Effect of continuous positive airway pressure associated to exercise on the breathing pattern and heart rate variability of patients undergoing coronary artery bypass grafting surgery: a randomized controlled trial

Continuous positive airway pressure (CPAP) has been used to improve gas exchange and diaphragmatic function, among others benefits. Moreover, it can be used to increase exercise tolerance and positively influence ventilatory function and breathing pattern (BP) during exercise. However, there is no information about the long-term effects of CPAP, as an adjunct to an inpatient cardiac rehabilitation (CR) program, on BP and heart rate variability (HRV) of patients after coronary artery bypass grafting surgery (CABG). Twenty patients were allocated to receive, after randomization, standard inpatient CR without CPAP (control group - CG) or CR with CPAP between 10 to 12 cmH2O (CPAP group - CPG) associated with the exercises. Participants were assessed preoperatively and on the discharge day, in the sitting rest position. Outcome measurements included BP variables, collected by respiratory inductive plethysmography, and HRV, collected by polar precision performance. The CPG presented lower values of percent rib cage inspiratory and expiratory contributions to tidal volume (%RCi and %RCe) at discharge time, compared to CG. No statistical differences between groups were observed for HRV variables and both groups presented lower values of these indices, compared to preoperative ones. In this context, the patients who received CPAP throughout the whole rehabilitation program were discharged with a better BP, which could indicate more synchronized breathing. CPAP did not influence cardiac autonomic modulation in the long term.

Effects of different levels of positive airway pressure on breathing pattern and heart rate variability after coronary artery bypass grafting surgery

The application of continuous positive airway pressure (CPAP) produces important hemodynamic alterations, which can influence breathing pattern (BP) and heart rate variability (HRV). The aim of this study was to evaluate the effects of different levels of CPAP on postoperative BP and HRV after coronary artery bypass grafting (CABG) surgery and the impact of CABG surgery on these variables. Eighteen patients undergoing CABG were evaluated postoperatively during spontaneous breathing (SB) and application of four levels of CPAP applied in random order: sham (3 cmH2O), 5 cmH2O, 8 cmH2O, and 12 cmH2O. HRV was analyzed in time and frequency domains and by nonlinear methods and BP was analyzed in different variables (breathing frequency, inspiratory tidal volume, inspiratory and expiratory time, total breath time, fractional inspiratory time, percent rib cage inspiratory contribution to tidal volume, phase relation during inspiration, phase relation during expiration). There was significant postoperative impairment in HRV and BP after CABG surgery compared to the preoperative period and improvement of DFAα1, DFAα2 and SD2 indexes, and ventilatory variables during postoperative CPAP application, with a greater effect when 8 and 12 cmH2O were applied. A positive correlation (P < 0.05 and r = 0.64; Spearman) was found between DFAα1 and inspiratory time to the delta of 12 cmH2O and SB of HRV and respiratory values. Acute application of CPAP was able to alter cardiac autonomic nervous system control and BP of patients undergoing CABG surgery and 8 and 12 cmH2O of CPAP provided the best performance of pulmonary and cardiac autonomic functions.

Estudo da modulação autonômica da freqüência cardíaca em repouso de pacientes idosos com doença pulmonar obstrutiva crônica / Study on autonomic heart rate modulation at rest among elderly patients with chronic obstructive pulmonary disease

OBJETIVO: Avaliar a variabilidade da freqüência cardíaca (VFC) de pacientes idosos com doença pulmonar obstrutiva crônica (DPOC) e de idosos saudáveis frente à mudança postural. MÉTODOS: Foram estudados 9 indivíduos com DPOC (70 anos) e 8 saudáveis (68 anos). A freqüência cardíaca e os intervalos R-R (iR-R) do eletrocardiograma foram registrados durante 360 s nas posturas supina e sentada. A VFC foi analisada no domínio do tempo (DT) (índice RMSSD - raiz quadrada da média dos quadrados das diferenças entre os iR-R sucessivos e SDNN - desvio-padrão da média dos iR-R normais em ms) e no domínio da freqüência (DF), pelas bandas de baixa (BF) e alta freqüência (AF) em unidades absolutas (ua) e normalizadas (un), e da razão BF/AF. Para análise intergrupo e intragrupo foram utilizados os testes de Mann-Whitney e Wilcoxon, respectivamente, com nível de significância de p< 0,05 (valores em mediana). RESULTADOS: No DT, o grupo controle (GC) apresentou valores significativamente maiores do RMSSD (14,6 versus 8,3ms) e SDNN (23,0 versus 13,5ms) na postura sentada, quando comparado ao grupo DPOC (GD). No DF, o GC apresentou valores significativamente maiores dos componentes de AF, na posição supina (39,0 versus 7,8 ua) e dos componentes de BF (146,7 versus 24,4 ua) e AF (67,6 versus 22,7 ua), na posição sentada, bem como do espectro total de potência (552,5 versus 182,9ms²). CONCLUSÃO: Pacientes portadores de DPOC apresentaram redução da VFC com diminuição da atividade simpática e vagal e não apresentaram ajustes autonômicos frente à mudança postural, assim como os idosos saudáveis.

OBJECTIVE: To evaluate heart rate variability (HRV) among elderly patients with chronic obstructive pulmonary disease (COPD) and healthy elderly individuals, during postural change. METHOD: Nine individuals with COPD (70 years old) and eight healthy individuals (68 years old) were studied. Heart rate and electrocardiographic R-R intervals (iR-R) were recorded for 360 seconds in the supine and seated positions. HRV was analyzed in the time domain (TD) (RMSSD index, i.e. the root mean square of the squares of the differences between successive iR-R records, and the SDNN index, i.e. the mean standard deviation of normal iR-R in ms) and in the frequency domain (FD), from the low-frequency (LF) and high-frequency (HF) bands in absolute units (au) and normalized units (nu), and the LF/HF ratio. The Mann-Whitney and Wilcoxon Tests respectively were utilized for inter--group and intra-group analysis, with a significant level of p< 0.05 (median values). RESULTS: In TD, the control group (CG) presented significantly higher values for the RMSSD index (14.6 versus 8.3 ms) and the SDNN index (23 versus 13.5 ms) in the seated position, in comparison with the COPD group (DG). In FD, the CG presented significantly higher values for HF components, in the supine position (39 versus 7.8 au), and for LF components (146.7 versus 24.4 au) and HF (67.6 versus 22.7 au), in the seated position, as well as for the total power spectrum (552.5 versus 182.9 ms²). CONCLUSION: Patients with COPD presented reduced HRV with decreased sympathetic and vagal activity. Additionally, neither the COPD patients nor the healthy elderly participants presented autonomic alterations with postural change.