Reliability of pressure pain threshold testing (PPT) in healthy pain free young adults

On determining the mechanical nociceptive threshold in pigs: a reliability study

Background

A pressure algometer is a valuable tool for assessing the mechanical nociceptive threshold (MNT) in clinical pain studies. Recent research has turned to large animal models of pain because of the closer anatomy and physiology to humans. Although the reliability and usefulness of the MNT have been extensively validated in humans, similar data from large animals is still sparse.

Objective

Therefore, the aim of the current study was to evaluate the reliability (within- and between-session) of MNT in the forelimb of pigs using a pressure algometer.

Methods

Nine animals were used (23-40 kg), and MNTs were measured at both the right and left limbs at three different sessions, with three repetitions per session. The intraclass correlation coefficient (ICC) was used as a metric for relative reliability. The standard error of measurement (SEM) and coefficient of variation (CV) was used to assess absolute reliability. Systematic bias was also evaluated.

Results

The average ICC was found to be 0.71 and 0.45 for the between-session and within-session, respectively. CV ranged from 17.9% to 20.5%, with a grand average of 19.1%. The grand average SEM was 249.5 kPa (16.6%). No systematic differences were found for the MNT between sessions, which suggests that there was no habituation to the stimulus.

Conclusion

The reliability indices obtained in this study are comparable to results obtained in other species or anatomical regions and substantiate the use of the pressure algometer as a valuable tool to investigate the nociceptive system in pigs and translation to the human nociceptive withdrawal reflex.

No relevant differences in conditioned pain modulation effects between parallel and sequential test design. A cross-sectional observational study

Background

Conditioned pain modulation (CPM) is measured by comparing pain induced by a test stimulus with pain induced by the same test stimulus, either during (parallel design) or after (sequential design) the conditioning stimulus. Whether design, conditioning stimulus intensity and test stimulus selection affect CPM remains unclear.

Methods

CPM effects were evaluated in healthy participants (N = 89) at the neck, forearm and lower leg using the cold pressor test as the conditioning stimulus. In three separate experiments, we compared the impact of (1) design (sequential versus parallel), (2) conditioning stimulus intensity (VAS 40/100 versus VAS 60/100), and (3) test stimulus selection (single versus dual, i.e., mechanical and thermal). Statistical analyses of the main effect of design (adjusted for order) and experiment were conducted using linear mixed models with random intercepts.

Results

No significant differences were identified in absolute CPM data. In relative CPM data, a sequential design resulted in a slightly lower CPM effect compared to a parallel design, and only with a mechanical test stimulus at the neck (−6.1%; 95% CI [−10.1 to −2.1]) and lower leg (−5.9%; 95% CI [−11.7 to −0.1]) but not forearm (−4.5%; 95% CI [−9.0 to 0.1]). Conditioning stimulus intensity and test stimulus selection did not influence the CPM effect nor the difference in CPM effects derived from parallel versus sequential designs.

Conclusions

Differences in CPM effects between protocols were minimal or absent. A parallel design may lead to a minimally higher relative CPM effect when using a mechanical test stimulus. The conditioning stimulus intensities assessed in this study and performing two test stimuli did not substantially influence the differences between designs nor the magnitude of the CPM effect.

Stretching and relaxing the plantar fascia may change plantar fascia thickness but not pressure pain thresholds: a cross-sectional study of patients with plantar fasciopathy

Background

Despite the established relevance of ultrasonography and assessment of pressure pain thresholds in patients with plantar fasciopathy, patient and probe positioning has been mostly ignored and are not necessarily reported in research. The primary aim of this study was to compare plantar fascia thickness in stretched and relaxed positions in patients with plantar fasciopathy. The secondary aim was to compare plantar heel pressure pain thresholds in these positions.

Methods

In this cross-sectional study, we measured the plantar fascia thickness with ultrasonography, and localised pressure pain thresholds using pressure algometry of 20 patients with plantar fasciopathy. These were assessed bilaterally, with the plantar fascia in both a stretched and relaxed position. In the stretched position, toes were maximally dorsiflexed, while in the relaxed position participants’ feet were hanging freely over the end of the table.

Results

The plantar fascia of the most symptomatic foot was significantly thicker when stretched compared with the relaxed position (sagittal: mean difference 0.2 mm, 95%CI: 0.1–0.4, P = 0.013; frontal: mean difference − 0.27, 95%CI: − 0.49 to − 0.06, P = 0.014). The plantar fascia was significantly thinner in the frontal plane compared with the sagittal plane in both positions (stretched: mean difference − 0.2 mm, 95%CI: − 0.42 to − 0.03, P = 0.025; relaxed: mean difference − 0.3 mm, 95%CI:-0.49 to − 0.08, P = 0.008). There was no difference between pressure pain thresholds in stretched or relaxed positions in either foot (P > 0.4).

Conclusions

The plantar fascia was significantly thicker in a stretched compared with a relaxed position and in the sagittal compared with the frontal plane, but differences were smaller than the standard deviation. Pressure pain thresholds were not different between the positions. These results highlight the importance of how ultrasonography is performed and reported in research to allow for replication.

Trial registration

The study was pre-registered September 25th, 2017 on ClinicalTrials.gov (NCT03291665).

An incremental dual-task paradigm to investigate pain attenuation by task difficulty, affective content and threat value

There is accumulating evidence that task demands and psychological states can affect perceived pain intensity. Different accounts have been proposed to explain this attenuation based either on how limited attentional resources are allocated to the pain stimulus or on how the threat value of the pain stimulus biases attention. However, the evidence for both proposals remains mixed. Here we introduce an incremental dual-task paradigm in which participants were asked to detect pain on their fingertip without any additional tasks during baseline phases or while concurrently detecting visual targets during task phases. The force applied to participants' fingertip in all phases increased incrementally until they detected moderate pain. In Experiment 1, we used coloured shapes and in Experiment 2 we used affective images as visual targets. We also manipulated the threat value of the pain stimulus in Experiment 2. For both experiments, we found that a concurrent task attenuated perceived pain intensity: mean force was significantly greater for the same moderate pain during task compared to baseline phases. Furthermore although task difficulty and affective content did not affect pain perception, the threat value of the pain stimulus moderated the magnitude of pain attenuation.

Pressure and cold pain threshold reference values in a large, young adult, pain-free population

Background and aims

Currently there is a lack of large population studies that have investigated pain sensitivity distributions in healthy pain free people. The aims of this study were: (1) to provide sex-specific reference values of pressure and cold pain thresholds in young pain-free adults; (2) to examine the association of potential correlates of pain sensitivity with pain threshold values.

Methods

This study investigated sex specific pressure and cold pain threshold estimates for young pain free adults aged 21–24 years. A cross-sectional design was utilised using participants (n =617) from the Western Australian Pregnancy Cohort (Raine) Study at the 22-year follow-up. The association of site, sex, height, weight, smoking, health related quality oflife, psychological measures and activity with pain threshold values was examined. Pressure pain threshold (lumbar spine, tibialis anterior, neck and dorsal wrist) and cold pain threshold (dorsal wrist) were assessed using standardised quantitative sensory testing protocols.

Results

Reference values for pressure pain threshold (four body sites) stratified by sex and site, and cold pain threshold (dorsal wrist) stratified by sex are provided. Statistically significant, independent correlates of increased pressure pain sensitivity measures were site (neck, dorsal wrist), sex (female), higher waist-hip ratio and poorer mental health. Statistically significant, independent correlates of increased cold pain sensitivity measures were, sex (female), poorer mental health and smoking.

Conclusions

These data provide the most comprehensive and robust sex specific reference values for pressure pain threshold specific to four body sites and cold pain threshold at the dorsal wrist for young adults aged 21–24 years. Establishing normative values in this young age group is important given that the transition from adolescence to adulthood is a critical temporal period during which trajectories for persistent pain can be established.

Implications

These data will provide an important research resource to enable more accurate profiling and interpretation of pain sensitivity in clinical pain disorders in young adults. The robust and comprehensive data can assist interpretation of future clinical pain studies and provide further insight into the complex associations of pain sensitivity that can be used in future research.