Chungkeun Lee

Adaptive threshold method for the peak detection of photoplethysmographic waveform

Photoplethysmography (PPG)-based temporal analyses have been widely used as a useful analytical method in physiological and cardiovascular diagnosis. Most of temporal approaches of PPG are based on detected peak points, peak and foot of PPG. The aim of presented study is the development of improved peak detection algorithm of PPG waveform. The present study demonstrates a promising approach to overcome respiration effect and to detect PPG peak. More extensive investigation is necessary to adapt for the cardiovascular diseases, whose PPG morphology has different form.

Electromechanical cardioplasty using a wrapped elasto-conductive epicardial mesh

A mesh made of a conductive nanowire composite can be wrapped around the heart to improve hemodynamics in experimental heart failure in rodents. An electromechanical hug for the heart Heart failure can be treated by pacemakers to keep the beats in rhythm, but pacemakers apply electrical stimulation at specific points and do not provide comprehensive coverage of the entire organ. Park and colleagues therefore devised an electric mesh that wraps around the heart to deliver electrical impulses to the whole ventricular myocardium. The heart wrap was made from silver nanowires embedded in a rubber polymer that could conform to the unique three-dimensional anatomy of different hearts. In rats that had a heart attack, the mesh integrated structurally and electrically with the myocardium and exerted beneficial effects, including preserved diastolic relaxation, reduced wall stress, and improved cardiac contractile function. The mesh also terminated induced ventricular arrhythmia, acting as an epicardial defibrillator. Such epicardial meshes have been tested in clinical trials before and were effective in preventing ventricular remodeling but showed controversial results in long-term survival. The authors hope that their device, which is designed to integrate more faithfully with the heart’s structure and electrical conduction system, is more consistent in people. Heart failure remains a major public health concern with a 5-year mortality rate higher than that of most cancers. Myocardial disease in heart failure is frequently accompanied by impairment of the specialized electrical conduction system and myocardium. We introduce an epicardial mesh made of electrically conductive and mechanically elastic material, to resemble the innate cardiac tissue and confer cardiac conduction system function, to enable electromechanical cardioplasty. Our epicardium-like substrate mechanically integrated with the heart and acted as a structural element of cardiac chambers. The epicardial device was designed with elastic properties nearly identical to the epicardial tissue itself and was able to detect electrical signals reliably on the moving rat heart without impeding diastolic function 8 weeks after induced myocardial infarction. Synchronized electrical stimulation over the ventricles by the epicardial mesh with the high conductivity of 11,210 S/cm shortened total ventricular activation time, reduced inherent wall stress, and improved several measures of systolic function including increases of 51% in fractional shortening, ~90% in radial strain, and 42% in contractility. The epicardial mesh was also capable of delivering an electrical shock to terminate a ventricular tachyarrhythmia in rodents. Electromechanical cardioplasty using an epicardial mesh is a new pathway toward reconstruction of the cardiac tissue and its specialized functions.

Cardiomyocytes from phorbol myristate acetate-activated mesenchymal stem cells restore electromechanical function in infarcted rat hearts

Despite the safety and feasibility of mesenchymal stem cell (MSC) therapy, an optimal cell type has not yet emerged in terms of electromechanical integration in infarcted myocardium. We found that poor to moderate survival benefits of MSC-implanted rats were caused by incomplete electromechanical integration induced by tissue heterogeneity between myocytes and engrafted MSCs in the infarcted myocardium. Here, we report the development of cardiogenic cells from rat MSCs activated by phorbol myristate acetate, a PKC activator, that exhibited high expressions of cardiac-specific markers and Ca2+ homeostasis-related proteins and showed adrenergic receptor signaling by norepinephrine. Histological analysis showed high connexin 43 coupling, few inflammatory cells, and low fibrotic markers in myocardium implanted with these phorbol myristate acetate-activated MSCs. Infarct hearts implanted with these cells exhibited restoration of conduction velocity through decreased tissue heterogeneity and improved myocardial contractility. These findings have major implications for the development of better cell types for electromechanical integration of cell-based treatment for infarcted myocardium.

Wavelet-based Multi-resolution Deformation for Medical Endoscopic Image Segmentation

Image segmentation is an essential technique in image analysis. In spite of issues in contour initialization, boundary concavities and high-level computation, active contour models (snakes) are popular and successful method for segmentation among researchers. Segmentation process in snakes consists of calculation of energy and deformation of contour. In this paper, we present a new deformation method for active contour model, multi-resolution deformation based on wavelet ensuring powerful time reduction, high accuracy supported by stable results in convergence of an initial contour to target boundary in medical image segmentation.

Robust and real-time monitoring of nerve regeneration using implantable flexible microelectrode array.

This paper presents a robust and quasi-real-time monitoring method for examining the degree of regeneration of peripheral nerves using a polymer-based implantable microelectrode array (IMA). The IMA was implanted in the sciatic nerves of rats using two different approaches: (1) direct implantation which was achieved by directly suturing to nerve stumps for short-term regeneration and (2) assembly implantation which was achieved by implanting the IMA assembled with a resorbable conduit that cross a 4-mm nerve defect. The regeneration of the injury was evaluated by measuring the nerve signals following foot pricking and impulse stimulating to the proximal stump. The direct implantation produced a peak voltage of 3.43 mV before amplification and a conduction velocity of 19.8m/s. The assembly implantation produced a peak voltage of 1.51 mV and a conduction velocity of 18 m/s. The degree of regeneration was also examined using gait and morphological analyses. The sciatic function index was -38.5+/-12.5 for direct implantation and -64.9+/-7.5 for assembly implantation. The morphologies of the regenerated nerves were examined using toluidine blue, transmission electron microscopy images, and pilot tests. Te regeneration ratios after the direct and assembly implantation were 45% and 21%, respectively.

Generation and performance analysis of frequency-hopping optical orthogonal codes with arbitrary time blank patterns

We propose a new generation algorithm for frequency-hopping optical orthogonal codes (FH-OOC). The new algorithm generalizes the conventional FH-OOCs by considering the time blank patterns between two adjacent symbols. We show that it can generate more available codes than the previous algorithm which does not consider the effect of time blank patterns. We also derive the upper bound of the new code set. We conduct the performance analysis by considering the interference from unwanted frequency components, and compare the bit error rate of the new codes with those of other code sets in various cases.

Miniaturized One-Point Detectable Electrocardiography Sensor for Portable Physiological Monitoring Systems

A mechanically flexible electrocardiography (ECG) sensor for one-point detection was proposed. The ECG sensor consists of an outer hook-shaped sensing electrode and an inner circular-shaped referencing electrode. The ECG measurement capability was examined by attaching the sensor to the human chest at different positions. Performance of the proposed sensor was then compared with that of the commercial Ag/AgCl electrodes. The results of this letter demonstrated that ECG could be measured using the proposed sensor at only one point on the body.

Relations between ac-dc components and optical path length in photoplethysmography

Photoplethysmography is used in various areas such as vital sign measurement, vascular characteristics analysis, and autonomic nervous system assessment. Photoplethysmographic signals are composed of ac and dc, but it is difficult to find research about the interaction of photoplethysmographic components. This study suggested a model equation combining two Lambert-Beer equations at the onset and peak points of photoplethysmography to evaluate ac characteristics, and verified the model equation through simulation and experiment. In the suggested equation, ac was dependent on dc and optical path length. In the simulation, dc was inversely proportionate to ac sensitivity (slope), and ac and optical path length were proportionate. When dc increased from 10% to 90%, stabilized ac decreased from 1 to 0.89 ± 0.21, and when optical path length increased from 10% to 90%, stabilized ac increased from 1 to 1.53 ± 0.40.

Implementation of Wearable Sensor Glove using Pulse-wave Sensor, Conducting Fabric and Embedded System

Today, there are research trends about the wearable sensor device that measures various bio-signals and provides healthcare services to user using e-health technology. This study describes the wearable sensor glove using pulse-wave sensor, conducting fabric and embedded system. This wearable sensor glove is based on the pulse-wave measurement system which is able to measure the pulse wave signal in much use of oriental medicine on the basis of a research trend of e-health system.

Frequency-hopping optical orthogonal codes with arbitrary time-blank patterns

We investigate a general scheme of frequency-hopping optical orthogonal codes with a specified distance between adjacent frequency symbols and propose a novel code that allows time blanks between adjacent frequency symbols in code sequences. A time blank represents the absence of frequency symbols in code sequences and makes no interference with frequency components. The insertion of time-blank patterns can provide ample scope to generate much more code sequences than the conventional codes lacking in time-blank patterns, and we show this by constructing an algorithm to generate the proposed code. The performance analysis demonstrates that its performance is superior to that of the conventional codes in terms of the bit error rate. We also derive the upper bound on the proposed code set.