Photoplethysmography-Based Continuous Systolic Blood Pressure Estimation Method for Low Processing Power Wearable Devices

Rolandas Gircys,Audrone Janaviciute,Gyte Damuleviciene,Agnius Liutkevicius,Vita Lesauskaite,Egidijus Kazanavicius

doi:10.3390/app9112236

Abstract

Regardless of age, it is always important to detect deviations in long-term blood pressure from normal levels. Continuous monitoring of blood pressure throughout the day is even more important for elderly people with cardiovascular diseases or a high risk of stroke. The traditional cuff-based method for blood pressure measurements is not suitable for continuous real-time applications and is very uncomfortable. To address this problem, continuous blood pressure measurement methods based on photoplethysmogram (PPG) have been developed. However, these methods use specialized high-performance hardware and sensors, which are not available for common users. This paper proposes the continuous systolic blood pressure (SBP) estimation method based on PPG pulse wave steepness for low processing power wearable devices and evaluates its suitability using the commercially available CMS50FW Pulse Oximeter. The SBP estimation is done based on the PPG pulse wave steepness (rising edge angle) because it is highly correlated with systolic blood pressure. The SBP estimation based on this single feature allows us to significantly reduce the amount of data processed and avoid errors, due to PPG pulse wave amplitude changes resulting from physiological or external factors. The experimental evaluation shows that the proposed SBP estimation method allows the use of off-the-shelf wearable PPG measurement devices with a low sampling rate (up to 60 Hz) and low resolution (up to 8-bit) for precise SBP measurements (mean difference MD = −0.043 and standard deviation SD = 6.79). In contrast, the known methods for continuous SBP estimation are based on equipment with a much higher sampling rate and better resolution characteristics.

Highlights

It is very important to be able to determine the moment when physiological parameters deviate from normal levels in order to prevent chronic diseases
The difference between measured and estimated systolic blood pressure (SBP) was calculated for each examination, including the mean difference (MD), the standard deviation (SD), and the relative error, in order to evaluate the performance of the proposed method (Table 1): Table 1
A Pearson’s correlation value shows that the estimated and measured SBP values correlated well (r = 0.86, p < 0.001). This statistically significant tight correlation shows that the proposed method is suitable for continuous systolic blood pressure estimation using PPG recording devices with a low sampling rate and low resolution

Summary

Introduction

It is very important to be able to determine the moment when physiological parameters deviate from normal levels in order to prevent chronic diseases. The dynamics of observed physiological parameters are more important over the long-run than accurate instant values, which are used in an emergency or cases of critical health disorders. It is important to detect the degree of a physiological parameter’s deviation from normal during a day, week, month or even a year, as well as the length of such a deviation. If deviation persists for a long time, this can suggest the risk of irreversible changes.

Results

Discussion

Conclusion