Analysis of Heart Rate variability (HRV) in Frequency Domain and Recurrence Quantification Analysis during the Treatment by Transcutaneous Vagus Nerve Stimulation

The aim of the present work has a methodological profile. It aims to analyze the HRV during thirty minutes transcutaneous Vagus Nerve Stimulation tVNS treatment. We used the linear methodology of the Fast Fourier Transform and an analysis of the variability of the R-R signal in frequency domain under such conditions of stimulation. As specialized method of analysis we used also the Recurrence Quantification Analysis (RQA). The importance to use a combination of such linear and non linear methodologies was to give results of physiological interest that is to say to ascertain, as well as possible, the influence of such tVNS treatment on HRV. We examined 50 young subjects in normal health conditions and 50 young subjects with Autonomic Nervous Dysfunction (ANS) as well as it is evidenced by HRV. The experiments were arranged in three phases, recording the data before, during, and after a 30-minute treatment. The analysis of the data was performed in the frequency domain evaluating the VLF, the LF, and the HF and the variability of the tachogram according to the 1996 Task Force Standards of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. In addition the Recurrence Quantification Analysis (RQA) was used. The indication arising from such methodological study is that the unbalanced initial ANS dysfunction of the examined subjects, as mirrored from the HRV analysis, compensates and balances with also a prevailing tendency to parasympathetic HRV modulation during the tVNS treatment.