Heart rate variability and pulmonary function behavior in patients undergoing coronary artery bypass grafting and physiotherapy intervention

Objective

To assess the behavior and relationship of heart rate variability (HRV) and pulmonary function in patients undergoing coronary artery bypass grafting (CABG) and physiotherapy intervention (PI).

Methods

Fourteen patients undergoing CABG and PI underwent a prospective study consisting of HRV analysis, spirometry and respiratory muscle strength (RMS) evaluation before and after (1 and 4 days) surgery. The heart rate (HR) and R-R intervals were recorded by the cardiofrequencimeter (Polar S810i), beat-to-beat, in the resting condition and 10 minutes in a supine position. HRV was evaluated in the time domain by the RMSSD index. The spirometry (Vitalograph 2120) was evaluated and the forced vital capacity (FVC), the forced expiratory volume in 1 second (FEV₁) and the maximal voluntary ventilation (MVV) were obtained. RMS was measured by maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) obtained by an aneroid manovacuometer (Ger-Ar). All patients had initiated PI after 24 hours of the extubation, following a program of steps previously established. The Friedman test followed by the Dunn post-hoc test was utilized to compare the variables among conditions before and after surgery, and Spearman correlation analysis to verify relationship among RMSSD and pulmonary parameters. The significance level was set at 5% for all analyses.

Results

Significant correlations were observed between the RMSSD and FVC, FEV₁, MMV and MIP (r = 0.6) and the RMSSD and MEP (r = 0.7). Table 1 presents the comparisons among conditions.

Table 1 Results of heart rate variability and pulmonary function on the preoperative, first postoperative and fourth postoperative days of CABG

Conclusion

The present findings showed that the RMSSD index associated positively with pulmonary function and that cardiac autonomic regulation is impaired after CABG. Additionally, the PI can be a potential therapeutic to reestablish the parasympathetic activity in these patients.