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 1 – Characteristics of the control and type 1 diabetes mellitus (DM1) groups Variables Control (n = 43) DM1 (n = 39) p value Age, years * 21.00 (5.00) 21.00 (7.00) 0.5397 Body mass, kg * 60.30 (22.80) 68.15 (22.90) 0.0129 Height, m† 1.69 (0.09) 1.73 (0.17) 0.4680 BMI, kg/m 2* 22.19 (4.67) 24.19 (5.84) 0.0216 Values in bold represent p < 0.05. * Median (interquartile range); † mean (standard deviation). BMI: body mass index. Table 3 represents the linear index values in the HRV frequency domain for both groups. Significantly lower values were observed in the DM1 group when compared to the control group for the LFms² and HFms 2 indexes. Regarding the effect of the difference between the groups, we obtained d = 0.9703 for the LFms 2 index, showing a large effect, and, for the HFms 2 index, d = 0.7759, considered a medium effect. For the other indexes, the effect was considered small, with d < 0.2. Table 4 shows the values obtained with the HRV symbolic analysis and SE for both groups. Significantly lower values were observed in the DM1 group when compared to the Control group for the 2ULV index, but this difference was considered as having a small effect (d = 0.4803). Table 5 shows the values of r, ICC and 95%CI obtained at the correlation of the linear indexes with SE and the indexes obtained in the symbolic analysis for the DM1 Group. The agreement shown by the ICC values was considered moderate for the associations of the RMSSD, SDNN, HF n.u. indexes with the 2LV index. The same was found regarding the association of RMSSD and HF n.u. indexes with the 2ULV index. High agreement was found for the LF n.u. index with the 0V index. Additionally, the 0V, 2LV, 2ULV and SE indexes showed a moderate correlation with SDNN, RMSSD, LF and HF indexes in ms 2 and n.u. and the LF/HF ratio, with the exception of the 2ULV index with the SDNN index, SE with the HFms 2 index, and 0V with the HFms 2 index, which showed a weak correlation. A strong correlation was found for the 0V indexes with LF n.u., HF n.u. and LF/HF, for the 2LV index with LFms² and for the SE index with LF/HF. The 1V index was the only one that did not show a significant correlation with the other HRV linear indexes and the 2ULV only for the HFms 2 index. Discussion The aim of this study was to compare HRV indexes obtained through symbolic analysis and SE in young adults with DM1 and healthy young individuals, associated with the analysis of indexes obtained in the time (RMSSD and SDNN) and frequency (LF, HF in ms 2 and in n.u., and LF/HF) domains, as well as verifying the existence of correlations between them in diabetic individuals. Our results show that individuals with DM1 have a reduction in the parasympathetic (RMSSD, HFms 2 and 2ULV), sympathetic (LFms 2 ) and global (SDNN) activities of the ANS. They also showed that the 0V (sympathetic), 2LV (parasympathetic), 2ULV (parasympathetic) and SE indexes have moderate correlation with the SDNN, RMSSD, LF and HF indexes in ms 2 and n.u. and LF/HF ratio, with the agreement of this association being considered moderate for the RMSSD, HF n.u., 2LV and 2ULV indexes, and high for LF n.u. and 0V indexes. The individuals with DM1 also had higher values of body mass and BMI in relation to the healthy subjects, which was also shown in the study of Javorka et al., 19 for the BMI variable, when evaluating 17 young adults (22.4 ± 1.0 years) with DM1. Based on the analysis of the HRV, it was possible to observe significantly lower values in the DM1 Group when compared to the Control, both for the SDNN and RMSSD indexes in the time domain and for the LFms 2 and HFms 2 indexes in the frequency domain, indicating a reduction in the global, sympathetic and parasympathetic activity of the ANS, with the effect of this difference being considered medium (HFms 2 ) and large (SDNN, RMSSD and LFms 2 ). Similar results were indicated by other studies 19-21 . Jaiswal et al., 20 when evaluating 354 young individuals with DM1 (18.8 ± 3.3 years), observed a reduction in the SDNN, RMSSD, HF n.u. LF n.u. indexes and LF/HF ratio. Javorka et al., 19 evaluated a smaller sample of 17 individuals with DM1 (22.4 ± 1.0 years), indicating that it was possible to observe a significant reduction in the SDNN, RMSSD, LFms 2 and HFms 2 indexes. Also, Dungan et al., 21 when evaluating 33 individuals with DM1 older than 18 years, also found a reduction in the HFms 2 index. These results show there is an autonomic alteration in DM1. Table 2 – Values of the heart rate variability linear indexes in the time 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 SDNN * 64.50 (36.20) 37.30 (29.90) 0.0001 1.21 Large RMSSD† 55.59 (21.60) 32.73 (17.43) 0.0001 1.203 Large Values in bold represent p < 0.05. * Median (interquartile range); † mean (standard deviation). SDNN: standard deviation of all normal R-R intervals recorded in a time interval, expressed in milliseconds; RMSSD: the square root of the mean of the squared differences between adjacent normal R-R intervals, in a time interval, expressed in milliseconds. 97