RESUMO
The purpose of the present study was to determine if autonomic heart rate modulation, indicated by heart rate variability (HRV), differs during supine rest and head-up tilt (HUT) when sedentary and endurance-trained cyclists are compared. Eleven sedentary young men (S) and 10 trained cyclists (C) were studied. The volunteers were submitted to a dynamic ECG Holter to calculate HRV at rest and during a 70° HUT. The major aerobic capacity of athletes was expressed by higher values of VO2 at anaerobic threshold and peak conditions (P < 0.05). At rest the athletes had lower heart rates (P < 0.05) and higher values in the time domain of HRV compared with controls (SD of normal RR interval, SDNN, medians): 59.1 ms (S) vs 89.9 ms (C), P < 0.05. During tilt athletes also had higher values in the time domain of HRV compared with controls (SDNN, medians): 55.7 ms (S) vs 69.7 ms (C), P < 0.05. No differences in power spectral components of HRV at rest or during HUT were detected between groups. Based on the analysis of data by the frequency domain method, we conclude that in athletes the resting bradycardia seems to be much more related to changes in intrinsic mechanisms than to modifications in autonomic control. Also, HUT caused comparable changes in sympathetic and parasympathetic modulation of the sinus node in both groups.
Assuntos
Adulto , Humanos , Masculino , Sistema Nervoso Autônomo/fisiologia , Exercício Físico/fisiologia , Frequência Cardíaca/fisiologia , Descanso/fisiologia , Teste da Mesa Inclinada , Estudos Transversais , Eletrocardiografia Ambulatorial , Teste de Esforço/métodos , Consumo de Oxigênio/fisiologia , Resistência Física/fisiologia , Nó Sinoatrial/fisiologia , Esportes/fisiologia , Decúbito Dorsal/fisiologiaRESUMO
We investigated the effects of aerobic training on the efferent autonomic control of heart rate (HR) during dynamic exercise in middle-aged men, eight of whom underwent exercise training (T) while the other seven continued their sedentary (S) life style. The training was conducted over 10 months (three 1-h/sessions/week on a field track at 70-85 percent of the peak HR). The contribution of sympathetic and parasympathetic exercise tachycardia was determined in terms of differences in the time constant effects on the HR response obtained using a discontinuous protocol (4-min tests at 25,50,100 and 125 watts on a cycle ergometer), and a continuous protocol (25 watts/min until exhaustion allowed the quantification of the parameters (anaerobic threshold, VO2,AT; peak O2 uptake, VO2 peak; power peak) that reflect oxygen transport. The results obtained for the S and the T groups were: 1) a smaller resting HR in T (66 beats/min) when compared to S (84 beats/min); 2) during exercise, a small increase in the fast tachycardia (delta0-10 s) related to vagal withdrawal (P<0.05, only at 25 watts) was observed in T at all powers; at middle and higher powers a significant decrease (P<0.05 at 50, 100 and 125 watts) in the slow tachycardia (delta1-4 min) related to a sympathetic-dependent mechanism was observed in T; 3) VO2AT (S=1.06 and T=1.33 l/min) and VO2 peak (S=1.97 and T=2.37 l/min) were higher in T (P<0.05). These results demonstrate that aerobic training can induce significant physiological adaptations in middle-aged men, mainly expressed as a decrease in the sympathetic effects on heart rate associated with an increase in oxygen transport during dynamic exercise.
Assuntos
Humanos , Masculino , Pessoa de Meia-Idade , Adaptação Fisiológica , Exercício Físico , Frequência Cardíaca/fisiologia , Esforço Físico , Sistema Nervoso Simpático , Sistema Nervoso ParassimpáticoRESUMO
The purpose of the present study was to evaluate the effects of aerobic physical training (APT) on heart rate variability (HRV) and cardiorespiratory responses at peak condition and ventilatory anaerobic threshold. Ten young (Y: median = 21 years) and seven middle-aged (MA = 53 years) healthy sedentary men were studied. Dynamic exercise tests were performed on a cycloergometer using a continuous ramp protocol (12 to 20 W/min) until exhaustion. A dynamic 24-h electrocardiogram was analyzed by time (TD) (standard deviation of mean R-R intervals) and frequency domain (FD) methods. The power spectral components were expressed as absolute (a) and normalized units (nu) at low (LF) and high (HF) frequencies and as the LF/HF ratio. Control (C) condition: HRV in TD (Y: 108, MA: 96 ms; P<0.05) and FD - LFa, HFa - was significantly higher in young (1030; 2589 ms²/Hz) than in middle-aged men (357; 342 ms²/Hz) only during sleep (P<0.05); post-training effects: resting bradycardia (P<0.05) in the awake condition in both groups; VO2 increased for both groups at anaerobic threshold (P<0.05), and at peak condition only in young men; HRV in TD and FD (a and nu) was not significantly changed by training in either groups. The vagal predominance during sleep is reduced with aging. The resting bradycardia induced by short-term APT in both age groups suggests that this adaptation is much more related to intrinsic alterations in sinus node than in efferent vagal-sympathetic modulation. Furthermore, the greater alterations in VO2 than in HRV may be related to short-term APT
Assuntos
Humanos , Masculino , Pessoa de Meia-Idade , Exercício Físico , Frequência Cardíaca , Fases do Sono , Vigília , Limiar Anaeróbio , Sistema Nervoso Autônomo , Pressão Sanguínea , Consumo de OxigênioRESUMO
Foram determinados os niveis de proteinas totais e fracoes separados por eletroforese em acetato de celulose e, de IgG, IgM e IgA por imunodifusao radial simples em imunoplacas confeccionadas no proprio laboratorio, de 60 amostras de sangue do cordao umbilical de recem-nascidos normais do Hospital das Clinicas da Faculdade de Medicina de Ribeirao Preto. A distribuicao dos valores de proteinas totais e fracoes foi examinada por meio de um diagrama de pontos, exceto para alfa-1-globulina, detectada somente em 36.66% dos soros.As IgG e IgM foram detectadas em 100% das amostras e a A em apenas 6,6% em baixas concentracoes. Os autores observaram diferencas de resultados do presente trabalho na literatura nacional e estrangeira.Consideram que a determinacao de faixa de normalidade para uso local constitui referencia mais apropriada
Assuntos
Recém-Nascido , Humanos , Masculino , Feminino , Proteínas Sanguíneas , Imunoglobulinas , Cordão Umbilical , Eletroforese das Proteínas SanguíneasRESUMO
Anaerobic threshold (AT) is usually estimated as a change point problem by visual analysis of the cardiorespiratory response to incremental dynamic exercice. In this study, two phase linear (TPL) models of the linear-linear and linear-quadratic type were used for the estimation of AT. The correlation coefficiente between the classical and statistical approaches was 0.88, and 0.89 after outlier exclusion. The TPL models provide a simple method for estimating AT that can be easily implemented using a digital computer for the automatic pattern recognition of AT
Assuntos
Humanos , Anaerobiose , Teste de Esforço , Frequência Cardíaca , Respiração , MatemáticaRESUMO
Foram estudados os efeitos da bromoergocriptina (mesilato de bromo-2-alfa-ergocriptina) sobre o desenvolvimento in vitro de blastocistos de coelha, de 6 dias.O desenvolvimento do blastocito foi avaliado atraves dos seguintes parametros: diametro da blastula, indice mitotico, proporcao de mitoses atipicas, percentagem de celulas vacuolizadas e desenvolvimento do polo embrionario. A avaliacao estatistica dos resultados, atraves da analise de variancia, nao demonstrou a existencia de alteracoes do desenvolvimento do blastocisto por efeito da droga, pela concentracao da mesma (0,1 micrograma/ml ou 1 micrograma/ml) ou pela duracao do cultivo (6 ou 12 h).Concluiu-se que a bromoergocriptina nao provoca alteracoes teratogenicas em embrioes de coelha no estagio de pre-implantacao
Assuntos
Animais , Blastômeros , Bromocriptina , Técnicas In Vitro , CoelhosRESUMO
A secrecao do hormonio luteinizante foi realizada em pacientes do sexo masculino com doenca de Chagas cronica e individuos controles sob condicoes basais (secrecao basal pulsatil) e de estimulo (testes do LH-RH e citrato de clomifene). O grupo chagasico mostrou uma maior dispersao dos niveis do LH integral em condicoes basais que os apresentados pelo grupo controle. A frequencia dos pulsos e a concentracao media de testosterona de 12 amostras por um periodo de 3 horas, foram normais. Alteracoes funcionais da secrecao do LH hipofisario seguindo-se infusoes aguda ou continua de LH-RH nao foram demonstradas. Entretanto, a liberacao de LH durante o teste do citrato de clomifene mostrou valores com maior dispersao, principalmente no 8o. dia no grupo chagasico em relacao ao controle. Esses resultados, provavelmente, sugerem a existencia de uma disfuncao hipotalamica na doenca de Chagas cronica
Assuntos
Adulto , Pessoa de Meia-Idade , Humanos , Masculino , Doença de Chagas , Hormônio Luteinizante , Clomifeno , Testes de Fixação de Complemento , Hormônio Liberador de GonadotropinaRESUMO
The authors present a review of their contributions over the last decade to the study of the autonomic control of heart rate during dynamic exercise under physiological and pathological conditions. These studies included the development of new methods for the evaluation of autonomic control of heart rate during dynamic exercise in man. Pharmacological blockade of sympathetic (propranolol) and parasympathetic (atropine) efferent nerves was used to demonstrate differences in time constants and power-dependent relative participation of each division of the autonomic nervous system, as predominant mechanisms responsible for the tachycardia occurring during dynamic exercise. These findings have permitted the use of properly standardized dynamic exercise (discontinuous protocol: step powers, seated position on a bicycle ergometer, 4-min duration), as a simple and noninvasive test for the evaluation of autonomic control of the sinus node. This test has proved to be useful for detecting physiological autonomic adaptations induced by aerobic training, as well as dysfunctions occurring in pathologic conditions such as Chagas' disease and hyperthyroidism.