Sudden changes in blood pressure are frequently caused by daily events such as exercise, stressful work, and moving between different temperature environments. Sometimes, an abrupt change in blood pressure can endanger human lives. To mitigate such a risk, several studies have previously proposed contactless methods for monitoring changes in blood pressure; however, the number of studies on this issue is insufficient. In previous methods, changes in blood pressure were estimated using the propagation time of the pulse waves obtained from two different skin areas on the basis of an analysis of images from video recordings, which is called a video plethysmogram. However, the relative positional relationship of the two skin areas had to be maintained during the measurement, making the approach restrictive. To solve this problem, in the present study, we propose a new method using the video plethysmogram obtained from only one skin area. In particular, the degree of distortion in the video plethysmogram is calculated as a new index to estimate the blood pressure. On the basis of the results of our experiments with 20 healthy human subjects, we ascertain that the proposed index obtained from the palm area is correlated with the blood-pressure variability as well as the previous approach.
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