Hemodynamic responses during simulated automobile driving in a monotonous situation

Integrated Thermofluid Lumped Parameter Model for Analyzing Hemodynamics in Human Fatigue State

It is well known that driving while fatigued is dangerous and can lead to serious traffic accidents. However, there is a lack of studies on the mechanism of fatigue. This paper sought to infer changes in the cardiovascular system through hand and head skin temperature peripheral factors via an integrated lumped parameter model. A multi-layer inner structure with variable blood perfusion was used to construct a full-body thermal model. The cardiovascular system model provided blood perfusion using lumped parameters. The peripheral resistance and heart rate in the cardiovascular system model were adjusted to match the experimental temperatures of the head and hands obtained from induced fatigue experiments. The simulation results showed that the heart rate and blood pressure decreased, and the peripheral skin resistance of the hands and head increased after fatigue. A decrease in heart rate and an increase in peripheral resistance affect the magnitude of blood flow to the periphery of the body, leading to a decrease in skin temperature during fatigue. The present integrated model elucidates a key effect of human fatigue on the cardiovascular system, which is expected to help improve the accuracy of fatigue monitoring systems.

Cardiovascular hemodynamic effects of Red Bull® Energy Drink during prolonged, simulated, monotonous driving

Purpose

The purpose of this study was to investigate the cardiovascular hemodynamic effects of Red Bull® Energy Drink during prolonged, simulated, monotonous driving.

Methods

This was a double-blind, within-subjects-design, crossover study. Twelve healthy volunteers (21.7 ± 0.8 years old) experienced each of three conditions at various times: 1) consumption of Red Bull® Energy Drink; 2) consumption of placebo-controlled drink; and 3) no test drink. All subjects undertook 90-min periods of simulated monotonous driving, during which physiological measurements were made. The variables recorded were cardiovascular indices, i.e., mean blood pressure (MBP), cardiac output (CO), electrocardiogram RR interval (RR), total peripheral-vascular resistance (TPR: = MBP/CO), and normalized pulse volume (NPV). Additional parameters were the standard deviation of lateral position, i.e., the weaving of the car, and subjective rating of sleepiness.

Results

CO, RR, and TPR during the monotonous task were significantly different in those consuming the energy drink as compared with those receiving the placebo and as compared with no drink values. The energy drink elicited a cardiac-dominant reaction pattern, while the other conditions demonstrated the vascular-dominant reaction pattern typically observed in monotonous driving tasks. The observed differences indicate the cardiovascular system being more aroused with the energy drink.

Conclusion

The effects of Red Bull® Energy Drink were reflected in cardiovascular hemodynamic phenomena especially to the heart function, and we conclude that consumption of this drink before long-distance driving in non-sleepy drivers could facilitate more physiologically active, and possibly safer, driving.

Simulated car driving in fMRI--Cerebral activation patterns driving an unfamiliar and a familiar route

Understanding the neuronal underpinnings of cognitive processes during car driving is essential to understanding the origin of automobile accidents. Using fMRI we aimed to reveal differences in activation distribution contrasting passively observing an unfamiliar versus a familiar route to analyse the importance of the degree of familiarity of a route on attention process. We developed a special driving simulation software known as "Mechanics & Traffic", which focuses on the physical properties of driving. Sixteen male police-academy students with special driving training were examined while passively watching the car on an unfamiliar route, following a training-period outside the scanner, and passively watching the car on the now familiar route. The driving task revealed activations in frontal, parietal, temporal, occipital lobes, the thalamus, and cerebellum. Direct comparison revealed significant activation for the unfamiliar route in the middle temporal and occipital cortex and in the cerebellum. Correlating activations with the influencing covariates of driving experience, the activation pattern was confirmed and an additional activation for the unfamiliar route was found in the inferior frontal and parahippocampal gyrus. The results give further evidence that driving a car is a complex cognitive skill. A training-period and a familiar, monotonous route seem to lead to a reduction in attention and perception processes which might be associated with a danger for commuters, even in specially trained drivers.

Relationship between salivary Chromogranin-A and stress induced by simulated monotonous driving

The purpose of the present study was to evaluate the use of salivary Chromogranin-A (CgA), which is already used in general as a mental stress marker, for studying the stressful situation created by simulated monotonous driving. After informed consent, 25 healthy male and female subjects were studied under constant environment-controlled conditions. We measured the following physiological variables: blood pressure (BP), cardiac output, total peripheral resistance (TPR), normalized pulse volume (NPV) as an index of alpha-adrenergic sympathetic activity to the finger arteriolar vessels, levels of cortisol and CgA during monotonous driving. The induced stress led to the expected decreases in NPV and increases in TPR and BP caused by peripherally related sympathetic acceleration. However, CgA levels were found to fall gradually in accordance with the gradual increase of subjective rating of stress (SRS) and significantly (p < 0.01) decreased over the period of the simulated monotonous driving. Our hypothesis for the gradual decrease of CgA levels during the simulated monotonous driving is as follows. CgA, catestatin and catecholamines are co-released into the extra-cellular environment. Peripheral sympathetic activity was accelerated by stress resulting from the simulated monotonous driving. Upon peripheral vessel constriction, an increase in TPR then increased BP which, in turn, activated catestatin. Consequently, secretion of CgA was blocked by the co-secreted catestatin from chromaffin granules. The results obtained strongly indicate that, although CgA has been reported as a possible marker of stress, CgA levels are not increased in the stressful situation of simulated monotonous driving.

A preliminary study on driver's stress index using a new method based on differential skin temperature measurement

Prolonged periods of driving in monotonous situations may lower a driver's activation state as well as increasing their stress level due to the compulsion to maintain safe driving, which may result in an increased risk of a traffic accident. There is therefore an opportunity for technological assessment of driver physiological status to be applied in-car, hopefully reducing the incidence of potentially dangerous situations. As part of our long-term aim to develop such a system, we describe here the investigation of differential skin temperature measurement as a possible marker of a driver's stress level. 10 healthy male subjects were studied, under environment-controlled conditions, whilst being subjected to simulated monotonous travel at constant speed on a test-course. We acquired measurements of relevant physiological variables, including truncal and peripheral skin temperatures (T(s)), beat-by-beat blood pressure (BP), cardiac output (CO), total peripheral resistance (TPR), and normalized pulse volume (NPV) used as an indicator of local peripheral vascular tone. We then investigated the driver's reactivity in terms of cardiovascular haemodynamics and skin temperatures. We found that the simulated monotonous driving produced a gradual drop in peripheral T(s) following the driving stress, which, through interpretation of the TPR and NPV recordings, could be explained by peripheral sympathetic activation. On the other hand, the truncal T(s) was not influenced by the stress. These findings lead us to suggest that truncal-peripheral differential T(s) might be used as a possible index indicative of the driver's stress.

Feasibility study on driver's stress detection from differential skin temperature measurement

Prolonged monotonous driving may lower a driver's awareness level as well as increasing their stress level due to the compulsion to maintain safe driving, which may result in an increased risk of a traffic accident. There is therefore an opportunity for technological assessment of driver physiological status to be applied in-car, hopefully reducing the incidence of potentially dangerous situations. As part of our long-term aim to develop such a system, we describe here the investigation of differential skin temperature measurement as a possible marker of a driver's stress level. In this study, healthy male (n=18) & female (n=7) subjects were investigated under environment-controlled conditions, whilst being subjected to simulated monotonous travel at constant speed on a test-course. We acquired physiological variables, including facial skin temperature which consists of truncal and peripheral skin temperatures (Ts) using thermography, beat-by-beat blood pressure (BP), cardiac output (CO), total peripheral resistance (TPR), and normalized pulse volume (NPV) used as an indicator of local peripheral vascular tone. We then investigated the driver's reactivity in terms of skin temperatures with this background of cardiovascular haemodynamics. We found that the simulated monotonous driving produced a gradual drop in peripheral Ts following the driving stress, which, through interpretation of the TPR and NPV recordings, could be explained by peripheral sympathetic activation. On the other hand, the truncal Ts was not influenced by the stress. These findings lead us to suggest that truncal-peripheral differential Ts could be used as a possible index indicative of the driver's stress.