Activation of Mechanoreflex, but not Central Command, Delays Heart Rate Recovery after Exercise in Healthy Men.

This study tested the hypotheses that activation of central command and muscle mechanoreflex during post-exercise recovery delays fast-phase heart rate recovery with little influence on the slow phase. Twenty-five healthy men underwent three submaximal cycling bouts, each followed by a different 5-min recovery protocol: active (cycling generated by the own subject), passive (cycling generated by external force) and inactive (no-cycling). Heart rate recovery was assessed by the heart rate decay from peak exercise to 30 s and 60 s of recovery (HRR30s, HRR60s fast phase) and from 60 s-to-300 s of recovery (HRR60-300s slow phase). The effect of central command was examined by comparing active and passive recoveries (with and without central command activation) and the effect of mechanoreflex was assessed by comparing passive and inactive recoveries (with and without mechanoreflex activation). Heart rate recovery was similar between active and passive recoveries, regardless of the phase. Heart rate recovery was slower in the passive than inactive recovery in the fast phase (HRR60s=20±8vs.27 ±10 bpm, p<0.01), but not in the slow phase (HRR60-300s=13±8vs.10±8 bpm, p=0.11). In conclusion, activation of mechanoreflex, but not central command, during recovery delays fast-phase heart rate recovery. These results elucidate important neural mechanisms behind heart rate recovery regulation.

Effects of postexercise cooling on heart rate recovery in normotensive and hypertensive men.

BACKGROUND: Postexercise heart rate recovery (HRR) is determined by cardiac autonomic restoration after exercise and is reduced in hypertension. Postexercise cooling accelerates HRR in healthy subjects, but its effects in a population with cardiac autonomic dysfunction, such as hypertensives (HT), may be blunted. This study assessed and compared the effects of postexercise cooling on HRR and cardiac autonomic regulation in HT and normotensive (NT) subjects. METHODS: Twenty-three never-treated HT (43 ± 8 years) and 25 NT (45 ± 8 years) men randomly underwent two exercise sessions (30 min of cycling at 70% VO2peak ) followed by 15 min of recovery. In one randomly allocated session, a fan was turned on in front of the subject during the recovery (cooling), while in the other session, no cooling was performed (control). HRR was assessed by heart rate reductions after 60 s (HRR60s) and 300 s (HRR300s) of recovery, short-term time constant of HRR (T30) and the time constant of the HRR after exponential fitting (HRRτ). HRV was assessed using time- and frequency-domain indices. RESULTS: HRR and HRV responses in the cooling and control sessions were similar between the HT and NT. Thus, in both groups, postexercise cooling equally accelerated HRR (HRR300s = 39±12 versus 36 ± 10 bpm, P≤0·05) and increased postexercise HRV (lnRMSSD = 1·8 ± 0·7 versus 1·6 ± 0·7 ms, P≤0·05). CONCLUSION: Differently from the hypothesis, postexercise cooling produced similar improvements in HRR in HT and NT men, likely by an acceleration of cardiac parasympathetic reactivation and sympathetic withdrawal. These results suggest that postexercise cooling equally accelerates HRR in hypertensive and normotensive subjects.

Metaboreflex activation delays heart rate recovery after aerobic exercise in never-treated hypertensive men.

KEY POINTS: Recent evidence indicates that metaboreflex regulates heart rate recovery after exercise (HRR). An increased metaboreflex activity during the post-exercise period might help to explain the reduced HRR observed in hypertensive subjects. Using lower limb circulatory occlusion, the present study showed that metaboreflex activation during the post-exercise period delayed HRR in never-treated hypertensive men compared to normotensives. These findings may be relevant for understanding the physiological mechanisms associated with autonomic dysfunction in hypertensive men. ABSTRACT: Muscle metaboreflex influences heart rate (HR) regulation after aerobic exercise. Therefore, increased metaboreflex sensitivity may help to explain the delayed HR recovery (HRR) reported in hypertension. The present study assessed and compared the effect of metaboreflex activation after exercise on HRR, cardiac baroreflex sensitivity (cBRS) and heart rate variability (HRV) in normotensive (NT) and hypertensive (HT) men. Twenty-three never-treated HT and 25 NT men randomly underwent two-cycle ergometer exercise sessions (30 min, 70% V̇O2 peak ) followed by 5 min of inactive recovery performed with (occlusion) or without (control) leg circulatory occlusion (bilateral thigh cuffs inflated to a suprasystolic pressure). HRR was assessed via HR reduction after 30, 60 and 300 s of recovery (HRR30s, HRR60s and HRR300s), as well as by the analysis of short- and long-term time constants of HRR. cBRS was assessed by sequence technique and HRV by the root mean square residual and the root mean square of successive differences between adjacent RR intervals on subsequent 30 s segments. Data were analysed using two- and three-way ANOVA. HRR60s and cBRS were significant and similarly reduced in both groups in the occlusion compared to the control session (combined values: 20 ± 10 vs. 26 ± 9 beats min-1 and 2.1 ± 1.2 vs. 3.2 ± 2.4 ms mmHg-1 , respectively, P < 0.05). HRR300s and HRV were also reduced in the occlusion session, although these reductions were significantly greater in HT compared to NT (-16 ± 11 vs. -8 ± 15 beats min-1 for HRR300s, P < 0.05). The results support the role of metaboreflex in HRR and suggest that increased metaboreflex sensitivity may partially explain the delayed HRR observed in HT men.

Análise crítica dos Estudos ACCORD versus SPRINT ­ Resultados e metas pressóricas / Critical analysis of ACCORD versus SPRINT trials ­ Results and blood pressure targets

A meta ideal para controle da pressão arterial tem sido amplamente discutida ao longo de décadas, sendo objetivo principal de diversos estudos. Se por um lado há os trabalhos que reforçam a importância de um controle mais rigoroso da pressão arterial para diminuir desfechos cerebrais ou cardiovasculares, de outro, aqueles que não demonstraram isso advogam a já tradicional meta da pressão arterial sistólica (PAS), inferior a 140mmHg. Tal controvérsia pode ser explicada pelo grupo de pacientes estudados, pelo maior ou menor poder estatístico do estudo, e pelos desfechos definidos como primários. Dentre esses estudos, especificamente nos pacientes com alto risco cardiovascular, destacam-se o ACCORD BP realizado somente com diabéticos e o SPRINT, realizado com pacientes de alto risco, porém sem diabetes e acidente vascular cerebral (AVC) prévio. Ambos foram ensaios clínicos randomizados e controlados, que compararam desfechos cardiovasculares ocorridos em grupos com controle intensivo da pressão arterial (PAS<120 mmHg) versus controle padrão (PAS<140 mmHg). Enquanto o estudo ACCORD BP não mostrou benefício frente ao controle intensivo, exceto pelo desfecho cerebral (um desfecho secundário), o SPRINT mostrou eventos significativamente menores nesse grupo, sendo inclusive interrompido precocemente. Além do delineamento, ambos os estudos são similares por se tratarem de pacientes de alto risco. Ao mesmo tempo, são diferentes pela exclusão de pacientes com AVC prévio e diabetes no SPRINT, enquanto pela não inclusão da insuficiência cardíaca nos desfechos primários do ACCORD BP. O objetivo desta presente revisão é justamente destacarmos esses pontos que, embora inicialmente controversos, nos permitirá concluir que metas distintas são necessárias para grupos populacionais distintos

The ideal target for blood pressure has been widely discussed for decades in several studies. If on one hand there are observational studies that reinforce the importance of a more rigorous blood pressure control to decrease cerebrovascular and cardiovascular outcomes, on the other hand, those investigations which have not shown these findings reinforce the already traditional systolic blood pressure (SBP) target of less than 140mmHg. This controversy can be explained by differences in the characteristics of patients included in the studies, the statistical power of the studies and differences in primary outcomes. Among these studies, particularly in patients with high cardiovascular risk, we highlight ACCORD BP, performed only in diabetic patients, and the SPRINT trial, carried out in high-risk patients without diabetes and no previous stroke. Both were randomized controlled trials that compared cardiovascular outcomes in patients with intensive blood pressure control (SBP<120 mmHg) versusstandard blood pressure control (SBP<140 mmHg). While the ACCORD BP study showed no benefit in intensive blood pressure control, except by stroke outcome (a secondary outcome), the SPRINT showed significantly lower events in patients randomized to intensive blood pressure control. In relation to the design, both studies are similar because they included high-risk patients. At the same time, they are different by excluding patients with previous stroke and diabetes in the SPRINT Trial, while the ACCORD BP did not include heart failure in the primary outcomes. The aim of this review is to discuss these important issues. Although controversial, both studies allow us to conclude that different goals are needed for different population subgroups.