Gender differences in electrical pain threshold responses to transcutaneous electrical nerve stimulation (TENS)

Electrical Ear Canal Stimulation as a Therapeutic Approach for Tinnitus-A Proof of Concept Study

Background: Tinnitus-the perception of sound despite the absence of an external source-can be a debilitating condition for which there are currently no pharmacological remedies. Our proof of concept study focused on the immediate effects of non-invasive electrical stimulation through the ear canal on loudness and tinnitus-induced distress. In addition, we aimed to identify variables that may affect the simulation outcomes. Methods: Sixty-six patients (29 women and 37 men, mean age 54.4 ± 10.4) with chronic tinnitus were recruited to the tertiary referral hospital between December 2019 and December 2021. They underwent 10 min of electrical stimulation through the ear canal for three consecutive days. Visual analog scales measured loudness and tinnitus-induced distress immediately before and after stimulation. Results: After three days of electrical stimulation, tinnitus loudness decreased in 47% of patients, 45.5% reported no change, and 7.6% reported worsening. Tinnitus severity decreased in 36.4% of cases, 59.1% of patients reported no change, and 4.5% reported worsening. Women responded positively to therapy earlier than men. In addition, tinnitus distress decreased in patients with compensated tinnitus but not in those with uncompensated tinnitus. Finally, patients with bilateral tinnitus improved earlier than those with unilateral tinnitus, and the age of the patients did not influence the stimulation results. Conclusions: Our proof of concept study confirms the potential of non-invasive electrical stimulation of the ear as a promising screening approach to identifying patients for more advanced electrostimulation treatment, such as an extracochlear anti-tinnitus implant. These findings have practical implications for tinnitus management, offering hope for improved patient care.

Randomized cross-over evaluation of investigator gender on pain thresholds in healthy volunteers

Background and aims: This randomized cross-over study in healthy volunteers was designed primarily to evaluate the potential impact of investigator gender on electrical pain threshold (EPT) and corresponding pain intensity levels, and secondly to evaluate potential differences in those interventions between female and male study participants. Methods: Forty adult volunteers (22 females) were included. An electrical stimulation device was used to determine EPT levels (in pain magnitude scores) in series of three in each study participant - once by a female, and once by a male investigator - according to a predefined cross-over design schedule. Corresponding levels of pain intensity were scored on a visual analog scale (VAS) slide ruler. Results: Study data was obtained and analysed in all participants. Significantly higher EPT levels were determined by the female investigator compared with the male investigator (median 22 (IQR 12-31) vs. 8 (6-10) pain magnitude scores; p<0.0001), despite similar levels of reported pain intensity (1.9 (1.2-3.0) vs. 2.0 (1.1-3.4) VAS units; p>0.300). There were no differences in EPT levels between female and male subjects evaluated by female (p>0.300) and male (p=0.125) investigators, or between the first and second series of stimulation (p>0.300). Conclusions: Our finding of significantly higher EPT levels when study participants of both genders - despite no difference in reported pain intensity - were evaluated by a female than by a male investigator, indicates a potential impact of investigator gender on the individual perception of pain. Implications: By contributing to a better understanding of how individual pain threshold levels are potentially influenced by investigator gender, this study might facilitate future evaluation of pain conditions in both preclinical and clinical settings.

Effect of Caudal Traction on Mechanical Nociceptive Thresholds of Epaxial and Pelvic Musculature on a Group of Horses With Signs of Back Pain

Direct muscular attachment from lumbar vertebrae to the caudal vertebrae of the tail suggests that caudal traction, also described as a tail pull, may affect lumbar vertebral segments and/or associated soft tissues in horses. Traction is a commonly used human manual therapy technique used for pain relief and anecdotally observed to relieve pain in horses. However, research is lacking validating the efficacy of manual caudal traction on the horse. The objective of this study was to determine if caudal traction has an effect on mechanical nociceptive thresholds (MNTs) in a group of horses with clinical signs of back pain. Pressure algometry was used to measure MNTs of five bilateral anatomical sites in the epaxial and pelvic musculature of 11 horses referred to physiotherapy because of clinical signs of back pain. Measurements were recorded both before and immediately after traction. A significant difference (P ≤ .05) was identified between mean before and after caudal traction algometry measurements in all described sites. The percentage of MNT increase was highest in the thoracic region (83%) compared with the lumbar (50%) and the pelvic (52.4%) regions. These results support an effect of caudal traction in increasing MNTs in the thoracolumbar and pelvic regions in horses. Further research to determine the clinical effect of this technique is warranted.

Genetics and Gender in Acute Pain and Perioperative Opioid Analgesia

Experimental and clinical acute pain research in relation to biological sex and genetics started in the 1980s. Research methods became more powerful and sensitive with the advancement in affordable gene sequencing methods and high-throughput genetic assays. Decades of research has identified several potential pharmaceutical targets, providing insights into future research direction, and understanding of acute pain and opioid analgesic effects in the clinical setting. However, there is insufficient evidence to make generalized recommendations for using genetic tests for clinical practice of acute pain management.

Effect of lidocaine cream analgesia for chest drain tube removal after video-assisted thoracoscopic surgery for lung cancer: a randomized clinical trial

BACKGROUND AND OBJECTIVES

Pain management makes an important contribution to good respiratory care and early recovery after thoracic surgery. Although the development of video-assisted thoracoscopic surgery (VATS) has led to improved patient outcomes, chest tube removal could be distressful experience for many patients. The aim of this trial was to test whether the addition of lidocaine cream would have a significant impact on the pain treatment during chest tube removal from patients who had undergone VATS for lung cancer.

METHODS

This clinical trial was a double-blind randomized study. Forty patients with histologically confirmed lung cancer amenable to lobectomy/segmentectomy were enrolled. All patients had standard perioperative care. Patients were randomly assigned to receive either epidural anesthesia plus placebo cream (placebo, Group P) or epidural anesthesia plus 7% lidocaine cream cutaneously around the chest tube insertion site and on the skin over the tube's course 20 min (Group L) before chest drain removal.

RESULTS

Visual analog scale (VAS) scores were higher in Group P (median 5, IQR, 3.25-8) than in Group L (median 2, IQR, 1-3). Pain intensities measured using a PainVision system were also higher in Group P (median 296.7, IQR, 216.9-563.5) than Group L (median 41.2, IQR, 11.8-97.0). VAS scores and the pain intensity associated with chest drain removal were significantly lower in Group L than Group P (p=0.0002 vs p<0.0001).

CONCLUSION

Analgesia using lidocaine cream is a very simple way to reduce the pain of chest tube removal after VATS.

TRIAL REGISTRATION NUMBER

UMIN000013824.

Does Studying Veterinary Medicine Improve Students' Haptic Perception Ability? A Pilot Study With Two Age-Groups

Haptic perception is an important tool for veterinarians. The present study analyzed the association between the haptic perception threshold of veterinary students and their palpatory experience. To approach this goal, 35 female students of veterinary medicine were divided into two groups with different levels of experience: (a) students with little practical experience, at the beginning of their studies (first year), and (b) students close to the end of their theoretical training (fourth year). To thoroughly evaluate the students' sense of touch, three different test procedures were used: the Haptic Threshold Test (HTT), the Haptic Figures Test (HFT), and tactile acuity. Contrary to our expectations, we found worse mean haptic perception thresholds (HTT) in the more experienced students than in the less experienced group. This effect was significantly correlated with age. Furthermore, we found that longer exploration times were not sufficient to compensate for shortcomings in haptic perception. We also found large interindividual differences. Future studies should investigate whether and to what extend these effects have an impact on students' palpation performance on simulators and live animals. Moreover, which beneficial effects may be achieved through an additional haptic training for students with inferior haptic thresholds should be investigated. Improving haptic perception abilities in veterinary students could be one important step toward achieving satisfactory Day One Competences in university graduates.

Aspects of Pain, Its Assessment and Evaluation from An Acupuncture Perspective

Pain is a major clinical problem that causes great suffering for the individual and incurs costs for society. Accurate assessment and evaluation of perceived pain is necessary for diagnosis, for choice of treatment, and for the evaluation of treatment efficacy. The assessment of an individual's pain is a challenge since pain is a subjective, multidimensional experience, and assessment is based on the person's own self-report. The results are often varied, possibly due to inter-individual variation, but also in relation to gender and aetiology.

A gold standard for pain assessment is still lacking, but rating scales, questionnaires, and methods derived from psychophysical concepts, such as threshold assessments and perceptual matching, are used. In the evaluation of pain and associated variables, both systematic and individual variation should be taken into account, as should pain-associated symptoms.

Recommendations for pain treatment should be based on the patient's specific needs. Therefore, it is important to assess the level of perceived pain taking individual variation into account. The methods used should preferably have proved to be useful in randomised controlled trials, and analysis of pain assessment should consider its non-metric properties. In the future, the use of studies with a naturalistic protocol together with individual assessment of individual pain responses could increase the internal and external validity.

Efficacy of cold application on pain during chest tube removal: a randomized controlled trial: A CONSORT-compliant article

BACKGROUND

Use of analgesics is the most common method to alleviate the pain induced by chest tube removal (CTR), but patient response to medication can vary and may not be achieved complete relaxation. This study was to determine the effectiveness of cold application in combination with standard analgesic administration before CTR on CTR-induced pain.

METHODS

A prospective, randomized, single-blind, sham-controlled study was conducted. In addition to the same routine care, subjects in the experimental group (n = 30) received cold application of 600-g ice packs 15 minutes before CTR, whereas subjects in the sham group (n = 30) received tap water packs. Numerical rating scale was used to measure pain intensity before, immediately after, and 10 minutes after CTR.

RESULTS

The generalized linear estimating equation (GEE) model, adjusted for other factors, both the groups demonstrated a trend toward decreased pain during CTR over time (P < .001), but no significant differences between the 2 groups (P = .65), even stratifying by gender. If we fixed experimental group, women significant reduced pain score of 2.7 on immediately after CTR compared with before CTR (P < .0001) and reduced pain score of 2.05 on 10 minutes after CTR compared with before CTR (P < .0001). The sham group had no similar performance as the experimental group. In the male subgroup, both experimental and sham groups, men significantly reduced pain score on immediately after CTR and 10 minutes after CTR compared with before CTR (P < .0001).

CONCLUSION

The results indicate that cold application is not more effective than sham treatment in decreasing pain during CTR, even among gender. Although statistically non-significant, clinically important differences of decreased pain score were observed with cold application among women (Clinical Trial Registration: clinicaltrials.gov identifier NCT03307239).

Toward a functional near-infrared spectroscopy-based monitoring of pain assessment for nonverbal patients

Pain diagnosis for nonverbal patients represents a challenge in clinical settings. Neuroimaging methods, such as functional magnetic resonance imaging and functional near-infrared spectroscopy (fNIRS), have shown promising results to assess neuronal function in response to nociception and pain. Recent studies suggest that neuroimaging in conjunction with machine learning models can be used to predict different cognitive tasks. The aim of this study is to expand previous studies by exploring the classification of fNIRS signals (oxyhaemoglobin) according to temperature level (cold and hot) and corresponding pain intensity (low and high) using machine learning models. Toward this aim, we used the quantitative sensory testing to determine pain threshold and pain tolerance to cold and heat in 18 healthy subjects (three females), mean age±standard deviation (31.9±5.5). The classification model is based on the bag-of-words approach, a histogram representation used in document classification based on the frequencies of extracted words and adapted for time series; two learning algorithms were used separately, K-nearest neighbor (K-NN) and support vector machines (SVM). A comparison between two sets of fNIRS channels was also made in the classification task, all 24 channels and 8 channels from the somatosensory region defined as our region of interest (RoI). The results showed that K-NN obtained slightly better results (92.08%) than SVM (91.25%) using the 24 channels; however, the performance slightly dropped using only channels from the RoI with K-NN (91.53%) and SVM (90.83%). These results indicate potential applications of fNIRS in the development of a physiologically based diagnosis of human pain that would benefit vulnerable patients who cannot self-report pain.

Maximum pain on visual analog scales in spinal disorders

BACKGROUND CONTEXT

Determining pain intensity is largely dependent on the patient's report.

PURPOSE

The objective of this study was to test the hypothesis that patients initially reporting a pain score of 10 out of 10 on the visual analog scale (VAS) would experience symptom improvement to a degree similar to patients reporting milder pain.

STUDY DESIGN

This study is a retrospective chart review.

PATIENT SAMPLE

A total of 6,779 patients seeking care for spinal disorders were included in the study.

OUTCOME MEASURES

The outcome measures used in the study were pain scores on the VAS pain scale, smoking status, morbid depression, gender, and the presence of known secondary gain.

MATERIALS AND METHODS

Patients with lumbar degenerative disk disease with or without spinal stenosis who reported a VAS pain score of 10 out of 10 were identified. Changes in reported VAS pain, patient age, smoking status, morbid depression, gender, and the presence of known secondary gain were examined.

RESULTS

A total of 160 individuals (2.9%) reported a maximum pain score of 10 out of 10 on a VAS at their initial presentation. The patients had a median improvement of 3 points in reported VAS pain between the first visit and the last follow-up appointment. The odds to improve by at least 40% on the VAS were 1.500 (95% confidence interval 1.090-2.065) compared with patients reporting submaximal pain. The proportion of patients with identifiable secondary gain was higher (p=.001) than that of patients with submaximal pain. Patients whose pain scores improved dramatically (ie, at least 4 points on the VAS) tended to be older (p=.001), to less often have secondary gain from their disease (p=.007), and to have a negative current smoking status (p=.002). Patients whose pain remained 10 out of 10 during the course of treatment smoked more frequently (p=.016).

CONCLUSIONS

Our analysis supports the need to consider the influence of secondary gain on the patients' reported VAS pain scores. Maximum pain seems to be a more acute phenomenon with some likelihood to significantly improve.

The immediate effects of lidocaine iontophoresis using interferential current on pressure sense threshold and tactile sensation

Iontophoresis is the noninvasive delivery of ions using direct current. The direct current has some disadvantages such as skin burning. Interferential current is a kind of alternating current without limitations of direct current; so the purpose of this study is to investigate and compare the effects of lidocaine, interferential current and lidocaine iontophoresis using interferential current. 30 healthy women aged 20-24 years participated in this randomized clinical trial study. Pressure, tactile and pain thresholds were evaluated before and after the application of treatment methods. Pressure, tactile and pain sensitivity increased significantly after the application of lidocaine alone (p < 0.005) and lidocaine iontophoresis using interferential current (p < 0.0001). Lidocaine iontophoresis using interferential current can increase perception threshold of pain, tactile stimulus and pressure sense more significantly than lidocaine and interferential current alone.

Measurement of pain and anthropometric parameters in women with chronic pelvic pain

RATIONALE, AIMS AND OBJECTIVES

To analyse anthropometric parameters, clinical pain and experimental pain in women with chronic pelvic pain (CPP).

METHODS

Ninety-one women with a clinical diagnosis of CPP, mean age of 40.03 ± 9.97 years, submitted to anthropometric evaluation based on body mass index (BMI) and percent body fat (%BF) using bioimpedance body composition monitor; pain intensity was determined by visual analogue scale (VAS), numerical categorical scale (NCS) and McGill Pain Questionnaire; experimental pain was determined by transcutaneous electrical nerve stimulation (TENS), and anxiety and depression symptoms were determined by the Hospital Anxiety and Depression scale.

RESULTS

A total of 54.8% of the women showed %BF >32 risk of disease associated with obesity. Regarding the anthropometric data, a statistically significant difference was observed between groups for both BMI and %BF (P<0.0001). In the analysis of pain intensity by the VAS, NCS and total McGill, there was no significant difference between the groups, and experimental pain by TENS revealed significant difference only between the normal weight and overweight groups (P=0.0154). The results of anxiety symptoms were above the cut-off point in all groups, with no significant difference between them (P=0.3710). The depression symptoms were below the cut-off point in the normal weight group and above the cut-off point in the overweight and obese groups, 9.469(4.501) and 9.741(4.848), respectively, with no significant difference between them (P=0.6476).

CONCLUSION

Evaluation of anthropometric parameters and pain measurements can be applied in clinical practice, making a contribution to the diagnosis and influencing the choice of a more effective treatment for women with CPP.

A systematic literature review of 10 years of research on sex/gender and experimental pain perception - part 1: are there really differences between women and men?

The purpose of this systematic review was to summarize and critically appraise the results of 10 years of human laboratory research on pain and sex/gender. An electronic search strategy was designed by a medical librarian and conducted in multiple databases. A total of 172 articles published between 1998 and 2008 were retrieved, analyzed, and synthesized. The first set of results (122 articles), which is presented in this paper, examined sex difference in the perception of laboratory-induced thermal, pressure, ischemic, muscle, electrical, chemical, and visceral pain in healthy subjects. This review suggests that females (F) and males (M) have comparable thresholds for cold and ischemic pain, while pressure pain thresholds are lower in F than M. There is strong evidence that F tolerate less thermal (heat, cold) and pressure pain than M but it is not the case for tolerance to ischemic pain, which is comparable in both sexes. The majority of the studies that measured pain intensity and unpleasantness showed no sex difference in many pain modalities. In summary, 10 years of laboratory research have not been successful in producing a clear and consistent pattern of sex differences in human pain sensitivity, even with the use of deep, tonic, long-lasting stimuli, which are known to better mimic clinical pain. Whether laboratory studies in healthy subjects are the best paradigm to investigate sex differences in pain perception is open to question and should be discussed with a view to enhancing the clinical relevance of these experiments and developing new research avenues.

Adult norms of the perceptual threshold of touch (PTT) in the hands and feet in relation to age, gender, and right and left side using transcutaneous electrical nerve stimulation

There is a lack of standardized and quantifiable measures of touch function, for clinical work. Furthermore, it is not possible to make accurate diagnostic judgments of touch function before normative values are estimated. The objectives of this study were to establish adult norms of the perceptual threshold of touch (PTT) for the hands and feet according to age and gender and to determine the effect of right/left side, handedness, height, weight, and body mass index (BMI) on the PTT. The PTT was assessed by using a high-frequency transcutaneous electrical nerve stimulator (Hf/TENS) with self-adhesive skin electrodes in 346 adults. The PTT was identified as the level registered in mA at which the participants perceived a tingling sensation. The PTT for all participants was a median of 3.75 mA (range 2.50-7.25) in the hands and a median of 10.00 (range 5.00-30.00) in the feet. With increasing age an increase of the PTT was found. Men reported higher PTT than women. The right hand had higher PTT than the left. Handedness, height, weight, and BMI did not affect the PTT. Adult norms of the PTT in the hands for age, gender, and right/left side are presented for four age groups. The present study's estimate of the PTT in the hands could be used as adult norms. Adult norms for the feet could not be estimated because the PTT values in the feet showed a great variance.

Diferenças de gênero no limiar sensitivo para estimulação elétrica nervosa em adultos jovens

OBJETIVO: Investigar diferenças de gênero no limiar neuronal sensitivo (LNS) para estimulação elétrica nervosa transcutânea (TENS) entre adultos jovens, e os presumíveis efeitos da termoterapia prévia. MÉTODOS: Foram divididos por gênero, 30 estudantes jovens sadios (15 homens e 15 mulheres entre 6/11 ciclo estral) com 22±2 anos de idade. TENS foi aplicada simultaneamente nos joelhos direito e esquerdo dos sujeitos com frequência de 20 Hz e duração de pulso 230µs. A amplitude da corrente elétrica (mǺ) foi aumentada gradativamente para registro do limiar de percepção (LS) e tolerância (LT), antes/após termoterapia. O aquecimento no joelho-D foi realizado por luz infravermelha (250 W) à 0≈70 cm perpendicularmente, e o resfriamento do joelho-E por compressa de gelo, ambos realizados durante 15 minutos. A temperatura tecidual foi registrada por termometria digital. Os dados foram analisados e diferenças estabelecidas em p<0.05. RESULTADOS: A temperatura tecidual após termoterapia foi diferente (p<0.05) entre gêneros. No LS basal para TENS não houve diferenças entre gêneros, porém, a termoterapia alteou o LS em ambos os sexos. O LT basal foi menor (p<0.05) em mulheres, entretanto, após a termoterapia aumentou (p<0.05) em ambos os sexos. CONCLUSÃO: Os LNS para TENS são gênero-termo-dependentes em jovens sadios.

On the threshold - evaluation of variability in effects of acupuncture in a gender perspective

Variable results of pain alleviation in response to acupuncture have been reported, complicating its interpretation. Sources of variability are probably multi-factorial, including the contribution of gender related effects. Gender related variation in perceived pain has been discussed frequently, but documented effects of acupuncture referring to gender are sparse. Furthermore, factors such as operationalisation of the outcome variable and the statistical method for evaluation could also be sources of variability. When pain is regarded as subjective, the produced data should be treated as ordinal. The rank-based method by Svensson, taking the non-metric qualities of the ordinal data into account as well as the variability at the group and the individual level, is therefore an alternative. The present commentary aims to (1) evaluate changes in electrical sensory thresholds and electrical pain thresholds after low frequency electro-acupuncture separately in healthy women and men; (2) introduce and exemplify the method by Svensson in a user-friendly approach. To analyze the systematic patterns of change in thresholds, indicating evidence of treatment on a group level, the relative position (RP) and relative concentration (RC), were measured. The variation related to the individual, the relative rank variation (RV) was also measured. The results were divergent between women (n = 23) and men (n = 22), i.e. unchanged sensory threshold after acupuncture at the group level in women while changed in men. The assessed pain threshold after acupuncture on the other hand was changed towards higher levels in women and unchanged in men. The individual variation was apparent in both women and men but larger in women. For statistical analysis of the variability for both group and individual related effects, the rank-based method by Svensson could be used. The present study indicates that evaluation of sensory and pain threshold response should be analysed separately in women and men.

Age, gender, and side differences of cutaneous electrical perceptual threshold testing in an able-bodied population

OBJECTIVE

To investigate age, gender, and left-right differences in cutaneous electrical perceptual threshold (EPT) testing in an able-bodied, Australian sample.

STUDY DESIGN

Prospective experimental.

SETTING

Hospital-based spinal cord injuries unit.

METHODS

Cutaneous electrical stimulation of the 28 dermatomes at ASIA sensory key points (C2-S4/S5) was performed on 29 female and 16 male healthy volunteers aged 21 to 76 years. Mean EPTs for each dermatome were compared (repeated measures ANOVA) for left-right, gender-related, and age-related (</ >50 years of age) differences.

RESULTS

There was no group difference between sides (repeated measures ANOVA, P = 0.934). Women across all ages had lower group mean EPTs than men (P < 0.0001). Women younger than age 50 years had lower mean EPTs than those older than age 50 years (P = 0.008). There was no group difference between younger and older men (P = 0.371). Analysis of individual dermatomes revealed no significant differences in thoracic dermatomes between genders or age groups, contrary to the limb dermatomes.

CONCLUSION

There were gender differences in EPT values across all ages. Women had higher EPTs as they advanced in age, but this was less clear in men. There was considerable somatotopic variability in EPTs, especially in the lower limbs. If EPT testing is to be applied to detect subclinical changes within a dermatome, establishment of age- and gender-specific somatotopic normograms is a prerequisite.

Is it all about sex? Acupuncture for the treatment of pain from a biological and gender perspective

Pain is a unique personal experience showing variability where gender and sex related effects might contribute. The mechanisms underlying the differences between women and men are currently unknown but are likely to be complex and involving interactions between biological, sociocultural and psychological aspects. In women, painful experimental stimuli are generally reported to produce a greater intensity of pain than in men. Clinical pain is often reported with higher severity and frequency, longer duration, and present in a greater number of body regions in women than in men. Women are also more likely to experience a number of painful conditions such as fibromyalgia, temporomandibular dysfunction, migraine, rheumatoid arthritis and irritable bowel syndrome. With regard to biological factors, quantitative as well as qualitative differences in the endogenous pain inhibitory systems have been implicated, as well as an influence of gonadal hormones. Psychosocial factors like sex role beliefs, pain coping strategies, and pain related expectancies may also contribute to the differences. Being exposed to repeated painful visceral events (eg menses, labour) during life may contribute to an increased sensitivity to, and greater prevalence of, pain among women. When assessing the outcome of pharmacological and non-pharmacological therapies in pain treatment, the factors of gender and sex should be taken into account as the response to an intervention may differ. Preferably, treatment recommendations should be based on studies using both women and men as the norm. Due to variability in results, findings from animal studies and experiments in healthy subjects should be interpreted with care.

Differences in electrical stimulation thresholds between men and women

OBJECTIVE

Surface electrical stimulation (ES) of skeletal muscle is used in a variety of clinical settings in healthy and unhealthy subjects of both sexes. Although women generally present larger amounts of subcutaneous adipose tissue than men, which could limit current flow to the stimulated muscle, sex-related differences in ES current levels have not been clearly demonstrated to date. We report data from healthy men and women.

METHODS

Sensory (current perception), motor (minimal knee extension torque production), and supramotor thresholds (10% of the maximal voluntary knee extension torque) and perceived pain during surface ES of the quadriceps femoris muscle were investigated in 40 healthy volunteers (20 men, 20 women).

RESULTS

Sensory threshold was lower in women than in men (-43%; p < 0.001). Similarly, female muscles required lower current amplitudes to attain the supramotor threshold (-17%; p < 0.01). The Visual Analogue Scale pain score was significantly greater in women than in men at motor threshold (+112%; p < 0.01) but not at supramotor threshold (+36%; p > 0.05).

INTERPRETATION

Collectively, our data demonstrate higher sensory and supramotor excitability to surface ES in female subjects and provide further evidence for a neurophysiological explanation for more pronounced pain perception in women. These observations may help clinicians to better understand the sex-specific response to ES and to design more rational stimulation treatments with the ultimate goal of optimizing patient care and safety.

Are reviews based on sham acupuncture procedures in fibromyalgia syndrome (FMS) valid?

In recent reviews regarding the efficacy of acupuncture in fibromyalgia syndrome (FMS) it has been concluded that acupuncture has no specific effect since the control procedure (superficial needling and/or needling away from 'specific' points) had similar effects. These conclusions may be questioned since superficial needling and/or needling away from specific trigger points is not inert. Also, manual acupuncture or mild electroacupuncture (EA) may not be sufficient to activate the endogenous pain inhibiting system. Patients with FMS suffer from allodynia, fatigue and muscle ache, which is partly explained by peripheral and central sensitisation. Sensitisation results in augmented and altered stimulus responses whereby light stimulation of the skin has as strong an effect as regular needling on the pain inhibitory system in FMS. Central sensitisation in FMS is also associated with expanded receptive fields of central neurons resulting in a larger topographic distribution of the pain. This would suggest that control procedures using needling away from the 'specific site' might have as strong an effect as needling within the most painful area. Also, repeated nociceptive input from muscles (as obtained by de qi) results in expansion of receptive fields which in turn may result in activation of descending pain inhibition outside the stimulated myotome. Sensitisation to pain, such as in FMS, may also be related to abnormalities in descending efferent pathways. As there is likely to be an imbalance between excitatory and inhibitory systems in FMS, stronger stimulation may therefore be needed to activate the descending pain inhibitory system. In studies using mild manual acupuncture or weak EA stimulation optimal pain inhibition may therefore not have been obtained. When conducting studies on acupuncture, the clinical condition or syndrome needs to be taken into account and the control procedure designed accordingly.

Speed of Injection Influences Efficacy of Inferior Alveolar Nerve Blocks: A Double-Blind Randomized Controlled Trial in Volunteers

This randomized double-blind crossover trial investigated the efficacy and discomfort associated with slow (60 seconds) and rapid (15 seconds) inferior alveolar nerve blocks (IANB) using 2.0 ml of 2% lidocaine with 1:80,000 epinephrine in securing mandibular first molar, premolar and lateral incisor pulp anesthesia in 38 healthy adult volunteers. Episodes of maximal stimulation (80 microA) without sensation on electronic pulp testing were recorded. Injection discomfort was self-recorded by volunteers on 100 mm visual analogue scales. Data were analyzed by McNemar, Friedman, Wilcoxon Signed Ranks, and paired t tests. Slow IANB produced more episodes of no response to maximal pulp stimulation than rapid IANB in molars (220 episodes versus 159, p < 0.001), premolars (253 episodes versus 216, p = 0.003) and lateral incisors (119 episodes versus 99, p = 0.049). Slow IANB was more comfortable than rapid IANB (p = 0.021).

Sex differences in the responses of spinal wide-dynamic range neurons to subcutaneous formalin and in the effects of different frequencies of conditioning electrical stimulation

The purpose of this study was to investigate sex-related differences in nociception elicited by s.c. injection of different concentrations (1-5%) of formalin. S.c. formalin-induced biphasic (early and late phases) persistent nociception was assessed by extracellularly recording the spontaneous activities of single spinal dorsal horn wide-dynamic range neurons in anesthetized male and female rats. The nociceptive responses of the dorsal horn wide-dynamic range neurons following s.c. injection of 5%, but not 1% and 2.5%, formalin in female rats were significantly stronger than the responses obtained in male rats. However, these concentration-dependent differences with respect to different sexes existed only in the late, but not the early, phase of formalin-induced nociception in intact, not spinal rats. The 5% formalin-induced late phase nociception in male rats was significantly depressed by 15 min of repeated conditioning electrical stimulation at a frequency of 5 Hz as well as 50 Hz during and after the period of conditioning electrical stimulation (intensity: 1 mA; pulse duration: 1 ms). In contrast, the inhibitory effect of 50 Hz conditioning electrical stimulation on the 5% formalin-elicited late phase response in female rats was markedly greater in magnitude and longer in duration than that of 5 Hz conditioning electrical stimulation. No significant depressive effects of 5 Hz conditioning electrical stimulation on formalin-induced nociception were found in female rats, indicating that the distinct effects of conditioning electrical stimulation at different frequencies are different in animals of opposite sexes. In conclusion, s.c. administration of different concentrations of formalin shows a distinct sex-related difference in its late tonic nociception of spinal nociceptive sensory neurons. Sex differences in formalin-induced tonic nociception are stimulus intensity dependent and related to the modulation from the supraspinal regions. S.c. formalin-induced late phase nociception in female rats is only sensitive to depression at a frequency of 50 Hz, but not 5 Hz, of conditioning electrical stimulation. This suggests that the involvement of the central mechanisms in the antinociceptive effects of conditioning electrical stimulation may be different at various frequencies of stimulation.