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We evaluated the quantitative relationship between the subjective stress value and heart rate variability. The mean values of R-R interval (RRI) and respiratory sinus arrhythmia (RSA), which were reported to be markedly affected by stress, were used as heart rate variability. The following mental workload was performed so as to give wide range loads to the subjects: presentation of research, asking questions in research presentation, research presentation practice, and supine rest. The subjective stress value was obtained as serial values from 1 to 5 by a newly-developed questionnaire. The correlation between the stress value and RRI or RSA when such wide range workload are given was evaluated. There was a high correlation between the subjective stress value and RRI (correlation coefficient, -0.637), but not between the subjective stress value and RSA (coefficient, -0.319) Signal processing of RRI was simpler than that of RSA. These results suggest the usefulness of RRI as an index of the subjective stress value.

An Evaluation of the Quantitative Relationship between the Subjective Stress Value and Heart Rate Variability