Summary
Objectives: The aim of this study is to present a method of assessing psychological tension that
is optimized to every individual on the basis of the heart rate variability (HRV)
data which, to eliminate the influence of the inter-individual variability, are measured
in a long time period during daily life.
Methods: HRV and body accelerations were recorded from nine normal subjects for two months
of normal daily life. Fourteen HRV indices were calculated with the HRV data at 512
seconds prior to the time of every mental tension level report. Data to be analyzed
were limited to those with body accelerations of 30 mG (0.294 m/s2) and lower. Further, the differences from the reference values in the same time zone
were calculated with both the mental tension score (Δtension) and HRV index values
(ΔHRVI). The multiple linear regression model that estimates Δtension from the scores
for principal components of ΔHRVI were then constructed for each individual. The data
were divided into training data set and test data set in accordance with the twofold
cross validation method. Multiple linear regression coefficients were determined using
the training data set, and with the optimized model its generalization capability
was checked using the test data set.
Results: The subjects’ mean Pearson correlation coefficient was 0.52 with the training data
set and 0.40 with the test data set. The subjects’ mean coefficient of determination
was 0.28 with the training data set and 0.11 with the test data set.
Conclusion: We proposed a method of assessing psychological tension that is optimized to every
individual based on HRV data measured over a long period of daily life.
Keywords
Long-term recording - tense - stress - heart rate variability - linear regression
model
