IJCS | Volume 33, Nº1, January / February 2019

85 was observed with the CG, which showed elevation of the two parameters during CB. Similar results were reported by Gunduz et al., 26 in COPD patients during SB, with lower RMSSD (25.0 ± 10.0 ms vs 60.0 ± 35.0 ms) and pNN50 values (11.8 ± 9.4 vs 15.7 ± 8.1%) compared with healthy individuals. Reis et al., 12 reported RMSSD values of 17.7 ± 6.1 ms and 18.3 ± 15.6ms during CB and SB, respectively in COPDpatients. These values were lower than those observed in controls, and lower than those presented by our volunteers with COPD. The authors, however, did not evaluate pNN50 in these patients. Although many clinicians believe that patients with COPD tend to have elevated cardiac sympathetic tone, the present study and other studies have shown that both the LF index (considered mainly as a sympathetic component) and the LF/HF ratio (considered mainly as a sympathetic component when greater than 1) in these patients are not different from those in healthy subjects (Tables 2 and 3). 12,28,29 In the present study, the absolute values found in the LF band (LFms 2 ) were lower in the COPD group than in CG. However, when these data were analyzed in standardized units (LFun), the percentage of sympathetic contribution to the autonomic modulation of the heart was not different between COPD patients and the CG. In other words, when ULF and VLF values were excluded from the analysis, the percentage of the LF band in COPD was similar to that presented by the CG. Our results are similar to those of Antonelli Incalzi et al., 29 who also reported that sympathetic modulation decreases according to the severity of COPD. They also confirm the statement by Carvalho et al. 5 who reported reductions in HRV indexes that reflect not only parasympathetic modulation alone but also sympathetic and parasympathetic modulation together in COPD patients. In relation to the absolute index of HF, COPD patients showed lower values as compared with the CG. This is in accordance with that observed by Pantoni et al., 9 who found lower values of the HF components in absolute units in these patients. This suggests that this parameter of the HRV analysis is decreased in COPD patients, and hence should be carefully observed when dealing with this group of patients. The lower values of HF in COPDweremore significant during CB than SB, which agrees with the data reported by Reis et al., 12 According to these authors, during CB, there is an increase in tidal volume and in respiratory rate in healthy individuals. Therefore, the respiratory pattern performed during the CB protocol could affect lung compliance and pulmonary stretch receptors, and consequently increase the values of LF, HF andTP indexes of HRV. On the other hand, in COPD patients, changes in chest expansion and pulmonary volume are less evident. The elevated and unchanged intrapulmonary pressure reduces venous return, resulting in lower RRi oscillations and changes in cardiocirculatory adjustments promoted by the autonomic nervous system. As a study limitation, we could not determine the exact volume of air mobilized during the breaths, whichwould allow the establishment of the relationship between the volume of air during breathing and respective changes in HRV measurements. Conclusion The study showed a reduction in cardiac sympathetic and parasympathetic modulation in patients with COPD during both SB and CB. These changes, together with the findings on TP, were the main contributions to the literature. These changes reinforce the need for the analysis of CAMas part of the evaluation of these patients aiming at early detection and treatment of possible cardiac dysautonomia. Author contributions Conception and design of the research: Paschoal MA. Acquisition of data: Gianfrancesco L, Camargo LT, Seixas NB. Analysis and interpretation of the data: Paschoal MA, Gianfrancesco L, Camargo LT, Seixas NB, Paschoal AB. Statistical analysis: Paschoal MA, Gianfrancesco L, Paschoal AB. Writing of the manuscript: Paschoal MA, Gianfrancesco L, Seixas NB. Critical revision of the manuscript for intellectual content: Paschoal MA. Potential Conflict of Interest No potential conflict of interest relevant to this article was reported. Sources of Funding There were no external funding sources for this study. Study Association This study is not associated with any thesis or dissertation work. Paschoal et al. Cardiac autonomic modulation in COPD Int J Cardiovasc Sci. 2020;33(1):79-86 Original Article