Short-term cardiovascular responses to changing task demands.

When measuring operator states the predictive power of cardiovascular and respiratory measures in relation to mental workload has been questioned. One of the main questions is to what extent do cardiovascular measures actually reflect mental workload. This question arises because good measures of mental workload should be sensitive to changes in mental effort alone and not to other influences or at least the changes associated with mental workload should be easy to isolate. In the case of cardiovascular measures, the physiological change brought on by the baroreflex is a compensatory control effect that can potentially overshadow changes in physiology due to mental effort and therefore reduce the usefulness of cardiovascular measures. However, this does not need to be the case. Despite the effects caused by the baroreflex differences in heart rate, heart rate variability and other cardiovascular measures associated with task related effort can still be found using short-term response patterns. The short-segment analysis approach described in this paper is based on a time-frequency method in which the spectral power of the cardiovascular measures in specified spectral bands is computed from small time segments, i.e. 30 s. To demonstrate the effectiveness of this technique two studies which made use of a simulation of an ambulance dispatcher's task are described, both with easy and difficult task conditions. A short-lasting increase in task demand was found to be reflected in short-lasting increases in heart rate and blood pressure in combination with corresponding decreases in heart rate variability and blood pressure variability. These effects were larger in easy task conditions than in hard conditions, likely due to a higher overall effort-level during the hard task conditions. However, the developed measures are still very sensitive to mental effort and if this brief segmentation approach is used cardiovascular measures show promise as good candidates for reflecting mental effort during the assessment of operator state.

Cardiovascular state changes during performance of a simulated ambulance dispatchers' task: potential use for adaptive support.

Adaptive support has the potential to keep the operator optimally motivated, involved, and able to perform a task. In order to use such support, the operator's state has to be determined from physiological parameters and task performance measures. In an environment where the task of an ambulance dispatcher was simulated, two studies have been carried out to evaluate the feasibility of using cardiovascular measures for adaptive support. During performance of this 2-3h lasting planning task, a pattern of results is found that can be characterized by an initial increase of blood pressure and heart rate and a decrease of heart rate variability (defense reaction pattern) followed by an ongoing increase of blood pressure counteracted by a decrease in heart rate. This pattern can be explained by an augmented short-term blood pressure control (baroreflex), which is reflected in an increase of baroreflex sensitivity. Additionally, in this latter phase heart rate variability (HRV) increases as a function of time, while blood pressure variability decreases. In the two studies performed, the baroreflex pattern was consistent for all the relevant variables. In both studies there were periods with high and low workload. Effects of task load are mainly reflected in the variability measures, while in the second study, additionally, blood pressure level was higher during periods with high task demands. The conclusion of the studies is that consistent cardiovascular response patterns can be recognized during this semi-realistic planning task, where variability measures are most sensitive to task demand changes, while blood pressure and baroreflex sensitivity are most informative with respect to cardiovascular state changes. These findings can be seen as a great potential benefit for future use in adaptive support applications.