PPG Device Design And Application In Arterial Stiffeness Assessment

Cardiovascular disease is one of the major causes of deaths today, due to the multiple complications, high incidence and mortality. Recent researches found that arterial structure and function changes are the initiating cause of the cardiovascular diseases, therefore, it is important to find the arterial vascular early change before the appearance of symptoms. Photoplethymography (PPG) is an optical non-invasive measurement techniques that can be used to record the blood volume changes. It is generally accepted that PPG provides rich information about cardiovascular system, especially the arterial properties .Focused on the arterial stiffening assessment, this paper designs a wireless finger PPG detection device and investigates the finger PPG waveform contour analysis method. The primary content as following:1) MSP430 based wireless finger PPG detection system design PPG technology was first introduced and used to detection blood flow change in 1936. However, it was used only in lab for a long time, because of the limitation of the LED and semiconductor. The rapid development of semiconductor technology made considerable improvements in the sensitivity and reliability of PPG, this made PPG and its applications get wide public concern. To promote the use of PPG in primary and community-based monitoring, This paper designs a small, reliable, simple-to-use device with the advanced semiconductor and communication technology.In this paper, a MSP430 based wireless PPG detection device is designed to acquire, process and transmit the finger PPG waveform. Benefiting from the rich peripheral resource of MCU and powerful process capability , the device do all analogy and digital PPG signal processes in MSP430. A RS232 serial port is designed to make sure that the device can communicate with most PC. CC2500 RF chips are used to transmit PPG data wirelessly. All unites designed independently to make the system small, flexible and scalability.2) assessment of arterial stiffness by PPG contour analysisDriven by the prevention of cardiovascular disease, PPG based arterial stiffness assessment is a hot topic in clinic research now. With the obvious physiological meaning , contour analysis of PPG has widespread application in the study of arterial property. In PPG waveform, Stiffness index (SI) and reflect index (RI) describe the velocity and reflection intensity of the pulse, they are two important parameters to reflect the arterial stiffening. However, they could not be used for elderly and cardiovascular disease patient, since the disappear of the reflected pulse. Second Derivative of PPG (SDPPG) is considered to be the accelerate signal of blood flow change. Amount of pathological and pharmacological experiments proved that the parameters of SDPPG (b/a,c/a,d/a) are significantly associated with arterial stiffening, but the reasons of change still not understood now.Focused on the dynamic process of blood volume increase, the paper study the PPG and SDPPG contour properties in the left ventricular systolic period, and the relationship between PPG rising contour and arterial stiffening. Experiment find a strong correlation between CT and age, SI and b/a, so it is maybe a useful and valuable arterial stiffening index that can be used for all groups of people. The paper explains the possible reasons of CT changes by comparison with ECG. Compared with ECG, the paper investigate the special points in SDPPG waveform, and paper propose that the parameter-Tab- may be the sign of rapid ejection period.Above all, this paper provide a wireless, portable finger PPG measurement system design, and CT, Tab may be two valuable parameters in artery stiffening assessment, however, this conclusion need more prove.