Articles: pain-threshold.
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Cardiac pain is a conscious experience that can be explored only indirectly with experimental approaches. The exact machanisms eliciting cardiac pain still remain obscure. The afferent fibres running in the cardiac sympathetic nerves are regarded as the essential pathway for the transmission of cardiac pain. ⋯ Ventricular sympathetic afferent fibres whether myelinated or unmyelinated, always possess some mechanosensitivity and respond to normal chemical and mechanical stimuli, thus displaying properties of polymodal receptors. Afferent vagal fibres may contribute to the mechanisms of cardiac nociception by modulating the threshold and characteristics of pain. Experimental studies identified three main mechanisms, which may be responsible for eliciting cardiac pain during ischemic periods in humans: a) nonphysiological motion of the ischemic left ventricular wall (bulging) and an excitation of mechanical receptors by passive stretching. b) The excitation of free sensory nerve endings by chemicals such as bradykinin, PGE(2), adenosin, histamin or potassium. c) A combination of a and b: algogenic chemicals may sensitize mechanical receptors and therefore lower their threshold for nociception.
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Conventional clinical dosages of local anesthetics may not be sufficient to block conduction of all afferent impulses, which is important for an effective epidural sensory blockade. Further depression of the transmission of information can be accomplished by central modulating mechanisms, preventing sensory perception. Since there are interindividual differences in the quality of modulating mechanisms, standardized depression of impulse propagation by the local anesthetic is associated with a wide variation in the total depression of afferent impulses. ⋯ Patients with a low pain threshold require a more highly concentrated local anesthetic. The addition of opioids to the local anesthetic will permit the use of lower concentrations of the local anesthetic itself. Optimal use of diagnostic, prognostic, and therapeutic epidural blockades is possible only if the influence of modulating mechanisms is taken into account.
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In repeated clinical studies a preponderance of pain syndromes on the left side of the body has frequently been observed. Experimental studies in humans revealed a lower pain threshold on the left, nondominant side. On the other hand, some studies do not confirm this lateralization. ⋯ For pain induced by pressure, lateral asymmetry increased with pain intensity, for the other two methods it was constant. Lateral asymmetry was found in all subjects, but significant differences could only be demonstrated in female Ss. It is concluded that both gender and handedness contribute to lateral asymmetry of pain sensitivity in man.
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The effectiveness of relaxation techniques as a means of increasing pain threshold and pain tolerance and of decreasing anxiety was tested. Forty-two physiotherapy students were divided into experimental and control groups and tested on pain threshold, pain tolerance and anxiety. ⋯ Their results showed that a single session of relaxation significantly increased their pain threshold and pain tolerance and decreased their anxiety about the situation. No such changes were noted when the control group was re-tested.