Table 4.

Heart rate variability frequency-domain variables adapted from [25]. Equations (19)–(25) are included.

Parameter (Unit)	Description	Equation	Equation Number
ULF power (ms2)	Absolute power of the ultra-low-frequency band (≤0.003 Hz)	$ULF={\int }_{0hz}^{0.003hz}f\left(\lambda \right)d\lambda$	(19)
VLF power (ms2)	Absolute power of the very-low-frequency band (0.003–0.04 Hz)	$VLF={\int }_{0.003hz}^{0.04hz}f\left(\lambda \right)d\lambda$	(20)
LF power (ms2)	Absolute power of the low-frequency band (0.04–0.15 Hz)	$LF={\int }_{0.04hz}^{0.15hz}f\left(\lambda \right)d\lambda$	(21)
LF power (%)	Relative power of the low-frequency band	$LF\%= \frac{{\int }_{0.04hz}^{0.15hz}f\left(\lambda \right)d\lambda }{{\int }_{0hz}^{0.4hz}f\left(\lambda \right)d\lambda }\times 100$	(22)
HF power (ms2)	Absolute power of the high-frequency band (0.15–0.4 Hz)	$HF={\int }_{0.15hz}^{0.40hz}f\left(\lambda \right)d\lambda$	(23)
HF power (%)	Relative power of the high-frequency band	$HF\%= \frac{{\int }_{0.15hz}^{0.4hz}f\left(\lambda \right)d\lambda }{{\int }_{0hz}^{0.4hz}f\left(\lambda \right)d\lambda }\times 100$	(24)
LF/HF (%)	Ratio of LF-to-HF power	$LF/HF= \frac{{\int }_{0.04hz}^{0.15hz}f\left(\lambda \right)d\lambda }{{\int }_{0.15hz}^{0.4hz}f\left(\lambda \right)d\lambda }\times 100$	(25)