Feasibility study on assessment of driver's stress from differential skin temperature measurement under simulated monotonous driving

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 drivers stress level. In this study, after giving informed consent 25 healthy male (n = 18) & female (n = 7) subjects (26.8 ± 8.0 S.D. yrs) 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 facialskin temperature which consists of truncaland peripheralskin temperatures (T _s) using thermography, beat-by-beat blood pressure (BP), cardiac output (CO), tota lperipheral resistance (TPR), and normalized pulse volume (NPV) used as an indicator of localperi pheral 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 gradualdrop in peripheralTs 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 Ts could be used as a possible index indicative of the driver's stress. In fact, a significant correlation was confirmed between stress reference of BP and differential skin temperatures.