Showing papers by "Barbara Griefahn published in 2001"

Development and validation of the predicted heat strain model

Abstract: 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.

Zur Validität der deutschen Übersetzung des Morningness-Eveningness-Questionnaires von Horne und Östberg

Abstract: Die Vergleichbarkeit mit der internationalen Literatur ist ein entscheidendes Kriterium bei der Wahl von Testinstrumenten. Zur Identifizierung der subjektiven zirkadianen Phasenlage (Chronotyp) werden im deutschen Sprachraum daher meist Ubersetzungen des Morningness-Eveningness-Questionnaires (MEQ, Horne & Ostberg, Int J Chronobiol 4:97–110, 1976) angewendet. In der vorliegenden Arbeit wurde die Validitat einer deutschen Ubersetzung des MEQ (D-MEQ) gepruft. Als Kriterien dienten der validierte Fragebogen zur subjektiven zirkadianen Phasenlage (SCP, R Moog, in Reinberg, Vieux, Andlauer (eds): night and shift work. Biological and social aspects. Pergamon Press Oxford, 1981) sowie der Nadir der Korperkerntemperatur und der Beginn der nachtlich erhohten Melatoninkonzentration im Speichel.

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

Abstract: 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.

Long-term stability of 6-hydroxymelatonin sulfate in 24-h urine samples stored at −20°C

Abstract: 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°C.

Évaluation du risque de contrainte thermique lors du travail en ambiances chaudes

Abstract: Objectif: L'objectif de la recherche a ete de coordonner le travail des principales equipes de recherche europeennes dans le domaine des facteurs thermiques afin d'ameliorer et de developper de maniere significative les methodes actuellement disponibles pour evaluer le risque d'astreintes thermiques lors du travail en ambiances chaudes. Resultats: - Influence des vetements sur les echanges thermiques Les effets dynamiques lies a la vitesse de l'air et l'effet de pompage lie aux mouvements et au travail sont pris en compte. - Prediction de la temperature cutanee moyenne Le modele a ete etendu a des conditions climatiques plus severes (rayonnement et humidite eleves, differents vetements...) et tient compte de la temperature centrale (rectale) pour la prediction de la temperature cutanee. - Criteres pour estimer des durees d'exposition acceptables dans les environnements chauds de travail Les criteres d'augmentation maximale de la temperature centrale et de perte hydrique acceptable ont ete revus pour des sujets acclimates et non acclimates. Ces limites protegent 95% de la population. - Strategie de mesure Une strategie a ete developpee pour evaluer les risques dans n'importe quelle situation de travail, avec des conditions variables de climat, de metabolisme ou de vetement. Des outils ont ete decrits en details pour les trois niveaux superieurs de la strategie SOBANE: ○ Une demarche d'Observation, pour l'identification des conditions qui pourraient mener a la contrainte thermique; ○ Une demarche d'Analyse, pour l'evaluation du probleme et l'optimisation des solutions quand la demarche d'Observation n'a pas abouti; ○ Une demarche d'Expertise lorsque l'etude specialisee de la situation de travail est indispensable. - Le Modele de prediction de la contrainte thermique (PHS: Predicted Heat Strain) Un nouveau modele de prediction de l'astreinte thermique a ete developpe et une revision de la norme ISO 7933 relative a la contrainte thermique en ambiances chaudes a ete preparee, en remplacement de l'indice de Sudation Requise qui devient ainsi obsolete. - Validation Le nouveau modele a ete valide a partir des donnees d'un ensemble d'experiences menees en laboratoire et sur le terrain et couvrant la gamme entiere des conditions pour lesquelles le modele a ete etendu, a savoir les conditions avec rayonnement, humidite ou vitesse d'air eleves et faibles, ainsi que pour des conditions fluctuantes au cours du temps.

Statistical Modelling of Physiological Heat Stress Response by Means of a Nonlinear Two‐Stage Model

Abstract: In the context of medical or biological studies, very often parameters of interest are measured repeatedly over time under a given set of conditions. This results in a set of (often similarly shaped) time series. Then, the objective is the determination of the functional relationship between the parameter of interest and time on the one hand, and the analysis of the variation of this functional relationship between experiments, on the other hand. This may be done by means of a two-stage model. The present work describes the theory of the two-stage model and its application to the increase of human core temperature for a set of 678 experiments where the subjects were exposed to warm and hot environments. The data originating from 6 European research institutes, have been pooled into one database for the Heat Stress Project within the scope of the BIOMED 2 programme of the European Union. A nonlinear two-stage model was applied, with a logistic function modelling the nonlinear time course of the core temperature, and with its parameters depending on air temperature, mean radiant temperature, air velocity, partial vapour pressure, clothing insulation, metabolic rate, gender, acclimatisation status and body surface area. We conclude that acclimatisation, clothing insulation, body surface area, air temperature, air velocity, partial vapour pressure, metabolic rate, and the difference between mean radiant temperature and air temperature play an important role for work in warm and hot environments. We show how our results can be used for the estimation of allowable exposure times for work in hot environments.