Non-invasive Continuous Blood Pressure Estimation Based On Pulse Transit Time

Hypertension or abnormally high blood pressure(BP)is a major risk factor that leads to serious diseases such as hypertensive heart disease,stroke,and coronary artery disease.Out-of-clinic BP measurement such as ambulatory BP monitoring(ABPM)or home BP monitoring(HBPM)is expected to improve hypertension detection in the mass population and could even help to control hypertension by providing timely and continual feedback to hypertension patients.However,the traditional cuff-based BP measurement is not suitable for ABPM or HBPM due to the population-averaged nature of the BP estimation algorithm,the limited frequency of measurement and the clumsiness of cuff wearing.Photoelectric plethysmography(PPG),as a low-cost and easy-to-operate noninvasive optoelectronic technology,gets rid of the defect of blood pressure measurement when measuring blood pressure with cuff.Pulse transit time(PTT)is defined as the difference between the peak time of photoplethysmography signal and the R peak time of ECG signal in the same cardiac cycle.At present,the cuffless continuous blood pressure estimation technology based on PTT does not need cuff,and can measure blood pressure anytime and anywhere without interfering with people's normal life.This method can not only provide the blood pressure value in the resting state,but provide the dynamic analysis of blood pressure,and can realize the development of ABPM and HBPM technology.However,the cuffless continuous BP estimation technique based on PTT has the problems of confusion of BP estimation models and inconsistency of calibration techniques for different models.Therefore,it is difficult to accurately quantify which BP estimation model has better estimation performance when estimating BP.Based on this,according to the different sources of BP modeling,the cuffless BP estimation model is divided into vascular elasticity(Vascular elasticity,VE)and elastic conduit(Elastic tubes,ET)estimation methods,and a unified calibration scale is established to standardize the blood pressure estimation performance of VE and ET estimation methods.For a long time,the calibration of cuff-less BP estimation model has been a huge challenge.Traditionally,the calibration method of ET model and VE model are the Least-square(LS)and the Point-to-point pairing(PTP)methods,respectively.The LS mothod requires all samples to participate in obtaining the unknown parameters of specific model.Although it can obtain a good BP estimation,it also leads to the absence of a huge number of samples used to determine the unknown parameters of the model in the early of BP long-term monitoring estimation.In contrast,the traditional one-point paired o PTP method only needs a set of cuff BP(SBP and DBP)and PTT one-to-one correspondence to determine the unknown parameters of specific model;although this mechanism makes the o PTP method simple and convenient,its uniqueness to the initial sample selection will also lead to the dilemma of initial value sensitivity.In order to improve the estimation performance of the BP model,this paper proposes three personalized calibration techniques to further standardize and fill the gap in the calibration technology of cuffless BP monitoring in terms of initial calibration and periodic calibration.The main research works are as follows:(1)study the BP estimation performance of VE and ET estimation methods.Considering the difference between the two initial calibration modes,a new unified calibration scale called a PTP calibration method,is proposed in this paper.The performance of VE estimation method and ET estimation method in BP estimation was evaluated by the correlation and consistency test between estimated BP and cuff reference BP.For a PTP calibration technology,without changing the calibration method in VE,it solves the dilemma of using all samples to obtain model parameters.Moreover,compared with the one-point paired o PTP calibration method used in the VE model,a PTP considers that there are still slight fluctuations in BP and PAT/PTT/PWV at rest,which is more in line with the actual situation.Compared with the LS calibrator used in the ET model,study shows that a PTP only requires fewer samples to complete the calibration of the undetermined parameters in the ET model,and the results still meet the AAMI standard.Therefore,the proposed a PTP method unifies the calibration methods used by the ET model and the VE model derived from different methodologies,and makes it possible to evaluate the blood pressure estimation performance of their respective models under the same calibration scale.(2)study the Point-to-point pairing calibration method based on the least square method.Here,the author fully combines the advantages and disadvantages of the LS and PTP methods,creatively introduces L-S method into PTP method,and proposes a LSbased PTP calibration method,abbreviated as L-PTP.For L-PTP technology,it can fully absorb the strong BP estimation performance of LS method and the simple and excellent properties o PTP method.Not only that,LPTP technology also reduces the initial value sensitivity of PTP and overcomes shortcomings L-S method that requires a large number of samples to obtain unknown parameters of the model.Studies have shown that this method can improve the estimation performance of different BP models.As same as o PTP method,LPTP method only requires a period of resting BP,PTT/PAT/PWV to complete the calibration in specific BP model.Due to this simple calibration step,LPTP calibration technology can be applied and extended to practice.(3)study the Point-to-point pairing calibration method with penalty factor.In the initial calibration phase,the participants need to remain at rest for 5-10 minutes.As we all know,BP is not a constant in this process,and it also fluctuates slightly.In view of this,based on PTP calibration method,this paper makes two calibration corrections and constructs a penalty factor which can adjust BP estimation in real time.Once the resting state is over,the penalty factor is determined and remains unchanged in the long-term BP estimation.For m PTP method,based on o PTP method,it is a mean estimation for BP and PTT/PAT/PWV at rest.For f PTP method,based on m PTP method,it creatively introduces a penalty factor which can adaptively adjust and correct the estimated BP error in real time according to a certain penalty mechanism.Here,when BP is estimated every time,the penalty factor is like a visible eye that can punish the larger estimated BP error in real time,so that it can better estimate BP,which is more in line with AAMI's Standard,better in the application and promotion of cuff-less BP monitoring technology.This research mainly conducts study on the cuff-less continuous BP estimation model and its personalized calibration technology.The former can be used for cardiovascular function health evaluation,early diagnosis and early warning of cardiovascular diseases;the latter can improve the estimation performance of the blood pressure model.Combining BP models and its calibration technology together has important significance in the prevention,diagnosis and prognosis of cardiovascular diseases.