Effects of alcohol on autonomic responses and thermal sensation during cold exposure in humans

We investigated the effects of alcohol on thermoregulatory responses and thermal sensations during cold exposure in humans. Eight healthy men (mean age 22.3 ± 0.7 year) participated in this study. Experiments were conducted twice for each subject at a room temperature of 18°C. After a 30-min resting period, the subject drank either 15% alcohol at a dose of 0.36 g/kg body weight (alcohol session) or an equal volume of distilled water (control session), and remained in a sitting position for another 60 min. Mean skin temperature continued to decrease and was similar in control and alcohol sessions. Metabolic rate was lower in the alcohol session, but the difference did not affect core temperature, which decreased in a similar manner in both alcohol and control sessions (from 36.9 ± 0.1°C to 36.6 ± 0.1°C). Whole body sensations of cold and thermal discomfort became successively stronger in the control session, whereas these sensations were both greatly diminished after drinking alcohol. In a previous study we performed in the heat, using a similar protocol, alcohol produced a definite, coordinated effect on all autonomic and sentient heat loss effectors. In the current study in the cold, as compared to responses in the heat, alcohol intake was followed by lesser alterations in autonomic effector responses, but increased changes in sensations of temperature and thermal discomfort. Overall, our results indicate that although alcohol influences thermoregulation in the cold as well as in the heat, detailed aspects of the influence are quite different.     

Challenges to temperature regulation when working in hot environments

The focus of this review is upon acute exposure to hot environments and the accompanying physiological changes. The target audience includes physiologists, physicians and occupational health and safety practitioners. Using the principles of thermodynamics, the avenues for human heat exchange are explored, leading to an evaluation of some methods used to assess thermally-stressful environments. In particular, there is a critique of the wet-bulb globe temperature (WBGT) index, and an overview of an alternative means by which such assessments may be undertaken (the heat stress index). These principles and methods are combined to illustrate how one may evaluate the risk of heat illness. Three general areas of research are briefly reviewed: the physiological impact of wearing thermal protective clothing, heat adaptation (acclimation) and whole-body pre-cooling. These topics are considered as potential pre-exposure techniques that may be used to reduce the threat of hyperthermia, or to enhance work performance in the heat.     

Heat stress of helicopter aircrew wearing immersion suit

The objectives of the present study were to define the lowest ambient air and cabin temperatures at which aircrews wearing immersion protection are starting to experience thermal discomfort and heat stress during flight operations, and to characterize during a flight simulation in laboratory, the severity of the heat stress during exposure to a typical northern summer ambient condition (25 degrees C, 40% RH). Twenty male helicopter aircrews wearing immersion suits (insulation of 2.2 Clo in air) performed 26 flights within an 8-month period at ambient temperatures ranging between -15 and 25 degrees C, and cabin temperatures ranging between 3 and 28 degrees C. It was observed based on thermal comfort ratings that the aircrews were starting to experience thermal discomfort and heat stress at ambient and cabin air conditions above 18 degrees C and at a WBGT index of 16 degrees C. In a subsequent study, seven aircrews dressed with the same clothing were exposed for 140 min to 25 degrees C and 40% RH in a climatic chamber. During the exposure, the aircrews simulated pilot flight maneuvers for 80 min followed with backender/flight engineer activities for 60 min. By the end of the 140 min exposure, the skin temperature, rectal temperature and heart rate had increased significantly to 35.7 +/- 0.2 degrees C, 38.4 +/- 0.2 degrees C and between 110 and 160 beats/min depending on the level of physical activity. The body sweat rate averaged 0.58 kg/h and the relative humidity inside the clothing was at saturation by the end of the exposure. It was concluded that aircrews wearing immersion suits during the summer months in northern climates might experience thermal discomfort and heat stress at ambient or cabin air temperature as low as 18 degrees C.     

The effects of wind and human movement on the heat and vapour transfer properties of clothing.

This paper integrates the research presented in the papers in this special issue of Holmér et al. and Havenith et al. [Holmér, I., Nilsson, H., Havenith, G., Parsons, K. C. (1999) Clothing convective heat exchange: proposal for improved prediction in standards and models. Annals of Occupational Hygiene, in press; Havenith, G., Holmér, I., den Hartog, E. and Parsons, K. C. (1999) Clothing evaporative heat resistance: proposal for improved representation in standards and models. Annals of Occupational Hygiene, in press] to provide a practical suggestion for improving existing clothing models so that they can account for the effects of wind and human movement. The proposed method is presented and described in the form of a BASIC computer program. Analytical methods (for example ISO 7933) for the assessment of the thermal strain caused by human exposure to hot environments require a mathematical quantification of the thermal properties of clothing. These effects are usually considered in terms of 'dry' thermal insulation and vapour resistance. This simple 'model' of clothing can account for the insulation properties of clothing which reduce heat loss (or gain) between the body and the environment and, for example, the resistance to the transfer of evaporated sweat from the skin, which is important for cooling the body in a hot environment. When a clothed person is exposed to wind, however, and when the person is active, there is a potentially significant limitation in the simple model of clothing presented above. Heat and mass transfer can take place between the microclimate (within clothing and next to the skin surface) and the external environment. The method described in this paper 'corrects' static values of clothing properties to provide dynamic values that take account of wind and human movement. It therefore allows a more complete representation of the effects of clothing on the heat strain of workers.     

The role of cold in ischaemic heart disease: a review

A review of the literature suggests that the geographical and social class distribution of ischaemic heart disease (IHD) could be partly explained by variations in degrees of cold exposure, which includes wind and rain as well as temperature, with frequent exposure to cold being more harmful than steady exposure. Blood pressure (BP) and serum cholesterol are raised in response to acute and chronic exposure to cold. Smoking and cold produce similar physiological changes which increase the risk of IHD, while regular exercise blunts the physiological effects of cold and other stresses. There are many acute responses to cold which could trigger a myocardial infarction (MI) and therefore cold is probably a major precipitating factor in many cases of MI. Public health measures to improve domestic housing and the working environment may produce a significant impact on the incidence of IHD.     

Heat balance when wearing protective clothing.

This issue of the Annals of Occupational Hygiene is dedicated to the topic of heat stress evaluation. For this evaluation, several evaluation programs and international standards are available. In order to understand the reasoning and underlying theory behind these programs and standards, a basic knowledge of heat exchange processes between workers and their environment is needed. This paper provides an overview of the relevant heat exchange processes, and defines the relevant parameters (air and radiant temperature, humidity, wind speed, metabolic heat production and clothing insulation). Further it presents in more detail the relation between clothing material properties and properties of clothing ensembles made from those materials. The effects of clothing design, clothing fit, and clothing air permeability are discussed, and finally an overview of methods for the determination of clothing heat and vapour resistance is given.     

Heat strain in cold

In spite of increased environmental cold stress, heat strain is possible also in a cold environment. The body heat balance depends on three factors: environmental thermal conditions, metabolic heat production and thermal insulation of clothing and other protective garments. As physical exercise may increase metabolic heat production from rest values by ten times or even more, the required thermal insulation of clothing may vary accordingly. However, in most outdoor work, and often in indoor cold work, too, the thermal insulation of clothing is impractical, difficult or impossible to adjust according to the changes in physical activity. This is especially true with whole body covering garments like chemical protective clothing. As a result of this imbalance, heat strain may develop. In cold all the signs of heat strain (core temperature above 38 degrees C, warm or hot thermal sensations, increased cutaneous circulation and sweating) may not be present at the same time. Heat strain in cold may be whole body heat strain or related only to torso or core temperature. Together with heat strain in torso or body core, there can be at the same time even cold strain in peripheral parts and/or superficial layers of the body. In cold environment both the preservation of insulation and facilitation of heat loss are important. Development of clothing design is still needed to allow easy adjustments of thermal insulation.     

Thermal characteristics of clothing ensembles for use in heat stress analysis

The Heat Stress Index was an early model for the assessment of heat stress. The International Organization for Standardization (ISO) standard for required sweat rate is the current generation of heat balance methods for occupational heat stress. The method assumes cotton clothing and works adequately for cotton/polyester blends. To extend the usefulness of the model, the thermal characteristics of a variety of commercially available and prototype protective clothing ensembles have been determined for application in the ISO method. The fundamental principle for assessing thermal characteristics of work clothing is establishing the critical environmental conditions in which test subjects were just able to maintain thermal equilibrium. Critical conditions were found for warm, humid conditions; hot, dry conditions; intermediate conditions of temperature and humidity; and/or moderate conditions in which metabolic rate was increased to a limiting thermal load. Typically, five subjects at each condition for each ensemble were used. Metabolic rate, average skin temperature, and the environmental conditions (air temperature and vapor pressure) were noted at the critical conditions, and the total insulation was estimated for each ensemble. From these values, the total evaporative resistance, the clothing factor for dry heat exchange (CFcl), and the clothing factor for evaporative cooling (CFpcl) were determined. When compared with reports of others on thermal characteristics the results agreed when pumping factors and clothing wetness were considered. The result was higher than expected values for CFcl and lower values for CFpcl.     

Calculating Workplace WBGT from Meteorological Data: A Tool for Climate Change Assessment

The WBGT heat stress index has been well tested under a variety of climatic conditions and quantitative links have been established between WBGT and the work-rest cycles needed to prevent heat stress effects at the workplace. While there are more specific methods based on individual physiological measurements to determine heat strain in an individual worker, the WBGT index is used in international and national standards to specify workplace heat stress risks. In order to assess time trends of occupational heat exposure at population level, weather station records or climate modelling are the most widely available data sources. The prescribed method to measure WBGT requires special equipment which is not used at weather stations. We compared published methods to calculate outdoor and indoor WBGT from standard climate data, such as air temperature, dew point temperature, wind speed and solar radiation. Specific criteria for recommending a method were developed and original measurements were used to evaluate the different methods. We recommend the method of Liljegren et al. (2008) for calculating outdoor WBGT and the method by Bernard et al. (1999) for indoor WBGT when estimating climate change impacts on occupational heat stress at a population level.     

The role of performance tests, manikins and test houses in defining clothing characteristics relevant to risk assessment.

Clothing is an important determinant of human heat exchange and accordingly a critical factor for heat stress risk assessment. A large number of international standards exist concerning protective properties of clothing. However, few standards deal with ergonomic properties and requirements of clothing, making it difficult to evaluate the function of a clothing ensemble in terms of both protection and physiological strain or discomfort. The paper examines existing test methods and procedures for improvement of the situation. Much of the work are presently at research stages, but should in the near future be available for test houses and consumers.     

Heat stress risk profiles for three non-woven coveralls

The ACGIH® Threshold Limit Value® (TLV®) is used to limit heat stress exposures so that most workers can maintain thermal equilibrium. That is, the TLV was set to an upper limit of Sustainable exposures for most people. This article addresses the ability of the TLV to differentiate between Sustainable and Unsustainable heat exposures for four clothing ensembles over a range of environmental factors and metabolic rates (M). The four clothing ensembles (woven clothing, and particle barrier, water barrier and vapor barrier coveralls) represented a wide range of evaporative resistances. Two progressive heat stress studies provided data on 480 trials with 1440 pairs of Sustainable and Unsustainable exposures for the clothing over three levels of relative humidity (rh) (20, 50 and 70%), three levels of metabolic rate (115, 180, and 254 Wm^?2) using 29 participants. The exposure metric was the difference between the observed wet bulb globe temperature (WBGT) and the TLV. Risk was characterized by odds ratios (ORs), Receiver Operating Characteristic (ROC) curves, and dose-response curves for the four ensembles. Conditional logistic regression models provided information on ORs. Logistic regressions were used to determine ROC curves with area under the curve (AUC), model the dose-response curve, and estimate offsets from woven clothing. The ORs were about 2.5 per 1°C-WBGT for woven clothing, particle barrier, and water barrier and for vapor barrier at 50% rh. When using the published Clothing Adjustment Values (CAVs, also known as Clothing Adjustment Factors, CAFs) or the offsets that included different values for vapor barrier based on rh, the AUC for all clothing was 0.86. When the fixed CAVs of the TLV were used, the AUC was 0.81. In conclusion, (1) ORs and the shapes of the dose-response curves for the nonwoven coveralls were similar to woven clothing, and (2) CAVs provided a robust way to account for the risk of nonwoven clothing. The robust nature of CAV extended to the exclusion of different adjustments for vapor barrier by rh.     

Clothing convective heat exchange--proposal for improved prediction in standards and models.

Convection is an important determinant for both sensible and evaporative heat exchange. Heat transfer by convection for normal boundary conditions is readily described by simple power functions. Clothing affects convection in various ways and existing characterisation of clothing by its static insulation values produces inaccurate prediction of sensible heat exchange, eventually leading to erroneous risk assessment. The present paper reviews various methods for evaluation of clothing convective (sensible) heat exchange. Based on available data, two equations are proposed for determination of the reduction of the total insulation values obtained under static, still wind conditions as a consequence of wind and walking effects. The equations apply from 0 to 1.84 clo, from 0.2 to 3 m/s and for walking speeds up to 1.2 m/s. The equations are incorporated in ISO 7933 to provide a more realistic and accurate prediction of sensible heat transfer through clothing.     

Criteria for assessing severely hot environments: from the WBGT index to the PHS (predicted heat strain) model

BACKGROUND: The present study deals with the main methods for assessment of hot environments: i.e., WBGT, SWreq and PHS. It is stressed how the WBGT index, which is strictly empirical, although a very practical tool for the assessment of the hot environments, can only be used for a rough evaluation of heat stress, and especially for a not very high metabolic rate (M<175 W/m2). On the contrary, the SWreq method, which is based on both subject-environment heat exchange and the effect of clothing, allows a better assessment of the work situation with a general reduction of the exposure limits with respect to WBGT, especially in non-uniform environments (ta not equal to tr). However, it should be noted that application of SWreq is required by the ISO standard 7243 when the WBGT limit values are exceeded. METHODS: In this study interest was extensively focused on the "Predicted Heat Strain" method, highlighting via a special software the differences in heat stress assessment related to this new approach, which will be adopted by the ISO in the next revision of standard 7933. RESULTS: The PHS method, unlike SWreq, allows the prediction of the time-response of the main physiological variables of interest (i.e., skin temperature, core temperature and sweat rate). Moreover thanks to better modelling of heat exchanges, the PHS method allows account to be taken of both movement and clothing effects, resulting in even more reduced exposure.     

A new whole-body vapor exposure chamber for protection performance research on chemical protective ensembles

A chemical vapor exposure chamber was designed to permit the study of whole-body vapor exposure of individuals wearing full protective clothing and equipment systems. A methodology also was developed to quantify the vapor protection performance of chemical protective ensembles (CPE) under safe and validated laboratory procedures. The principal research objectives were to (1) provide a methodology to accurately assess the performance of CPE and equipment under different environmental and chemical vapor challenge conditions; (2) quantify the vapor protection on a per body region basis; (3) have a systems level tool to aid in the research and development of more effective CPE for use in chemical biological environments; and (4) have a safe and reliable means of qualifying new CPE on the basis of vapor protection. Although designed for the evaluation of military-style protective equipment, the procedures apply equally to other styles of CPE used by civilian agencies such as firefighters, police, and hazmat units. The chamber and methodology were specifically designed to examine the vapor protection performance of clothing ensembles, including the details of protection variation over the body. A variety of exposure conditions appropriate to indoor and outdoor scenarios are possible, including the effects of wind, temperature, and relative humidity. Protection performance results from a number of individuals wearing typical military-style CPE are presented. These results demonstrate that there is no such thing as a unique protection performance level obtained for a given CPE. Rather, the individual and the ensemble interact differently in each situation, resulting in a protection performance distribution for individuals, and for groups of wearers, even under a standardized set of exposure conditions.     

Application of the remaining vaccine vial monitor life calculation to field temperature monitoring data to improve visibility into cold chain equipment performance

Vaccine Vial Monitors (VVM) are used to estimate if a vaccine has been exposed to excessive hot temperatures. This endpoint measurement is useful in determining if a vaccine is safe to be administered to a patient, but it does not pinpoint where in the cold chain a vaccine was exposed to excessive heat. With the expansion and technological advancement of cold chain equipment temperature monitoring, it is now possible to remotely estimate VVM status as a vaccine moves through the cold chain. In the present study, we examine the application of the mathematical principles backing VVMs on real, continuous, temperature monitoring data in Africa. Results suggest that exposure to short bursts of hot temperature or long power outages may still allow for safe distribution of affected vaccines. The remaining VVM life calculation could improve managerial visibility into cold chain equipment performance allowing for better data-driven planning and maintenance decisions.     

Protective clothing in hot environments

The high level of protection required by personal protective clothing (PPC) severely impedes heat exchange by sweat evaporation. As a result work associated with wearing PPC, particularly in hot environments, implies considerable physiological strain and may render workers exhausted in a short time. Recent development of algorithms for describing the heat transfer, accounting for pumping and wind effects, comprises improvement of the prediction of thermal stress. Realistic corrections can then be made to the available measures of thermal insulation and evaporative resistance of a given clothing ensemble. Currently this information is incorporated in international standards for assessment of thermal environments. Factors, such as directional radiation and wetting of layers, were studied in a recently completed EU research project. The development of advanced thermal manikins and measurement procedures should provide better measures for predictive models. As with all methods and models, the results need validation in realistic wear trials in order to prove their relevance and accuracy.     

Evaluation of Occupational Cold Environments: Field Measurements and Subjective Analysis

The present work is dedicated to the study of occupational cold environments in food distribution industrial units. Field measurements and a subjective assessment based on an individual questionnaire were considered. The survey was carried out in 5 Portuguese companies. The field measurements include 26 workplaces, while a sample of 160 responses was considered for the subjective assessment. In order to characterize the level of cold exposure, the Required Clothing Insulation Index (IREQ) was adopted. The IREQ index highlights that in the majority of the workplaces the clothing ensembles worn are inadequate, namely in the freezing chambers where the protection provided by clothing is always insufficient. The questionnaires results show that the food distribution sector is characterized by a female population (70.6%), by a young work force (60.7% are less than 35 yr old) and by a population with a medium-length professional career (80.1% in this occupation for less than 10 yr). The incidence of health effects which is higher among women, the distribution of protective clothing (50.0% of the workers indicate one garment) and the significant percentage of workers (>75%) that has more difficulties in performing the activity during the winter represent other important results of the present study.     

冬泳运动员的冷适应水平

我国北方冬泳运动员经常接触的冷水环境,为一般人日常生活中绝难经历的严酷冷应激条件。在手指浸泡冰水的试验中,冬泳者指温高、血管舒张反应比对照组较早出现。尽管其在冷中有较强的保持肢端温度的能力,但4h的全身冷暴露过程中,其体心温度及股皮温却低于对照组,较少发生寒战,痛感轻,代谢率也不似对照组那样地明显增强。表明冬泳者属于低体温——隔热型的冷适应。     

21d间歇性冷刺激对大鼠耐寒能力的影响及机制

目的观察间歇性冷刺激对大鼠耐寒能力的影响。方法雄性SD大鼠12只,按体重(110±5)g随机平均分为对照组(n=3)、间歇性冷刺激组(n=3)、急性冷暴露组(n=3)和间歇性冷刺激并急性冷暴露组(n=3)。间歇性冷刺激组(3 w)与间歇性冷刺激并急性冷暴露组(3 w+cold)接受4℃,4 h/d冷刺激,共21 d;对照组(con)和急性冷暴露组(cold)进行室温饲养。3周后,cold和3 w+cold组在第2 d接受-15℃,4 h冷暴露,观察大鼠肛温变化及棕色脂肪组织形态和功能的改变。结果 -15℃冷暴露4 h导致急性冷暴露组(cold)大鼠肛温明显下降(P<0.05),下降(2.64±0.182)℃,而间歇性冷刺激并急性冷暴露组(3 w+cold)大鼠肛温无明显改变,下降(0.32±0.531)℃;棕色脂肪组织形态观察显示:急性冷暴露组(cold)大鼠肩胛间区棕色脂肪面积较小边界不清,充血明显,色泽呈暗红色,间歇性冷刺激并急性冷暴露组(3 w+cold)肩胛间区棕色脂肪面积较大,边界较清晰,充血明显,色泽呈深棕色。Western blot检测发现,间歇性冷刺激可使大鼠棕色脂肪组织线粒体CoxⅣ及解耦连蛋白1(UCP1)含量明显升高。结论 21 d间歇性冷刺激可以显著提高大鼠耐寒能力,棕色脂肪组织形成、线粒体CoxⅣ和UCP1含量增加可能是其耐寒能力提高的主要因素。