Aging Independently of the Hormonal Status Changes Pain Responses in Young Postmenopausal Women

Both aging and hormonal status have an effect on pain perception. The goal of this study was to isolate as much as possible the effect of aging in postmenopausal women. Thirty-two women with regular menstrual cycles (RMW) and 18 postmenopausal women (PMW) underwent a 2-minute cold pressor test (CPT) to activate DNIC with a series of tonic heat pain stimulations with a contact thermode to assess ascending pain pathways. We found that this procedure induced much less pain during the first 15 seconds of stimulation the PMW group (P = 0.03), while the mean thermode pain ratings, pain tolerance, pain threshold, and DNIC analgesia were similar for both groups (P > 0.05). The absence of the peak pain in the PMW was probably due to reduced function of the myelinated Aδ fibers that naturally occurs with age

Reduced analgesic effect of acupuncture-like TENS but not conventional TENS in opioid treated patients

Abstract : Evidence from recent animal studies indicates that the analgesic effect of low frequency TENS is reduced in opioid tolerant animals. The aim of the present study was to compare the analgesic effect of conventional (high frequency) and acupuncture-like (low frequency) TENS between a group of opioid treated patients and a group of opioid-naive patients in order to determine if this cross-tolerance effect is also present in humans. Twenty-three chronic pain patients (11 who took opioids and 12 who did not) participated in the study. Participants were assigned in a randomized cross-over design to receive alternately conventional and acupuncture-like TENS. There was a significant reduction in pain during and after conventional TENS when compared to baseline for both the opioid and non-opioid group (p.09). The reduced analgesic effect of acupuncture-like TENS in opioid treated patients is coherent with previous animal studies and suggests that conventional TENS should be preferred in patients taking opioids on a regular basis. Perspective: This study shows that patients taking opioids on a regular basis are less susceptible to benefit from acupuncture-like TENS. This phenomenon is probably attributable to the fact that the analgesia induced by acupuncture-like TENS and opioids are mediated by the same receptors (i.e. μ opioid receptors)

Deciphering the role of endogenous opioids in high frequency TENS using low and high doses of naloxone

Abstract : Previous human studies have shown that the analgesic effect of high frequency TENS could not be reversed by low doses of naloxone. The aim of the present study was to reinvestigate the possible contribution of opioid receptors in high frequency TENS analgesia by using low (0.02 mg/kg) and high (0.14 mg/kg) doses of naloxone. Naloxone (high and low doses) and saline were administered intravenously to young healthy adults using a double-blind randomised cross-over design. For each visit, TENS (100 Hz, 60 sec) was applied for 25 minutes to the external surface of the left ankle. TENS intensity was adjusted to obtain strong but comfortable (innocuous) paresthesias. Experimental pain was evoked with a 1 cm2 thermode applied on the lateral aspect of the left heel. Subjective pain scores were obtained before, during and after TENS. Because preliminary analyses showed that the order of presentation affected the pattern of results, only the first visit of every participant could be analyzed without fear of contamination from possible carry-over effects. These revealed that TENS maintained its analgesic properties following the injection of saline (p<.001) and the injection of a low dose of naloxone (p<.05). However, when a high dose of naloxone was administered, TENS analgesia was completely blocked (p=.20). These results strongly suggest that high frequency TENS involves opioid receptors. An insufficient amount of opioid antagonist likely prevented previous human studies from discovering the importance of opioid receptors in producing high frequency/ low intensity TENS analgesia

A web app-based music intervention reduces experimental thermal pain: A randomized trial on preferred versus least-liked music style

Digital technologies are increasingly being used to strengthen national health systems. Music is used as a management technique for pain. The objective of this study is to demonstrate the effects of a web app-based music intervention on pain. The participants were healthy adults and underwent three conditions: Conditioned Pain Modulation (CPM), Most-Liked Music (MLM) and Least-Liked Music (LLM). The music used is MUSIC CARE©, a web app-based personalized musical intervention (“U” Sequence based on a musical composition algorithm). Thermal pain was measured before starting the 20-min music intervention and after three time points for each music condition: 2.20, 11.30, and 20 min. Mean pain perceptions were significantly reduced under both LLM and MLM conditions. Pain decrease was more important under MLM condition than LLM condition at 2.20 min with a mean difference between both conditions of 9.7 (±3.9) (p = 0.0195) and at 11.30 min [9.2 (±3.3), p = 0.0099]. LLM is correlated with CPM but not MLM, suggesting different mechanisms between LLM and MLM. Musical intervention, a simple method of application, fits perfectly into a multidisciplinary global approach and helps to treat the pain and anxiety disorders of participants.Clinical trial registration: [https://clinicaltrials.gov/ct2/show/NCT04862832], ClinicalTrials.gov [NCT04862832]

Evidence of descending inhibition deficits in atypical but not classical trigeminal neuralgia

Abstract : Trigeminal neuralgia (TN) is a rare neuropathic facial pain disorder. Two forms of TN, classical TN (CTN) and atypical TN (ATN), are reported and probably have different aetiologies. The aim of the present study was to evaluate the functional integrity of the diffuse noxious inhibitory controls (DNIC) in (1) a group of patients with classical trigeminal neuralgia (CTN), (2) a group of patients with atypical trigeminal neuralgia (ATN), and (3) a group of healthy controls in order to determine if a descending pain modulation deficit could participate in the pathophysiology of TN pain. DNIC responses of 14 CTN patients, 14 ATN patients and 14 healthy controls were obtained by comparing thermode-induced facial heat pain scores before and after activating DNIC. DNIC was triggered using a standard counter-irritation paradigm (i.e., immersion of the arm in painfully cold water). General sensitivity to pain was also evaluated by measuring mechanical pain thresholds over 18 points located outside the trigeminal territory. Healthy participants and CTN patients showed a 21% and 16% reduction in thermode-induced pain following the immersion, respectively (all p-values <.01), whereas ATN patients experienced no change (p=.57). ATN patients also had more tender points (mechanical pain thresholds < 4.0 kg) than CTN and healthy controls (all p-values < .05). Taken together, these results suggest that the underlying physiopathology differs between CTN and ATN and that a deficit in descending inhibition may further contribute to the pain experienced by patients with ATN

The effect of conditioning stimulus intensity on conditioned pain modulation (CPM) hypoalgesia

Contexte: L’ampleur et la durée de la modulation de la douleur conditionnée (MDC) dépendent probablement de la nature et de l’intensité du stimulus de conditionnement. Objectifs: Le but de cette étude était de mesurer l’effet de l’intensité du stimulus de conditionnement sur la durée de l’hypoalgésie par MDC. Méthodes: Dans cette étude en simple aveugle, non randomisée, à mesures répétées, nous avons évalué l’hypoalgésie par MDC chez 20 participants en bonne santé à la suite de tests au froid à 7 ° C et 12 ° C. Le stimulus du test, une stimulation thermique de 60 secondes, a été administré avant le test au froid et immédiatement après, puis à nouveau à des intervalles de cinq minutes jusqu’à ce que les scores de douleur des participants reviennent aux niveaux antérieurs au stimulus de conditionnement. Deux seuils d’hypoalgésie ont été utilisés pour établir le retour au niveau antérieur au stimulus de conditionnement : à l’intérieur de - 10 / 100 de la situation de départ et à l’intérieur de - 20 / 100 de la situation de départ. Résultats: L’hypoalgésie par MDC, définie comme une réduction des niveaux de douleur > 10 / 100, n’a pas duré plus longtemps après le test au froid plus intense de 7 ° C que le test au froid de 12 ° C (32 minutes comparativement à 20 minutes, respectivement ; P = 0,06) ; des résultats similaires ont été obtenus lorsque l’hypoalgésie par MDC était définie comme une réduction des niveaux de douleur > 20 / 100 (16 minutes après le test au froid à 7 ° C comparativement à 9 minutes après le test au froid à 12 ° C ; P = 0,33). La durée de l’hypoalgésie par MDC était significativement plus longue lorsque le seuil 10 / 100 était utilisé comparativement au seuil 20 / 100, quelle que soit la température du test au froid (P = 0,008 pour le test au froid à 12 ° C ; P < 0,001 pour le test au froid à 7 ° C). Conclusions: Le stimulus de conditionnement plus intense n’a pas induit d’hypoalgésie par MDC de plus longue durée comparativement au stimulus de conditionnement moins intense. Le choix du seuil pour ce qui constitue une hypoalgésie par MDC a eu un effet significatif sur les résultats.Abstract : Background: The magnitude and duration of conditioned pain modulation (CPM) likely depends on the nature and intensity of the conditioning stimulus (CS). Aims: The aim of this study was to measure the effect of CS intensity on the duration of CPM hypoalgesia. Methods: In this single-blind, nonrandomized, repeated measures study, we assessed CPM hypoalgesia in 20 healthy participants following cold pressor tests (CPT) at 7°C and 12°C. The test stimulus, a 60-s heat stimulation, was administered before the CPT and immediately after, and again at 5-min intervals until participants’ pain scores returned to pre-CS levels. Two hypoalgesia thresholds were used to establish return to pre-CS level: within −10/100 of baseline and within −20/100 of baseline. Results: CPM hypoalgesia, when defined as a reduction in pain levels >10/100, did not last longer following the more intense 7°C CPT compared to the 12°C CPT (32 min vs. 20 min, respectively; P = 0.06); similar results were obtained when CPM hypoalgesia was defined as a reduction in pain levels of >20/100 (16 min following the 7°C CPT vs. 9 min following the 12°C CPT; P = 0.33). The duration of CPM hypoalgesia was significantly longer when the 10/100 threshold was used compared to the 20/100 threshold, regardless of CPT temperature (P = 0.008 for the 12°C CPT; P < 0.001 for the 7°C CPT). Conclusions: The more intense CS did not induce CPM hypoalgesia of longer duration compared to the less intense CS. The choice of threshold for what constitutes CPM hypoalgesia did have a significant effect on the results

Temporal Summation of Pain Is Not Amplified in a Large Proportion of Fibromyalgia Patients

Background. Recently, it has been proposed that fibromyalgia (FM), a chronic widespread pain syndrome, results from overactive endogenous excitatory pain mechanisms. Experimental studies using temporal summation paradigms have confirmed this hypothesis but have included small samples of patients, prompting our group to perform a large-scale study. Methods. Seventy-two female FM patients and 39 healthy females participated in the study. The temporal summation test consisted of a 2-minute continuous and constant heat pulse administered with a thermode on the participants' left forearm. Experimental temperature was set at a value individually predetermined to induce a 50/100 pain rating. Results. Relative to controls, FM patients had lower thermal pain thresholds and lower temporal summation of pain. However, 37 FM patients required experimental temperatures lower than the minimal temperature used in controls (45°C). Nevertheless, temporal summation was not increased in the other FM subgroup, relative to controls, despite equivalent experimental temperatures. Discussion. Our results suggest that temporal summation of pain is normal, rather than increased, in a large proportion of FM patients. Future studies on temporal summation in FM will need to be careful since some FM patients require abnormally low experimental temperatures that may confound results and make necessary to separate patients into subgroups

High Speed Range Enhancement of a Switched Reluctance Motor with Continous Mode

International audienceThis paper describes an original method for the elaboration of control laws for Switched Reluctance Motor for high speed operation. In this case, the control optimization relies on the choice of optimal turn-on and turn-off angles to ensure, in general, high global efficiency, in classical supply mode with full wave voltage. Then, after showing the influence of number of turns, a new supply mode called the continuous mode is described. This mode, used with a higher number of turns, allows to reduce the inverter current rating and hence silicon requirements without compromising performance at high speed. This make SRM competitive compared to other technologies (synchronous and induction motors). The simulation results for a 12/8 SRM are presented and compared to those for an induction motor

Altered autonomic nervous system reactivity to pain in trigeminal neuralgia

BACKGROUND: In the last two decades, there has been increasing evidence to suggest that trigeminal neuralgia (TN) may be linked to a dysfunction of the autonomic nervous system (ANS). The aim of the present study was to formally test this hypothesis by comparing the reactivity of the ANS to experimental pain in a population of TN patients and healthy controls. METHODS: Twelve patients diagnosed with classical TN and 12 healthy controls participated in the study. Cardiac activity was assessed while participants were instructed to rest and again during a cold pressor test (CPT). Heart rate variability analyses were performed off-line to obtain parasympathetic (high-frequency) and sympathetic (low-frequency) indices. RESULTS: At baseline, ANS measures did not differ between healthy controls and TN patients, and both groups showed a similar increase in heart rate during the CPT (all p-values > .05). However, TN patients showed a greater increase in cardiac sympathetic activity and a greater decrease in cardiac parasympathetic activity during CPT compared to healthy controls (all p-values < .05). Importantly, changes in sympathetic reactivity, from baseline to CPT, were negatively associated with the number of pain paroxysms experienced each day by TN patients in the preceding week (r = -.58, p < .05). CONCLUSION: These results suggest that TN, like many other short-lasting, unilateral facial pain conditions, is linked to ANS alterations. Future studies are required to determine if the altered ANS response observed in TN patients is a cause or a consequence of TN pain