Research On Blood Pressure Measurement Method Based On Pulse Transit Time

Various cardiovascular diseases, especially hypertension, had become ‘thefirst killer’ which has threated humans healthy. To measure blood pressureeffectively is very important for the prevention and treatment of hypertension.Human blood pressure is a dynamically variable value; one-time measurementcannot reflect the level of the patient’s blood pressure and cardiovascularsituation. Beat-to-beat blood pressure measurement can only suitable for thereal-time monitoring of the changing of blood pressure, and also helpful to thejudgment of the therapeutic effect of antihypertensive drugs. Currently, commonblood pressure measuring apparatus are using batch-type method, which cannotmeet the need of the continuous detection of the blood pressure.This thesis has researched a method to estimate arterial pressure based onthe pulse transit time, which could achieved long-term continuous measurementof blood pressure. After had collected ECG(Electrocardiogram) signal andPPG(Photoplethysmography) signal, and furthermore had extracted the featurepoint of ECG and PPG signals, choosing the time difference between the R-wavepeak and the feature point of PPG signal. Before estimated blood pressure basedon the linear model between arterial blood pressure and pulse transit time, It haddesigned experiments to calibrated parameters. Two different methods had beendesigned. The first one was changed blood pressure through external forces, tocalibrate the algorithm parameter by measurement the blood pressure and pulsetransit time before and after exercise. Another one was based on the principle ofthe hydrostatic pressure difference, to calibrate the parameters by changes inposition. This paper had use three methods to measure the pulse transit time, theywere respectively choose the maximum point of first-differential, the highest andlowest points as the end of the pulse transit time. Considered the individualdifferences, the choice of pulse transit time would had an impact on bloodpressure estimation, a program for choosing the pulse transit time at second timehad been designed. It would select the most appropriate pulse transit time due tothe measurement results.The experimental results had showed that: The results of blood pressureestimation by the way to choose the max point of first-differential of PPG signalas the end of pulse transit time had the min error. The results of blood pressureestimation by the way to choose the maximum point of first-differential of PPGsignal as the end of pulse transit time had the maximum error. The way tochoosing pulse transit time at second time could avoid the wrong choice by most people’s experience effectively, ensured optimal measurement solution of pulsetransit time for each individual. Results of artery systolic pressure estimationthrough the calibration parameters came from the position changing experimentalhad a higher accuracy rate than results came from the exercise experiment.