外文文献翻译压电传感器测定动脉脉搏波速度电子教案.docx

1、外文文献翻译压电传感器测定动脉脉搏波速度电子教案 Piezoelectric sensor determination of arterial pulse wave velocityArterial pulse wave velocity (APWV) is a measure of the elasticity (or stiffness) of peripheral arterial blood vessels. The pulse referred to here will be the pressure pulse as opposed to the flow pulse measur

2、ed by ultrasound Doppler.The pressure pulse velocity varies over the range from about 12 m s1 to15 m s1 in stiff peripheral arteries, whereas in normal arteries it has a velocity in the range of 7 to 9 m s1.The aim of this project was the development of a fast and easy to use system for the determin

3、ation of peripheral arterial pulse wave velocity. The principle of the PWV measurement is based on simultaneous measurement of two pulse waves at two different positions, such as the radial artery at the wrist and the brachial artery just above the elbow. By determining the pulse transit time betwee

4、n these points and the distance measured between the two locations, pulse wave velocity may then be calculated. The pressure pulse detection is done by using two piezoelectric sensors which generate a measurable voltage at the output contacts if they are mechanically deformed. The deformation produc

5、ed voltage is first amplified and filtered and then digitalized with a data acquisition card. The analysis of the data obtained from the sensors includes a filtering process, the calculation of the PWV with three different methods foot-to-foot, cross-correlation and peak-to-peakand the determination

6、 of the arterial pulse rate. Extensive measurements with human test subjects were carried out to optimize the techniques of data acquisition and analysis. For example, it was found that the best procedure was to hold the sensors in place using elastic straps alone. The data analysis was upgraded wit

7、h an additional software module, which deletes, in effect, outriders or invalid measurements. With the optimized system, a series involving eight test subjects ranging in age from 22 to 32 years was completed (all normotensive). The arterial pulse wave velocities determined covered a range from 6 m

8、s1to 12 m s1, with an average standard deviation of less than 2.5 m s1for individual results. These are slightly higher,but close to published APWV data. The results showed that reproducible results can be obtained with the existing PWV acquirement and analysis system.The measurement of arterial pul

9、se wave velocity (APWV) is one of the methods used to measure physiological changes in peripheral vascular disease. Others include pressure pulse contour, arterial elasticity, pulsatile flow, complex vascular impedance and cardiac work.There have been many investigations over the past 30 years or so

10、 to relate changes in age and progress of arterial disease, to vessel pathology and distensibility based on the propagation characteristics of the arterial pulse (Malindzak and Meredith 1970, McCormack 1981, Persson et al 2001, Ramsey 1995, Wilkinson 1998). They have only been partially successful f

11、rom a clinical point of view, mainly due to the difficulty in controlling the effects of patient parameters (autonomic system, patient movement, etc).Early on, the methods of determining APWV involved direct invasive measurement of the pulse pressure at two points along an arterial segment and measu

12、ring the time taken for the pulse to travel the length of the segment. Such investigations had to be limited to animals usually dogs. The sensor technique used in this work involves the piezoelectric effect in polyvinyllidene fluoride (PVDF), which produces an output voltage in response to mechanica

13、l pressure on the material. Three methods of APWV determination are used: foot-to-foot APWV; peak-to-peak APWV and cross-correlation APWV. The FFAPWV and CCAPWV methods are less sensitive to pressure wave reflections at bifurcations, etc in the arterial tree, than the PPAPWV method. Mean values and

14、standard deviations were computed for all three methods and compared.Foot-to-foot APWV (FFAPWV). This is based on the velocity of the foot, or leading edge, of the pressure pulse wave. The arrival times of the foot of the pulse wave at two positions along the artery are recorded. If t is the differe

15、nce in arrival times and s the distance between the two recording positions (proximal and distal), the FFAPWV is simplyFFAPWV = s/t.Peak-to-peak APWV (PPAPWV). This is completely analogous to the FFAPWV except that the points of observation are the two (proximal and distal) peaks of the pulse wave a

16、ndPPAPWV = s/t.Apparent pulse wave velocity (AAPWV). The pressure wave may be represented as aFourier series,P(t) = P0 +Pn sin(nt + n) Where P0 is the mean fluid pressure, n is the harmonic number, Pn is the amplitude of the nth harmonic and n is the phase angle of the nth harmonic.The spatial rate

17、of change of the phase for one harmonic based on two simultaneous pressure measurements separated by a distance _s along an artery, is related to the apparent arterial pulse wave velocity (AAPWV) by the following equation,AAPWVn = (s)n(f )(360o)/(x1 x2)Where AAPWV n is the apparent pulse wave veloci

18、ty for the nth harmonic, f is the heart rate,x1 is the phase angle for the proximal harmonic n and x2 is the phase angle for the distal harmonic n.Cross-correlation PWV. If the arterial pulse at the proximal measurement position is represented by the pressure time series P(x1, t) and that at the dis

19、tal position by P(x2, t) andthe cross-correlation coefficient is x1,x2( ), then will have a maximum value at some time lag.The correlation function can be expressed asx1,x2( ) = (1/T )P(x1, t)P(x2, t) dt.The value of at which maximum correlation occurs represents the transit time (_t) of the pressur

20、e wave from position x1 to position x2 along the arterial segment. From the separation distance and transit time data the correlation arterial pulse wave velocity isCCAPWV = (x2 x1)/ t.In this work normal, young test subjects were used, and it has the primary objectives of optimizing the measurement

21、 procedures and establishing the statistical spread and mean values of the observed PWVs for a specific peripheral arterial segment. Based on this, it is planned to use the system in clinical trials involving patients with peripheral arterial disease (due to diabetes, hypertension, etc), pre-, durin

22、g and post treatment (pharmaceutical or surgical).Analogue and digital circuitryAnalogue charge amplifier. Piezoelectric materials convert mechanical stress or strain into proportionate electrical energy, by producing a charge when subjected to mechanical stress. The charge is converted to a voltage

23、 by an operational amplifier connected as a current integrator, called a charge amplifier. The signal output of the amplifier is approximately 30 mV. It is augmented by signal amplification.Analogue signal amplification . This is done by use of an inverting amplifier. Because a dc signal appears at

24、the output of the charge amplifier, dc offset removal is essential and is implemented in the inverting summing The next phase of the analogue circuitry is a low pass filter to remove the 50 Hz noise interference.Digital controlled data acquisition and analysis. A data acquisition board (DAQ) is requ

25、ired when the transducer signals need interfacing with a PC. The board contains 12 bit plus sign and a successive approximation and self-calibrating analogue-to-digital (ADC) converter. The ADC incurs a systematic error known as the quantization error. It is due to limited resolution and with the an

26、alogue input limit set at 5 to +5 V, the quantization error of the A/D converter used here was calculated to be 0.122 mV.The data acquisition and analysis was done using Lab Viewa powerful instrumentation and analysis programming language for PCs.Digital data acquisition program. The data acquisitio

27、n circuit performs all the necessary operations for the data acquisition with Lab View. The functions of the circuit initialize the data acquisition and read the data from the acquisition card. These data are stored for later use in the data analysis part of the program.Lab View programs are called

28、virtual instruments (VIs) because of their appearance and operations are analogous to measuring instruments. A VI that is called within another VI is called a sub-VI and is analogous to a subroutine in text-based languages.The data acquisition, analysis and presentation are comprised of three main p

29、rocedures:(1) Data acquisition card to interface the hardware to the PC.(2) Data acquisition program to acquire and store data in a spreadsheet file.(3) Data analysis to carry out digital signal processing, calculate PWV and present results.PWV Calculation 1. PWV calculation using peak detection. To

30、 calculate PWV using peaks, the location of the peaks must first be determined, so that the transit time of the wave between the peaks can be determined. It was found that the best method of peak detection is the derivative of the curve method. If the first derivative of a curve is zero, then an ext

31、reme value can existeithera peak or a turning point. It is necessary to take the second derivative at this pointif this is also zero, then an extreme value exists. The second VI used to determine the PWV is PWVcalc, using the time separation between the located peaks.2. PWV with pressure wave foot d

32、etection. The VI named PWV Foot determines the leading edge (foot) of the pressure wave at the upstream and downstream locations. The VI named PWVcalc is again used to compute the PWV from the time separation between the two leading edges (foot-to-foot APWV or FFAPWV).3. PWV with cross-correlation. The PWV determination with cross-correlation is done with the VI named CalcPWV. The VI is in two parts: a part for the initialization function and a part for the calculation of the CCAPWV.In all cases PWV values are assembled in an array and the mean value,