IJCS | Volume 33, Nº1, January / February 2019

83 Table 3 - Parameters of time and frequency domains of the heart rate variability during controlled breathing (CB) COPD (n = 18) CG (n = 12) p-value TD RRi (ms) 912.2 907.6 0.72 SD iRR (ms) 44.7 64.9 0.02* RMSSD (ms) 26.7 48.3 0.004* pNN50 (%) 5.1 11.7 0.01* FD TP (ms²/Hz) 2,555.3 18,447.1 p < 0.0001* LF (ms²) 1,197.9 2,848.6 0.05* LF (un) 84.1 71.9 0.31 HF (ms²) 232.8 780.0 0.004* HF (un) 15.8 28.0 0.31 LF/HF 7.4 5.9 0.27 CG: control group; COPD: chronic obstructive pulmonary disease; TD: time domain; DF: frequency domain; SD: standard deviation; RRi: RR intervals; RMSSD: root mean square standard deviation of RRi; pNN50: percentage of adjacent RRi that are equal or superior to 50ms; TP: total power; LF: low frequency; HF: high frequency; ms: milliseconds; Hz: Hertz; u.n.= normalized units. * p ≤ 0.05, Mann–Whitney U test; data expressed in median. Figure 1 - Median values of total power (TP) in the Control Group (CG) and in Chronic Obstructive Pulmonary Disease (COPD) group during spontaneous breathing (SB) and controlled breathing (CB); Mann–Whitney U test. With respect to clinical data, although COPD patients showed higher BP values than controls, these values were within normal range and probably had no effect on autonomic modulation. 21,22 Similarly, despite lower in COPD than controls, SpO 2 values were also within normal standards. According to Schettino et al., 23 and Dourado et al., 24 significant falls in SpO 2 may occur even in the resting state; however, these changes are documented only in advanced stages of the disease. In a previous study by our group published in 2002, 11 which included analysis of HRV in COPD, we already showed that patients with COPD had lower values of Paschoal et al. Cardiac autonomic modulation in COPD Int J Cardiovasc Sci. 2020;33(1):79-86 Original Article