Evaluation of the heat strain by heart rate

Citation
Jp. Meyer et al., Evaluation of the heat strain by heart rate, TRAV HUMAIN, 64(1), 2001, pp. 29-44
Citations number
32
Language
FRANCESE
art.tipo
Article
Categorie Soggetti
Psycology,"Engineering Management /General
Journal title
TRAVAIL HUMAIN
ISSN journal
0041-1868 → ACNP
Volume
64
Issue
1
Year of publication
2001
Pages
29 - 44
Database
ISI
SICI code
0041-1868(200103)64:1<29:EOTHSB>2.0.ZU;2-I
Abstract
Thermal strain remains difficult to quantify in actual work conditions desp ite the standardization of several strain models. Indeed, occupational phys icians must record numerous parameters in order to use these models, which makes them difficult to apply. In addition, these models are appropriate on ly in cases of long lasting exposure. In exposures shorter than one hour, w hich are the most frequent at the workplace, the time limit values (TLV) co mputed by these models appear unsafe. The purpose of this study was to show that the recording of heart rate (HR) allows a simple determination of saf e TLV. In this study, rest HR increases due to thermal strain (EPCT) were r ecorded on 98 workers during 131 actual work periods representing 18 differ ent work situations. The EPCT is the difference in beats per minute (bmp) b etween the mean HR of the 3rd, 4th and 5th minutes of rest after the end of the exposure and sitting at rest HR before the exposure. In this filed study, oral temperature was considered as a good index of cor e temperature. variation in oral temperature (dtbu) from the beginning to t he end of the heat exposure is related to EPCT : dtbu = 0,032 EPCT. This re lationship is significant (p < .0001) and the standard error of the estimat ion (see) is 0,18<degrees>C. Because this study was conducted on a large sa mple of workers, the results allow to compute a safety limit of EPCT which protect 95% of the population against an increase of core temperature great er than 1 degreesC. Thus, maximal mean dtbu increase is given by : mean + 1 ,65 see equals 1 degreesC. The mean dtbu increase must then be lower than 0 ,7 degreesC (1 - (1,65.0,18)) which corresponds to a maximal EPCT increase (0,7/0,032) of 21 beats per minute (bpm). From our results, it is concluded that as long as the EPCT value remains equal or below 20 bpm the increase in oral temperature is lower than 1 degreesC for 95% of the exposed populat ion, rendering the thermal strain acceptable. This result has been obtained from recordings out of almost one hundred wor ks in various working and exposure conditions. The EPCT limit of 20 bpm can be used safely to define the physiological acceptability of the heat expos ure at a workplace and, if necessary, to determine TLV. Easy use of heart r ate recorders means than heart rate can be a reference parameter for the th ermal strain quantification as well as for the evaluation of physical workl oad. Indeed, in the conditions of the present field study, the physical wor k load reach frequently levels which induce high and even hazardous heart r ate.