information about the presence and severity of OSA, suggesting that HRV can be helpful in a quick diagnosis of OSA, potentially reducing the development of comorbidities.