Haemodynamic Responses to Static and Dynamic Handgrip before and after Autonomic Blockade

Abstract

1. Six healthy men performed static and dynamic handgrip to local muscular fatigue in approximately 6 min under control conditions, i.e. without drugs and after combined parasympathetic and beta-adrenergic blockade with atropine and metoprolol. 2. From rest to exercise at fatigue, systolic, diastolic and mean arterial pressures increased by 32 +/- 4 and 39 +/- 3 mmHg, 24 +/- 3 and 26 +/- 4 mmHg, and 26 +/- 3 and 30 +/- 3 mmHg respectively for static and dynamic handgrip. There were no significant differences between the pressor responses for the two modes of contraction. Cardiac output increased significantly only during dynamic exercise. Total peripheral resistance increased by 2.3 +/- 1.0 units for static handgrip (P less than 0.05) and by 0.7 +/- 0.8 unit (P greater than 0.05) for dynamic handgrip. Autonomic blockade abolished the heart rate response to both static and dynamic handgrip. For both modes of contraction the systolic arterial pressure responses were 9-12 mmHg lower (P less than 0.05) after autonomic blockade, but the diastolic and mean pressure responses were not significantly affected. A significant increase in cardiac output persisted during dynamic exercise. The increase in peripheral resistance during static exercise tended to be greater after blockade. Plasma noradrenaline and adrenaline levels showed only minor elevations in response to static and dynamic handgrip and were not changed by autonomic blockade. 3. These data indicate that when performed to a common end-point with identical small muscle groups static and dynamic exercise produce an equally large pressor response, which is only slightly attenuated by autonomic blockade.

Physiological responses to four hours of low-level repetitive work

“…In our study, the combination of low-level intermittent handgrip and attention demands resulted in considerable increases in urinary concentrations of epinephrine, norepinephrine, and cortisol when compared with the corresponding concentrations on the reference day. Two previous studies have shown that plasma concentrations of norepinephrine, but not epinephrine, increase in response to short-term dynamic handgrip at 25% MVC (4,5). Due to considerable differences in physical demands and duration, comparisons with these studies must be made with caution.…”

“…The physiological responses to dynamic whole-body physical demands such as running or cycling are well established for concentrations of epinephrine, norepinephrine, and cortisol (1), and they are known to some degree for adrenocorticotrophic hormone (ACTH), dehydroepiandrosterone sulfate (DHEA-S), prolactin, and testosterone (2,3), whereas the physiological responses to low-level physical demands such as dynamic handgrip work are less clear (4,5).…”

Influence of nebivolol on the cardiovascular hemodynamics during postural changes and isometric exercise

“…If, however, the cardiac output cannot increase normally, as occurs when the increase in heart rate is inhibited due to beta blockade, the same increase in blood pressure is achieved by increased constriction of the systemic vessels [18,19]. The prime purpose of this reflex seems to be the increase in blood flow to the contracting muscle, and it calls on any combination of cardiac output and peripheral vascular resistance to achieve this goal [20].…”

Different responses of muscle sympathetic nerve activity to sustained and rhythmic handgrip exercises.

“…Rhythmic exercise is associated with relatively large increases in heart rate and cardiac output and marked reductions in total peripheral resistance, which result in only small increases in mean arterial pressure. In contrast to this, sustained exercise produces pronounced increases in mean arterial pressure, normally brought about by moderate increases in heart rate and cardiac output with little or no change in total peripheral resistance (LIND and McNicoL, 1967;BLOMQvisT et al, 1981;LEwis et al, 1983). The difference in responses of total peripheral resistance to sustained and rhythmic exercises may be due to differences in sympathetic tone innervating the vasculature of the visceral, as well as the skeletal muscles.…”

“…Therefore, the difference in MSA activation during sustained and rhythmic contractions is not explained, it seems, by the difference in reflex activation by afferent input from peripheral chemoreceptors. LEWIS et al (1983) showed that the rhythmic handgrip led to significant increases both in heart rate and cardiac output, but sustained handgrip did not induce significant changes in these parameters. The increase in cardiac output during rhythmic exercises was probably induced by increases in the venous return of blood to the heart due to muscle pumping effects.…”