Cardiovascular Metrics of Autonomic Nervous System Response to Mental Effort
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Helsinki University of Technology |
Diplomityö
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Date
2008
Department
Major/Subject
Lääketieteellinen tekniikka
Mcode
Tfy-99
Degree programme
Language
en
Pages
100 (+1)
Series
Abstract
The amount of mental workload in occupational tasks has increased, calling for the measurement of mental workload to guarantee safe and efficient working conditions. The measurement of mental workload is especially important in safety-critical professions, where metrics of mental workload could be used as pre-alarm systems for operators. The aim of this thesis was to investigate the response of cardiovascular metrics to mental workload. The correlation between perceived subjective task difficulty, measured using the NASA Task Load Index (TLX), and objective task difficulty, measured by cardiovascular metrics, was investigated. The performance of the Surgical Stress Index (SSI) in the novel application as a metric of mental workload was studied. Electrocardiograms, continuous blood pressure, respiration and photoplethysmographic (PPG) waveform were recorded from subjects during the performance of a computerised multitask test inducing different levels of mental workload. Several time and frequency-domain cardiovascular metrics were calculated from the recorded signals. Differences between low and high mental workload was studied and the classification performance of the cardiovascular metrics was analysed using prediction probability and receiver operating characteristics (ROC) analysis. The agreement between subjective and objective workload measures was good. The time-domain metrics performed better than the frequency-domain metrics. The cardiovascular metrics of blood pressure, heart rate and vasoconstriction that best classified mental workload were, in order, average mean blood pressure, average interbeat interval length and standard deviation of photoplethysmographic amplitude. The SSI was found to be a promising index of mental workload. The findings indicate that the cardiovascular metrics can be used in measuring mental workload, although further research is needed to establish normal levels for different types and degrees of workload.Description
Supervisor
Meriläinen, PekkaThesis advisor
Hirvonen, KatiHuiku, Matti
Keywords
cardiovascular metrics, kardiovaskulära variabler, mental workload, mental belastning, classification, klassificering, SSI, SSI