Heart rate at the onset of static exercise in man with partial neuromuscular blockade.

Reeves

et al. 1989

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SUMMARY1. We tested the hypothesis that afferent nerves from working muscles are important in determining the heart rate and blood pressure responses to brief maximal static exercise.2. In twenty human subjects, the heart rate and arterial blood pressure responses to a brief maximal voluntary handgrip were studied before and after axillary nerve anaesthesia or to maximal one-leg knee extension before and after epidural anaesthesia at L3-L4. Maximal knee extension could not be acomplished without performing a 'Valsalva-like' manoeuvre, but during handgrip it was possible to avoid the use of muscles other than those directly involved in the contraction. Heart rate and blood pressure were also monitored during a Valsalva manoeuvre of similar duration to the maximal voluntary contractions (4 s).3. During handgrip with normal breathing, axillary nerve anaesthesia reduced the heart rate response but had no effect on the blood pressure response.4. During a Valsalva manoeuvre, blood pressure increased but heart rate remained stable as long as expiratory pressure was maintained. During one-leg knee extension, epidural anaesthesia reduced the blood pressure response; however, the reduction in blood pressure was probably due to a reduction in the simultaneously performed 'Valsalva-like' manoeuvre.5. The results of this study suggest that afferent input from the working muscles is of importance for the heart rate responses to brief static muscle contractions. That such influence may be important for the blood pressure response remains unproven.

Section: Discussionmentioning

confidence: 99%

“…At the onset of a strong isometric (static) muscle contraction, heart rate increases and even the first heart beat comes faster (Hollander, 1975;Secher, 1985;Iwamoto, Mitchell, Mizuno & Secher, 1987). Vagal withdrawal is the efferent limb of this initial heart rate response (Freyschuss, 1970;Hollander, 1975).…”

Section: Introductionmentioning

confidence: 99%

Cardiovascular responses to brief static contractions in man with topical nervous blockade.

Lassen

Reeves

et al. 1989

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“…However, in experimental models in which one of the components is increased or decreased, the other may produce a near appropriate cardiovascular response. For example, some studies have emphasized the importance of the central neural component (Freyschuss, 1970;Goodwin, McCloskey & Mitchell, 1972;Schibye, Mitchell, Payne & Saltin, 1981;Secher, 1985;Leonard et al 1985) and others have emphasized the importance of the reflex neural component (Alam & Smirk, 1937;Hultgren & Sj6holm, 1982). Also animal studies have shown that cardiovascular responses similar to those occurring during exercise can be produced by either central or reflex neural mechanisms.…”

Section: Discussionmentioning

confidence: 99%

Epidural anaesthesia and cardiovascular responses to static exercise in man.

Reeves

Rogers

et al. 1989

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SUMMARY1. In human subjects, sustained static contractions of the knee extensors were performed in one leg with the same absolute (10% of the initial maximal voluntary contraction) and relative (30 % of the maximal voluntary contraction immediately prior to the static exercise) intensities before and during epidural anaesthesia. Epidural anaesthesia reduced strength to 62 + 8 % of the control value and partially blocked sensory input from the working muscles. During contractions performed with the same relative force, the increases in mean arterial pressure and heart rate were greater during control contractions than during epidural anaesthesia. During contractions at the same absolute force, there was no significant difference in magnitude of cardiovascular responses between control contractions and contractions performed during epidural anaesthesia.2. The metabolic role in the exercise pressor reflex was assessed by applying an arterial leg cuff 10 s before cessation of exercise and through the following 3 min of recovery. Although mean arterial pressure and heart rate decreased immediately after cessation of exercise, application of the arterial occlusion cuff resulted in higher post-exercise mean arterial pressure and heart rate values. Control and epidural mean arterial pressures during arterial occlusion were not significantly different.3. The results of this study suggest that the reflex neural mechanism rather than the intended effort (central command) is important in determining the blood pressure and heart rate responses to static exercise in man. That is, when epidural anaesthesia diminishes sensory feedback and produces muscular weakness, central command does not determine the cardiovascular response. This conclusion, however, is opposite to that derived from experiments with partial neuromuscular blockade which demonstrated the importance of central command in determining the cardiovascular response to static exercise (Leonard, Mitchell, Mizuno, Rube, Saltin & Secher, 1985). Taken together, these two studies are complementary and support the concept that both central and reflex neural mechanisms play roles in regulating arterial blood pressure and heart rate during static exercise in man.

“…Heart rate and mean arterial pressure increase immediately at the onset of static exercise (Freyschuss, 1970;Hollander, 1975;Secher, 1985;Iwamoto, Mitchell, Mizuno & Secher, 1987;Lassen, Mitchell, Reeves, Rogers & Secher, 1989). Two neural mechanisms have been considered to explain this instantaneous increase in heart rate.…”

Section: Introductionmentioning

confidence: 99%

Heart rate and arterial blood pressure at the onset of static exercise in man with complete neural blockade.

Friedman

Frank

et al. 1990

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SUMMARY1. We tested the 'muscle-heart reflex' hypothesis for the immediate increases in heart rate and blood pressure at the onset of static exercise in man by performing complete blockade of afferent nerves from the working muscles. Brief (5 s) maximal static hand-grip contractions were performed without performing a Valsalva-like manoeuvre and with no increase in central venous pressure both before and after combined axillary and radial blockade with lidocaine. Muscle strength was reduced to near zero. The effectiveness of the afferent neural blockade was evaluated by recording the heart rate and blood pressure responses and rating the perceived pain during a cold pressor test of the blocked and contralateral unblocked hand.2. The cold pressor test increased blood pressure but had no effect on heart rate. Afferent neural blockade eliminated the increase in blood pressure and the perceived pain associated with the cold pressor test. Maximal hand-grip contractions resulted in immediate and similar increases in heart rate and blood pressure before and after afferent neural blockade of the arm.3. The results of this study suggest that the immediate increases in heart rate and blood pressure at the onset of static exercise in man occur when the 'muscle-heart reflex' is inoperable.