Research On The PTT-based Blood Pressure Measurement In Hypertensive Patients

Hypertension is a common chronic disease,severe cases can lead to heart and kidney and other organ damage,is caused by cardiovascular and cerebrovascular diseases,one of the risk factors.Assessment of blood pressure and risk factors is the main basis for diagnosis and treatment of hypertension.Continuous ambulatory blood pressure monitoring and management,to help test the real-time understanding of blood pressure changes,early detection and timely control of the disease and reduce the risk of cardiovascular and cerebrovascular disease.At present,the noncuff-band continuous blood pressure measurement method in healthy people has been able to meet the international AAMI standards for health monitoring is of great significance.However,the PTT(Pulse Transit Time)-based blood pressure algorithm does not hold true for the hypothesis of the vascular model in hypertensive patients whose physiological characteristics and regulatory mechanisms have changed.Therefore,the study on the application of blood pressure algorithm to hypertensive patients presents an improved algorithm for hypertension.Continuous blood pressure monitoring in patients with hypertension is of great significance.In this paper,63 testers conducted a two-month follow-up test,divided into three hours a day for comparative testing.The experimental results show that PTTbased blood pressure estimation algorithm has a good effect on estimating healthy individuals,but it is not effective for patients with hypertension.After analyzing the problems in this model,we began to analyze the physiological characteristics of hypertensive patients and the mechanism of blood pressure regulation.Compared with healthy people,the heart rate variability(HRV)spectrum energy of high blood pressure patients moves to the low frequency part and has a high LF-HF energy ratio.Low-frequency part of the sympathetic nerve activity by the regulation,and vascular compliance are closely related.Therefore,it can be considered that the blood pressure regulation of hypertensive patients in its low frequency part of the abnormal.On the other hand,the analysis of blood pressure variability showed that the pulse pressure was mainly regulated by the high-frequency part,the diastolic pressure was mainly regulated by the low-frequency part,and the systolic blood pressure was the sum of the two.After the spectral analysis of PTT,we found that PTT spectrum energy is mainly concentrated in the high frequency part,and the pulse pressure difference spectrum range.Therefore,we can infer that PTT can track changes in high-frequency part of blood pressure,and for the low-frequency part of the tracking effect is poor.Hypertensive patients often accompanied by changes in vascular compliance is subject to low frequency sympathetic abnormalities of the regulation.Therefore,a single PTT parameter of the blood pressure estimation algorithm for hypertensive patients,the lack of low-frequency part of the blood pressure tracking,resulting in poor estimates.In response to the above analysis,we propose a new parametric photoplethysmography intensity ratio(PIR)to characterize the changes in the diameter of the heart during systolic and diastolic events.Through spectral analysis,we found that the spectral changes concentrated in the low-frequency part,and the diastolic pressure of the same spectral range.Therefore,we propose a new blood pressure estimation algorithm based on PTT and PIR for hypertensive patients,which can track the change of blood pressure at low frequency and high frequency simultaneously.Experimental results show that the PTT-PIR-based blood pressure estimation algorithm has significantly improved the estimation of blood pressure in hypertensive patients.