Resolving Ambiguities in the LF/HF Ratio: LF-HF Scatter Plots for the Categorization of Mental and Physical Stress from HRV

Abstract

It is generally accepted that the activities of the autonomic nervous system (ANS), which consists of the sympathetic (SNS) and parasympathetic nervous systems (PNS), are reflected in the low- (LF) and high-frequency (HF) bands in heart rate variability (HRV)—while, not without some controversy, the ratio of the powers in those frequency bands, the so called LF-HF ratio (LF/HF), has been used to quantify the degree of sympathovagal balance. Indeed, recent studies demonstrate that, in general: (i) sympathovagal balance cannot be accurately measured via the ratio of the LF- and HF- power bands; and (ii) the correspondence between the LF/HF ratio and the psychological and physiological state of a person is not unique. Since the standard LF/HF ratio provides only a single degree of freedom for the analysis of this 2D phenomenon, we propose a joint treatment of the LF and HF powers in HRV within a two-dimensional representation framework, thus providing the required degrees of freedom. By virtue of the proposed 2D representation, the restrictive assumption of the linear dependence between the activity of the autonomic nervous system (ANS) and the LF-HF frequency band powers is demonstrated to become unnecessary. The proposed analysis framework also opens up completely new possibilities for a more comprehensive and rigorous examination of HRV in relation to physical and mental states of an individual, and makes possible the categorization of different stress states based on HRV. In addition, based on instantaneous amplitudes of Hilbert-transformed LF- and HF-bands, a novel approach to estimate the markers of stress in HRV is proposed and is shown to improve the robustness to artifacts and irregularities, critical issues in real-world recordings. The proposed approach for resolving the ambiguities in the standard LF/HF-ratio analyses is verified over a number of real-world stress-invoking scenarios.

Can Wearable Devices Accurately Measure Heart Rate Variability? A Systematic Review

“…31 In addition, heart rate and HRV analysis have been used for estimation of mental stress and athlete's fi tness levels, fatigue and overload. 5 The quantifi cation of ANS function is feasible by calculating several HRV parameters according to time-domain, frequency-domain and nonlinear analysis of consecutive RR intervals. 1 These indices represent different components of the sympathetic and/or parasympathetic system of the ANS.…”

“…Decreased HRV has been reported as a predictive factor for adverse outcomes in disease states and has been found to be associated with fatigue, stress, and even burnout during athletic performance. [3][4][5] High HRV is an indication of a better general health status as it allows better adjustment to external and internal stimuli. 6 Due to the fact that traditional HRV recording methods, such as using electrocardiography (ECG) and specialized software, often involve expensive equipment, which is primarily found in research laboratories, alternative methods have been used, yet, with variable results.…”

Prognostic Accuracy of Heart Rate Variability Analysis in Neonatal Encephalopathy: A Systematic Review

“…HRV analysis quantifies variations in heartbeat intervals, offering a non-invasive measure of autonomic function, as it reflects the actions of the sympathetic and parasympathetic nervous systems. The simplest measure of HRV is determined by the standard deviation of the difference between consecutive RR intervals (SDNN), but many other measures of HRV continue to be developed [6, 7]. Currently, HRV analyses can include not only linear measures in time and frequency domains but also several non-linear metrics derived from complexity analysis [8].…”

The Female Heart: Sex Differences in the Dynamics of ECG in Response to Stress

“…The controversy surrounding this conjecture was highlighted in several studies where the effects of mental stress on the LF and HF components of HRV were found to be neither consistent, nor correlate with the trends seen in physical stress (Berntson et al, 1994). However, despite the uncertainty over the physiological interpretatio ns of the LF and HF components, and whether or not they respectively represent the activities of the SNS and PNS (Berntson et al (1994), Eckberg (1997), Berntson and Cacioppo (2004), Billman (2013) and von Rosenberg et al (2017)), it comes as a surprise that until recently, the theories regarding the relationships between stress, HR and HRV were developed without accounting for, or appreciating sex differences. To this end, this work aims to quantify and demystify the effects of sex differences on the dynamics of ECG, in a proof-of-concept study based on ECG recordings from participants who have been subjected to a mental stressor.…”