The nociceptive withdrawal reflex: Normative values of thresholds and reflex receptive fields

Assessments of spinal nociceptive withdrawal reflexes can be used in human research both to evaluate the effect of analgesics and explore pain mechanisms related to sensitization. Before the reflex can be used as a clinical tool, normative values need to be determined in large scale studies. The aim of this study was to determine the reference values of spinal nociceptive reflexes and subjective pain thresholds (to single and repeated stimulation), and of the area of the reflex receptive fields (RRF) in 300 pain-free volunteers. The influences of gender, age, height, weight, body-mass index (BMI), body side of testing, depression, anxiety, catastrophizing and parameters of Short-Form 36 (SF-36) were analyzed by multiple regressions. The 95% confidence intervals were determined for all the tests as normative values. Age had a statistically and quantitatively significant impact on the subjective pain threshold to single stimuli. The reflex threshold to single stimulus was lower on the dominant compared to the non-dominant side. Depression had a negative impact on the subjective pain threshold to single stimuli. All the other analyses either did not reveal statistical significance or displayed quantitatively insignificant correlations. In conclusion, normative values of parameters related to the spinal nociceptive reflex were determined. This allows their clinical application for assessing central hyperexcitability in individual patients. The parameters investigated explore different aspects of sensitization processes that are largely independent of demographic characteristics, cognitive and affective factors.

Test-retest reliability of the nociceptive withdrawal reflex and electrical pain thresholds after single and repeated stimulation in patients with chronic low back pain

Recent studies have shown that the nociceptive withdrawal reflex threshold (NWR-T) and the electrical pain threshold (EP-T) are reliable measures in pain-free populations. However, it is necessary to investigate the reliability of these measures in patients with chronic pain in order to translate these techniques from laboratory to clinic. The aims of this study were to determine the test-retest reliability of the NWR-T and EP-T after single and repeated (temporal summation) electrical stimulation in a group of patients with chronic low back pain, and to investigate the association between the NWR-T and the EP-T. To this end, 25 patients with chronic pain participated in three identical sessions, separated by 1 week in average, in which the NWR-T and the EP-T to single and repeated stimulation were measured. Test-retest reliability was assessed using intra-class correlation coefficient (ICC), coefficient of variation (CV), and Bland-Altman analysis. The association between the thresholds was assessed using the coefficient of determination (r (2)). The results showed good-to-excellent reliability for both NWR-T and EP-T in all cases, with average ICC values ranging 0.76-0.90 and average CV values ranging 12.0-17.7%. The association between thresholds was better after repeated stimulation than after single stimulation, with average r (2) values of 0.83 and 0.56, respectively. In conclusion, the NWR-T and the EP-T are reliable assessment tools for assessing the sensitivity of spinal nociceptive pathways in patients with chronic pain.

Cost-effective intervention thresholds against osteoporotic fractures based on FRAX® in Switzerland

FRAX-based cost-effective intervention thresholds in the Swiss setting were determined. Assuming a willingness to pay at 2× Gross Domestic Product per capita, an intervention aimed at reducing fracture risk in women and men with a 10-year probability for a major osteoporotic fracture at or above 15% is cost-effective.

Extended frequency range hearing thresholds and otoacoustic emissions in acute acoustic trauma

We sought to evaluate the relative value of pure tone audiometry (PTA), extended high-frequency audiometry (EFA) and transiently evoked otoacoustic emissions (OAE) and distortion products when monitoring acute acoustic trauma (AAT).

Absolute height-specific thresholds to identify elevated blood pressure in children

Identification of children with elevated blood pressure (BP) is difficult because of the multiple sex, age, and height-specific thresholds to define elevated BP. We propose a simple set of absolute height-specific BP thresholds and evaluate their performance to identify children with elevated BP in two different populations.

Chronic phantom limb pain: the effects of calcitonin, ketamine, and their combination on pain and sensory thresholds

BACKGROUND: Calcitonin was effective in a study of acute phantom limb pain, but it was not studied in the chronic phase. The overall literature on N-methyl-D-aspartate antagonists is equivocal. We tested the hypothesis that calcitonin, ketamine, and their combination are effective in treating chronic phantom limb pain. Our secondary aim was to improve our understanding of the mechanisms of action of the investigated drugs using quantitative sensory testing. METHODS: Twenty patients received, in a randomized, double-blind, crossover manner, 4 i.v. infusions of: 200 IE calcitonin; ketamine 0.4 mg/kg (only 10 patients); 200 IE of calcitonin combined with ketamine 0.4 mg/kg; placebo, 0.9% saline. Intensity of phantom pain (visual analog scale) was recorded before, during, at the end, and the 48 h after each infusion. Pain thresholds after electrical, thermal, and pressure stimulation were recorded before and during each infusion. RESULTS: Ketamine, but not calcitonin, reduced phantom limb pain. The combination was not superior to ketamine alone. There was no difference in basal pain thresholds between the amputated and contralateral side except for pressure pain. Pain thresholds were unaffected by calcitonin. The analgesic effect of the combination of calcitonin and ketamine was associated with a significant increase in electrical thresholds, but with no change in pressure and heat thresholds. CONCLUSIONS: Our results question the usefulness of calcitonin in chronic phantom limb pain and stress the potential interest of N-methyl-D-aspartate antagonists. Sensory assessments indicated that peripheral mechanisms are unlikely important determinants of phantom limb pain. Ketamine, but not calcitonin, affects central sensitization processes that are probably involved in the pathophysiology of phantom limb pain.

Psychologic factors are related to some sensory pain thresholds but not nociceptive flexion reflex threshold in chronic whiplash

OBJECTIVES: Sensory hypersensitivity, central hyperexcitability [lowered nociceptive flexion reflex (NFR) thresholds], and psychologic distress are features of chronic whiplash. However, relationships between these substrates are not clear. This study tested the hypothesis that psychologic distress and catastrophization are correlated with sensory hypersensitivity and NFR responses in chronic whiplash. METHODS: Pressure and thermal pain thresholds (mean values across 3 body sites), NFR threshold, and pain at threshold Visual Analog Scale were measured in 30 participants with chronic whiplash and 30 asymptomatic controls. Pain and disability levels Neck Disability Index, psychologic distress (GHQ-28), and catastrophization (PCS) were also measured in the whiplash group. RESULTS: Whiplash injured participants demonstrated lowered pain thresholds to pressure and cold (P<0.05); lowered NFR thresholds (P=0.003), and demonstrated above threshold levels of psychologic distress (GHQ-28) and levels of catastrophization comparable with other musculoskeletal conditions. There were no group differences for heat pain thresholds or pain at NFR threshold. In the whiplash group, PCS scores correlated moderately with cold pain threshold (r=0.51, P=0.01). In contrast, there were no significant correlations between GHQ-28 scores and pain threshold measures or between psychologic factors and NFR responses in whiplash participants. There were no significant correlations between psychologic factors and pain thresholds or NFR responses in controls. DISCUSSION: We have demonstrated that psychologic factors have some association with sensory hypersensitivity (cold pain threshold measures) in chronic whiplash but do not seem to influence spinal cord excitability. This suggests that psychologic disorders are important, but not the only, determinants of central hypersensitivity in whiplash patients.

Impact of coil position and electrophysiological monitoring on determination of motor thresholds to transcranial magnetic stimulation

OBJECTIVE: We compared motor and movement thresholds to transcranial magnetic stimulation (TMS) in healthy subjects and investigated the effect of different coil positions on thresholds and MEP (motor-evoked potential) amplitudes. METHODS: The abductor pollicis brevis (APB) 'hot spot' and a standard scalp position were stimulated. APB resting motor threshold (APB MEP-MT) defined by the '5/10' electrophysiological method was compared with movement threshold (MOV-MT), defined by visualization of movements. Additionally, APB MEP-MTs were evaluated with the '3/6 method,' and MEPs were recorded at a stimulation intensity of 120% APB MEP-MT at each position. RESULTS: APB MEP-MTs were significantly lower by stimulation of the 'hot spot' than of the standard position, and significantly lower than MOV-MTs (n=15). There were no significant differences between the '3/6' and the '5/10' methods, or between APB MEP amplitudes by stimulating each position at 120% APB MEP-MT. CONCLUSIONS: Coil position and electrophysiological monitoring influenced motor threshold determinations. Performing 6 instead of 10 trials did not produce different threshold measurements. Adjustment of intensity according to APB MEP-MT at the stimulated position did not influence APB MEP amplitudes. SIGNIFICANCE: Standardization of stimulation positions, nomenclature and criteria for threshold measurements should be considered in design and comparison of TMS protocols.

Bone-anchored Hearing Aids: correlation between pure-tone thresholds and outcome in three user groups

OBJECTIVE: To investigate correlations between preoperative hearing thresholds and postoperative aided thresholds and speech understanding of users of Bone-anchored Hearing Aids (BAHA). Such correlations may be useful to estimate the postoperative outcome with BAHA from preoperative data. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS:: Ninety-two adult unilaterally implanted BAHA users in 3 groups: (A) 24 subjects with a unilateral conductive hearing loss, (B) 38 subjects with a bilateral conductive hearing loss, and (C) 30 subjects with single-sided deafness. INTERVENTIONS: Preoperative air-conduction and bone-conduction thresholds and 3-month postoperative aided and unaided sound-field thresholds as well as speech understanding using German 2-digit numbers and monosyllabic words were measured and analyzed. MAIN OUTCOME MEASURES: Correlation between preoperative air-conduction and bone-conduction thresholds of the better and of the poorer ear and postoperative aided thresholds as well as correlations between gain in sound-field threshold and gain in speech understanding. RESULTS: Aided postoperative sound-field thresholds correlate best with BC threshold of the better ear (correlation coefficients, r2 = 0.237 to 0.419, p = 0.0006 to 0.0064, depending on the group of subjects). Improvements in sound-field threshold correspond to improvements in speech understanding. CONCLUSION: When estimating expected postoperative aided sound-field thresholds of BAHA users from preoperative hearing thresholds, the BC threshold of the better ear should be used. For the patient groups considered, speech understanding in quiet can be estimated from the improvement in sound-field thresholds.