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Biomedical subjects

B Griefahn

Publications and source records attributed to B Griefahn.

At least 19 recordsLinked to original sources
PubMed2004

Annoyance from multiple transportation noise: statistical models and outlier detection.

OBJECTIVE: Statistical models for the annoyance from multiple transportation noise are needed to understand and predict the annoyance resulting from specific noise exposures. METHODS: Models from the class of generalized linear models are suggested and discussed. Observations which are not well explained by the considered model are regarded as outliers. Outlier detection methods are applied to the data modelled by robust estimates using different link functions. RESULTS: The discussed methods are applied to data from a laboratory experiment using generalized linear models. While considering outliers, a generalized linear model with a complementary log-log link is found to be a good choice in modelling the exposure-response relationship between noise levels and annoyance.

Humans↗
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

Experiments on the effects of a continuous 16.7 Hz magnetic field on melatonin secretion, core body temperature, and heart rates in humans.

The present study investigated the hypothesis that a strong extremely low frequency magnetic field partially suppresses the synthesis of melatonin and subsequently elevates the core body temperature. Seven healthy young men (16-22 years) took part in a control and in an exposure session. Three men experienced first the control and then the exposure session, four men experienced the sessions in reverse order. Control sessions were performed as constant routines, where the participants spent 24 hour periods continuously in bed while air temperature was 18 degrees C, illumination less than 30 lux, and the sound pressure level 50 dBA. The exposure sessions differed from that protocol only between 6 pm and 2 am when a strong extremely low frequency magnetic field was continuously applied (16.7 Hz, 0.2 mT). Assuming that the participants were unable to perceive the field consciously, they were blind against the actual condition. Salivary melatonin levels were determined hourly; body core temperatures and heart rates were registered continuously throughout. Neither of these parameters revealed alterations that can be related to the influence of the magnetic field. The present results, taken together with other investigations using that particular field, lead to the hypothesis that the effects most likely, occur, only after repetitive exposures to intermittent fields.

Adolescent↗
PubMed2001

The impact of draught related to air velocity, air temperature and workload.

This experimental study was designed to test the hypotheses that the effects of draught increase with higher air velocity, with lower air temperature, and with lower workload. Thirty healthy young males were exposed to horizontal draught during 55 min while they operated an arm ergometer in a standing posture. Air velocity, air temperature, and workload were varied in 3 steps each, between 11 and 23 degrees C, 0.1 and 0.3 m/s, and 104 to 156 W/m2, respectively. The 27 combinations were distributed over subjects in a fractional factorial 3(3)-design. The participants were clothed for thermal neutrality. Workload was measured at the end of the sessions by respirometry. Draught-induced annoyance was determined every 5 min, separately for 10 body sites. Corresponding skin temperature was also recorded. The hypotheses were verified for the influence of air velocity and air temperature. Regarding workload, local heat production is probably decisive, meaning that draft-induced local annoyance is inversely related to workload in active but independent from workload in non-active body areas. To improve the situation for the workers concerned it is suggested to apply protective gloves that cover an as great area of the forearms as possible and to limit airflows to mean velocities of less than 0.2 m/s (with turbulence intensities of 50%).

Adult↗
PubMed2001

Long-Term stability of 6-hydroxymelatonin sulfate in 24-h urine samples stored at -20 degrees C.

The purpose of the present feasibility study was to determine whether the concentration of 6-hydroxymelatonin sulfate (6-OHMS) remains stable in urine samples stored over at least 15 yr. To test this, 117 twenty-four-hour urine samples were analyzed, which were obtained from healthy children ages 8 to 9 yr within the periods of 1985-1987,1991-1993, and 1997-1999. 6-OHMS concentrations were determined by enzyme-linked immunosorbent assay. The statistical analyses clearly indicate that the concentration of 6-OHMS remains stable for at least 15 yr if the urine is stored at -20 degrees C.

Child↗
PubMed2001

Development and validation of the predicted heat strain model.

Eight laboratories participated in a concerted research project on the assessment of hot working conditions. The objectives were, among others, to co-ordinate the work of the main European research teams in the field of thermal factors and to improve the methods available to assess the risks of heat disorders at the workplace, and in particular the "Required Sweat Rate" model as presented in International Standard ISO 7933 Standard (1989). The scientific bases of this standard were thoroughly reviewed and a revised model, called "Predicted Heat Strain" (PHS), was developed. This model was then used to predict the minute by minute sweat rates and rectal temperatures during 909 laboratory and field experiments collected from the partners. The Pearson correlation coefficients between observed and predicted values were equal to 0.76 and 0.66 for laboratory experiments and 0.74 and 0.59 for field experiments, respectively, for the sweat rates and the rectal temperatures. The change in sweat rate with time was predicted more accurately by the PHS model than by the required sweat rate model. This suggests that the PHS model would provide an improved basis upon which to determine allowable exposure times from the predicted heat strain in terms of dehydration and increased core temperature.

Algorithms↗
PubMed2000

[Noise effects not only the ears. But can damage to health be objectively evaluated?].

Noise is an unwanted sound and/or a potential health hazard. Apart from noise-induced hearing loss noise causes numerous psychosocial and unspecific vegetative effects. Disturbances of communication are most frequently complained, and sleep disturbances ar regarded as most deleterious. These reactions may then cause performance decrements, annoyance and behavioral alterations. The permanent influence of noise may contribute to the multifactorial genesis of cardiovascular diseases, particularly of hypertension.

Aircraft↗
PubMed2000

Prediction of the average skin temperature in warm and hot environments.

The prediction of the mean skin temperature used for the Required Sweat Rate index was criticised for not being valid in conditions with high radiation and high humidity. Based on a large database provided by 9 institutes, 1999 data points obtained using steady-state conditions, from 1399 experiments and involving 377 male subjects, were used for the development of a new prediction model. The observed mean skin temperatures ranged from 30.7 degrees C to 38.6 degrees C. Experimental conditions included air temperatures (Ta) between 20 and 55 degrees C, mean radiant temperatures (Tr) up to 145 degrees C, partial vapour pressures (Pa) from 0.2 to 5.3 kPa, air velocities (v(a)) between 0.1 and 2 m/s, and metabolic rates (M) from 102 to 620 W. Rectal temperature (T(re)) was included in the models to increase the accuracy of prediction. Separate models were derived for nude (clothing insulation, I(cl), < or = 0.2 clo, where 1 clo = 0.155 m2 x degrees C x W(-1), which is equivalent to the thermal insulation of clothing necessary to maintain a resting subject in comfort in a normally ventilated room, air movement = 10 cm/s, at a temperature of 21 degrees C and a humidity of less than 50%) and clothed (0.6 < or = I(cl) < or = 1.0 clo) subjects using a multiple linear regression technique with re-sampling (non-parametric bootstrap). The following expressions were obtained for nude and clothed subjects, respectively: T(sk) = 7.19 + 0.064Ta + 0.061Tr + 0.198Pa - 0.348v(a) + 0.616T(re) and T(sk) = 12.17 + 0.020Ta + 0.044Tr + 0.194Pa - 0.253v(a) + 0.0029M + 0.513T(re). For the nude and clothed subjects, 83.3% and 81.8%, respectively, of the predicted skin temperatures were within the range of +/- 1 degree C of the observed skin temperatures. It is concluded that the proposed models for the prediction of the mean skin temperature are valid for a wide range of warm and hot ambient conditions in steady-state conditions, including those of high radiation and high humidity.

Clothing↗
PubMed2000

Limits of and possibilities to improve the IREQ cold stress model (ISO/TR 11079). A validation study in the field.

Estimated insulation (Icl) of clothing worn by workers daily exposed to air temperatures between 0 and 15 degrees C was compared with the corresponding insulation calculated for thermal neutrality using the IREQ-model (IREQneutral, ISO/TR 11079). The goal was to determine possible limitations of the applicability of the IREQ-model and to stress to necessities and possibilities to improve the model. Sixteen female and 59 male workers (16-56 yr) were monitored during their work. According to their cold stress at the workplace they were allocated to three groups (33 persons were exposed to constant temperatures of more than 10 degrees C, 32 to less than 10 degrees C, and 10 persons experienced frequent temperature changes of 13 degrees C. Another categorization concerned workload (8 persons worked at metabolic rates of less than 100 W/m2, 50 persons worked at 101-164 W/m2, and 17 worked at more than 165 W/m2, respectively). The analysis of the differences between estimated worn insulation (Icl) and calculated IREQneutral revealed that the IREQ-model applies for air temperatures up to 15 degrees C and for temperature changes of 13 degrees C (at least) but needs to be improved with respect to gender. The IREQ model does not apply sufficiently for high and largely varying workloads (165 W/m2 and more). However, these situations are beyond the currently available possibilities to protect workers adequately with conventional clothing material. A suitable short-term measure is a more even work flow by avoiding activities with very high and low metabolic rates.

Adult↗
PubMed2000

Contrast thresholds and fixation disparity during 5-Hz sinusoidal single- and dual-axis (vertical and lateral) whole-body vibration.

The present study assumed that whole-body vibration, transmitted through the seat, impairs spatial retinal resolution and oculomotor alignment parallel to the vibration axis. More specifically, that the decrement increases gradually from single-axis lateral via single-axis vertical and dual-axis linear to dual-axis circular motion. Twenty participants (19-26 years of age) with good vision volunteered for the experiment where in three sessions one of the following three conditions, contrast threshold, nonius bias or fixation disparity, for vertically and horizontally oriented test patterns was determined during five experimental conditions. The latter comprised a control (a(z) = a(y) = 0) and four conditions where 5-Hz sinusoidal motion of 1.2 ms(-2) rms were applied separately, either in the vertical or in the lateral direction, or simultaneously in both directions, once without and once with a phase shift of 90 degrees, thus causing dual-axis linear or circular motion. Contrast thresholds for horizontal gratings and the variability of vertical fixation disparity increased significantly whenever the participants were exposed to vertical motion (alone or combined with lateral motion). These effects may result in an increased difficulty in properly recognizing characters and graphic patterns containing horizontal lines and in the development of asthenopic complaints.

Adult↗
PubMed2000

Drafts in cold environments--the significance of air temperature and direction.

This paper concerns the influence of air temperature and of the direction of drafts on subjective and physiological responses. In three experimental series 58 healthy persons (50 men, 8 women, 20-29 yrs) were exposed to drafts in overall 446 experimental sessions. Drafts were applied either horizontally or vertically with mean air velocities of 0.1 to 0.3 m/s and a turbulence intensity of 50%. Air temperature was varied between 11 and 23 degrees C and metabolic rates between < 70 and 156 W/m2. These parameters were kept constant during the single one-hour sessions. The subjects were dressed for thermal neutrality. Draft-induced annoyance was registered every 5 minutes using a list of prescribed body parts and skin temperature was measured at the forearm and at the neck. Subjective and physiological responses were systematically related to air temperature. Draft-induced general annoyance, draft-induced local annoyance (neck, forearm) and the drop of the corresponding skin temperature were inversely related to air temperature. Concerning the direction horizontal drafts seem to cause somewhat stronger reactions. The predictive model developed by Toftum underestimates the percentage of persons annoyed. A modified version increases the predictive power significantly.

Adult↗
PubMed1999

The significance of lateral whole-body vibrations related to separately and simultaneously applied vertical motions. A validation study of ISO 2631.

Sensitivity of lateral motions relative to vertical motions were determined and compared to predictions provided by ISO 2631. Two experiments were executed where lateral and vertical motions were applied consecutively or simultaneously and where the magnitude of a single- or dual-axis test signal was adjusted until it was judged as equivalent to a preceding single-axis reference motion of the same frequency. Experiment 1: References consisted of vertical sinusoidal motions presented with 1.6-12.5 Hz and weighted accelerations of a(zw) = 0.3, 0.6 and 1.2 m s(-2) r.m.s., single-axis test signals were lateral motions of the same frequency. 26 subjects (15 men, 11 women, 20-56 yr) participated in the experiments. Accelerations adjusted for lateral vibrations above 1.6 Hz were considerably lower than predicted suggesting that the weighting factors provided in ISO 2631 are incorrect. Experiment 2: References consisted of single-axis vertical or lateral sinusoidal motions presented with 1.6-12.5 Hz and a weighted acceleration of a(zw) = 1.25 m s(-2) r.m.s. The dual-axis test signals consisted of a constant fraction of the reference acceleration (10, 25, 50, 75, 90%) and a perpendicularly oriented adjustable component. 31 subjects (15 men, 16 women, 19-51 yr) participated in the experiments. Both experiments revealed that ISO 2631 is qualitatively valid, the weighting of lateral motions above 1.6 Hz, however, should be increased in order to meet the actual sensitivity particularly in case of multi-axis vibrations.

Acceleration↗
PubMed1999

Fixation disparity and nonius bias.

Fixation disparity, i.e. the vergence error within Panum's area, can be measured psychophysically with two nonius (vernier) lines that are presented dichoptically, i.e. one to each eye. The observer adjusts these nonius lines to subjective alignment; the resulting physical nonius offset indicates the amount of fixation disparity. The present experiments investigate the relation between fixation disparity and the nonius bias, which is the physical offset of the nonius lines that is adjusted by the observer in order to perceive them as aligned when both nonius lines are presented to both eyes (binocular nonius bias) or both to the left or both to the right eye (monocular nonius bias). It was found that (1) the fixation disparity is correlated with the binocular nonius bias in the horizontal and vertical meridian and (2) the binocular nonius bias can be predicted from the average of the right eye and left eye monocular nonius bias. To remove the influence of the nonius bias on measured fixation disparity it is possible to calculate the fixation disparity relative to the individual binocular nonius bias, rather than to the physical coincidence of the nonius lines. This procedure tends to increase the correlation between fixation disparity and the tonic resting position of vergence. We discuss the clinical relevance of the dichoptic nonius method for measuring fixation disparity and its limitations as compared to physical recordings of eye position.

Convergence, Ocular↗
PubMed1998

Calcium metabolism and growth during early treatment of children with X-linked hypophosphataemic rickets.

UNLABELLED: To evaluate the effect of early treatment on calcium metabolism and growth of infants with X-linked hypophosphataemic rickets (XLH), we enrolled eight infants (one boy) with XLH in a prospective study before and during combined treatment with 40 60 mg/kg per day phosphate and 20-40 ng/kg per day 1,25(OH)2D3 (calcitriol). The duration of treatment ranged from 12 to 68 months (median 27 months). We measured the height and several indices of calcium and bone metabolism before and at intervals of 6 weeks to 3 months thereafter during treatment. The diagnosis XLH was established between the age of 3 to 12 weeks by the detection of elevated alkaline phosphatase activities (n = 8) and urinary hydroxyproline (n = 7), whereas only five patients had also hypophosphataemia. Six of seven untreated patients had decreased 1,25(OH)2 vitamin D levels in serum. During treatment alkaline phosphatase and hydroxyproline decreased to normal or slightly elevated levels, whereas serum phosphate remained below the normal range. Several patients treated with more than 40-50 mg/kg per day phosphate developed secondary hyperparathyroidism. One patient receiving a low dose of 20 ng/kg per day calcitriol had prolonged radiological and biochemical signs of rickets and growth delay. The other patients presented with no or only slightly transient signs of rickets. Three patients developed moderate nephrocalcinosis. The statural growth rate decreased slightly below 2 SDs without a further decrease in two patients and remained within the normal range in the other patients. Only four patients developed moderate leg deformities. CONCLUSIONS: Early treatment with calcitriol at a daily dose of at least 30-40 ng/kg and phosphate at a daily dose of maximal 40-50 mg/kg improves mineral metabolism and seems to obviate severe growth delay and leg deformities.

Adolescent↗
PubMed1998

Equivalent sensation curves of simultaneous lateral and vertical sinusoidal whole-body vibration.

BACKGROUND: To evaluate the effects of whole body vibration on discomfort, the sensitivity to different frequencies as well as to different vibration axes must be regarded. This experimental study investigates the significance of lateral relative to vertical motions in the sensation of dual axis sinusoidal vibrations in sitting posture. The results are discussed in the context of the evaluation procedure proposed in the international standard ISO 2631 (13). METHODS: The experiments, in which 31 volunteers (16 female, 15 male, 19 51 yr) participated, used the method of adjustment. The subjects compared a single axis reference motion (aw = 1.25 ms(-2) rms) with a dual axis test motion of the same frequency. The magnitude of the test signal's component along the reference axis was kept constant at a fractional level of the reference magnitude (10, 25, 50, 75 or 90%). The component perpendicular to the reference axis was adjusted by the subjects until the test signal was rated as being equally strong as the reference. Both vertical and lateral reference motions were applied. The frequencies used were 1.6, 3.15, 6.3 and 12.5 Hz. RESULTS: The shape of the resulting right-downwards bent equivalence curves was reasonably well fitted using the frequency weightings and evaluation procedure of ISO 2631. However, there were considerable quantitative discrepancies for frequencies above 1.6 Hz with an underestimation of the effects of lateral vibrations by a factor of 1.5-2. Therefore, it is concluded that lateral vibrations above 1.6 Hz need more weight in the evaluation of discomfort caused by multi-axis whole body vibrations.

Acceleration↗
PubMed1997

Technical note. Comparison between estimated worn clothing insulation and required calculated clothing insulation in moderately cold environments (0 degree C < or = ta < or = +15 degrees C).

Six female and 33 male workers of the food industry (16-55 years), divided into three groups according to climatic conditions at the workplaces, were monitored during a typical shift. Fourteen subjects worked continuously in 0-7 degrees C, 18 in 13-15 degrees C and seven moved frequently between these climatic areas. Mean metabolic rates, heart rates, rectal temperatures and skin temperatures at the trunk and at the feet were similar between each of the three groups. Considerable differences between estimated clothing insulations worn and calculated required clothing insulations (IREQneutral) were statistically analyzed. The results suggest that--apart from a limited overestimation--this discrepancy is mainly related to the difference between time-adjusted averages of metabolic rates of the single activities and the respective daily minimum suggesting the need for an adequate weighting for the metabolic rates, particularly if workers are at least temporarily exposed to air temperatures of more than 7-13 degrees C.

Adolescent↗
PubMed1997

Acclimation to three different hot climates with equivalent wet bulb globe temperatures.

The present study examined 2 hypotheses: Irrespective of the actual composition of thermal factors, the course of acclimation is similar in hot climates which are equivalent in terms of the WBGT. Acclimation to a defined hot thermal environment confers equal acclimation to any other equivalent climate. These hypotheses were supported with 3 substantially different but equivalent climates with WBGTs between 33.4 and 33.6 degrees C. Eight subjects (6 male, 2 female, 19-32 yrs) executed a treadmill walk (4 x 25 min, 4 km/h, 0 degree) while exposed to either a warm-humid, a hot-dry or a radiant heat condition on 15 consecutive days. On the following 2 days, those adapted to the warm-humid or to the radiant heat condition were exposed to the hot-dry climate and those adapted to the latter were exposed to the warm-humid climate. During the experiments, rectal temperatures, skin temperatures at three sites (forehead, chest, leg) and heart rates were measured continuously. Sweat loss was determined by weighing the subjects before and after the daily trials and during the breaks. At the same time, the subjects rated their actual well-being. Disregarding minor differences during the courses of acclimation, both hypotheses were verified.

Acclimatization↗