The use of isometric exercise as a means of evaluating the parasympathetic contribution to the tachycardia induced by dynamic exercise in normal man

Abstract

Fourteen normal subjects were submitted to isometric exercise (IE), dynamic exercise (DE) and a combination of the two (IE + DE). The main purpose of the present study was to use IE as a means of evaluating the mechanism of the heart rate (HR) increase induced by DE. To this end, the magnitude of the IE (handgrip) was standardized so as to cause an elevation of HR almost exclusively by vagal withdrawal: IE was performed using a dynamometer strain-gauge system with a linear response at 75% of maximum voluntary contraction (MVC) for 10 s, repeated at 1 min intervals. The change in HR evoked by IE under control conditions was compared with that evoked during DE, and during the corresponding recovery period. DE was performed by the legs, with the subject in the seated position for 4 min, at workloads of 55 and 105 watts, separated by a rest period. In the combined protocol, IE was performed at the beginning of DE, as well as at 1, 2 and 3 min during DE, and at 0, 1, 2, 3 and 5 min during recovery period. The following results were obtained: (1) IE associated with DE always induced smaller increase in heart rate than IE alone, and this effect was more marked at 105 than at 55 W; this finding suggested a workload-dependent vagal withdrawal at the very beginning of DE that was sustained until the end of effort.(ABSTRACT TRUNCATED AT 250 WORDS)

Is cardiac autonomic modulation during upper limb isometric contraction and Valsalva maneuver impaired in COPD patients?

“…The HR response to the VM is mainly influenced by cardiac autonomic control, which is responsible for the rapid increase phase, with vagal withdrawal over the sinus node, as well as for the reduction after cessation of the VM, with vagal tone activation. These adjustments may occur in response to the activation of cardiopulmonary receptors and arterial baroreceptors 17,19,37,38…”

Resposta da frequência cardíaca durante o exercício isométrico de pacientes submetidos à reabilitação cardíaca fase III

“…The central mechanism activates neuronal pathways from central nervous system to modify the activities of sympathetic and parasympathetic systems, consequently determining some cardiovascular responses 1 . In addition, evidences from electromyography records show that the activation of more motor units of muscle fibers recruited during a contraction is related to the neural mechanism of central command, which determines immediate changes in the level of efferent activity from SNS and PNS, acting on heart, and of SNS, acting on blood vessels 17,18 . Poliana H. Leite, Ruth C. Melo, Marcelo F. Mello, Ester da Silva, Audrey Borghi-Silva, Aparecida M. Catai Moreover, the reflex neural mechanism, related to mechanical and metabolic activities from the muscle in contraction, also determines the level of autonomic activity on cardiovascular system.…”

A influência da idade e da reposição hormonal sobre a modulação autonômica do coração e o limiar de anaerobiose.

“…Quanto à posição corporal, não observamos diferenças significativas nos valores de VFC entre as posições supina e sentada, tanto para as voluntárias jovens, como para as PMCRH. Outros estudos também não observaram alterações nos índices temporais de VFC com a mudança postural (MARÃES, 1999;RIBEIRO, 2001;RIBEIRO et al, 2001a;SILVA et al, 2001 (ROBINSON et al, 1966;NORDENFELT, 1971;MACIEL et al, 1986;GALLO Jr et al, 1988;SEALS & VÍCTOR, 1991;NÓBREGA & ARAÚJO, 1993).…”

“…Na análise no domínio do tempo, a FC instantânea e os intervalos R-R são determinados e posteriormente analisados por meio de cálculos repouso, manobras autonômicas e durante exercício físico (GROSSMAN et al, 1991;AHMED et al, 1994;MUKAI & HAYANO, 1995;BARBOSA et al, 1996;YAMASAKI et al, 1996;ALONSO et al, 1998;MARÃES et al, 2000a;2000b;MASSIN et al, 2000;RIBEIRO et al, 2000;2001a;ROSÁRIO et al, 2000;SILVA et al, 2001;CATAI et al, 2002 (SATO et al, 1980;MACIEL et al, 1986;GALLO Jr et al, 1988;MITCHELL, 1990).…”

“…Diversos estudos, com ou sem bloqueio farmacológico, demonstraram que a resposta da FC durante o exercício dinâmico é mediada por modificações na atividade dos eferentes simpático e parassimpático e que a relativa contribuição destas eferências estão na dependência da intensidade e duração do esforço (ROBINSON et al, 1966;NORDENFELT, 1971;MACIEL et al, 1986;GALLO Jr et al, 1988;SEALS & VÍCTOR, 1991;NÓBREGA & ARAÚJO, 1993 (MACIEL et al, 1986;GALLO Jr et al, 1988;YAMAMOTO et al, 1991;NÓBREGA & ARAÚJO, 1993;TULPPO et al, 1996) ALONSO et al (1998)…”