| In the past two decades, clinics manometry appeared, marking the blood pressure measurement has entered a new era. Since then, the white-coat hypertension, hidden hypertension, blood pressure morning peak, nighttime blood pressure, high blood pressure alone or phenomenon is new subtypes that have been discovered, therefore, blood pressure measurement search gets more attention from. Currently, blood pressure measurement is developing automation, telemetry, real-time monitoring and information networking. It not only makes pressure measurement in clinical diagnosis and treatment more convenient, comprehensive and accurate, but also has a revolutionary impact on hypertension management and prevention community. The current common arterial blood pressure measurement is direct manometry catheter, noninvasive indirect pressure measurement method and so on.Direct measurement system is a measurement that sensors immersed in blood, because of the damage to skin and vascular, it is also called injury measurement. In general, direct measurement is not only more accurate, but also can record and observe the blood pressure continuously, understand pressure changes in moment and realize the measuring of true mean pressure. In critically ill patients rescue therapy, the patient’s condition can be described as the ever-changing, to keep abreast of the rapid changes in hemodynamic in patients in order to make timely treatment is one of the key point of the rescue of critically ill patients, so the patients need to be monitored continuously, to realize continuous real-time monitoring, it must get instantaneous and continuous dynamic changes in blood pressure by direct measurement methods at this stage, so that to adjust the drug and the dosage timely. So that the indirect measurement is applied more. Corresponding to the indirect measurement is the direct measurement, which also known as non-invasive measurement, has gone through 100 years of history, blood pressure measured with it is closed to aortic pressure, and it is the most commonly used method in clinical diagnosis, However, because there are some limitations, until now, it is only suitable for the discontinuous measurement either manually or automatically, and can’t track to the dynamic changes in blood pressure, and it is impossible to obtain a continuous blood pressure. Are there any blood pressure measurement methods to combine the advantages of both the direct and the indirect methods, in another word, is there any blood pressure measurement methods that can measure blood pressure continuously and non-invasively? It’s the significance meaning of the non-invasive and continuous blood pressure measurement. The existing technology is artery unloading technology, tonometry force method, and pulse wave velocity/pulse wave propagation time measurement method, etc. The former two methods have been sold as products, for example, CNAP is the delegate of artery unloading technology and the T-LINE series as the delegate of tonometry force method, but CNAP is bulky and expensive and T-LINE series is too difficult to be laid up in the right spot, as long as the patients slightly change, it has to be repositioned, and it is inconvenient to use. So we did the research on pulse wave propagation time measurement method, which aims to get rid of disadvantages of other methods and realize noninvasive continuous blood pressure measurement.Pulse wave velocity measurement method is based on a positive correlation between the characteristics of the arterial pulse wave propagation along the proposed rate and arterial blood pressure, blood pressure is calculated indirectly with the pulse wave velocity, and the pulse wave velocity is the passing time between two points of an artery. So that we can estimated arterial blood pressure values indirectly with the pulse wave transit time as the same theory. It is Empirically think that blood pressure and pulse wave velocity accord with a quasi-linear relationship:Under the same physiological conditions, systolic and diastolic blood pressure and pulse wave velocity was in a certain function, the relationship of the coefficients and constants vary from individual to individual, and need to be determined experimentally. But in everyday life state pulse rate measurement is somewhat difficult to accurately measured, so that it is replaced by the passing time between R wave of ECG and a feature point of fingertip pulse wave. Although it has a good correlation with the true pulse wave velocity, relationships are not the same in different individual relationships. To figure out the relationship, we need to do experiment with electronic sphygmomanometer measurements and instruments measurements.When determining the relationship between PWTT and blood pressure, we did a series of experiments, first, we set up the experimental platform:A multiparameter board FYO8O3 produced by Shenzhen Aidekang is used as our Monitoring module. This board can monitoring multi-parameter, including ECG, respiratory waveforms, pulse waveforms care, The sampling frequency of ECG waveform is 500Hz, The pulse waveform sampling frequency is 125Hz, these two parameters is just in double relationship. The relevant literature （the Swallow） pointed out that the larger the sampling frequency, the higher the accuracy of the results, therefore, we changed the PPG sampling frequency to 500Hzas large as the ECG frequency, so that the PWTT values obtained after the difference will be more accurate. In addition, the board also monitors parameters such as blood pressure and heart rate（HR）, which can provide reference values of blood pressure and predict diastolic blood pressure as the second parameter HR, and lead selection setting function can send the module through programming commands from the original default five leads converted to three leads. Because the experiment conducted in the winter, the chest leads may be inconvenient in the experiment. If we convert it to three leads, it only occupies the volunteers’ two hands and an ankle, which is a good solution to this problem, and reduces the complexity of the operation. In addition, the experimental hardware also integrates a Bluetooth module; this system uses Bluetooth technology to realize the transmission of physiological data and receiving control commands related to the experiment. The design uses HC05 type Bluetooth module as the system of data transmission module. Its Rate is up to 2.1Mbps, which meets the system transmission frequency requirements. We used Matlab2010 as our Software platform. Because of its powerful data processing capabilities, it’s a good choice to achieve PWTT calculation and subsequent data processing and evaluation. We control the home care module Through the GUI interface and Bluetooth and acquire real-time data such as ECG and pulse wave data and then display them on GUI in order to observe the waveform and calculate the PWTT. By the way, the original ECG and PPG signal must be unpacked first, and this provides the security for our experimental data.Two pulse wave propagation times were used in this paper. It’s also an important part of the calculation PWTT this experiment. The ability to accurately calculate the PWTT process is the key to whether the normal conduct follow-up experiments and computing PWTT focus also lies in how to find feature points accurately. The Feature points used in this article are mainly two, one is the ECG waveform characteristic points, namely ECG waveform R wave peaks, and the other is the pulse wave feature points, that is to say, that pulse wave or pulse wave peak fastest rising point.To form a complete set of experimental system that enables non-invasive blood pressure measurement and continuous measurement, we have a total of five series of experiments designed. Omron HEM-7051-type instrument is used as a control group of blood pressure measuring.We did the experiments in strict accordance with the principle of blood pressure measurement. Firstly, to validate whether there is universal relevance between blood pressure and pulse wave propagation time, that is to say, whether that is a relationship to meet the public demand, and the forecast results show that prediction error is large, since there are individual differences, a relationship is difficult to measure blood pressure accurately. Secondly, to optimize the experimental program, we considered individual differences, then acquired a fitting function which used PWTT and HR as independent variables and systolic and diastolic blood pressure as the dependent variables, and can predict blood pressure accurately, then we forecast the results and assessed the accuracy, the results show that the accuracy in this experiment is improved compared to the experimental one. Thirdly, To obtain two kinds of PWTT definitions Respectively, one is the interval time from the ECG R-wave peak to the pulse wave peak, the other is the interval time from the ECG R-wave peak to the fastest rise point of pulse wave. We will get the two fitting function of these PWTTs and predict Blood pressure, then the final evaluation and comparison of accuracy implies that the first PWTT can better predict blood pressure. Fourth, forecast and evaluate blood pressure in different period, then observe whether it can achieve continuous measurement of blood pressure, which determines a predictive each individual is able to predict a long and stable blood pressure, the results show that within a certain time frame, the blood pressure predicted is stable, but when it reached a certain time, the prediction error increases, and over time, the error continues to increase, according to the experimental results, we can find the time that the blood pressure changed a lot, and then we can do the correction. Fifth, we used one-point calibration method, i.e. after the start prediction, at least more three times cuff blood pressure, HR and PWTT is measured in about one hour. These data will be fitting with the two sets of recent data before to find a new function simultaneously. Then we predict the blood pressure with this fit and find the error was reduced.The article focuses on non-invasive continuous blood pressure measurement based on PWTT, and there are three main points in innovation:first, combined with the home care module, the method extracted pulse wave propagation time, and it can both take advantage of individual differences, and make pressure measurement more accurate, at the same time, it makes the instrument portable, and, continuous non-invasive blood pressure function makes the home monitor works better, second, we proposed a new fitting relationship between diastolic and pulse wave propagation time, adding "HR" as the second argument which totally considered the influencing factors of diastolic pressure, and it makes the prediction more accurate, third, there generally are two definitions of PWTT, one is the time period from the ECG R-wave peak to the peak of pulse wave, the other is the time period from the ECG R wave peak to the point that pulse wave rises fastest. Scholars always do research based on these two kinds of PWTTs respectively but nobody knows which definition is better, in this paper, a comparison was made between these PWTTs to find the better one. Fourth, In order to achieve real continuous blood pressure, this experiment also made a long time forecast and corrected the fitting function at a certain time when the prediction error is large, as a result, we get a good feedback.Finally, the experimental evaluation results show that the method of measuring blood pressure based on PWTT continuously and non-invasively proposed in this paper can well predict either systolic or diastolic blood pressure and make the continuity real, and the results are in line with the assessment AAMI standards. If the method can be really used in home care monitor, it will helps a lot. All in all, the paper provided a reference in new areas for domestic medical and mobile health development, and is with a high value and prospects. |
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