Articles: function.
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Cerebral potentials evoked by cutaneous heat stimuli from an infrared laser (LEP) enable overall controls of thin fibre function and anterolateral tract projection, which is of special meaning in the diagnosis of normal and disturbed pain pathways. Owing to the long-wave radiation, the laser energy is completely absorbed within the most superficial skin layers only a few 100 mum in depth and activates only the most superficial afferents, i.e. the thermo- and nociceptive A, delta and C fibres. According to the particular fibre spectrum activated, a single laser stimulus elicits a typical double pain sensation: the first pain appears with a mean reaction time of approximately 400 ms and is described as a sharp and stinging, well-localizable pinprick sensation; this pain is induced by A delta fibre activity with a mean conduction velocity of 14 m/s. ⋯ Both sensations and both evoked potentials can emerge to very different degrees in healthy subjects and in patients with neurological diseases. The diagnostic practicability of LEP is individuals illustrated with reference to patients with syringomyelia suffering from a dissociated sensory loss in cutaneous sensibility. In contrast to conventional electrical nerve stimuli, the laser stimuli allow monitoring of disturbances in the protopathic system projected to the anterolateral columns.
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The quantitative approach to the study of descending inhibition of spinal nociceptive transmission was initiated in Heidelberg through the use of natural, noxious stimulation and examination of the modulation of the encoding properties of spinal dorsal horn neurons. This important approach required control of the noxious stimulus, which had previously been inadequately considered, and the parametric assessment of modulatory influences on the encoding properties of spinal dorsal horn neurons. As a consequence, descending inhibition of spinal nociceptive transmission was found not to be homogeneous throughout the brainstem, but rather to be significantly different from different brainstem nuclei. ⋯ Most recently, the same approach has been profitably applied to studies that have focused onfacilitatory influences descending from many of the same brainstem sites. As a consequence, it has been proposed that there exists an endogenous pain facilitating system analogous to the well-accepted endogenous pain inhibitory system. While the function of the facilitatory system remains unknown, it is proposed that it may be important to long-lasting pain conditions that exist in the absence of pathology.
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In contrast to pain from the skin, muscle pain is often referred to regions remote from the lesion. For instance, trigger points in neck muscles can elicit pain in the head. The convergence-projection theory of Ruch is still the central concept for the explanation of pain referral. ⋯ Therefore, the present paper presents another mechanism, which consists in acute changes in dorsal horn synaptic connections following nociceptive input from muscle. Results from animal experiments indicate that dorsal horn neurons possess ineffective synaptic connections with the body periphery, which become effective under the influence of a painful stimulus and lead to a mislocalization of pain. The neuropeptide substance P is probably involved in the changes in functional organization that occur in the dorsal horn during muscle pain and its referral.
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Journal of anesthesia · Oct 1993
Effects of halothane and isoflurane anesthesia on sympathetic adrenal nerve responses to carbon dioxide challenge in rats.
We studied the influence of two volatile anesthetics, halothane and isoflurane, on the circulatory and sympathetic nerve responses to carbon dioxide (9% CO2) in rats. Systolic blood pressure was depressed throughout the CO2 challenge and after an initial reduction, a gradual increase was observed in heart rate. Sympathetic adrenal nerve action potentials (SANA) significantly increased in contrast to negative responses in the circulatory functions. ⋯ The maximum changes in SANA from the baseline values were 110% and 40% for the halothane and isoflurane groups, respectively. The sympathetic reflex response to hyperacapnia was retained at 1.5 MAC for both anesthetics, though isoflurane depressed these responses more markedly than halothane. Our results suggest that halothane is a more preferable anesthetic than isoflurane when viewed from the standpoint of preservation of sympathetic nerve response in such undesirable situations as severe hypercapnia occurring during anesthesia.
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Sixteen experienced and 15 inexperienced observers watched videotapes showing participants of a back school program perform simple tasks to assess the functional adequacy of their posture. They had received basis or more extensive observer training. Intraclass correlation coefficients were computed as a measure of intra-and interobserver reliability. ⋯ By selecting the most reliable items two alternative measures of overall posture were constructured whose reliability coefficients ranged fromr=0.89 to 0.93 for the group of experienced observers. The reliability of the judgments by the more extensively trained inexperienced observers was also satisfactory. The observation method presented here can thus be regarded as a reliable and potentially valid instrument for assessing the outcome of back school programs.