Mechanisms of blood pressure control following acute exercise in adolescents: Effects of exercise intensity on haemodynamics and baroreflex sensitivity.

NEW FINDINGS: What is the central question of this study? What are the autonomic and vascular components of the baroreflex during hypotension following different exercise intensities in adolescents? What is the main finding and its importance? Hypotension after high-intensity exercise lasted 60 min, whereas following moderate-intensity exercise, blood pressure was restored after 20 min. Stroke volume and peripheral resistance responses were different between intensities. Post both exercise intensities, baroreflex sensitivity was lowered mainly due to the autonomic component, which returned to baseline 60 min post-exercise. The different haemodynamic stimuli indicate potential differences in cardiovascular health benefits of exercise intensity in healthy adolescents. ABSTRACT: This work aimed to investigate the time course of changes in baroreflex sensitivity (BRS) and its vascular and autonomic components after different exercise intensities in adolescents. Thirteen male adolescents (age 13.9 ± 0.5 years) completed on separate days in a counterbalanced order (1) high-intensity interval exercise (HIIE): 8 × 1 min running at 90% of maximal aerobic speed with 75 s of active recovery; (2) moderate-intensity interval exercise (MIIE): 10-12 bouts of 1 min running at 90% of gas exchange threshold with 75 s of active recovery; and (3) resting as a control. Supine heart rate and blood pressure were monitored continuously at baseline, and 5 and 60 min following the conditions. A cross-spectral method (low frequency gain; LFgain ) was used to determine BRS gain. Arterial compliance (AC) was assessed as the BRS vascular component. LFgain /AC was used as the autonomic component. LFgain decreased 5 min post-exercise bouts (HIIE P < 0.001; MIIE P = 0.002), but returned to baseline at 60 min post-exercise. AC increased at 5 min post-exercise for all conditions (P = 0.048), and returned to baseline at 60 min post-exercise. LFgain /AC decreased 5 min post-exercise bouts (HIIE P = 0.001; MIIE P = 0.004), but returned to baseline values at 60 min post-exercise. Mean arterial pressure was lowered by both exercise intensities at 5 min post-exercise, but remained decreased at 60 min post-exercise following HIIE only. In conclusion, BRS decreases 5 min following exercise in adolescents independent of exercise intensity and is mainly driven by a lowered autonomic response. At 60 min post-exercise, the ability of BRS to regulate blood pressure is restored after MIIE but not after HIIE, indicating exercise intensity-dependent mechanisms.

Reliability of autonomic and vascular components of baroreflex sensitivity in adolescents.

Improvements in the autonomic and vascular systems are implicated in cardiovascular disease risk reduction. Baroreflex sensitivity (BRS) is composed of vascular and autonomic components. This study aimed to investigate between- and within-day reliability of BRS and its autonomic and vascular determinants in adolescents. Thirteen male adolescents (14·1 ± 0·5 y) participated in this study. For between-day reliability, participants completed four experimental visits separated by a minimum of 48-h. For within-day reliability, participants repeated BRS assessments three times in the morning with one hour between the measures. BRS was evaluated using the cross-spectral gain (LFgain) between blood pressure and heart rate interval. BRS was further divided into: 1) vascular component using arterial compliance (AC); and 2) autonomic component measured as LFgain divided by AC (LFgain/AC). LFgain, AC and LFgain/AC presented between-day coefficient of variation (CV) of 20%, 17%, and 20%, respectively. Similarly, variables associated with blood pressure control, such as cardiac output, mean arterial pressure, heart rate and total peripheral resistance, presented CVs ranging from 6% to 15%. Within-day reliability was poorer compared to between-day for LFgain (25%), AC (25%), and LFgain/AC (31%), as well as all hemodynamic variables (CVs from 11% to 22%, except heart rate with presented CV of 6%). This study indicates suitable between- and within-reliability of BRS and its autonomic and vascular determinants, as well as hemodynamic variables associated with BRS, in adolescents.