Separate estimation of long- and short-term systolic blood pressure variability from photoplethysmograph

This paper proposed a method to monitor systolic blood pressure (BP) variability without using a cuff during the daytime. In this method, BP variability of long-term and short-term were separated and estimated respectively from features of phoplethysmograph (PPG) through the use of a frequency filter. Then, total variability was obtained from the combination of long-term and short-term. BP by using a cuff (ground truth) and PPG of nine healthy young subjects were measured during the daytime; then BP variability was estimated from PPG to verify the validity of our method. As a result, the correlation coefficients between measured BP variability and estimated BP variability was improved from r = 0.35 in previous method to r = 0.41 in proposed method. In particular, the estimation results in short-term BP variability showed good accuracy (r = 0.67). This method of estimating BP variability has the potential to be a simple and continuous BP monitoring system during the daytime.

I. Introduction

Blood pressure (BP) is an important index in health care, since it is influenced by cardiovascular diseases and stress. Measurement of BP is usually done using a cuff as shown in Fig. 1(a). However, measurement by cuff cannot discover state of rapid BP variation in daytime because measuring by cuff is difficult under continuous measurement regime amid movement. Therefore, many research of estimating BP without a cuff have recently been reported [1] [2] [3] [4] for the continuous and wearable BP measurement. Figure 1.

Instrument to measure BP and pulse wave by (a) sphygmomanometer, and by (b) PPG sensor