Modulação autonômica cardíaca: influência da aptidão aeróbia, nível de atividade física e idade

Abstract

The autonomic nervous system (ANS) modulates heart rate (HR) at rest and dynamic situations. At rest the heart rate variability (HRV) is constitute noninvasive tool for evaluate of the ANS. In dynamic situations rest - exercise transient (Ton) and provocative tests as active postural maneuver (APM) are able to modify the SNA dynamics contributing to cardiovascular assessment. Factors such as aerobic fitness, physical activity level (PAL) and age may directly influence the cardiac autonomic modulation at rest. However, in dynamic situations the influence of these factors is poorly understood and contradictory. The study objective was to determine the associations of aerobic fitness, physical activity and aging with cardiac autonomic modulation at rest, in the Ton and the orthostatic posture. The first study examined the relationship between aerobic fitness and cardiac autonomic modulation in 28 young men, with control of the PAL. We analyzed the HR and HRV in resting condition and, for the analysis of the Ton, was calculated rates amplitude, delta HR and RMSSD 15 s. There was no relationship between aerobic fitness and HRV at rest (r = -0.22 SDNN, pNN50 r = -0.25, HF In (ms2) r = -0.31; p>0,05). In Ton, we found that the group with higher level of aerobic fitness had a higher amplitude (61.5 ± 14.6 bpm in group high VO2 and 46.2 ± 11.8 bpm in group low VO2; p<0,05) and delta HR 60s (47.2 ± 11.7 bpm in group high VO2 and 36.4 ± 12.2 bpm in group VO2 below; p<0,05). The second study evaluated the relationship between PAL and cardiac autonomic modulation in 26 young men, with control of aerobic fitness and physical activity levels measured at different raw of the Baecke score sports. We analyzed the HR and HRV in resting condition and for analysis of the Ton, were calculated rates of amplitude, delta HR and RMSSD for 15 s. There was no relation between PAL and HRV at rest (r = -0.32 SDNN, pNN50 r = -0.26, HF In (ms2) r = 0.37; p>0,05) and Ton (Aon r = -0.04, D60s r = -0.34; p>0,05). The third study examined the influence of age on the APM on 20 men, divided into two groups, Group EV: individuals over 50 years (n = 10), Group JV: young (n = 10). HRV was measured in the supine position (20 min) and after the APM, and analyzed the last 5 minutes. HRV was calculated by linear indices and nonlinear indices of entropy. EV Group decreased HRV at rest and less adaptability to AMP (RMMSD: 62.8 ± 20.7 ms

8 to 33.8 ± 8.3 ms in the JV after AMP and 18.1 ± 12.7 to 14, 4 ± 13.7 ms in EV after AMP; HF In (ms2): 7.2 ± 0.8 to 5.9 ± 0.7 ms2 in the JV after AMP and 4.7 ± 1.1 to 3.6 ± 1.3 ms2 in EV after AMP; p <0,05). The EV group showed no significant change in the indices as linear mechanisms of adaptation to the AMP and the reduction of entropy may be an explanation for a rise in HR with AMP (correlation between delta HR and delta entropy ApEn r = -0.48 and SampEn r =- 0.65; p <0,05). We can see that aerobic fitness and physical activity level did not influence the cardiac autonomic modulation at rest in young individuals with homogeneous characteristics. With respect to dynamic situations only aerobic fitness was able to influence the Ton. Age influences the response of ANS both at rest when after AMP, with distinct physiological mechanisms of adaptation to orthostatic posture. In addition, non-linear indices provided additional information the adaptability of the ANS with aging in the AMP.