IJCS | Volume 33, Nº1, January / February 2019

84 Table 4 - Medications used by chronic obstructive pulmonary disease (COPD) patients during data collection COPD Group Medications 1 Losartan, Haloperidol, acetylsalicylic acid (ASA) 2 Alenia 3 ASA, Sinvastatin 4 Formoterol 5 Alenia spray 6 Without medications during data collection 7 Alenia, ASA, Budesonide 8 Aerogold, Sinvastatina, Losartan, AAS, Alenia, Budesonide 9 Aerolin spray, Salbutamol, Simvastatin 10 Captopril, Alenia 11 Simvastatin 12 Simvastatin, Aerolin, AAS 13 Simvastatin, Enalapril 14 Ferrous sulfate, Alenia, azathioprine, folic acid 15 Carvedilol, Furosemide, Alenia 16 Alenia, Enalapril 17 Enalapril, hydrochlorizide, Alenia, Aerolin 18 Without medications during data collection SD RRi than healthy individuals, corroborating other works. 20,25,26 A reduction in SD RRi can be associated with the time a disease affects the cardiovascular system, disease severity and the use of some drugs. The SD RRi is also influenced by respiratory, vasomotor and thermoregulatory stimuli, among others. 27 Another result obtained by us in 2002 11 and confirmed in the present study was that COPD patients had lower TP values during SB. In the present study, besides the fact that TP values in COPD were decreased during SB, they were also lower than CG group during CB. These results lead us to suggest that the investigation of the TP index is fundamental when the aim is to evaluate the presence of cardiac dysautonomia in COPD patients (Figure 1). Therefore, we have one index of TD (SD RRi) and one index of FD (TP) that confirm the reduction in HRV in the COPD group. Maybe the most important problem that causes changes in the indexes of total variability is related to characteristics of the respiratory system in COPD. The less compliant thoracic-pulmonary system does not allow great changes in tidal volume, regardless of the form of breathing interfering with the venous return to the heart. This lower complacency decreases the volume of blood directed to the right atrium during the inspiratory phase and the lower venous return tends to decrease HRV at rest, and thereby is one of the important factors involved in the reduction of the autonomic modulation of the heart of these patients. The impaired blood flow from the right ventricle to the lungs may also contribute to these HRV changes. Patients with COPD have greater resistance to blood circulation in the heart-lung circuit, which requires more force from the heart. This may result in increased sympathetic tone and decreased vagal tone. 11,21 Other aspects to be considered in HRV reduction, according to Van Gestel and Steier, 28 are recurrent hypoxemia, hypercapnia, increased intrathoracic pressure due to airway obstruction, increased respiratory effort, and asystemic inflammation. Our results suggest that the tendency of increase in sympathetic tone to overcome altered pressure in the heart-lung circuit of COPD, has interfered with the absolute and relative index values of the LF component - LF (ms 2 ) and LF (un) - during the SB, so that they did not differ from the values presented by the CG. Also, during SB, TP values in COPD patients were only 7.1% of those shown by the CG. However, in CB, TP increased by 27.0% in the COPD group compared to that obtained during SB and was 13.8% of that presented by the CG. These findings reveal that in COPD, even with its limitations related to complacency of the thoracic- pulmonary system, the TP is increased by almost 100% during deeper, oriented breathing. Despite this, COPD patients still showed significantly lower values of TP (p< 0.0001) than theCG. Therefore,we suggest that, during diaphragmatic breathing, COPD patients experience positive changes in CAM, 14 despite significantly lower values of PT compared with controls. Considering the analysis of HRV through TD variables, it is known that the lower the frequencies of the ventilatory cycles, as performed during the CB trial, the higher the values of TD indexes in HRV. 14 However, the COPD group showed similar pNN50 and RMSSD values during both CB and SB, differently from what Paschoal et al. Cardiac autonomic modulation in COPD Int J Cardiovasc Sci. 2020;33(1):79-86 Original Article