ABC | Volume 111, Nº1, July 2018

Original Article Oliveira et al Nonlinear dynamics in young adults with type 1 diabetes Arq Bras Cardiol. 2018; 111(1):94-101 Table 3 – Linear index values of heart rate variability in the frequency domain of the control and type 1 diabetes mellitus (DM1) groups Index Control (n = 43) DM1 (n = 39) p value Cohen's d Effect size LF ms 2* 1,203.00 (1148,00) 402.00 (531.00) 0.0001 0.9703 Large HF ms 2* 963.00 (866.00) 386.00 (583.00) 0.0001 0.7759 Medium LF n.u.† 49.76 (16.72) 54.54 (14.83) 0.1770 -0.332 Small HF n.u.† 50.23 (16.72) 45.45 (14.84) 0.1770 0.3325 Small LF/HF * 0.97 (1.05) 1.13 (0.82) 0.3071 -0.537 Small Values in bold represent p < 0.05. * Median (interquartile range); † mean (standard deviation). LF: low-frequency component; HF: high-frequency component. Table 4 – Values of the symbolic analysis and Shannon entropy of the control and type 1 diabetes mellitus (DM1) groups Index Control (n = 43) DM1 (n = 39) p value Cohen's d Effect size 0V% * 17.93 (13.33) 23.04 (18.24) 0.1290 -0.352 Small 1V% * 47.69 (7.62) 48.79 (4.81) 0.4920 -0.091 Small 2LV%† 11.99 (6.49) 11.73 (6.71) 0.8613 0.0393 Small 2ULV% * 20.24 (12.73) 15.33 (9.22) 0.0114 0.4803 Small ES† 3.74 (0.40) 3.61 (0.45) 0.1663 0.3053 Small Values in bold represent p < 0.05. *mean (standard deviation); †median (interquartile range). 0V: pattern without variation; 1V: pattern with 1 variation; 2LV: pattern with two similar variations; 2ULV: pattern with two different variations; SE: Shannon entropy. Despite the similar results, our study did not show a statistically significant difference between the groups when analyzing the LF and HF indexes in normalized units and in the LF/HF ratio. Other methods of HRV analysis addressed in this study were non-linear: SE and symbolic analysis. This was recently described by Porta et al. 9 and is based on the quantification of the information carried in a time series, allowing the development of patterns , denominated symbols (0V, 1V, 2LV and 2ULV), through specific calculations 9 that indicate the autonomic behavior. The values obtained with the symbolic analysis in this study were significantly lower in the DM1 group when compared with the control for the 2ULV index, showing a parasympathetic decrease, although the magnitude of this difference was small. A parasympathetic reduction through symbolic analysis has also been observed by other authors. 10,19 Javorka et al., 19 when comparing the symbolic analysis in young adults with DM1 (21.9 ± 0.9 years) with healthy subjects of the same age group, observed a reduction of 2LV%, which reflects sympathetic and parasympathetic modulation, with parasympathetic predominance. A similar result was observed in the study by Moura-Tonello et al. 10 who, when comparing adults (50.53 ± 6.96 years) with DM2 with healthy individuals, showed that, in diabetic individuals, there was a 2LV% reduction and an increase of 0V%, which reflects the sympathetic activity. Regarding SE, used to quantify the complexity/regularity of heart rate fluctuations, 8 no statistically significant difference was found when comparing the DM1 group with the healthy group. Corroborating our results, other authors also pointed out the lack of alteration in the complexity evaluated by SE, both in adults with DM2 10 and in young individuals with DM1. 19 These results suggest that, despite the autonomic imbalance, identified through other HRV indexes, the autonomic complexity seems to have no influence in these populations. Another point addressed in this study was the existence of an agreement in the correlations between linear and non‑linear indexes (symbolic analysis). Moderate agreement was observed in the correlations of the RMSSD and HF n.u. indexes with the 2ULV and 2LV indexes of the symbolic analysis, and SDNN with 2ULV, in addition of a high concordance in the correlation between the LF n.u. and 0V indexes. These results demonstrate that the indexes obtained through the symbolic analysis show moderate and high agreement with the indexes obtained in the time and frequency domains, indicating they can also be used in the ANS analysis, since they showed similar results to those of the linear analyses and were able to identify changes in autonomic modulation, as well as the traditional HRV indexes. HRV alterations have been pointed out as a strong indicator of risk related to cardiovascular events, both in healthy individuals and in those with an already established disease. 22 This condition increases the risk of sudden death due to cardiac arrhythmias and is associated with elevated mortality rates from other causes, 23 indicating that cardiac autonomic dysfunction in patients already at risk, such as those with DM, may be a complicating agent. 24 HRV reduction is described as the first sign of CAN, 25 with a mortality rate that 98