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Table 2 Time-domain linear and nonlinear and frequency-domain HRV measures used in this study.

From: Electrochemotherapy of colorectal liver metastases - an observational study of its effects on the electrocardiogram

Parameter Unit Description
   Time-domain measures
mean NN ms Mean of normal-to-normal (NN) intervals
SDNN ms Standard deviation of NN intervals; an estimate of overall HRV
SDSD ms Standard deviation of differences between adjacent NN intervals; an estimate of short-term HRV; associated with parasympathetic activity
RMSSD ms Square root of the mean of the sum of the squares of differences between adjacent NN intervals; an estimate of short-term HRV; associated with parasympathetic activity
pNN50 % Number of pairs of adjacent NN intervals differing by more than 50 ms divided by the total number of all NN intervals
   Nonlinear measures
SD1 ms Standard deviation of the Poincaré plot perpendicular to the line-of-identity; the shortest diameter of the fitted ellipse; an estimate of short-term HRV; associated with parasympathetic activity
SD2 ms Standard deviation of the Poincaré plot along the line-of-identity; the longest diameter of the fitted ellipse; an estimate of long-term HRV; associated with sympathetic activity
SD1/SD2 - Ratio of SD1 to SD2; describes the ratio of short-term to long-term HRV; describes the relationship between parasympathetic and sympathetic activity
   Frequency-domain measures
LF ms2 Power in low frequency range (0.04-0.15 Hz); estimate of long-term HRV; reflects both sympathetic and parasympathetic activity
nLF n.u. Normalized power of LF; LF/(LF+HF)x100; estimate of long-term HRV; reflects both sympathetic and parasympathetic activity
HF ms2 Power in high frequency range (0.15-0.4 Hz); estimate of short-term HRV; reflects parasympathetic (vagal) activity
nHF n.u. Normalized power of HF; HF/(LF+HF)x100; estimate of short-term HRV; reflects parasympathetic activity
LF/HF - Ratio between LF and HF range powers; describes the relationship between sympathetic and parasympathetic activity, i.e. sympathovagal balance
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