Effect of Tubocurarine on Human Soleus and Gastrocnemius Muscles

112

SUMMARY1. In human subjects sustained static contractions of the quadriceps femoris in one leg were performed with the same absolute and the same relative intensity before and after partial neuromuscular blockade with either decamethonium or tubocurarine which reduced strength to about 50 % of the control value. During the contractions performed with the same absolute force, the magnitude of the cardiovascular responses (heart rate and blood pressure) was greater during neuromuscular blockade than during control contractions. During the contractions involving the same relative force the magnitude of the cardiovascular responses was almost the same with and without neuromuscular blockade. These findings were independent of the drug used.2. The metabolic part of the exercise pressor reflex was assessed by the application of an arterial cuff I min before cessation of exercise and for the following 3 min of rest. Although heart rate and blood pressure decreased after cessation of exercise, application of the tourniquet resulted in higher post-exercise values and this effect was seen both with and without neuromuscular blockade.3. Muscle biopsies from the subjects' m. vastus lateralis were analysed for fastand slow-twitch fibre composition showing 27-66 % slow-twitch fibres. No correlation was found between cardiovascular responses to static exercise, with or without neuromuscular blockade, and fibre type predominance. 4. The results suggest that the involvement of fast-or slow-twitch muscle fibres does not play a dominant role in the cardiovascular responses to static exercise in man. Both central command and reflex neural mechanisms are of importance, and it appears that these two control mechanisms are redundant and that neural occlusion may be operative. However, when partial neuromuscular blockade induces a disproportion between an increase in central command and a constant or decreasing muscle tension and metabolism, the larger signal arising from central command determines the magnitude of the cardiovascular responses.

Section: B Leonard and Others B Effect Of Tubocurarinementioning

confidence: 96%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Partial neuromuscular blockade and cardiovascular responses to static exercise in man.

Leonard¹,

Mitchell²,

Mizuno³

et al. 1985

112

“…The maintained mechanogram (and integrated electromyogram) shows the pattern of 2 Hz peaks. This pattern of 'single' contractions may reflect a primary reliance on fast-twitch muscle fibres as tubocurarine has a preference for slow-twitch fibres (Paton & Zaimis, 1951;Zaimis, 1953;Jewell & Zaimis, 1954;Bonde-Petersen et al 1975;Secher, Rube & Secher, 1982). A primary reliance on fast-twitch muscle fibres might explain the lower mechanical efficiency seen when tubocurarine is given as these fibres (during static contractions in the hamster (Goldspink, Larson & Davies, 1970), mouse (Crow & Kushmerick, 1982), and cat (Folkow & Halicka, 1968)) have been shown to produce a lower force-time integral per ATP-molecule turn-over than slow-twitch fibres.…”

Section: Discussionmentioning

confidence: 99%

Cardiovascular, ventilatory and catecholamine responses to maximal dynamic exercise in partially curarized man.

Galbo

Kjær

Secher

1987

101

SUMMARY1. In ten young men the ventilator, cardiovascular, catecholamine and metabolic responses to maximal dynamic leg exercise on a stationary bicycle were followed during partial neuromuscular blockade with tubocurarine. Maximal exercise was performed when the drug effect was at its maximum as well as during the subsequent reduction in the effect allowing a gradually increasing work intensity. The results were compared with those obtained during submaximal and maximal exercise performed without tubocurarine. Partial neuromuscular blockade decreased hand-grip strength to 41±+ 1-1 % (s.E. of mean) and the maximal work load to 27 + 2-4% of control values. Voluntary effort was maximal and the rate of perceived exertion was high at all levels ofexercise with tuboeurarine indicating a maintained intense central nervous motor command.2. During maximal action of the drug oxygen uptake was 1-67 + 0-11 1/min while only 0-91 + 0-13 1/min (P < 0-01) at the same work intensity without neuromuscular blockade. This difference may reflect a dominant reliance on fast-twitch muscle fibres when work was performed under the influence of tubocurarine.3. Compared at a given oxygen uptake ventilation was higher during work with tubocurarine than during control exercise (e.g. 55 + 4-2 and 40 + 2-2 1/min, respectively (P < 0-01), at a mean oxygen uptake of 1 9 1/min), while heart rate did not differ significantly (146 + 4-4 and 139 + 3-0 beats/min). With decreasing drug effect both variables increased towards the maximum values of 138 ± 4-5 1/min and 183 + 3.9 beats/min, respectively, achieved in control experiments at an oxygen uptake of 3-8 ± 0-2 1/min. Like heart rate the mean arterial blood pressure increased with increasing work load and was similar at a given oxygen uptake with and without tubocurarine. 4. During maximal exercise at peak tubocurarine effect plasma adrenaline and noradrenaline concentrations were smaller than during control maximum, 1-6 + 0-27 versus 3-4 +0-55 nmol/l (P < 0-01) and 7-5 + 1-3 versus 12-6 + 1-8 nmol/l (P < 0-05), respectively. However, comparisons at identical oxygen uptake rates revealed that catecholamine responses were markedly enhanced during tubocurarine treatment.Also, blood lactate concentrations were smaller at peak tubocurarine action than H. GALBO AND OTHERS during control maximum, 19+0042 mmol/l and 641+0-49 mmol/l (P < 001). In contrast the concentration of free fatty acids was higher in tubocurarine experiments: 0.5 + 0-07 against 0-3 + 0-03 mmol/l (P < 0-01) in agreement with the view that lactate inhibits the release of free fatty acids.5. The higher ventilations and plasma catecholamine values at given oxygen uptake rates in tubocurarine compared to control experiments suggest that activity in motor centres in the central nervous system (central command) has a role in regulation of these variables. On the other hand ventilation, heart rate, arterial blood pressure and, less so, catecholamine concentrations were much smaller than during control maximal exercise, and increased as abs...

“…Experiments involving muscle fatigue and partial neuromuscular blockade may therefore be of special interest. In both animal and human experiments decamethonium and tubocurarine have been shown to have a preference for fast-and slow-twitch muscle fibres, respectively (Paton & Zaimis, 1951;Zaimis, 1953;Jewell & Zaimis, 1954;Molbech & Johansen, 1969;Secher, R0rsgaard & Secher, 1978;Petrofsky & Lind, 1980;Secher, Rube & Secher, 1982.…”

Section: Introductionmentioning

confidence: 99%

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

Secher¹

1985

In human subjects the length of the first complete cardiac cycle after the onset of static finger or hand muscle contractions was recorded. Graded contractions as well as maximal contractions in which muscle fatigue was provoked by ischaemia were studied. Maximal finger muscle contractions were also weakened by partial neuromuscular blockade with either decamethonium or tubocurarine. The change in R‐R interval at the onset of exercise was variable and in part dependent on the length of the last R‐R interval before the onset of exercise. The largest decreases were seen when the preceding R‐R interval was long. During graded submaximal and maximal contractions a correlation was demonstrated between the change of the R‐R interval at the onset of exercise and the contraction intensity. At the onset of the weakest contractions a 3% prolongation of the R‐R interval was seen while the strongest contractions were associated with a shortening of 8%. At the onset of all maximal contractions, whether fatigued due to ischaemia or weakened by decamethonium or tubocurarine, a decrease in R‐R interval was seen independent of the force developed. When compared at the same resting R‐R interval, contractions performed with hand muscles elicited a greater shortening of R‐R interval than contractions with finger muscles. The results suggest that the initial change in heart rate at the onset of static muscle contractions is related to the voluntary effort rather than to the force developed, the state of the working muscles or to the type of muscle fibres involved. It may thus be elicited by 'cortical irradiation' rather than by a 'muscle‐heart reflex'. Its size depends on the length of the preceding R‐R interval, the intended contraction intensity and the muscle mass involved.