The utility of low frequency heart rate variability as an index of sympathetic cardiac tone: A review with emphasis on a reanalysis of previous studies

Abstract

This article evaluates the suitability of low frequency (LF) heart rate variability (HRV) as an index of sympathetic cardiac control and the LF/high frequency (HF) ratio as an index of autonomic balance. It includes a comprehensive literature review and a reanalysis of some previous studies on autonomic cardiovascular regulation. The following sources of evidence are addressed: effects of manipulations affecting sympathetic and vagal activity on HRV, predictions of group differences in cardiac autonomic regulation from HRV, relationships between HRV and other cardiac parameters, and the theoretical and mathematical bases of the concept of autonomic balance. Available data challenge the interpretation of the LF and LF/HF ratio as indices of sympathetic cardiac control and autonomic balance, respectively, and suggest that the HRV power spectrum, including its LF component, is mainly determined by the parasympathetic system.

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“…Indeed, it has now been established that LF is not an index of pure sympathetic activity, but a mix of sympathetic, parasympathetic, and baroreflex influences (Shaffer, McCraty, & Zerr, 2014). This interpretation issue makes it problematic to use LF/HF as an index of sympathovagal balance (Reyes del Paso, Langewitz, Mulder, van Roon, & Duschek, 2013), which is why we decided not to report this ratio, although it is still widely used in the literature. Besides, LF/HF is anyway redundant information with LFnu and HFnu, these three measures being mathematically equivalent and displaying a curvilinear relationship (Heathers, 2014).…”

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“…The spectral power was expressed in ms 2 and integrated into two frequency bands of interest: the high frequency (HF) power band (0.15–0.40 Hz), which reflects the parasympathetic influence and is related to the respiratory sinus arrhythmia [20], and the low frequency (LF) power band (0.04–0.15 Hz), which is assumed to have a dominant sympathetic component [21]. In addition, the LF band has been associated with modulation of cardiac autonomic outflows by baroreflexes [22].…”

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“…In spite of some controversy [37], it is commonly accepted that LF is associated with sympathetic activity [8,11], i.e., variations in the low-frequency PSD values from HRV reflect changes in the sympathetic nervous system. On the other hand, HF has been related to the respiratory rhythms and, therefore, to the parasympathetic activity [8,11].…”