Systems to Assess Stress, Vigilance and Fatigue in Work Contexts
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Doctoral Researcher
NameDipl.-Ing. Hannes Ernst
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Research Topic
CPPS are expected to fundamentally change the work conditions for operators, and the effects of these changes on autonomous and physiological operator states remain to be investigated. Therefore, new biomedical measurement procedures and technologies shall be developed.
In psychology, mental stress, vigilance or fatigue can be assessed by physiological measures of the body responses to defined stimuli or tasks. The human body reacts to extrinsic stimuli, and body function is measured by different sensor and electrode technologies (e.g. ecg, respiration, blood pressure, pupillary reflexes). In this way, the human’s reactions to specific events are investigated, while there is less focus on a continuous monitoring.
Conversely, in clinical medicine (e.g. sleep medicine, cardiology, intensive care medicine) similar measurement methods assess the autonomous state of the vegetative nerve systems while the organism is not stimulated by external influences. Instead, deviations from the initial state may be interpreted as internal events, either pathophysiological (sudden cardiac death, crises) or physiological (sleep phases). However, biosignal analysis is typically restricted to stationary conditions where the human does not move, which facilitates measurement and minimizes artefacts.
Both approaches suffer from significant disadvantages when being applied to work environments: The physiological approach requires specified extrinsic stimuli or events (which often are absent or cannot be defined objectively), while the medical one only detects strong pathophysiological deviations. Therefore, a promising strategy pursued in this thesis is to combine both approaches: If internal events can be identified (such as patterns of eye/body movements or physical and cognitive procedures in the work flow), they might serve as markers for an assessment of more subtle autonomous reactions. This can allow for a continuous monitoring and interpretation of human states even in the absence of external events, by linking changes in autonomous reactions to specific internal changes.
Current work focuses on acute mental stress, as highly automated production systems primarily impose mental workload on operators. A comprehensive laboratory study was conducted to investigate how body functions (in particular cardiovascular and respiratory systems as well as influences of the autonomic nervous system) can be assessed without contact using camera-based photoplethysmography (also called imaging photoplethysmography). The measurement with cameras offers many advantages, for example, no contact to the body (sensors and electrodes) and no cable connections are required. The procedure avoids waste from consumables (e.g. electrodes) and offers hygienic advantages (reduced disinfection effort because there is no body contact). Cameras detect these changes, which allows the acquisition of photoplethysmographic signals. The frequency of the optical modulation by blood corresponds to the heart rate, the regularity provides information about heart rate variability and the amplitude about the regulation of peripheral blood vessels. Parameters on respiration, blood pressure and oxygen saturation can also be obtained from the data. Conversely, changes in vital signs characterizing these body functions can be used to characterize changes in the activity of the autonomic nervous system. Camera-based photoplethysmography is therefore suitable for unobtrusive vital sign monitoring and mental stress detection.
Methodological research on camera-based photoplethysmography primarily addresses robust signal extraction. Especially in the context of work, motion is to be expected, which impairs the optical assessment of skin perfusion with cameras. For example, optimization approaches to combine different color channels (typically red, green, and blue) and quality markers to assess the reliability of the measured vital signs have been developed. Detailed information can be found in the publications listed here: Profil Dipl.-Ing. Hannes Ernst