To tolerate weather and to tolerate pain: two sides of the same coin? The Tromsø Study 7

Interindividual variability in cold-pressor pain sensitivity is not explained by peripheral vascular responding and generalizes to a C-nociceptor-specific pain phenotype

ABSTRACT

Pain sensitivity of healthy subjects in the cold-pressor (CP) test was proposed to be dichotomously distributed and to represent a pain sensitivity trait. Still, it has not been systematically explored which factors influence this pain sensitivity readout. The aim of this study was to distinguish potential contributions of local tissue-related factors such as perfusion and thermoregulation or gain settings in nociceptive systems. Cold-pressor-sensitive and CP-insensitive students screened from a medical student laboratory course were recruited for a CP retest with additional cardiovascular and bilateral local vascular monitoring. In addition, comprehensive quantitative sensory testing according to Deutscher Forschungsverbund Neuropathischer Schmerz standards and a sustained pinch test were performed. Cold pressor was reproducible across sessions (Cohen kappa 0.61 ± 0.14, P < 0.005). At 30 seconds in ice water, CP-sensitive subjects exhibited not only more pain (78.6 ± 26.3 vs 29.5 ± 17.5, P < 0.0001) but also significantly stronger increases in mean arterial blood pressure (12.6 ± 9.3 vs 5.6 ± 8.1 mm Hg, P < 0.05) and heart rate (15.0 ± 8.2 vs 7.1 ± 6.2 bpm, P < 0.005), and lower baroreflex sensitivity, but not local or vasoconstrictor reflex-mediated microcirculatory responses. Cold-pressor-sensitive subjects exhibited significantly lower pain thresholds also for cold, heat, and blunt pressure, and enhanced pain summation, but no significant differences in Aδ-nociceptor-mediated punctate mechanical pain. In conclusion, differences in nociceptive signal processing drove systemic cardiovascular responses. Baroreceptor activation suppressed pain and cardiovascular responses more efficiently in CP-insensitive subjects. Cold-pressor sensitivity generalized to a pain trait of C-fiber-mediated nociceptive channels, which was independent of local thermal and vascular changes in the ice-water-exposed hand. Thus, the C-fiber pain trait reflects gain setting of the nociceptive system.

Water temperature during the cold pressor test: A scoping review

The cold pressor test (CPT) is a commonly used method to induce pain and stress in experimental settings. Previous research has found that the temperature of the water used in the test significantly affects outcome measures such as pain tolerance. Variations in CPT protocols, specifically regarding temperature, have been criticized. Hence, our objective is to investigate water temperature and associated methodological factors through a scoping review of the CPT in adults. Among 331 included trials, the most commonly reported temperature was 1°C (33.8°F). Reporting of the water temperature was adequate (93% of all trials), but a precise range within which the temperature was maintained was reported only in 27% of all trials. Pain measurement was the primary focus for most studies (90%), predominantly utilizing pain tolerance as the main outcome (78%). Water circulation was reported in 44% of studies, and 10% reported manually agitating the water. The most common maximum immersion time (i.e., ceiling time) was 180 s; notably, 64% of trials lacked information on participant awareness of this limit specification. The limb most immersed was the hand (76%). Overall, multiple methodological factors significantly impacting outcome measures were inconsistently implemented or reported. For future studies, we advocate for precise standardization of the water temperature used during the CPT. We suggest using 1°C (33.8°F), especially when assessing pain tolerance. A cooling apparatus allowing precise temperature control and continuous water circulation is advised. At the bare minimum, the temperature should be monitored continuously. While other decisions regarding the implementation of the CPT may differ depending on the specific aims of the respective study, it remains essential to standardize the water temperature and to provide a comprehensive report of the experimental protocol.

Expressed Beliefs about the Cause of Pain in a Pediatric Population: A Qualitative Study

(1) Background: The aims of this study are to explore what beliefs children and adolescents manifest about the cause of the pain they describe, to compare whether there are differences between beliefs by age and the persistence of pain, and to relate the explanations of the cause of pain with current scientific evidence. (2) Methods: a cross-sectional qualitative study was used. The primary endpoint of the study was obtaining explanations of the cause of pain recorded by means of an open-ended question. The participants were school-age children attending a charted school in the province of Barcelona. (3) Results: The children and adolescents proposed a diverse range of explanations for the cause of pain that they reported in their responses. The most frequent explanation for the cause of pain were pathologies and injuries (45.95%), ergonomic issues (22.60%) and psychological issues (15.95%). (4) Conclusions: There is a lot of variety in the explanations that young people give about the cause of their pain in schoolchildren aged between 10 and 16 years old. There exists a high prevalence of explanations non-associated with tissue damage (ENAD) concerning the causes of pain described. It is necessary that future health prevention programs dedicated to early ages consider which beliefs about the cause of pain are the most frequent in the pediatric population.

Intrafasciomembranal Fluid Pressure: A Novel Approach to the Etiology of Myalgias, Part II

The fascia forms a hierarchy of spaces (small and large compartments) that contain and enclose muscle fibers, fiber bundles, skeletal muscles, and compartments of several skeletal muscles. Solid fascia serves as a membrane that enables an increased volume and fluid pressure within such a fasciomembrane, an intrafasciomembrial fluid pressure (IFMFP). Increased IFMFP provides a theoretical model and a common explanation for the etiology of the myalgias: trigger point (TrP), chronic exertional compartment syndrome (CECS), overtraining syndrome (OTS), and delayed onset muscle soreness (DOMS). Many myalgias and their symptoms are poorly understood, and this review aims to provide an extension to this theoretical model and novel approach. This review suggests that the swelling from elevated IFMFP also likely leads to a longitudinal shortening of the same affected tissue. This model of swelling and shortening provides additional explanations for the changes in the lines of force through the body that can lead to changes in the body's posture and, thus, to compensatory movements. This new approximation also provides a biomechanical explanation for the thickening of the fascia and referred pain, and also suggests that IFMFP is a factor in weather-related pain.

Cold exposure and musculoskeletal conditions; A scoping review

Background: Musculoskeletal conditions are major contributors to years lived with disability. Cold exposure can be a risk factor, but any conclusion is obscure.

Aim: The aim of the present scoping review was to identify the existing evidence of an association between cold exposure and musculoskeletal conditions. The aim also included to consider pain in different regions and their assessment, as well as different measures of cold exposure, effect sizes, and to assess the feasibility of future systematic reviews and meta-analyses.

Eligibility criteria: The studies must have: an epidemiological design, defined cold exposure to come prior to the health outcome, defined exposure and outcome(s), existence of effect estimate(s) or data that made it possible to calculate such an estimate. Further, studies were required to be in English language and published in peer-reviewed journals. Studies that had a specific goal of studying cold exposure as an aggravator of already existing health problems were excluded.

Sources: We searched Ovid MEDLINE(R) and Epub Ahead of Print, In-Process and Other Non-Indexed Citations, Daily and Versions(R), and Embase Classic + Embase for original studies.

Charting method: The included studies were reviewed for study population, measurement of exposure and outcome, and effect size. Each publication was assessed for risk of bias.

Results: The included studies were heterogeneous in populations, measures of cold exposure and musculoskeletal conditions. Most studies used self-reported data. They were mostly cross-sectional studies, only two were prospective and one was a case-control study. Associations were found for different cold exposures and regional musculoskeletal conditions, but the heterogeneity and lack of studies impeded valid synthesis of risk magnitude, or meta-analyses.

Conclusion: The studies identified in this review indicate that cold exposure increases the risk of musculoskeletal conditions. However, there is a need for studies that better assess temporality between exposure and outcome. Future studies should also include better exposure assessment, including both objective measurements and measures of subjective experience of cold exposure. The heterogeneity in measurement of exposure and outcome impeded any meta-analysis.