Clinical Applications of Heart Rate Variability in the Triage and Assessment of Traumatically Injured Patients

Table 2

Definitions of frequency-domain metrics of heart rate variability.

Variable	Abbreviation	Description	Interpretation
Total power	TP	Total power of periodic oscillations in the ECG signal—represents total RR interval spectral power	Global measure of autonomic function [3]
High frequency power	HF	Power spectral density of high-frequency oscillations (0.15–0.4 Hz)	Function of respiratory rhythms under vagal (parasympathetic) regulation [18, 24, 31]
Low frequency power	LF	Power spectral density of low-frequency oscillations (0.04–0.15 Hz)	Baroreceptor reflex-related modulation of cardiac pacemaker activity via sympathetic and parasympathetic stimulation [4, 18, 31]
Very low frequency power	VLF	Power spectral density at very-low-frequency oscillations (<0.04 Hz)	Associated with vasomotor, thermal, and humoral regulation via sympathetic nerve activity [24, 31]
Low/high frequency ratio	LF/HF	Ratio of low-frequency power to high-frequency power	Represents ratio of sympathetic to parasympathetic nerve activity [31]