Acta physiologica Scandinavica
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Acta Physiol. Scand. · Jul 2001
Clinical TrialEffects of heterotopic- and segmental counter-stimulation on the nociceptive withdrawal reflex in humans.
A nociceptive withdrawal reflex in 12 human volunteers was elicited by painful electrical stimulation applied to the cutaneous innervation area of the sural nerve. The evoked electromyographic reflex activities were recorded with surface electrodes placed on the short head of the biceps femoris muscle ipsi-lateral to sural nerve stimulation, before, during and after conditioning stimuli. The nociceptive withdrawal reflex was conditioned by nociceptive and non-nociceptive, heterotopic and segmental counter-stimulation. ⋯ Segmental nociceptive counter-stimulation inhibited the pain rating and tended to inhibit the nociceptive withdrawal reflex. There was no obvious correlation between visual analogue scale (VAS) and the nociceptive withdrawal reflex elicited by sural nerve stimulation neither in the group nor in the individual subject. This suggests that the nociceptive withdrawal reflex cannot always be used as a quantitative measure of pain.
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Acta Physiol. Scand. · Jul 2001
Diffusion-limited tissue equilibration and arteriovenous diffusion shunt describe skeletal muscle nitrous oxide kinetics at high and low blood flows in sheep.
This study evaluated the relative importance of perfusion and diffusion mechanisms in compartmental models of blood : tissue inert gas exchange in skeletal muscle. Nitrous oxide kinetics in a hind limb skeletal muscle bed were determined during and after 20 min of nitrous oxide inhalation, at separate low and high steady states of hind limb blood flow in five sheep under halothane anaesthesia. Nitrous oxide concentrations in arterial and femoral vein blood were determined using gas chromatographic analysis and femoral vein blood flow was monitored continuously. ⋯ The data was best described by allowing, in addition to diffusion-limited tissue equilibration, counter current diffusion of nitrous oxide between arterial and venous blood. The level of tissue blood flow modifies the magnitudes of both these diffusion effects. These results suggest a dual role of diffusion in blood : tissue inert gas equilibration in skeletal muscle.
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Acta Physiol. Scand. · Jul 2001
Additive hypothermic effects of the 5-HT1A receptor agonist 8-OH-DPAT and the dopamine D2/3 receptor agonist 7-OH-DPAT in the rat.
The objective of this study was to examine possible interactions between serotonergic and dopaminergic agents lowering core temperature via stimulation of 5-HT1A and dopamine (DA) D2 receptors, respectively. The effects of the 5-HT1A receptor agonist (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin HBr (8-OH-DPAT) and the DA D2/3 receptor agonist 7-OH-DPAT on core temperature was monitored in adult male Wistar rats, approximately 300 g body weight. ⋯ As expected, 7-OH-DPAT [0.5 and 2.0 micromol x kg(-1) subcutaneous (s.c.)] as well as 8-OH-DPAT (0.15-2.4 micromol x kg(-1) s.c.), produced a dose-dependent hypothermia. When combined, there were additive effects of the two compounds, although the effects of 7-OH-DPAT were attenuated by 8-OH-DPAT at the higher doses (0.6-2.4 micromol x kg(-1)), in all probability because of emerging DA D2 receptor blocking properties of the latter compound.
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New or increased muscular weakness, fatigue and muscle and joint pain with neuropathic electromyography (EMG) changes in a person with a confirmed history of polio constitute the cardinal symptoms of the post-polio syndrome. Unusual tiredness or fatigue is a common complaint in late polio subjects as is intolerance to cold. Fatigue in polio subjects can have several explanations: emotional fatigue, central nervous system fatigue, 'general' fatigue and/or neuromuscular fatigue. ⋯ Possible explanations may be an imperfection in the sarcoplasmatic reticulum with altered calcium release mechanisms (activation) or in sliding filament function (contractile properties). This may be a secondary effect to the enlarged muscle fibres. However, the prolonged subjective feeling of fatigue reported despite unchanged maximal voluntary contraction (MVC) remains unexplained.
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Acta Physiol. Scand. · Apr 2000
ReviewOxygen supply to contracting skeletal muscle at the microcirculatory level: diffusion vs. convection.
An adequate supply of oxygen is essential for the normal function of all cells. Because skeletal muscle cells have the ability to vary their oxygen demand by over an order of magnitude on going from rest to vigorous contraction, it is important that mechanisms be in place to ensure that the supply of oxygen is maintained at sufficient levels. Microcirculation plays a critical role in this process, as the terminal branches of this intricate network of blood vessels determine the distribution of perfusion, as well as the structural framework for diffusion. ⋯ Diffusive interactions among neighbouring capillaries have also been observed. In contracting muscles, microvessels observed immediately following the period of stimulation exhibit enhancements of both convective (increased flow of red blood cells) and diffusive (increased perfused capillary surface area) transport. The use of computational models in the interpretation of experimental studies is leading to an increased understanding of the processes that underlie the oxygen transport system in skeletal muscle.