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Biomedical subjects

I Holmér

Publications and source records attributed to I Holmér.

At least 19 recordsLinked to original sources
PubMed2006

Temperature limit values for touching cold surfaces with the fingertip.

OBJECTIVES: At the request of the European Commission and in the framework of the European Machinery Directive, research was performed in five different laboratories to develop specifications for surface temperature limit values for the short-term accidental touching of the fingertip with cold surfaces. METHODS: Data were collected in four laboratories with a total of 20 males and 20 females performing a grand total of 1655 exposures. Each touched polished blocks of aluminium, stainless steel, nylon-6 and wood using the distal phalanx of the index finger with a contact force of 1.0, 2.9 and 9.8 N, at surface temperatures from +2 to -40 degrees C for a maximum duration of 120 s. Conditions were selected in order to elicit varying rates of skin cooling upon contact. Contact temperature (TC) of the fingertip was measured over time using a T-type thermocouple. RESULTS: A database obtained from the experiments was collated and analysed to characterize fingertip contact cooling across a range of materials and surface temperatures. The database was subsequently used to develop a predictive model to describe the contact duration required for skin contact temperature to reach the physiological criteria of onset of pain (15 degrees C), onset of numbness (7 degrees C) and onset of frostbite risk (0 degrees C). CONCLUSIONS: The data reflect the strong link between the risk of skin damage and the thermal properties of the material touched. For aluminium and steel, skin temperatures of 0 degrees C occurs within 2-6 s at surface temperatures of -15 degrees C. For non-metallic surfaces, onset of numbness occurs within 15-65 s of contact at -35 degrees C and onset of cold pain occurs within 5 s of contact at -20 degrees C. The predictive model subsequently developed was a non-linear exponential expression also reflecting the effects of material thermal properties and initial temperature. This model provides information for the protection of workers against the risk of cold injury by establishing the temperature limits of cold touchable surfaces for a broad range of materials, and it is now proposed as guidance values in a new international standard.

Adolescent↗
PubMed2004

Cold but comfortable? Application of comfort criteria to cold environments.

UNLABELLED: Fanger defined two physiological criteria that are basic requirements for people's perception of thermal neutrality and, eventually, thermal comfort. Mean skin temperature and evaporative heat loss are defined as functions of metabolic rate. The equations are derived from experiments in light clothing at or close to normal indoor climate. Relations between skin temperature and sweating on the one hand and thermal sensation and comfort on the other are well recognized; the precise description of the relationships vary and may differ from normal indoor environments to more extreme thermal stress. In moderately cold environments (around +10 degrees C) ISO/DIS 7730 and ISO/DIS 11079 prescribe significantly different responses. Evaluation of the rationale behind the comfort criteria and the basic heat transfer equations in the two models reveals some clear differences. By modification of the sweating criteria and some of the heat transfer equations, predictions become much more similar. It is concluded that the basic comfort criteria may apply also to moderately cold and cold environments, but must consider the complex heat transfer through multilayer clothing in a more adequate way. PRACTICAL IMPLICATIONS: The suggested, modified comfort criteria incorporated either in the PMV-index or in the IREQ-index, provide more realistic and reliable prediction of heat balance and conditions for comfort in cool and cold environments.

Body Temperature Regulation↗
PubMed2003

Comfort climate evaluation with thermal manikin methods and computer simulation models.

With increasing demand for acceptable environment in the modern workplace is it necessary, already in the construction phase, to estimate what effect different environmental factors have on the occupants. Thermal sensation is affected by many factors in the work place environment, especially thermal factors and effects from air movement caused by different ventilation principles. A series of full scale measurements as well as numerical calculations have been carried out in order to investigate whether Computational Fluid Dynamics (CFD) calculations and measurements with a thermal manikin are able to predict the perceived thermal climate. When human thermal sensation is linked together in measurements and calculations, the thermal situation in the work place environment is visualized. The results show relatively good agreement with the measurements made in the real environment. However, numerical and experimental methods need to be further developed. Evaluation methods of this type, will enable engineers to make better predictions and early decisions in the design and construction process. This also opens possibilities to use results from a number of full scale tests providing means to improve the comfort, health and productivity in working life.

Air Movements↗
PubMed2002

Assessment of the risk of heat disorders encountered during work in hot conditions.

OBJECTIVE: To co-ordinate the work of the main European research teams in the field of thermal factors in order to develop and improve significantly the methods presently available for assessing the risks of heat disorders encountered during work in hot conditions. METHOD: Each item from the required sweat rate model was reviewed on the basis of the most recent literature. A database with 1,113 laboratory and field experiments, covering the whole range of hot working conditions, was assembled and used for the validation. RESULTS: Influence of clothing ensemble on heat exchange: methods and formulas were developed that take into account the dynamic effects associated with forced convection and the pumping effect associated with body movements and exercise. Prediction of the average skin temperature: the model used in the required sweat rate standard ISO 7933 was extended to cover more severe conditions with high radiation and high humidity and different clothing and take into account the rectal temperature for the prediction of the skin temperature. Criteria for estimating acceptable exposure times in hot work environments: criteria were reviewed and updated concerning the maximum increase in core temperature and the acceptable water loss, for acclimatised and nonacclimatised subjects. These limits are intended to protect 95% of the population. Measuring strategy: a strategy was developed to assess the risks in any working situation with varying conditions of climate, metabolic rate or clothing. A detailed methodology was developed in three stages: an "observation" method for the recognition of the conditions that might lead to thermal stress; an "analysis" method for evaluating the problem and optimising the solutions; and an "expert" method for in-depth analysis of the working situation when needed. VALIDATION: the different results were used to prepare a revision of the interpretation procedure proposed in the ISO standard 7933. We validated the modified approaches using the database. This involved the whole range of conditions for which the model was extended, namely conditions with high and low radiation, humidity and air velocity as well as fluctuating conditions. Based on these results, the predicted heat strain model was developed: it is presently proposed as an ISO and CEN standard.

Biomechanical Phenomena↗
PubMed2001

[Functionality of inhalation aerosols is inadequate or lost at low temperature].

Correct and safe performance of metered-dose inhalers are necessary for efficient treatment of asthma under all climatic conditions. The spray mechanism malfunctioned when canister temperature was below -15 degrees C. The range and propagation of the spray plume at canister temperatures below 10 degrees C deviated clearly from those at 20 degrees C. Also the composition and particle concentration of the spray plume at low temperatures differed from those at more normal temperatures. Information must be provided to the effect that a canister must not be cold when used.

Administration, Inhalation↗
PubMed2001

Effects of metabolic rate on thermal responses at different air velocities in -10 degrees C.

The effects of exercise intensity on thermoregulatory responses in cold (-10 degrees C) in a 0.2 (still air, NoWi), 1.0 (Wi1), and 5.0 (Wi5) m x s(-1) wind were studied. Eight young and healthy men, preconditioned in thermoneutral (+20 degrees C) environment for 60 min, walked for 60 min on the treadmill at 2.8 km/h with different combinations of wind and exercise intensity. Exercise level was adjusted by changing the inclination of the treadmill between 0 degrees (lower exercise intensity, metabolic rate 124 W x m(-2), LE) and 6 degrees (higher exercise intensity, metabolic rate 195 W x m(-2), HE). Due to exercise increased heat production and circulatory adjustments, the rectal temperature (T(re)), mean skin temperature (Tsk) and mean body temperature (Tb) were significantly higher at the end of HE in comparison to LE in NoWi and Wi1, and T(re) and Tb also in Wi5. Tsk and Tb were significantly decreased by 5.0 m x s(-1) wind in comparison to NoWi and Wi1. The higher exercise intensity was intense enough to diminish peripheral vasoconstriction and consequently the finger skin temperature was significantly higher at the end of HE in comparison to LE in NoWi and Wi1. Mean heat flux from the skin was unaffected by the exercise intensity. At LE oxygen consumption (VO2) was significantly higher in Wi5 than NoWi and Wi1. Heart rate was unaffected by the wind speed. The results suggest that, with studied exercise intensities, produced without changes in walking speed, the metabolic rate is not so important that it should be taken into consideration in the calculation of wind chill index.

Adult↗
PubMed2001

Validation of methods for determination of metabolic rate in the Edholm scale and ISO 8996.

The aim of this study was to validate the Edholm scale (Edholm, 1966) and the ISO 8996 standard (International Organization for Standardization [ISO], 1990) by comparing the metabolic rates estimated for both methods with the actual measured metabolic rate (MMeas) in 6 manual material handling tasks simulated under laboratory conditions. The metabolic rate was calculated from oxygen consumption VO2 (19 participants) according to Standard No. ISO 8996 (ISO, 1990). Additionally, the participants estimated perceived exertion using the Borg scale. The metabolic rates derived from the Edholm scale (MEdh) overestimated 5 of 6 activities by 34-50% (alpha = .05). The metabolic rates derived from ISO 8996 (MISO) overestimated all activities by 7-38% (alpha = .05).

Adult↗
PubMed2000

Face temperature and cardiorespiratory responses to wind in thermoneutral and cool subjects exposed to -10 degrees C.

The effects of the thermal state of the body (slightly cool and neutral) and moderate wind speeds on face temperature, blood pressure, respiratory function and pain sensation during cold exposure were studied on eight healthy male subjects. They were dressed in cold-protective clothing and preconditioned at + 20 degrees C (TN) and -5 degrees C (CO) for 60 min, then exposed to -10 degrees C and 0 m x s(-1) (NoW), 1 (W1) and 5 (W5) m x s(-1) wind for 30 min. Thus, each individual was exposed six times. The exposure to wind entailed a combination of strong cooling of the bare face and mild body cooling. The forehead, cheek and nose temperatures decreased during cold exposure, and the decrease was greater at higher air velocities (P < 0.0001). All subjects reported pain sensations at 5 m x s(-1). At the end of exposure only the nose temperature was significantly lower in CO than in TN subjects; it was about 2 degrees C and reached 0 degrees C in two experiments. The systolic and diastolic blood pressure (SBP and DBP, respectively) increased significantly by 7.7 and 5.9 mmHg, respectively, during preconditioning at -5 degrees C, but did not change at + 20 degrees C. SBP and DBP increased during exposure to -10 degrees C in TN by approximately 9 mmHg. However, the total average increase of blood pressure (1-90 min) was similar in TN and CO (SBP 15 mmHg and DBP 13 mmHg). SBP and DBP increased more during exposure to 5 m x s(-1) at -10 degrees C than NoW. Blood pressure responses as observed in this study (SBP and DBP up to 51 and 45 mmHg, respectively) are potential health risks for hypertensive individuals and angina patients. Respiratory functions (FVC, FEV1) were reduced by about 3% by the cold (-5 and -10 degrees C) compared to pre-experiment values. Furthermore, the Wind Chill Index seems to underestimate the cooling power of 5 m x s(-1) at -10 degrees C of bare skin (e.g. face). Therefore it needs to be revised and we suggest that it is expanded to include risk levels for pain sensation.

Adult↗
PubMed2000

Thermal responses to cold wind of thermoneutral and cooled subjects.

The effects of initial thermal state on thermoregulatory responses to cold (-10 degrees C) in a 0.2 (still air), 1.0, and 5.0 m. S(-1) wind speed were studied. Eight young male subjects were first preconditioned in thermoneutral (+20 degrees C, TN) or cool (-5 degrees C, CO) environment for 60 min. After preconditioning the subjects were exposed to wind at -10 degrees C in a standing position, facing the wind, for 30 min. Precooling decreased mean skin temperature (Tsk) by 4.0 (SEM 0.1) degrees C (P < 0.001) and increased heat flux by 57 (SEM 2) W x m(-2) (P < 0.001) in comparison to TN. Cooling rate of Tsk was faster (P < 0.001) in TN than in CO at every wind speed. Even so, Tsk ended up at a lower level in CO (P < 0.001-0.01) than in TN at every wind speed. Local skin temperatures of hand, finger, foot and toe were significantly lower in CO than in TN at the end of all exposures to wind. Heat flux from the skin was 8% higher (NS) in TN at 5.0 m x s(-1) wind speed in comparison to CO. A 5.0 m x s(-1) wind speed increased oxygen consumption significantly (P < 0.001) in both CO and TN in comparison to still air. At 5.0 m x s(-1) wind speed the general thermal sensation was the same (cold) in both TN and CO, despite the higher Tsk in TN. In conclusion, Tsk decreased more rapidly in TN, probably due to rapid skin vasoconstriction and redistribution of circulation to the central body. Probably for the same reason, dry heat loss from the skin was at nearly the same level in both TN and CO. Although the initial thermal state did not affect the amount of heat loss, it significantly affected the peripheral temperatures and thermal sensations and should therefore be taken into consideration in the prediction of thermophysiological responses to wind.

Adult↗
PubMed2000

Prediction of duration limited exposure for participants wearing chemical protective clothing in the cold.

The suitability of the IREQ (insulation required) index for predicting the thermal responses of 6 participants wearing chemical protective clothing was tested during exercise at -20 and -25 degrees C. IREQ was used to calculate duration limited exposure (DLE). Measured DLE correlated (r =0.899, p <0.001) with the predicted DLE. In exposures exceeding 40 min, however, the predicted DLE tended to be 10-20 min too short compared to the measured one. During short exposures the prediction was 5-20 min too long. The results show that IREQ overestimated the cold strain in participants wearing chemical protective clothing during cold exposures longer than 40 min. Nevertheless, predicted DLE never exceeded measured times and thus the prediction was always safe from the occupational point of view.

Adult↗
PubMed2000

Validation of a model for prediction of skin temperatures in footwear.

A model for foot skin temperature prediction was evaluated on the basis of 2 experiments on subjects at various environmental temperatures (light seated manual work at -10.7 degrees C (Study 1), and a short walking period in combination with standing and sitting at +2.8 degrees C, -11.8 degrees C and -24.6 degrees C (Study 2), with boots of 3 insulation levels. Insulation of the footwear was measured on a thermal foot model. Predicted and measured data showed a relatively good correlation (r = 0.87) at the 2 colder conditions in Study 2. The environmental temperature of 2.8 degrees C was not low enough at the chosen activity for a considerable foot skin temperature drop. In Study 1 the predicted temperature stayed higher for the whole exposure period and the difference between the predicted and the measured foot skin temperatures grew proportionally with time, while subsequent warm-up curves at room temperature were almost parallel. In Study 1 the correlation was 0.95. However, the paired t-test showed usually significant differences between measured and predicted foot skin temperatures. The insulation values from thermal foot measurements can be used in the model calculations. Lotens' foot model is lacking activity as direct input parameter, however, the blood flow is used instead (effect through Tcore). The Lotens foot model can give reasonable foot skin temperature values if the model limitations are considered. Due to the lack of activity level input, it will be difficult to make any good estimation of foot skin temperature during intermittent exercise. The rate of the foot temperature recovery after cold exposure was somewhat overestimated in the model--the warm-up of the feet of the subjects started later and was slower in the beginning of the warm-up than in the prediction. It could be useful to develop the model further by taking into consideration various wetness and activity levels.

Foot↗
PubMed2000

Strategies for prevention of cold stress in the elderly.

Human health and wellbeing require simple and effective strategies for prevention and alleviation of harmful effects of cold exposure. Adoption of a strategy should consider the type of cold stress; (1) whole body cooling, (2) extremity cooling, (3) convective cooling (wind chill), (4) conductive cooling (contact), and (5) airway cooling. The prime goal is to prevent tissue cooling. The risk, nature and magnitude of strain depend largely on the cooling effect, which results from the interaction of climate factors (mainly air temperature and wind), protection (clothing) and metabolic heat production (activity, "behaviour"). The effects (strain) of tissue cooling are acute, progressive or chronic. Acute effects are primarily thermoregulatory reflexes mediated by the sympathetic system and comprise immediate cardiovascular and respiratory reactions. Progressive effects are characterized by gradual temperature drop in peripheral or core tissues. This results in pain, neuro-muscular insufficiency, sensory loss and, eventually, cold injury. Chronic effects are likely to affect peripheral nerves and vessels, as well as cardio-respiratory function. The progressive degradation of physiological functions in the elderly increases the risk of harmful effects with cold exposure. This requires careful examination of relevant assessment criteria, as well as the development of simple and efficient strategies for prevention of cold stress.

Aged↗
PubMed1999

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.

Body Temperature Regulation↗
PubMed1999

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.

Bias↗
PubMed1999

Determination of heat loss from the feet and insulation of the footwear.

This study compared the methods of determining the footwear insulation on human participants and the thermal foot model. Another purpose was to find the minimal number of measurement points on the human foot that is needed for insulation calculation. Bare foot was tested at 3 ambient temperatures on 6 participants. Three types of footwear were tested on 2 participants. The mean insulation for a bare foot obtained on the participant and model were similar. The insulation of warm footwear measured by the 2 methods was also similar. For thin footwear the insulation values from the participants were higher than those from the thermal model. The differences could be related to undefined physiological factors. Two points on foot can be enough to measure the insulation of footwear on human participants (r =.98). However, due to the big individual differences of humans, and good repeatability and simplicity of the thermal foot method, the latter should be preferred for testing.

Adult↗
PubMed1999

A comparison of two methods of determining thermal properties of footwear.

The present European Standard for footwear testing (Standard No. EN 344:1992; European Committee for Standardization [CEN], 1992) classifies footwear thermally by a temperature drop inside the footwear during 30 min at defined conditions. Today, other methods for footwear thermal testing are also available. The aim of this study was to compare EN 344:1992 with a thermal foot method. Six boots were tested according to both methods. Additional tests with modified standard tests were also carried out. The methods ranked the footwear in a similar way. However, the test according to standard EN 344:1992 is a pass-or-fail test, whereas data that is gained from the thermal foot method gives more information and allows further use in research and product development. A change of the present standard method is suggested.

Body Temperature Regulation↗