The use of non-invasive measures to predict thermal strain: How accurate are universal models?

Over the past few decades there has been an upsurge in the development of monitoring devices that estimate levels of thermal strain non-invasively. However, developing a non-invasive monitoring device that estimates body core temperature (Tc) with a certain level of accuracy that is satisfactory over multiple heat stress scenarios and a wide range of body core temperatures has been shown to be a difficult task [1]. The aim of this study was to investigate the potential of using a combination of simple non-invasive measures to estimate rectal temperature (Tre) (used as a reference for Tc) over multiple types of heat stress scenarios within a varied population

Prediction of core body temperature from multiple variables

This paper aims to improve the prediction of rectal temperature (Tre) from insulated skin temperature (Tis) and micro-climate temperature (Tmc) previously reported (Richmond et al., Insulated skin temperature as a measure of core body temperature for individuals wearing CBRN protective clothing. Physiol Meas 2013; 34:1531–43.) using additional physiological and/or environmental variables, under several clothing and climatic conditions. Twelve male (25.8±5.1 years; 73.6±11.5kg; 178±6cm) and nine female (24.2±5.1 years; 62.4±11.5kg; 169±3cm) volunteers completed six trials, each consisting of two 40-min periods of treadmill walking separated by a 20-min rest, wearing permeable or impermeable clothing, under neutral (25°C, 50%), moderate (35°C, 35%), and hot (40°C, 25%) conditions, with and without solar radiation (600W m−2). Participants were measured for heart rate (HR) (Polar, Finland), skin temperature (Ts) at 11 sites, Tis (Grant, Cambridge, UK), and breathing rate (f) (Hidalgo, Cambridge, UK). Tmc and relative humidity were measured within the clothing. Tre was monitored as the 'gold standard' measure of Tc for industrial or military applications using a 10cm flexible probe (Grant, Cambridge, UK). A stepwise multiple regression analysis was run to determine which of 30 variables (Tis, Ts at 11 sites, HR, f, Tmc, temperature, and humidity inside the clothing front and back, body mass, age, body fat, sex, clothing, Thermal comfort, sensation and perception, and sweat rate) were the strongest on which to base the model. Using a bootstrap methodology to develop the equation, the best model in terms of practicality and validity included Tis, Tmc, HR, and 'work' (0 = rest; 1 = exercise), predicting Tre with a standard error of the estimate of 0.27°C and adjusted r2 of 0.86. The sensitivity and specificity for predicting individuals who reached 39°C was 97 and 85%, respectively. Insulated skin temperature was the most important individual parameter for the prediction of Tre. This paper provides novel information about the viability of predicting Tc under a wide range of conditions, using predictors which can practically be measured in a field environment

Arch Environ Occup Health

There is a substantial burden of occupational health effects from heat exposure. We sought to assess the accuracy of estimated core body temperature (CBT|) derived from an algorithm that uses sequential heart rate and initializing CBT,| compared with gastrointestinal temperature measured using more invasive ingestible sensors (CBT|), among outdoor agricultural workers. We analyzed CBT| and CBT| data from Washington State, USA, pear and apple harvesters collected across one work shift in 2015 (13,413 observations, 35 participants) using Bland Altman methods. The mean (standard deviation, range) CBT| was 37.7 (0.4, 36.5-39.4)\ub0C. Overall CBT bias (limits of agreement) was -0.14 (\ub10.76)\ub0C. Biases ranged from -0.006 to -0.75\u2009\ub0C. The algorithm, which does not require the use of ingestible sensors, may be a practical tool in research among groups of workers for evaluating the effectiveness of interventions to prevent adverse occupational heat health effects.K01 OH010672/OH/NIOSH CDC HHSUnited States/U54 OH007544/OH/NIOSH CDC HHSUnited States/U54OH007544/ACL/ACL HHSUnited States

Prediction of Core Body Temperature Based on Skin Temperature, Heat Flux, and Heart Rate Under Different Exercise and Clothing Conditions in the Heat in Young Adult Males

Non-invasive, multi-parameter methods to estimate core body temperature offer several advantages for monitoring thermal strain, although further work is required to identify the most relevant predictor measures. This study aimed to compare the validity of an existing and two novel multi-parameter rectal temperature prediction models. Thirteen healthy male participants (age 30.9 ± 5.4 years) performed two experimental sessions. The experimental procedure comprised 15 min baseline seated rest (23.2 ± 0.3°C, 24.5 ± 1.6% relative humidity), followed by 15 min seated rest and cycling in a climatic chamber (35.4 ± 0.2°C, 56.5 ± 3.9% relative humidity; to +1.5°C or maximally 38.5°C rectal temperature, duration 20–60 min), with a final 30 min seated rest outside the chamber. In session 1, participants exercised at 75% of their heart rate maximum (HR max) and wore light athletic clothing (t-shirt and shorts), while in session 2, participants exercised at 50% HR max, wearing protective firefighter clothing (jacket and trousers). The first new prediction model, comprising the input of 18 non-invasive measures, i.e., insulated and non-insulated skin temperature, heat flux, and heart rate (“Max-Input Model”, standard error of the estimate [SEE] = 0.28°C, R2 = 0.70), did not exceed the predictive power of a previously reported model which included six measures and no insulated skin temperatures (SEE = 0.28°C, R2 = 0.71). Moreover, a second new prediction model that contained only the two most relevant parameters (heart rate and insulated skin temperature at the scapula) performed similarly (“Min-Input Model”, SEE = 0.29, R2 = 0.68). In conclusion, the “Min-Input Model” provided comparable validity and superior practicality (only two measurement parameters) for estimating rectal temperature versus two other models requiring six or more input measures

Assessment of Heat Stress for Outdoor Work Conditions in Saudi Arabia

Outdoor workers have an increased risk of heat stress in Saudi Arabia since it is one of the hottest places in the Middle East. Recently, the government decided to limit outdoor work hours during the months of June, July, and August every year, and banned working under the direct sunlight from 12:00 to 03:00 p.m., although outdoor workers in the petroleum, natural gas, or emergency maintenance work industries are exempt from this prohibition. Traditionally, the efforts by safety and health professionals to mitigate work-related heat injury has been directed toward the assessment of environmental heat stress (e.g., wet-bulb globe temperature), rather than toward the associated physiological strain responses (e.g., heart rate and core temperatures). However, because a worker’s physiological response to given heat stress is modified independently by individual factors of each worker (e.g., age, sex, chronic disease, others), it becomes challenging to protect workers on an individual basis from heat-related injury without assessing those physiological responses. The primary objective of this study was to examine whether limiting work hours will reduce the risk of heat stress among outdoor workers or not. That can be achieved by (1) examining if the ban on three-month midday outdoor work needs to be extended to cover the period from June 1st to September 30th (2) examining if the midday break between 12:00 pm and 03:00 pm need to be extended by a few more hours. A field study was carried out in Dammam City on Saudi Arabia’s eastern coast where the humidity reaches 95% and temperature can reach 47°C (116.6°F) during summer months. The core temperature of 20 subjects matched for age, gender, and experience subjects was monitored while they performed their normal duties in the outdoor environment of Dammam City. The core temperature of these outdoor workers was measured using a novel non-invasive measurement method. The obtained results showed that subjects were under the risk of heat stress over a large part of the workday and their body temperature exceeds the allowable core temperature (38.5°C; 101.3°F) which the ACGIH has proposed to protect workers from experiencing heat stress. The intensity of exposure was high from (10:00-12:00 a.m.) that is not included in the midday break. A control group (non-policy) which did not experience the mid-day break showed essentially the same core body temperature as the experimental (policy) group. Among chief findings was that complying with a midday break work ban (12:00–3:00 p.m.) was not effective in reducing heat stress risk under the conditions and limitations of the design. The policymakers should be informed that this particular policy is not helpful and does not significantly lower core body temperatures. Some policy modifications are suggested which might better impact core body temperatures under these extreme conditions