Effects of different extreme cold exposure on heart rate variability.

Frequent extreme cold events in recent years have brought serious threats to outdoor workers and rescuers. Changes in ambient temperature are associated with altered cardiac autonomic function. The study aims to investigate heart rate variability (HRV) and its relationship to other physiological parameters under extreme cold exposures. Twelve males underwent a 30-min preconditioning phase in a neutral environment followed by a 30-min cold exposure (-5, -10, -15, and -20 °C). Time-domain indexes(meanRR, SDNN, RMSSD, and pNN50), frequency domain indexes [Log(HF), Log(LF), and low frequency/high frequency (LF/HF)], parasympathetic nervous system (PNS), and sympathetic nervous system (SNS) were analysed. Results showed all HRV indexes of four cold exposures were significant. The decrease in temperature was accompanied by progressive PNS activation with SNS retraction. SDNN was the most sensitive HRV index and had good linear relationships with blood pressure, pulse, and hand temperature. The results are significant for formulating safety protection strategies for workers in extremely cold environments.Practitioner Summary: This study investigated heart rate variability (HRV) in 12 males during a 30-min cold exposure (-5, -10, -15, and -20 °C). Results showed all HRV indexes of four cold exposures were significant. The decrease in temperature was accompanied by progressive PNS activation with SNS retraction. SDNN was the most sensitive HRV index and had good linear relationships with blood pressure, pulse, and hand temperature.

Prediction of human thermal comfort preference based on supervised learning.

Human thermal comfort is relevant to human life comfort and plays a pivotal role in occupational health and thermal safety. To ensure that intelligent temperature-controlled equipment can deliver a sense of cosiness to people while improving its energy efficiency, we designed a smart decision-making system that sets the thermal comfort adjustment preference as a label, reflecting both the human body's thermal feeling and its acceptance of the thermal environment. By training a series of supervised learning models underpinned by environmental and human features, the most appropriate adjustment mode in the current environment was predicted. To bring this design into reality, we tried six supervised learning models, and then, by comparison and evaluation, we identified that the Deep Forest's performance was the best. The model takes into account objective environmental factors and human body parameters. In this way, it can achieve high accuracy in application and good simulation and prediction results. The results can provide feasible references for feature selection and model selection in further research with the aim of testing thermal comfort adjustment preference. The model can provide recommendations for the thermal comfort preference in a specific place at a particular time, as well as guidance on human thermal comfort preference and thermal safety precautions in specific occupational groups.

Heat Strain Evaluation of Power Grid Outdoor Workers Based on a Human Bioheat Model.

Power grid outdoor workers are usually exposed to hot environments and could suffer the threats to occupational health and safety like heat strain and injury. In order to predict and assess the thermophysiological responses of grid workers in the heat, the clothing thermal insulation of grid worker ensembles was measured by a thermal manikin and a multi-segment human bioheat model was employed to evaluate the thermophysiological response parameters of grid workers such as core temperature, skin temperature and sweat loss. The results show that working in a hot environment can cause a obvious increase in core temperature and skin temperature of grid workers, and the acceptable maximum working time of grid workers varies greatly in different hot environments. A reasonable work organization strategy can effectively decrease the core temperature and sweat loss, increasing the duration of acceptable maximum working time for grid workers. This study is helpful to assess heat-related risks of grid workers and support power grid companies to rationalize work organization strategies and personal protection guidelines.

Human physiological responses of exposure to extremely cold environments.

Extremely cold events have occurred more frequently in the past few years. People exposed to extremely cold exposure could suffer the threats of human health and safety like cold stress and injury. This study aims to investigate human physiological responses of exposure to extremely cold environments and the moment of temperature step. The experiments of 12 subjects exposed to three different cold exposure conditions (-5 °C, -10 °C, -15 °C) were carried out in a climate chamber. Most critical physiological parameters, including the core temperature, local skin temperature, blood pressure, heart rate, respiration rate and blood oxygen saturation, were measured to evaluate human physiological responses. In the particular short term study, the results show that the local skin temperature and blood pressure are the most significant indexes for evaluating the risk of cold strain in extremely cold environment. The finger temperature is a critical index of hand and finger flexibility, and it will lead to serious injuries and reduced manual performance when exposed to below -5 °C for more than 20 min. The high physiological strain at the very beginning moment of cold exposure can significantly affect the ability to make correct judgment and action, and it is suggested that the personnel adapt for 3 min after entering into the extremely cold environment to stabilize physiological parameters and thus enhancing the safety and occupational performance. The experimental data of this study is also of great significance for the development and validation of thermophysiological models.

Effects of workload on human cognitive performance of exposure to extremely cold environment.

Many jobs like outdoor work and emergency rescue have to be exposed to extremely cold environments. The combined effects of the cold exposure and work intensity on human cognitive performance remain unclear. In this paper, the experiments of six Chinese young men exposed to an extremely cold environment (-10 °C) were conducted in a climatic chamber. The work intensity level was graded according to the metabolic rate corresponding to three walking speeds. Nine cognitive functions and one perceived were recorded to evaluate the subjects' cognitive performance, including NCTB (seven items), Stroop, and RPE were measured. The increase of workload from moderate to high could lead to the acceleration of fatigue speed and the aggravation of fatigue degree 5 min earlier. Moderate work intensity is a noteworthy work level in extremely cold environment, which is an inflection point in the impact of fatigue and cognitive levels. The manual dexterity significantly increases by the workload intensity, and the high work intensity makes the hands more dexterous (29% increase). Extremely cold environment has a significant effect on short-term memory (decreased 33%). The selective attention was reduced by 16% in the extremely cold environment. With the moderate work intensity in extremely cold environment, the perceived judgment response speed would decrease. The combined effects of the extremely cold environment and the workload on the cognitive functions of psychomotor ability and attention or sensorimotor speed should be paid more attention to.