Table 3. Linear and Nonlinear Measures of Heart Rate (HR) Dynamics of the First 24 Postoperative Hours
Results of all the patients and separately of Group A and B patients. Analyses of standard deviation of all R-R intervals (SDNN), R-R interval, low frequency (LF), high frequency (HF), approximate entropy (ApEn), and Poincaré plot were performed on 1,000-beat segments. Short-term (α1) and intermediate-term (α2) correlation properties (DFA) were performed in segments of 8,000 beats. Very low frequency of spectral power (VLF), ultra low frequency band (ULF), and scaling exponent of the power law relationship (β-slope) were analyzed in epochs of 24 h. Significance levels were tested with Mann–Whitney U test. Values are means (median) ± SD (range). Group A and B: Intensive care unit stay ≤ 48 h and > 48 h, respectively.
*P < 0.05 between groups A and B.
SD1 = instantaneous beat-to-beat heart rate variation; SD2 = continuous long-term heart rate variation.