Content
1.ANS related features, extracted from ECG
1.1. Heart Rate Variability Analysis (HRV)
1.2. SKNA
1. ANS related features, extracted from ECG
A heart rate (HR) that is complex and constantly changing is a sign of healthy regulatory systems that can effectively adapt to environmental and psychological challenges [1]. Rapid fluctuations in HR reflect the autonomic nervous system’s (ANS) cardiac regulatory impacts, likewise its dynamic interaction with cardiovascular and respiratory functions [2]. The Autonomic Nervous System (ANS) is in charge of involuntary bodily functions including heart rate and its fluctuations around the mean value. The ANS is divided into two components, the sympathetic (SNS), and the parasympathetic nervous system (PNS), both provide sensory input and motor output to the Central Nervous System (CNS).
The SNS activation leads to a state of overall elevated activity and attention, so-called the “fight and flight” response, in which blood pressure and heart rate increases and the PNS promotes the “rest and digest” state which causes lower heart rate [3].
We can extract two features from ECG that represent the ANS state; HRV and SKNA, which are mentioned below.
Heart Rate Variability (HRV) is assessed by calculating changes of time interval between two QRS complexes.
Additionally, Skin Sympathetic Nerve Activity (SKNA) is another index of ECG, extracted from high frequency components and directly records sympathetic nervous terminals activity of torso reflected on the skin. Being one of the most imperative indicators of ANS activity, SKNA can be extracted from 500-1000 Hz frequency range of ECG, where is not related to cardiac waves components [3].
1.1. Heart Rate Variability Analysis (HRV)
The physiological phenomenon of fluctuation in the time interval between successive heartbeats in milliseconds is known as heart rate variability, or HRV. A typical, healthy heart does not beat uniformly like a metronome; instead, there is continual variance in the milliseconds between heartbeats.
HRV is a non-invasive index of autonomic nervous system activity that is regulated by the autonomic nervous system (ANS) and its sympathetic and parasympathetic branches. The sympathetic branch of the ANS controls the stress or fight or flight response, preparing us to act, react, and perform in response to the various demands that life places on us.
The parasympathetic side is the rest and digest system, which helps the body to relax and heal “once the struggle is over.” The sympathetic branch increases the heart’s contraction rate and force (cardiac output) while decreasing HRV, which is necessary during exercise and psychologically or physically stressful conditions. After the tension has passed, the parasympathetic branch decreases the heart rate and boosts HRV to restore homeostasis. The heart can respond swiftly to stimuli because of the inherent interaction between the two systems.
Higher HRV has been linked to lower morbidity and mortality [4], as well as better psychological well-being and quality of life [5].
1.2. SKNA
The relationship between the heart and brain is through the autonomic nervous system (ANS). One of the most significant biomarkers to monitor neurocardiology is SKNA, a novel way to evaluate the real-time sympathetic nervous system (SNS) activity noninvasively. Having an amplitude of 0.5-100 µV [6] or mostly 60 µV [7]. SKNA is morphologically correlated with heart rate acceleration and precedes the onsets of cardiac arrhythmia research related to cardiac nerve function including ventricular arrhythmia. SKNA, ECG, and heart rate can be illustrated in a single time axis, and the disturbance of SKNA can be analyzed with the fluctuation of heart rate, providing a clear view of ANS controlling the heart rhythm. Also, the frequency and amplitude of SKNA can be used as a sign to track the effects of interventions and even Sleep quality assessment [6]. SNS should be triggered under certain experiments such as Coldwater pressor test (CPT) and Valsalva maneuver. SKNA significantly increased during the CPT and Valsalva maneuver and then reduced significantly during recovery [8]. Besides these two common ways, another research conducted the SKNA recording invasively during sputum suctioning for patients in ICU [6]. In general, CPT, Valsalva maneuver, startling, loud noise and exercise can increase average amplitude of SKNA and burst area [3].
References
[1] T. Pham, Z. J. Lau, S. Chen, and D. Makowski, “Heart Rate Variability in Psychology: A Review of HRV Indices and an Analysis Tutorial,” Sensors, vol. 21, no. 12, p. 3998, 2021.
[2] T. Ziemssen and T. Siepmann, “The Investigation of the Cardiovascular and Sudomotor Autonomic Nervous System—A Review,” (in English), Frontiers in Neurology, Review vol. 10, no. 53, 2019-February-12 2019.
[3] T. Kusayama et al., “Simultaneous noninvasive recording of electrocardiogram and skin sympathetic nerve activity (neuECG),” Nature protocols, vol. 15, no. 5, pp. 1853-1877, 2020.
[4] J. T. Bigger, J. L. Fleiss, L. M. Rolnitzky, and R. C. Steinman, “The ability of several short-term measures of RR variability to predict mortality after myocardial infarction,” (in eng), Circulation, vol. 88, no. 3, pp. 927-34, Sep 1993.
[5] J. F. Thayer, A. L. Hansen, E. Saus-Rose, and B. H. Johnsen, “Heart Rate Variability, Prefrontal Neural Function, and Cognitive Performance: The Neurovisceral Integration Perspective on Self-regulation, Adaptation, and Health,” Annals of Behavioral Medicine, vol. 37, no. 2, pp. 141-153, 2009.
[6] Y. Xing et al., “A Portable NeuECG Monitoring System for Cardiac Sympathetic Nerve Activity Assessment,” in 2020 International Conference on Sensing, Measurement & Data Analytics in the era of Artificial Intelligence (ICSMD), 2020, pp. 407-412: IEEE.
[7] X. Liu et al., “Using an ambulatory electrocardiogram monitor to record skin sympathetic nerve activity,” Heart Rhythm, 2021.
[8] C. Liu and J. Li, Feature Engineering and Computational Intelligence in ECG Monitoring. Springer, 2020.
