Background The nociceptive flexion reflex is a physiological, polysynaptic reflex triggered by a nociceptive stimulus activating a withdrawal response. In chronic musculoskeletal-related pain conditions, a decreased nociceptive flexion reflex threshold has been suggested as a possible recognition evidence for central sensitization that may cause alteration of central nervous system processing. Objective The aim of the study was to systematically review reported comparisons of the nociceptive flexion reflex threshold in chronic pain patients and healthy individuals. Methods Electronic databases covering studies published between January 1990 and December 2019 were systematically searched. After application of exclusion criteria, 20 studies including 28 trials were included in this review. For meta-analysis, we used a random-effects model and funnel plot for publication bias. This research was registered at PROSPERO (CRD42019140354). Results Compared with healthy controls, standardized mean differences in nociceptive flexion reflex threshold were significantly lower in the total sample of chronic pain patients. Subgroup analysis indicated a homogenous decreased nociceptive flexion reflex threshold in studies reporting fibromyalgia, chronic pain, and joint pain while heterogeneity existed in other included pain conditions. Conclusions A lower nociceptive flexion reflex threshold in patients experiencing chronic pain conditions may imply hyperexcitability in central nervous system processing. As a preliminary study, the findings would act as a basis for developing a methodology assisting current clinical practices

The main purpose of this paper is to design a high pressure regulator which reduces an input pressure varying between 400 to 500 bars to 350 bars constant pressure. First of all, for mathematical simulation of regulator’s performance, the related equations were derived. Because of nonlinearity and coupling, these equations were solved by using numerical methods. Also, the effects of different parameters variation on regulator performance were investigated. One of the most important parameters in regulator performance is the preload of control spring. Deriving the maximum and minimum values of the spring force from the mathematical simulation, the proper spring was designed. In the next step, Finite element analysis, considering thermal effects, was performed using commercial software ABAQUS. To achieve sufficient safety factor, thicknesses were specified by trial and error. The results were in good agreement with the analytical solution.

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