IJCS | Volume 33, Nº1, January / February 2019

81 Therefore, it was possible to obtain HR recordings under stationary conditions, which visually confirmed by the HR tachogram analysis. The data obtained during SB and CB was analyzed in the time domain (TD) and frequency domain (FD) of HRV. In the TD the following parameters were assessment, according to the European Society of Cardiology and the NorthAmerican Society of Pacing and Electrophysiology Task Force. 18 a) mean RRi; b) standard deviation of the mean RRi (SD RRi) - that depends on cardiac sympathetic and parasympathetic tones; c) square root of the mean of the sum of the squares of differences between adjacent normal to normal (NN) intervals (RMSSD), which expresses cardiac parasympathetic tone; d) mean HR (bpm); e) number of pairs of adjacent NN intervals differing by more than 50ms in the entire recording divided by the total number of all NN intervals (pNN50), which expresses cardiac parasympathetic tone. The results of RRi, SD RRi and RMSSD were expressed in milliseconds (ms), while pNN50 values were expressed as percentage. In the FD, the following indexes were calculated based on the fast Fourier transform (FFT) algorithm: a) Total power (TP) – obtained in the range of 0.0 to 0.4Hz; it is composed of the sum of the following indices: ultra-low frequency (ULF 0.0 to 0.003Hz), very low frequency (VLF – 0.003 to 0.04Hz), low frequency (LF - 0.04 to 0.15Hz) and high frequency (HF - 0.15 to 0.4Hz) power. 18 The TP expresses the total variability resulting from the fundamental oscillatory components present during recording; b) density of oscillatory components present in the LF band reflecting both sympathetic and cardiac parasympathetic activities; 1,19 c) density of oscillatory components present in the HF band, reflecting the cardiac parasympathetic activity. 1,19 LF and HF were also calculated in normalized units (n.u.) as proposed by Pagani et al., 20 and the European Society of Cardiology and the NorthAmerican Society of Pacing and Electrophysiology Task Force, 18 and expressed as the percentage of contribution of each branch of the ANS to the autonomic modulation of the heart. Finally, the LF/HF ratio was also calculated. Statistical Analysis Values of the TD and FD indexes of the HRV were inserted in tables and analyzed by the GraphPad Prism 4.0 ® statistical program (San Diego, California, USA). The Shapiro-Wilk test was used to test normality of data distribution and showed a non-normal distribution of HRV values, which were then compared by the Mann- Whitney test was then used to compare these the clinical and anthropometric data. Also, this same test was applied to compare the HRV parameters obtained during SB and CB within group and between the groups. Due to their normal distribution, anthropometric and clinical data were compared by the paired Student’s t test to analyze the differences between the means. The level of significance was set at p < 0.05. Results There was no significant difference in anthropometric data between the CG and the COPD group (Table 1). The COPD group showed significantly higher BP values and lower SpO 2 compared with controls. During SB, in the TDparameters, statistical differences were found in SD RRi and RMSSD index, which were reduced in individuals with COPD (Table 2). In the FD, TP and HF were statistically lower in the COPD group, confirming the reduction of both parasympathetic and sympathetic cardiac tones in COPD. During CB, the COPD group showed significantly lower values of SD RRi, RMSSD and pNN50 (Table 3). For the HRV indexes in FD, significant differences were found in PT, LF (ms²) and HF (ms²), which were reduced in the COPD group. Figure 1 depicts the values of median TP during SB and CB, showing a great difference (p < 0.0001) between the groups, with higher values for the CG. Table 4 shows the medications used by the patients during data collection. It is noteworthy that, at the request of the ethics committee, the researchers did not interfere with patients’ usual medications during data collection. Discussion The main finding of the present study was that COPD patients showed changes in CAM, characterized by lower sympathetic and parasympathetic modulation during SB and CB. In addition to this, other relevant results are discussed below. First, it is worth pointing out that all factors that could be sources of bias in the analyses were controlled during patients’ selection and before and during data collection. These factors included age, body weight, functional Paschoal et al. Cardiac autonomic modulation in COPD Int J Cardiovasc Sci. 2020;33(1):79-86 Original Article