Antonio Claudio Lucas da Nóbrega

Activation of the insular cortex during dynamic exercise in humans

1 The insular cortex has been implicated as a region of cortical cardiovascular control, yet its role during exercise remains undefined. The purpose of the present investigation was to determine whether the insular cortex was activated during volitional dynamic exercise and to evaluate further its role as a site for regulation of autonomic activity. 2 Eight subjects were studied during voluntary active cycling and passively induced cycling. Additionally, four of the subjects underwent passive movement combined with electrical stimulation of the legs. 3 Increases in regional cerebral blood flow (rCBF) distribution were determined for each individual using single‐photon emission‐computed tomography (SPECT) co‐registered with magnetic resonance (MR) images to define exact anatomical sites of cerebral activation during each condition. 4 The rCBF significantly increased in the left insula during active, but not passive cycling. There were no significant changes in rCBF for the right insula. Also, the magnitude of rCBF increase for leg primary motor areas was significantly greater for both active cycling and passive cycling combined with electrical stimulation compared with passive cycling alone. 5 These findings provide the first evidence of insular activation during dynamic exercise in humans, suggesting that the left insular cortex may serve as a site for cortical regulation of cardiac autonomic (parasympathetic) activity. Additionally, findings during passive cycling with electrical stimulation support the role of leg muscle afferent input towards the full activation of leg motor areas.

Posicionamento oficial da Sociedade Brasileira de Medicina do Esporte e da Sociedade Brasileira de Geriatria e Gerontologia: atividade física e saúde no idoso

Antonio Claudio Lucas da Nobrega, Elizabete Viana de Freitas, Marcos Aurelio Brazao de Oliveira,Marcelo Bichels Leitao, Jose Kawazoe Lazzoli, Ricardo Munir Nahas, Claudio Aparicio Silva Baptista,Felix Albuquerque Drummond, Luciano Rezende, Josbel Pereira, Maurilio Pinto,Rosana Bento Radominski, Neiva Leite, Edilson Schwansee Thiele, Arnaldo Jose Hernandez,Claudio Gil Soares de Araujo, Jose Antonio Caldas Teixeira, Tales de Carvalho,Serafim Ferreira Borges e Eduardo Henrique De Rose

Cardiovascular responses to active and passive cycling movements

Ten healthy subjects were evaluated at rest and at 5 min of unloaded active (AC) and passive (PC) cycling. Passive limb movements were accomplished using a tandem bicycle with a second rider performing the movements. We measured heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), oxygen uptake (VO2), rating of perceived exertion (RPE), and electrical activity (EMG) of lower limbs muscles. Values for stroke volume (SV) and peripheral vascular resistance (PVR) were calculated. EMG, RPE, and VO2 were higher during AC than during PC (P < 0.001). CO increased during both modes of cycling, but during AC it resulted from a HR acceleration (73 +/- 2 at rest to 82 +/- 2 beats.min-1 at 60 rpm; P < 0.001) with no change in SV whereas during PC, SV increased from rest (65 +/- 4 at rest to 71 +/- 3 ml at 60 rpm; P = 0.003) along with no change in HR. PVR remained constant during PC, but decreased by 13% during AC (P < 0.001) and MAP increased only during PC (93 +/- 2 at rest to 107 +/- 2 mm Hg at 60 rpm). These results supports the concept that central command determines the HR response to dynamic exercise. The increase in SV and consequently in MAP during PC was probably due to increased venous return and/or to muscle mechanoreceptor-evoked increased myocardial contractility.

Heart rate transient at the onset of active and passive dynamic exercise

At the onset of dynamic exercise there is an almost instantaneous heart rate (HR) acceleration caused by neural activation of central motor areas (central command) and stimulation of mechanoreceptors located in the moving limbs. Aiming to identify the independent contribution of the peripheral mechanism to the initial HR response to exercise, 29 subjects performed two 4-s bouts of unloaded cycling (active (AEx) and passive (PEx)) on an adapted commercial tandem bicycle. PEx was accomplished by having a staff member pedal while sitting on the rear seat. The HR was continuously measured from electrocardiographic tracings. Records of electromyography (EMG) were obtained in a small sample of subjects during the exercise tasks. The number of pedal rotations was very similar (mean +/- SE) (AEx = 7.4 +/- 0.3, PEx = 7.5 +/- 0.2, P = 0.455), determining significant HR changes (P < 0.001) that were similar in the two types of exercise (AEx from 92 to 125 bpm: 35.9% increase; PEx from 87 to 111 bpm: 27.6% increase; P = 0.185). Contrasting to AEx, no muscle contraction was observed by EMG during PEx, suggesting that central command was absent. We concluded that independent activation of mechanoreceptors can promote HR acceleration at the onset of dynamic exercise.

Cholinergic stimulation with pyridostigmine increases heart rate variability and baroreflex sensitivity in rats

OBJECTIVE Impaired parasympathetic modulation increases the risk for sudden death in patients with heart diseases. Therefore, cholinergic stimulation may have a potential protective role. The aim of this study was to verify the effects of pyridostigmine bromide, a reversible cholinesterase inhibitor, on heart rate (HR), blood pressure (BP), HR and BP variability, and baroreflex sensitivity (BS). METHODS Male Wistar rats were divided in two groups: (1) treated with pyridostigmine in drinking water (7 days, n=10; PYR) and (2) a control group (n=12; CTR). BP was recorded in freely moving rats, and HR and BP variability were quantified by the standard deviation (S.D.) of the mean values during a 30-min period and by spectral analysis. BS was assessed by the ratio between pulse interval and BP power spectra (spontaneous BS) and also by the changes on HR produced by phenylephrine and sodium nitroprusside-induced BP changes. RESULTS Treated rats had a PYR intake of 7.91+/-1.90 mg/day (approximately 31 mg/kg/day). There were no differences between groups concerning resting HR (P=0.158), systolic BP (P=0.481), and BP variability (P=0.201). On the other hand, treatment with PYR increased HR variability on the time domain (S.D.-PYR: 13.5+/-5.3 ms vs. CTR: 9.9+/-3.6 ms; P=0.034) and frequency domain (Total power--PYR: 208.3+/-157.7 ms(2) vs. CTR: 109.2+/-65.6 ms(2); P=0.030). BS was also augmented with PYR for both the spontaneous method (High frequency band--PYR: 2.55+/-1.06 ms/mm Hg vs. CTR: 1.85+/-0.60 ms/mm Hg; P=0.033) and the drug-induced reflex bradycardia (PYR: 2.48+/-1.02 bpm/mm Hg vs. CTR: 1.54+/-0.58 bpm/mm Hg; P=0.024) and reflex tachycardia (PYR: 4.08+/-1.04 bpm/mm Hg vs. CTR: 2.95+/-1.30 bpm/mm Hg; P=0.037). CONCLUSIONS In conclusion, treatment with pyridostigmine increased HR variability and BS in normal rats with no modifications on basal hemodynamic parameters. Considering that reduced HR variability and baroreflex sensitivity are independent risk factors in heart disease, the present results support the concept that cholinergic stimulation with pyridostigmine may become a therapeutic option for vagal dysfunction.

Neural Regulation of Cardiovascular Response to Exercise: Role of Central Command and Peripheral Afferents

During dynamic exercise, mechanisms controlling the cardiovascular apparatus operate to provide adequate oxygen to fulfill metabolic demand of exercising muscles and to guarantee metabolic end-products washout. Moreover, arterial blood pressure is regulated to maintain adequate perfusion of the vital organs without excessive pressure variations. The autonomic nervous system adjustments are characterized by a parasympathetic withdrawal and a sympathetic activation. In this review, we briefly summarize neural reflexes operating during dynamic exercise. The main focus of the present review will be on the central command, the arterial baroreflex and chemoreflex, and the exercise pressure reflex. The regulation and integration of these reflexes operating during dynamic exercise and their possible role in the pathophysiology of some cardiovascular diseases are also discussed.

Heart rate responses to deep breathing and 4-seconds of exercise before and after pharmacological blockade with atropine and propranolol

Two autonomic tests which evaluate cardiac vagal activity, the respiratory sinus arrhythmia and the newer 4-second exercise test, have been compared. From electrocardiograph tracings, respiratory sinus arrhythmia was quantified by the ratio between the longest R-R interval during expiration and the shortest one during inspiration (E/I ratio), and the 4-second exercise test by the ratio between the last R-R interval before and the shortest one during exercise (B/C ratio). In 29 healthy subjects there was a correlation (R = 0.60,p < 0.05) between the responses to the two tests. In a group of six healthy subjects the same tests were performed after autonomic blockade with intravenous atropine and/or propranolol. The heart rate rise during the 4-second exercise test was nearly abolished by atropine (mean ± SD) (B/C: control = 1.53/0.33; after atropine = 1.04/0.03), whereas RSA was diminished to a lesser extent (E/I: control = 1.59/0.24; after atropine = 1.13/0.07). β-adrenoceptor blockade did not affect the test ratios (after propranolol: B/C = 1.51/0.33 and E/I = 1.45/0.14). Successive tests during the following hour after atropine infusion showed a somewhat faster recovery of the respiratory sinus arrhythmia than the heart rate acceleration induced by the 4-second exercise test (p < 0.05). We conclude that there may be some difference in the mechanisms which contribute to the heart rate changes in these two autonomic cardiovascular tests; these remain to be clarified. The 4-second exercise test may be an alternative to the respiratory sinus arrhythmia test in the non-invasive evaluation of cardiac parasympathetic activity.

Coronary artery bypass surgery and longitudinal evaluation of the autonomic cardiovascular function

IntroductionImbalance in autonomic cardiovascular function increases the risk for sudden death in patients with coronary artery disease (CAD), but the time course of the impact of coronary artery bypass grafting (CABG) on autonomic function has been little studied. Thus, the purpose of the present study was to determine the effects of the CABG on the cardiovascular autonomic function.MethodsPatients undergoing CABG (n = 13) and two matched control groups (patients with CAD who refused surgical treatment [n = 9], and healthy volunteers [n = 9]) underwent a prospective longitudinal study consisting of autonomic evaluation before and after (3, 6, 15, 30, 60, and 90 days) surgery, including measurement of heart rate variability (HRV), respiratory sinus arrhythmia (RSA), and Valsalva maneuver.ResultsAfter CABG there was a decrease in, and a later recovery of, (1) the HRV in the time domain and in the frequency domain, (2) RSA, and (3) Valsalva maneuver.ConclusionsCABG caused an impairment, reversible after 60 days, of cardiovascular autonomic function, with a maximal decrease on about the sixth day after surgery.

Cholinergic stimulation with pyridostigmine reduces ventricular arrhythmia and enhances heart rate variability in heart failure.

BACKGROUND Increased ventricular arrhythmia density and reduced heart rate variability are associated with risk of death in patients with heart failure. Cholinesterase inhibition with pyridostigmine bromide increases heart rate variability in normal subjects, but its effect on patients with heart failure is unknown. In this study, we tested the hypothesis that short-term administration of pyridostigmine bromide, a cholinesterase inhibitor, reduces ventricular arrhythmia density and increases heart rate variability in patients with congestive heart failure. METHODS Patients with heart failure and in sinus rhythm participated in a double-blind, cross-over protocol, randomized for placebo and pyridostigmine (30 mg orally 3 times daily for 2 days). Twenty-four hour electrocardiographic recordings were performed for arrhythmia analysis and for the measurement of time domain indices of heart rate variability. Patients were separated into 2 groups, according to their ventricular arrhythmia density. The arrhythmia group (n = 11) included patients with >10 ventricular premature beats (VPBs) per hour (VPBs/h), and the heart rate variability group (n = 12) included patients with a number of VPBs in 24 hours not exceeding 1% of the total number of R-R intervals. RESULTS For the arrhythmia group, pyridostigmine resulted in a 65% reduction of ventricular ectopic activity (placebo 266 +/- 56 VPBs/h vs pyridostigmine 173 +/- 49 VPBs/h, P =.03). For the heart rate variability group, pyridostigmine administration increased mean R-R interval (placebo 733 +/- 22 ms vs pyridostigmine 790 +/- 33 ms, P =.01), and in the time domain indices of heart rate variability root-mean-square of successive differences (placebo 21 +/- 2 ms vs pyridostigmine 27 +/- 3 ms, P =.01) and percentage of pairs of adjacent R-R intervals differing by >50 ms (placebo 3% +/- 1% vs pyridostigmine 6% +/- 2%, P =.03). CONCLUSION In patients with heart failure, pyridostigmine reduced ventricular arrhythmia density and increased heart rate variability, most likely due to its cholinomimetic effect. Long-term trials with pyridostigmine in heart failure should be conducted.

Atividade física e saúde na infância e adolescência

Um estilo de vida ativo em adultos está associado a uma redução da incidência de várias doenças crônico-degenerativas bem como a uma redução da mortalidade cardiovascular e geral. Em crianças e adolescentes, um maior nível de atividade física contribui para melhorar o perfil lipídico e metabólico e reduzir a prevalência de obesidade. Ainda, é mais provável que uma criança fisicamente ativa se torne um adulto também ativo. Em conseqüência, do ponto de vista de saúde pública e medicina preventiva, promover a atividade física na infância e na adolescência significa estabelecer uma base sólida para a redução da prevalência do sedentarismo na idade adulta, contribuindo desta forma para uma melhor qualidade de vida. Nesse contexto, ressaltamos que a atividade física é qualquer movimento como resultado de contração muscular esquelética que aumente o gasto energético acima do repouso e não necessariamente a prática desportiva. Este documento, elaborado por médicos especialistas em exercício e esporte, baseia-se em conceitos científicos e na experiência clínica, tendo como objetivos: 1) estabelecer os benefícios da atividade física na criança e no adolescente; 2) caracterizar os elementos de avaliação e prescrição do exercício para a saúde nessa faixa etária; 3) estimular a recomendação e a prática da atividade física nas crianças e adolescentes, mesmo na presença de doenças crônicas, visto que são raras as contra-indicações absolutas.