Investigation of Heart Rate Variability using Wavelet Packet Transform in Major Depressive Disorder

Abstract

Depression is a common mood disorder that is characterized by impairment of mood regulation, and loss of interest in enjoyable activities. According to the previous studies, it has been reported that this disorder is related with elevated rates of cardiovascular morbidity and mortality. Therefore, as an important indicator for diagnosis and classification of cardiac dysfunctions, heart rate variability (HRV) has been widely used in depression. Differ from the previous studies in this field, wavelet packet transform (WPT) is used for determination of effective very low frequency (VLF), low frequency (LF), and high frequency (HF) bands in HRV signals of depressed patients in this study. Twenty patients who met the DSM-IV criteria for major depressive disorder and age, gender-matched twenty healthy controls were participated for this study. HRV data of these participants were first were recorded using the Brainamp ExG data acquisition system and then decomposed into sub-bands including VLF, LF, HF using WPT with 9 level Daubechies (db4) family and variations of energy in these bands were analyzed in MATLAB. The HRV measures as each sub-band average energy and sympathovagal balance (LF/HF ratio) were compared statistically between patients and controls. The results of this study indicates that especially the mean energy values of sub-frequency ranges in VLF band for each participant are higher than that the values of other bands as LF and HF. In addition, the mean energy values of the regions in LF band of control subjects are significantly lower than the same measure of patients. In contrast, in comparison with control subjects, patients with major depression exhibited low HF band energy. Finally, results indicate that sympathovagal balance that reflects the equilibrium between sympathetic and parasympathetic activity of the autonomic nervous system in patients was higher than that of control subjects indicating autonomic dysfunction throughout the entire experiment. It can be conclude that low cardiovagal activity in patients with major depression may contribute to the higher cardiac dysregulations of these patients.