Psychological stress evokes rapid changes to the cardiovascular and neuroendocrine systems, responses that can become habituated following repeated exposure. This study, comprising of 2 phases, suggests that the immune system follows a similar trend. Phase 1: 15 healthy subjects (aged between 26 and 56 years) provided capillary blood samples before and after completing 3 basic tasks using, in turn, two automotive touch screen interfaces (Interface 1 -antecedent version, Interface 2 -improved version). Using a chemiluminescent technique termed Leukocyte Coping Capacity (LCC), the ability of leukocytes to produce reactive oxygen species in vitro was assessed. Significant differences in leukocyte activity were shown between treatment groups, where the greatest post-test decrease occurred after using Interface 1. Phase 2: a randomly selected sub-group (n=4) underwent weekly repeat testing using both interfaces. Significant differences in post-test leukocyte reactivity were exhibited between test weeks for each interface -the magnitude of response decreasing with successive exposure.

Assessing psychological stress and mental workload within work-based scenarios relies heavily upon qualitative, subjective, self-assessment techniques, many of which were originally intended for identifying specific pathological disorders and have reduced sensitivity when evaluating everyday stressors. Quantitative measures involve monitoring changes in the cardiopulmonary system and stress hormone concentration. Although these (e.g. heart rate and blood pressure) provide a basic, reactive indication of the presence of a psychological stressor, many are subject to influence by other bio-mechanisms, or are unable to provide rapid results due to complex laboratory analysis. This study demonstrates how immune responsiveness, known to be influenced by psychological stress, can be used to assess changes in mental workload. Healthy male and female subjects (aged between 26 and 55 years) provided capillary blood samples before and after completing the same, basic, driver-related tasks followed by a simple manoeuvre in two unfamiliar motor vehicles. Using a chemiluminescent technique termed Leukocyte Coping Capacity (LCC), the ability of leukocytes to produce reactive oxygen species in vitro was assessed. Significant post-stressor changes in leukocyte activity were demonstrated between treatment groups. These findings add weight to the proposition that leukocyte activation is a useful quantitative measure of psychological stress and mental loading in humans. This study demonstrates the diagnostic ability of LCC for use during ergonomic evaluation, however the potential industrial applications for this technique are numerous and diverse. KEY WORDSChemiluminescence; Ergonomics; Leukocytes; Mental Workload; Psychological Stress; Reactive Oxygen Species. 3 ABBREVIATIONSHmax-RLU adj , maximum control adjusted leukocyte activity; LCC, leukocyte coping capacity; RLU adj , control adjusted relative light units; T-max, time taken (minutes) to reach maximum control adjusted leukocyte activity; T=5, 10, and 15minutes, control adjusted leukocyte activity at 5, 10, and 15 minutes, respectively, into the 45 minute chemiluminescence sampling protocol. INTRODUCTIONEvaluation of psychological stress -a threat which would not require a physiological response which elicits physiological consequences (Segerstrom and Miller, 2004) relies heavily upon qualitative psychometric measures. Examples include: Present State Examination (Baker et al., 2003), the Brief Symptom Inventory (Brosig et al., 2007;Cuculi et al., 2006;Fellinger et al., 2007;Mansbach et al., 2005), and the BussDurkee Hostility Inventory (Bag et al., 2005). All were primarily designed to identify specific pathologic disorders, and validated using dysfunctional clinical populations with abnormal statistical distributions. Consequently these proved to have limited sensitivity when used to test below intended critical diagnostic thresholds (Lemyre and Tessier, 1988) -such as when investigating psychological and physiological transient laboratory stressors.As psychological...

The aim of this study was to assess the effect of watching a psychological stressful event on the activation of leukocytes in healthy human volunteers. Blood samples were obtained from 32 healthy male and female subjects aged between 20 and 26 years before, during and after either watching an 83-minute horror film that none of the subjects had previously seen (The Texas Chainsaw Massacre, 1974) or by sitting quietly in a room (control group). Total differential cell counts, leukocyte activation as measured by the nitroblue tetrazolium (NBT) test, heart rate and blood pressure (BP) measurements were taken at defined time points. There were significant increases in peripheral circulating leukocytes, the number of activated circulating leukocytes, haemoglobin (Hb) concentration and haematocrit (Hct) in response to the stressor. These were accompanied by significant increases in heart rate, systolic and diastolic BP (P<0.05 from baseline). This is the first reported study on the effects of observing a psychologically stressful, albeit fictitious event on circulating leukocyte numbers and the state of leukocyte activation as determined by the nitrotetrazolium test.

Although much work has been conducted to quantify the long-term physiological effects of psychological stress, measures of short-term, low-level stress have been more elusive. This study assessed the effect of exposure of volunteers to a mild, brief, psychologically stressful event, on the functional ability of leukocytes in whole blood to respond to phorbol 12-myristate 13-acetate (PMA) in vitro. Volunteers operated a car electric window and adjusted it to 4 pre-determined positions. Between each operation the mechanism's polarity was covertly altered (group B) or remained unaltered (group A). For each treatment group 10 different subjects provided capillary blood samples pre- and post-stressor. Using a chemiluminescent technique termed leukocyte coping capacity, the ability of leukocytes to produce reactive oxygen species (ROS) in vitro was assessed. ROS release differed significantly at 10 min post-stressor between treatment groups, suggesting exposure to acute psychological stress leads to a reduced ability to respond to bacterial challenge.

Technology can enhance or diminish a user's psycho-physiological stress level; the ability to quantify these responses can help evaluate and refine design. The capability of drivers to accomplish basic tasks utilizing differing sensory modalities while maintaining lane discipline within a computer-simulated environment was assessed. Fifteen healthy subjects provided capillary blood samples before and after using three human-machine interface designs-touch-screen, voice control, and multimodal. Using a chemiluminescent technique termed Leukocyte Coping Capacity, the ability of leukocytes to produce reactive oxygen species in vitro was assessed. Significant poststressor changes in leukocyte activity of varying magnitude were observed following the use of all interfaces; with the multimodal interface provoking the most pronounced response and voice control the least. Although still requiring further research, the results support the proposition for using immune responsiveness as a means for quantifying psychological stress during assessment of ergonomic design and psycho-physiological and social interaction. This research was sponsored by Jaguar Cars Limited, Engineering Centre, Whitley, Coventry, United Kingdom. This work formed part of a PhD program of research. The PhD studentship was sponsored by financial assistance, the supply of test vehicles, and other specialist equipment including driving simulation technology by Jaguar and Land Rover Research and Development, Jaguar Cars Limited. The sole request of the sponsor was for the research team to design a simulator-based study incorporating production test vehicles for the purpose of testing and investigating the ability of the Leukocyte Coping Capacity protocol and other physiological parameters to act as a means for objectively quantifying changes in stress level following interaction with human-machine interfaces of differing ergonomic design.