Neurosensory and vascular function after 14 months of military training comprising cold winter conditions

Raynaud's phenomenon in the feet of Arctic open-pit miners

The literature on Raynaud's phenomenon (RP) in the feet is scarce, especially in the occupational setting. The primary aim of our study was to investigate the occurrence of RP in the feet of miners. As part of the MineHealth project, written surveys and clinical examinations were completed by 260 Arctic open-pit miners working in northern Sweden and Norway (participation rate 53.6%). Data on RP were collected using standardised colour charts and questionnaire items. Clinical examination included assessing the perception of vibration and pain in both feet. There were eight women and three men who reported RP in the feet. Four also had RP in their hands but none acknowledged any first-degree relatives with the condition. Nine reported exposure to foot-transmitted vibration and one to hand-arm vibration. Seven showed signs of neurosensory injury in the feet. To conclude, the occurrence of RP in the feet of miners was 4.4%. Most cases with RP in the feet did not report the condition in the hands and were exposed to vibration transmitted directly to the feet. There were no reports of a hereditary component. Most cases with RP in the feet also had clinical findings suggestive of peripheral neuropathy in the feet.

The classification of freezing cold injuries - a NATO research task group position paper

INTRODUCTION

Freezing cold injuries (FCI) are a common risk in extreme cold weather operations. Although the risks have long been recognised, injury occurrences tend to be sparse and geographically distributed, with relatively few cases to study in a systematic way. The first challenge to improve FCI medical management is to develop a common nomenclature for FCI classification. This is critical for the development of meaningful epidemiological reports on the magnitude and severity of FCI, for the standardisation of patient inclusion criteria for treatment studies, and for the development of clinical diagnosis and treatment algorithms.

METHODOLOGY

A scoping review of the literature using PubMed and cross-checked with Google Scholar, using search terms related to freezing cold injury and frostbite, highlighted a paucity of published clinical papers and little agreement on classification schemes.

RESULTS

A total of 74 papers were identified, and 28 were included in the review. Published reports and studies can be generally grouped into four different classification schemes that are based on (1) injury morphology; (2) signs and symptoms; (3) pathophysiology; and (4) clinical outcome. The nomenclature in the different classification systems is not coherent and the discrete classification limits are not evidence based.

CONCLUSIONS

All the classification systems are necessary and relevant to FCI medical management for sustainment of soldier health and performance in cold weather operations and winter warfare. Future FCI reports should clearly characterise the nature of the FCI into existing classification schemes for surveillance (morphology, symptoms, and appearance), identifying risk-factors, clinical guidelines, and agreed inclusion/exclusion criteria for a future treatment trial.

Occupational cold exposure is associated with upper extremity pain

Background

Occupational cold exposure is common in Sweden but potential impacts on musculoskeletal disorders have not been thoroughly investigated. The primary aim of this study was to determine the associations between occupational contact and ambient cooling in relation to pain in the upper extremity.

Methods

In this cross-sectional study, a digital survey was conducted on a population-based sample of women and men between 24 and 76 years of age, living in northern Sweden. Occupational cold exposure, heavy manual handling, work with vibrating tools as well as the presence of upper extremity pain at different sites were subjectively reported. Associations between exposure and outcome were evaluated using multiple binary logistic regression.

Results

The final study sample included 2,089 (54.4%) women and 1,754 men, with a mean age of 56 years. Hand pain was reported by 196 (5.2%), lower arm pain by 144 (3.8%), and upper arm pain by 451 (11.9%). Severe ambient cooling for more than half of the working time was statistically significantly associated with hand pain (OR: 2.30; 95% CI: 1.23-4.29) and upper arm pain (OR: 1.57; 95% CI: 1.00-2.47) but not lower arm pain (OR: 1.87; 95% CI: 0.96-3.65) after adjusting for gender, age, body mass index, current daily smoking, heavy manual handling, and work with vibrating tools.

Conclusions

Occupational cold exposure was statistically significantly associated with hand pain and upper arm pain. Therefore, occupational cold exposure should be recognized as a potential risk factor for musculoskeletal disorders in the upper extremity.

Peripheral sensory function in non-freezing cold injury patients and matched controls

NEW FINDINGS

What is the central question of this study? Is peripheral sensory function impaired in the chronic phase of non-freezing cold injury (NFCI)? What is the main finding and its importance? Warm and mechanical detection thresholds are elevated and intraepidermal nerve fibre density is reduced in individuals with NFCI in their feet when compared to matched controls. This indicates impaired sensory function in individuals with NFCI. Interindividual variation was observed in all groups, and therefore a diagnostic cut-off for NFCI has yet to be established. Longitudinal studies are required to follow NFCI progression from formation to resolution ABSTRACT: The aim of this study was to compare peripheral sensory neural function of individuals with non-freezing cold injury (NFCI) with matched controls (without NFCI) with either similar (COLD) or minimal previous cold exposure (CON). Thirteen individuals with chronic NFCI in their feet were matched with the control groups for sex, age, race, fitness, body mass index and foot volume. All undertook quantitative sensory testing (QST) on the foot. Intraepidermal nerve fibre density (IENFD) was assessed 10 cm above the lateral malleolus in nine NFCI and 12 COLD participants. Warm detection threshold was higher at the great toe in NFCI than COLD (NFCI 45.93 (4.71)°C vs. COLD 43.44 (2.72)°C, P = 0.046), but was non-significantly different from CON (CON 43.92 (5.01)°C, P = 0.295). Mechanical detection threshold on the dorsum of the foot was higher in NFCI (23.61 (33.59) mN) than in CON (3.83 (3.69) mN, P = 0.003), but was non-significantly different from COLD (10.49 (5.76) mN, P > 0.999). Remaining QST measures did not differ significantly between groups. IENFD was lower in NFCI than COLD (NFCI 8.47 (2.36) fibre/mm2 vs. COLD 11.93 (4.04) fibre/mm2 , P = 0.020). Elevated warm and mechanical detection thresholds may indicate hyposensitivity to sensory stimuli in the injured foot for individuals with NFCI and may be due to reduced innervation given the reduction in IENFD. Longitudinal studies are required to identify the progression of sensory neuropathy from the formation of injury to its resolution, with appropriate control groups employed.

Human performance research for military operations in extreme cold environments

OBJECTIVES

Soldier performance in the Arctic depends on planning and training, protective equipment, and human physiological limits. The purpose of this review was to highlight the span of current research on enhancing soldier effectiveness in extreme cold and austere environments.

METHODS

The practices of seasoned soldiers who train in the Arctic and cold-dwelling natives inform performance strategies. We provide examples of research and technology that build on these concepts.

RESULTS

Examples of current performance research include evaluation of equipment and tactics such as the bioenergetics of load carriage over snow in Norwegian exercises; Canadian field monitoring of hand temperatures and freezing cold injuries for better protection of manual dexterity; and Dutch predictive modeling of cold-wet work tolerances. Healthy young men can respond to cold with a substantial thermogenic response based on US and Canadian studies on brown adipose tissue and other mechanisms of non-shivering thermogenesis; the potential advantage of greater fat insulation is offset in obese unfit subjects by a smaller thermogenic response. Current physiological studies are addressing previously unanswered problems of cold acclimation procedures, thermogenic enhancement and regulation, and modulation of sympathetic activation, all of which may further enhance cold survival and expand the performance envelope.

CONCLUSION

There is an inseparable behavioral component to soldier performance in the Arctic, and even the best equipment does not benefit soldiers who have not trained in the actual environment. Training inexperienced soldiers to performance limits may be helped with personal monitoring technologies and predictive models.

Expert consensus on the prevention, diagnosis and treatment of cold injury in China, 2020

Cold injury refers to local or systemic injury caused by a rapid, massive loss of body heat in a cold environment. The incidence of cold injury is high. However, the current situation regarding the diagnosis and treatment of cold injury in our country is not ideal. To standardize and improve the level of clinical diagnosis and treatment of cold injury in China, it is necessary to make a consensus that is practical and adapted to the conditions in China. We used the latest population-level epidemiological and clinical research data, combined with relevant literature from China and foreign countries. The consensus was developed by a joint committee of multidisciplinary experts. This expert consensus addresses the epidemiology, diagnosis, on-site emergency procedures, in-hospital treatment, and prevention of cold injury.

A 4-year follow-up of non-freezing cold injury with cold allodynia and neuropathy in 26 naval soldiers

Background and aims Non-freezing cold injuries (NFCI), which typically may occur in military personnel, may result from exposure to cold, at temperatures around 0 °C or above, and worsened by wind and moisture. The injury is due to cooling but not freezing of tissue like in frostbite. NFCI may result in in chronic neuropathy and cold hypersensitivity. A recent retrospective study of small-and large fibres has suggested that NFCI results in neuropathic pain due to a sensory neuropathy and question a longitudinal study to verify a possible observation of improvement of NFCI over time. The present study is a 4-year follow-up investigation of large - and small-fibre function in 26 naval cadets and officers who were exposed to cold injury during the same military expedition. Methods The 26 soldiers were investigated clinically (with investigation of motor function, reflexes, sensibility), with nerve conduction studies (NCS) of major nerves in upper- and lower extremity, small fibre testing (QST, measurement of thermal thresholds), measurements of subcutaneous fat tissue and maximal O2 uptake. Investigations found place 2 months following the actual military expedition, with follow-up investigations of affected soldiers at 6-12 months and up to 3-4 years. In order to elucidate possible mechanisms (disinhibition of cold pain by myelinated nerve fibres) of cold allodynia, cold pain thresholds were measured following an ischemic block of conduction of large and small myelinated nerve fibres. Results Of 26 soldiers, 19 complained of numbness in feet and a large majority of 16 of cold hypersensitivity 2 months following injury. There were significant alterations of both large- and small-fibre function, indicating a general large- and small-fibre neuropathy. The most prominent finding was a pronounced cold allodynia, inversely correlated with the amount of subcutaneous fat. During the first year, results of NCS and thermal testing gradually normalized in most. Seven soldiers developed chronic symptoms in the form of cold hypersensitivity and with findings of cold allodynia, which was not further enhanced, but abolished following block of conduction of myelinated nerve fibres. Seven soldiers were free of symptoms from that start of the investigation, probably because they had been more eager to keep their legs moving during the exposure to cold. Conclusions Of a total of 26 soldiers, only seven developed chronic symptoms of cold hypersensitivity, corresponding to the finding of cold allodynia by thermal testing. The cold allodynia may not be explained by disinhibition of cold pain by myelinated fibres as in healthy subjects. A large majority recovered from an initial large-and small fibre neuropathy, demonstrating that recovery from NFCI may occur. Implications Although large-and small fibre neuropathy may be restored following cold injury, there is a risk of a permanent and disabling cold hypersensitivity, corresponding to the findings of cold allodynia. It is of uttermost importance to secure military personnel from the risk of cold injuries. It seems important to avoid immobilisation of extremities during exposure to cold.

Can sensation of cold hands predict Raynaud's phenomenon or paraesthesia?

Background

Raynaud’s phenomenon and neurosensory symptoms are common after hand-arm vibration exposure. Knowledge of early signs of vibration injuries is needed.

Aims

To investigate the risk of developing Raynaud’s phenomenon and paraesthesia in relation to sensation of cold hands in a cohort of male employees at an engineering plant.

Methods

We followed a cohort of male manual and office workers at an engineering plant in Sweden for 21 years. At baseline (1987 and 1992) and each follow-up (1992, 1997, 2002, 2008), we assessed sensation of cold, Raynaud’s phenomenon and paraesthesia in the hands using questionnaires and measured vibration exposure. We calculated risk estimates with univariate and multiple logistic regression analyses and adjusted for vibration exposure and tobacco usage.

Results

There were 241 study participants. During the study period, 21 individuals developed Raynaud’s phenomenon and 43 developed paraesthesia. When adjusting the risk of developing Raynaud’s phenomenon for vibration exposure and tobacco use, the odds ratios were between 6.0 and 6.3 (95% CI 2.2–17.0). We observed no increased risk for paraesthesia in relation to a sensation of cold hands.

Conclusions

A sensation of cold hands was a risk factor for Raynaud’s phenomenon. At the individual level, reporting a sensation of cold hands did not appear to be useful information to predict future development of Raynaud’s phenomenon given a weak to moderate predictive value. For paraesthesia, the sensation of cold was not a risk factor and there was no predictive value at the individual level.

Relation between finger cold-induced vasodilation and rewarming speed after cold exposure

Purpose

The risk for local cold injuries has been linked to poor cold-induced vasodilation (CIVD) during cold exposure and to poor rewarming after cold exposure. The purpose of this study is to establish the relation between CIVD and rewarming speed.

Methods

Twelve participants immersed one hand in ice water for 30 min to evoke CIVD and the other hand in ice water for 10 min to investigate the rewarming profile. The ring, middle and index fingertip temperatures were monitored during hand immersion and the resistance index of frostbite (RIF) was calculated. RIF depends on minimal (T_min) and mean (T_mean) finger skin temperature and onset time. Rewarming was quantified using an infrared imaging system and the rewarming speed over 19 min was determined.

Results

T_min (5.8 ± 3.0 °C) and T_mean (10.4 ± 3.0 °C) caused non-distinctive contributions to the total RIF-scores so that onset time (12.7 ± 3.1 min) became the dominant factor. A significant negative correlation between RIF and rewarming speed was found (r_s = − 0.60, p = 0.041).

Conclusions

The negative relation between RIF and rewarming speed may be explained by the common observation that onset time relates to the temperature of fingertip tissue, while T_min, T_mean and rewarming speed relates to body thermal status. The rewarming test is to be preferred over the CIVD test in terms of ease of use, but the predictive value of the rewarming test for cold injuries is limited, cannot replace the RIF since onset time of finger vasodilation is not included and should be further investigated.

Cold sensitivity and associated factors: a nested case-control study performed in Northern Sweden

Purpose

To identify factors associated with the reporting of cold sensitivity, by comparing cases to controls with regard to anthropometry, previous illnesses and injuries, as well as external exposures such as hand–arm vibration (HAV) and ambient cold.

Methods

Through a questionnaire responded to by the general population, ages 18–70, living in Northern Sweden (N = 12,627), cold sensitivity cases (N = 502) and matched controls (N = 1004) were identified, and asked to respond to a second questionnaire focusing on different aspects of cold sensitivity as well as individual and external exposure factors suggested to be related to the condition. Conditional logistic regression analyses were performed to determine statistical significance.

Results

In total, 997 out of 1506 study subjects answered the second questionnaire, yielding a response rate of 81.7%. In the multiple conditional logistic regression model, identified associated factors among cold sensitive cases were: frostbite affecting the hands (OR 10.3, 95% CI 5.5–19.3); rheumatic disease (OR 3.1, 95% CI 1.7–5.7); upper extremity nerve injury (OR 2.0, 95% CI 1.3–3.0); migraines (OR 2.4, 95% CI 1.3–4.3); and vascular disease (OR 1.9, 95% CI 1.2–2.9). A body mass index ≥ 25 was inversely related to reporting of cold sensitivity (0.4, 95% CI 0.3–0.6).

Conclusions

Cold sensitivity was associated with both individual and external exposure factors. Being overweight was associated with a lower occurrence of cold sensitivity; and among the acquired conditions, both cold injuries, rheumatic diseases, nerve injuries, migraines and vascular diseases were associated with the reporting of cold sensitivity.

Thermal perception thresholds among workers in a cold climate

Purpose

To investigate whether exposure to cold could influence the thermal perception thresholds in a working population.

Methods

This cross-sectional study was comprised of 251 males and females and was carried out at two mines in the northern part of Norway and Sweden. The testing included a baseline questionnaire, a clinical examination and measurements of thermal perception thresholds, on both hands, the index (Digit 2) and little (Digit 5) fingers, for heat and cold.

Results

The thermal perception thresholds were affected by age, gender and test site. The thresholds were impaired by experiences of frostbite in the fingers and the use of medication that potentially could affect neurosensory functions. No differences were found between the calculated normative values for these workers and those in other comparative investigations conducted in warmer climates.

Conclusions

The study provided no support for the hypothesis that living and working in cold climate will lead to impaired thermal perception thresholds. Exposure to cold that had caused localized damage in the form of frostbite was shown to lead to impaired thermal perception.

Neurovascular hand symptoms in relation to cold exposure in northern Sweden: a population-based study

PURPOSE

To describe the self-reported ambient cold exposure in northern Sweden and to relate the level of cumulative cold exposure to the occurrence of sensory and vascular hand symptoms. We hypothesize that cold exposure is positively related to reporting such symptoms.

METHODS

A questionnaire about cold exposure and related symptoms was sent out to 35,144 subjects aged 18-70 years and living in northern Sweden.

RESULTS

A total of 12,627 out of 35,144 subjects returned the questionnaire (response rate 35.9%). Subjects living in the rural alpine areas reported more extensive cold exposure both during work and leisure time compared to the urbanized coastal regions. Frostbite in the hands was present in 11.4% of men and 7.1% of women, cold sensitivity was present in 9.7 and 14.4%, and Raynaud's phenomenon was present in 11.0% of men and 14.0% of women. There was a positive association between cumulative cold exposure and neurovascular hand symptoms.

CONCLUSION

The present study demonstrates that the cold environment in northern Sweden might be an underestimated health risk. Our hypothesis that cold exposure is positively related to reporting of neurovascular hand symptoms was supported by our findings. In addition, such symptoms were common not only in conjunction with an overt cold injury. Our results warrant further study on pathophysiological mechanisms and suggest the need for confirmatory prevalence studies to support national public health planning.