Efeito do exercício muscular inspiratório sobre a modulação autonômica cardíaca em idosos

Abstract

Inspiratory muscle training promotes positive chronic effects on physiological variables in different populations, including the elderly. However, knowledge is scarce in relation to the acute cardiovascular effects promoted by the inspiratory muscle exercise (IME). Considering that physiological aging impairs cardiac autonomic modulation and that it is noticeably affected by breathing, it becomes relevant to investigate the acute and late responses of a single IME session on the autonomic control of the heart beats in elderly. Fifteen non-smokers and sedentary elderly were randomly assigned to two exercise sessions: moderate intensity IME (40% maximal inspiratory pressure) and Sham (no resistive load). Cardiac autonomic modulation was assessed by the following measures of heart rate variability (HRV) calculated in time and frequency domains: mean duration of normal RR intervals (MNN), standard deviation of normal RR intervals (SDNN), root of the mean square differences of successive normal RR intervals (RMSSD), power of the spectral bands of low (LF) and high (HF) frequencies in absolute (ms2) and normalized (n.u.) units, and LF/HF ratio. The acute effect was studied by comparing the HRV measures obtained from the short-term electrocardiogram (ECG) signal at baseline (before exercise) and for one hour post-exercise recovery (Rec 1 = 10’- 15’; Rec 2 = 25’- 30’; Rec 3 = 40’- 45’and Rec 4 = 55’- 60’). The late effect was investigated by the analysis of the HRV measures obtained from the long-term ECG signal, collected continuously by ambulatory monitoring equipment, comparing every hour after the device was placed in relation to the first hour, and also between the periods wake-night (18:00 to 21:00), sleep (00:00 to 05:00) and wake-day (08:00 to 14:00), determined by the participant’s records. The two-factor analysis of variance with repeated measures was used for all comparisons, followed by Tukey's post hoc, and significance level α = 95% was considered. In addition, the effect size (Cohen's d) was calculated to assess the magnitude of the acute effect observed in each exercise session. There was a significant increase in MNN (P <0.001) throughout the recovery. In addition, SDNN (P = 0.01) and RMSSD (P <0.001) measures and LF (ms2) (P <0.001) and HF (ms2) (P <0.001) spectral bands increased significantly from Rec 2 compared to baseline. No differences were found for the other HRV measures, as well as between the exercise sessions for neither variable. The analysis of Cohen's d showed that the moderate load potentiated the acute effect observed in HRV measures. Late, interventions did not promote significant effects on cardiac autonomic modulation, since the changes observed during the hours following the exercise sessions and in the sleep and wake periods are related to the changes inherent to the circadian rhythm: increase of measures that reflect vagal modulation during sleep. Thus, it was concluded that a single moderate-intensity IME session promotes an acute improvement in cardiac autonomic modulation and does not generate significant late effects on HRV measures in elderly men.