Gi-Ryon Kim

Vascular Variation of PTT and the Vascular Characteristic Index According to the Posture Change

The analysis of an arterial stiffness is essential for estimating the cardiovascular disease. Many indices suck as pulse transit time (PTT), reflection index (RI), stiffness index (ST) and characteristic impedance (Zc) are introduced to assess arterial stiffness. The purpose of this study is to analyze the variation aspect of PTT and the vascular characteristic index according to the posture change in the human body. The PTT is defined as the time interval between the peak of QRS complex in ECO and the characteristic point of the pulse wave. In this study, the characteristic point of the pulse wave is obtained using the maximum of the second derivative and peak point of PPQ signal, which is known to be noise resistant and to contribute a stable result. The vascular characteristic index was acquired through the analysis of waveform in peripheral pulse. The variation aspect of PTT and characteristic index according to the posture change were analyzed and the usefulness of those parameters was also evaluated. Experimental result indicated all parameters changed significantly according to the posture change. Therefore, proposed method can be an indispensable complement to existing methods for the non-invasive assessment of the vascular characteristics and body condition. It is possible to make ubiquitous healthcare monitoring because of simplicity, convenience and ease to access.

Changes of Pulse Wave Velocity in Arm According to Characteristic Points of Pulse Wave

Pulse wave velocity has widely been used in the evaluation of atherosclerosis. In this study, we observed the change of pulse wave velocity according to characteristic points of pressure pulse waves which were recorded at brachial and radial artery. In order to evaluate the versatility of determination of the transit time between two points of measuring site, we measured PWV in seven methods : (1) the first derivative method, (2) the second derivative, (3) the minimum, (4) the intersecting a line tangent, (5) the maximum, (6) the middle point between minimum and maximum, (7) the intersecting two line tangents. Noninvasive brachial and radial pressure waveforms were recorded in 5 volunteers with external pressure transducers. The results showed that pulse wave velocity were dependent on the characteristic points.

Implementation and evaluation of the sensor assessing pressure and photoplethysmogram

Pulse sensors generally have characteristics that cause a analytical error by the interference of signals according to tiny motion of body and pressure applied to skin. To resolve this problem, we implemented the sensor that is capable of simultaneously measuring pressure and PPG(photoplethymogram) in a state attached to skin. Pressure and PPG was recorded at the finger and wrist respectively to evaluate the usefulness of the implemented sensor. Then, it was observed that the shape of PPG from sensor changed by pressure pushing down skin. Results of this study suggested that it is possible to monitor a degree of skin pressurization and to guarantee a reliable measurement by simultaneously measuring pressure and PPG using implemented integrated sensor when measuring PPG on the wrist or the finger.

Development of PC-based and portable high speed impedance analyzer for biosensor

For more convenient electrode-electrolyte interface impedance analysis in biosensor, a stand-alone impedance measurement system is required. In our study, we developed a PC-based portable system to analyze impedance of the electrochemical cell using microprocessor. The devised system consists of signal generator, programmable amplifiers, A/D converter, low pass filter, potentiostat, I/V converter, microprocessor, and PC interface. As a microprocessor, PIC16F877 which has the processing speed of 5 MIPS was used. For data acquisition, the sampling rate at 40 k samples/sec, resolution of 12 bit is used. RS-232 with 115.2 kbps speed is used for the PC communication. The square wave was used as stimuli signal for impedance analysis and voltage-controlled current measurement method of three-electrode-method were adopted. Acquired voltage and current data are calculated to multifrequency impedance signal after Fourier transform. To evaluate the implemented system, we set up the dummy cell as equivalent circuit of which was composed of resistor, parallel circuit of capacitor and resistor connected in parallel and measured the impedance of the dummy cell; the result showed that there exist accuracy within 5 % errors and reproduction within 1 % errors compared to output of Hioki LCR tester and HP impedance analyzer as a standard product. These results imply that it is possible to analyze electrode-electrolyte interface impedance quantitatively in biosensor and to implement the more portable high speed impedance analysis system compared to existing systems.

Color Correction in Portable-type Urine Analyzer

Color correction methods of chromaticity coordinates using Color Matching Function (CMF) were studied to develop a device-independent portable-type urine analyzer. The reflection spectra were measured for the degrees of 10 test items of the urine reagent strip (urine strip) to develop a portable-type urine analyzer. A computer simulation was performed to quantitatively distinguish the color reactions of the urine system, by using the spectral power distribution of Light Emitting Diode(LED), the reflection of a urine strip, and spectral sensitivity of a photodiode. To develop a device-independent system, chromaticity coordinates were modified to reduce the color deviations in the urine strip, by using the temperature compensation of LED and the color transformation by CMF. The experimental values obtained by developed urine system exhibited the accuracy above 95% for all color samples.

A Vascular Characteristic Index of Blood Pressure Variation using the Pulse Wave Signal

Pulse waves continuously change with respect to the characteristics and status of the cardiovascular system and in relation to the blood pressure (BP) and the pulse wave velocity (PWV). Monitoring the vascular condition by analyzing the variations in pulse waveforms has been used to diagnose vascular disorders and in drug treatment of arteriosclerosis and peripheral circulatory obstruction. In this paper, we investigated the vascular characteristic index with regard to the BP and classified by pulse wave signals. The pressure pulse wave and photoplethysmography (PPG) were measured simultaneously while subjects exercised, producing changes in the BP, to analyze the variation in the vascular characteristic index. We investigated the correlation between the BP and vascular characteristic index with regard to the classification methods of the pulse wave. The reflection index (RI) and vascular stiffness index were correlated with the diastolic BP, but no correlation was found between these parameters and the systolic BP. These results suggest the possibility of estimating BP through simple measurements of pulse waves.

Estimating blood pressure using the pulse transit time of the two measuring from pressure pulse and PPG

Blood pressure (BP), one of the most important vital signs, is used to identify an emergency state and reflects the blood flow characteristics of the cardiovascular system. The conventional noninvasive method of measuring BP is inconvenient because patients must wear a cuff on their arm and the measurement process takes time. This paper proposes an algorithm for estimating the BP using the pulse transit time (PTT) of the photoplethysmography (PPG) and pressure pulse from finger at the same time as a more convenient way to measure the BP. After recording the electrocardiogram (ECG), measuring the pressure pulse, and performing PPG, we calculated the PTT from the acquired signals. Then, we used a multiple regression analysis to measure the systolic and diastolic BP indirectly. Comparing the BP measured indirectly using the proposed algorithm and the real BP measured with a sphygmomanometer, the systolic pressure had a mean error of mmHg and a standard deviation of 2.530 mmHg, while the diastolic pressure had a satisfactory result, i.e., a mean error of mmHg and a standard deviation of 1.396 mmHg. These results are more superior than existing method estimating blood pressure using the one PTT and satisfy the ANSI/AAMI regulations for certifying a sphygmomanometer i.e., the measurement error should be within a mean error of mmHg and a standard deviation of 8 mmHg. These results suggest the possibility of applying our method to a portable, long-term BP monitoring system.