Study On Subclinical Arterial Elastic Function Based On Photoplethysmography

Cardiovascular and cerebrovascular diseases (CCD) are major threats to human health nowadays. Once severe CCD events happen, such as myocardial infarction, cerebral infarction, intermittent lameness and vascular dementia, people can not recover completely. However, early detection and treatment can prevent those severe CCD events. Artery is the main target organ of CCD. As an asymptomatic and unconscious subclinical process in the early stage,structural and functional changes of arterial wall which is mostly suffered atherosclerosis or arteriosclerosis, are the common pathological bases of CCD. Changes of arterial elastic function emerge earlier than obvious structural changes of vessel cavity in the early stage. Thus, subclinical arterial function has great preventive value to be investigated.Based on photoplethysmography (PPG) technology, detection of subclinical artery elastic function and risk evaluation of subclinical artery disease are investigated. This paper mainly includes the following distinctive works accomplished:1) Artery elastic function detection and risk evaluation platform has been designed and made, which includes dual channel photoplethysmography module and artery-suppress module that also can measure blood pressure. Signals are filtered using wavelet transform and 3σthreshold method. Baseline drift of PPG signal is cut off using compensation method. Determinations of mean artery pressure, systolic and diastolic pressure are analyzed using oscillation method and PPG.2) PPG signal is analyzed in time domain and frequency domain. Time domain features detections are analyzed in detail. Indicators of large artery stiffness, such as SI (stiffness index) and FtPWV (finger-toe pulse wave velocity), and indicator of small artery elasticity named RI (reflection index) are dynamically detected. An new overall artery elastic function indicator named Kf is proposed from the frequency point of view, which represent 8~12Hz attenuation speed in power spectral density.3) During the course of suppressing artery in an approximate linear way, normalized pulse transit time is dynamic detected to evaluate middle artery compliance which varies with transmural pressure. Indicator of middle artery compliance named NPTT30 is got which needs no emendation according to blood pressure and promises a higher resolution for subclinical artery elasticity function discrimination.4) Based on the principle of brachial artery flow mediated dilation, a new method using PPG signal to discriminate endothelium dysfunction has been investigated. Experiment shows this method can discriminate endothelium dysfunction caused by blood pressure elevation.5) Based on multi-indicator detection and rough set theory, risk classification and indicators of subclinical artery disease are discussed. Indicators for subclinical artery disease determination are found. RH is the early subclinical indicator. Kf combined with RH is the middle stage indicator of subclinical arterial disease. SI is an independent indicator of late subclinical arterial disease.