Examining the association between the low-to-high-frequency ratio and impedance derived measures of cardiac autonomic balance and regulation
Copyright 2016, ISA All Rights Reserved. Autonomic balance refers to the relative equilibrium between the parasympathetic (PNS) and sympathetic (SNS) branches of the autonomic nervous system (ANS) in the optimal regulation of physiological function, including heart rate. Conversely, autonomic imbalance is characterized as hypoactive PNS and hyperactive SNS activity, and there is significant clinical interest in this pattern given its strong association with multiple disease states, including cardiovascular and all-cause mortality. It has been theorized that the low-to-high frequency (LF/HF) spectral power ratio of heart rate variability (HRV) can be used as a relative index of autonomic (im)balance. However, continuing debate over the validity of the low frequency (LF) component of HRV, as an index of SNS activity, calls into question this putative function of the LF/HF ratio. Researchers have previously described a quantitative model of Cardiac Autonomic Regulation (CAR), representing the degree of SNS and PNS co-activation, and Cardiac Autonomic Balance (CAB), representing the propensity toward dominance of either the SNS or PNS. The present study examined the direct association between LF/HF ratio and CAB/CAR, under resting-baseline (tonic) conditions, in a sample of 50 apparently healthy participants (78% female, mean age = 18.80 years). CAR and CAB scores were determined using established formulae, and measures of HRV were derived using standard spectral analytic techniques. Greater CAR scores reflect greater activity of both the PNS and SNS, whereas both greater CAB scores and lower LF/HF ratios reflect greater PNS activity relative to SNS activity. Results showed the LF/HF ratio to be significantly related (moderate to strong) to both CAB and CAR (each p < .05). Additionally, Bland-Altman plots showed good agreement between the LF/HF ratio and both CAB and CAR scores, with at least 94% of the sample falling within the limits of agreement. While the exact nature of LF-HRV component remains controversial, the present data indicate that in a resting state, the LF/HF ratio is indeed related to and may serve as a useful proxy of autonomic balance. These findings suggest that research using the LF/HF ratio as a surrogate index of ANS balance and regulation may indeed be appropriate, especially in settings where assessing SNS activity (e.g., impedance cardiograph) may be difficult.
Williams, DWP; Hill, LBK; Koenig, J; Thayer, JF
Proceedings of the 53rd Annual Rocky Mountain Bioengineering Symposium, Rmbs 2016 and 53rd International Isa Biomedical Sciences Instrumentation Symposium
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International Standard Book Number 13 (ISBN-13)