The role of the sympathetic component of the autonomic nervous system on pain before and after third molar extraction– an observational cohort study

Table 1 Selected measures of heart rate variability (HRV)

Time domain statistical measures
Variable	Units	Description		Involved component of the autonomic system
SDNN	ms	Standard deviation of all NN intervals; reflects all the cyclic components during the entire recording; depends on the duration of the recording		both
RMSSD	ms	Square root of the mean of the sum of the squares of differences between adjacent NN intervals		parasympathetic
NN50	count	Number of pairs of adjacent NN intervals differing by more than 50 ms in the entire recording		parasympathetic
pNN50	%	NN50 count divided by the total number of all NN intervals		parasympathetic
Frequency domain measures
*Variable*	*Units*	*Description*	*Frequency range (Hz)*	*Involved component of the autonomic system*
Total power	ms²	Whole variance of NN intervals	≤ 0.4	both
LF	ms²	Power in low frequency range; includes the slow oscillations of blood pressure via the baroreflex (Mayer’s waves)	0.04 to 0.15	both
HF	ms²	Power in high frequency range; reflects the HRV evoked by breathing via the stretch receptors (“respiratory arrhythmia”)	0.15 to 0.45	parasympathetic
LF/HF	ratio	Surrogate of the relative part of the sympathetic component		sympathetic

Abbreviations: NN, normal-to-normal intervals. References:
ESC-NASPE. Heart rate variability. Standards of measurement, physiological interpretation, and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Eur Heart J. 1996;17:354-81
Ramos G, Carrasco S, Medina V. Time-frequency analysis of the heart rate variability during the Valsalva manoeuvre. J Med Eng Technol. 2000;24:73-82

ISSN: 1471-2253