Mining Project: Predicting the Impact of Heat Strain on Cognitive Functions in Miners
To establish whether easily measured physiologic (i.e. heart rate, internal body temperature) and environmental parameters (i.e. air temperature, relative humidity, and wet bulb globe temperature) can effectively predict heat strain-related cognitive impairment among miners.
Heat stress refers to the total heat load placed on the body, from external environmental sources and from physical exertion, whereas heat strain refers to the physical strain the body experiences as a result of heat stress. Heat strain can lead to serious injury. A possible mechanism by which this occurs is through heat-related cognitive dysfunction. However, a literature search revealed no studies on heat-related cognitive function in U.S. miners. Studies are needed to evaluate the effects of heat exposure on miners’ cognitive performance, assess which mining job tasks are at highest risk of impact from heat exposure, determine the most appropriate cognitive tests for the mining environment, and investigate the effectiveness of the designed solutions.
Despite the use of various heat indices at mines throughout the world, a standard heat index has not been identified in the mining industry. Furthermore, most indices have been evaluated primarily as predictors of elevated body temperatures that can lead to heat illness. Each index has limitations, and studies have demonstrated poor correlation between indices and physiologic evidence of heat strain. Furthermore, indices do not account for individual variability in heat tolerance that is partly a result of personal risk factors such as previous heat illness, age, lack of acclimatization, pregnancy, obesity, alcohol use, certain medications, and other health conditions. Heat exposure may precipitate other adverse consequences and has been associated with cognitive impairment and increased injury risk. Thus, it is reasonable to hypothesize that heat exposure might contribute to injuries in the mining industry. Cognitive impairment has been measured using different methods and instruments in several studies, but methodologies have not been developed for practical application in the mining industry. Determining predictors of cognitive impairment using more easily measured indicators could have widespread benefit in mining.
To address these issues, this project has three research aims:
- Determine if an increase in heat stress from environmental parameters such as temperature and humidity and the subsequent increase in heat strain (heart rate and body temperature) correlates with decreased cognitive performance.
- Assess the extent to which identification and assessment of personal risk factors can improve the prediction of cognitive impairment.
- Develop recommendations to improve the detection, mitigate the risk, and identify workers with increased susceptibility to heat-related cognitive impairment among miners.
To accomplish these aims, Mining Program researchers will investigate the relationship between miners’ cognitive performance and physiologic and environmental measurements of heat strain using both laboratory and field research. Questionnaires and interviews will be used to collect data on personal risk factors, metabolic work load, clothing, and hydration status. Heart rate and temperature monitors will measure physiologic factors. Data on body mass index, hydration level, fatigue, and overall fitness will be collected. Various cognitive tests will be employed to evaluate aspects of cognitive function, including sustained attention, task switching, visual scanning, and executive function.
Laboratory research will consist of evaluating cognitive changes among subjects performing exercise (e.g. walking on a treadmill) or simulated mining work (e.g. hanging ventilation bags) in a chamber in which temperature and relative humidity conditions can be precisely controlled. Mixed effects modelling methods will be used to evaluate any association between cognitive test results, physiologic and environmental measurements, and personal risk factors for both field and laboratory data. The predictive power of specific combinations of physiologic and environmental measurements and risk factors on miner cognitive performance will be assessed.
Field research will entail measuring participants’ continuous heart rates and body temperatures as they perform their job tasks in hot environments. Environmental conditions (dry bulb temperature, humidity, and wet bulb globe temperature) in participants’ work areas will also be measured. Cognitive testing will be administered two times per shift to evaluate changes from baseline.
This project research is expected to have the following potential impacts:
- provide information on which cognitive tests are most useful and feasible for mining environments;
- provide a better understanding of the most important personal factors to consider in predicting which miners are at highest risk of adverse outcomes;
- provide information that can be useful in influencing health and safety policies and education programs on heat stress; and
- develop a tool for use at individual worksites to provide miner-specific information relating to the risk of cognitive deficits and recommendations for controls of the work environment as well as rest and hydration to prevent escalation of risk.
Ultimately, findings from this research will increase knowledge of heat strain in U.S. mining and provide information on the extent to which heat strain affects cognitive performance. The study will contribute scientific evidence that the mining industry and other industries whose workers experience heat exposure can use to develop guidelines and policies to mitigate the risk of heat strain and its complications.