Pain
The somatosensory system processes four broadly distinct sensory modalities: tactile, proprioceptive, thermal sensations, and pain. Interspersed between the delivery of a noxious stimulus and the subjective dimension of pain is a series of complex chemica
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Pain
Introduction The somatosensory system processes four broadly distinct sensory modalities: tactile, proprioceptive, thermal sensations, and pain. Interspersed between the delivery of a noxious stimulus and the subjective dimension of pain is a series of complex chemical and electrical events including local positive feed forward and negative feedback circuits, neuronal networks, and the involvement of several brain modules, including those of the vegetative nervous system. Pain stimulates different physiological responses like increased breathing, heart rate, blood pressure, sweating, and general arousal. Pain is a multidimensional phenomenon being influenced and stimulating different further body systems. Pain is also a major medical problem. Most patients going to general practitioners do this because of (acute or chronic) pain. The history of pain treatment efforts is as old as humanity, but only in the last 200 years major achievements beyond opium treatment have been made. Today, we are not able to imagine human life without local anesthesia at the dentist, general anesthesia for operations, epidurals in painful births, or pain treatment in cancer. Paradoxically, the burden of pain in the industrialized world seems rather to increase despite better treatment options. While cancer pain in more than 95 % of cases can be treated, if only existing recommendations are used properly, back pain, headaches, or fibromyalgia have a major impact on the quality of life of a sizable part of the population. HRV has been used to evaluate pain physiology and also to gain insight in pain syndromes that still puzzle us today. The direction is similar to that in other clinical conditions. Can we understand? Can we identify patient subgroups? Do HRV parameters correlate with outcome and can they be used for prognosis?
G. Ernst, Heart Rate Variability, DOI 10.1007/978-1-4471-4309-3_12, © Springer-Verlag London 2014
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Pain
Experimental Pain Models and Acute Pain Experimental pain models have been used for decades and are well established by now. Standards have been described and substantial studies have been published. Models include tools as simple as cold water and the time period until the participant feels pain (pain threshold) and until the pain is unbearable (pain tolerance). Other methods include electrically induced pain, capsaicin (the substance in chilli) injections, heat, ischemia, and others. Pain models are a convenient approach to look at HRV changes. Subjects undergoing cold pressure tests showed a small increase of normalized total power, decrease in HF, and increase in LF and VLF, all of them statistically not significant Madan et al. (2005). Using the cold pressure test (here: 6 min cold water) in another study showed HRV decreases of LF and HF in healthy subjects (Wirch et al. 2006). In a study focused on the gender effect of experimenters on subjective pain reports of healthy persons, a heat pain paradigm was used. A 30 × 30 mm aluminum contact electrode was applied on the right volar forear
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