Jae-Geol Cho

Ultra Short Term Analysis of Heart Rate Variability for Monitoring Mental Stress in Mobile Settings

Heart rate variability (HRV) analysis is commonly used as a quantitative marker depicting the activity of autonomous nervous system (ANS) that may be related to mental stress. For mobile applications, short term ECG measurement may be used for HRV analysis since the conventional five minute long recordings might be inadequately long. Short term analysis of HRV features has been investigated mostly in ECG data from normal and cardiac patients. Thus, short term HRV features may not have any relevance on the assessment of acute mental stress. In this study, we obtained ultra short term HRV features from 24 subjects during baseline stage and Stroop color word test. We validated these HRV features by showing significant differences in HRV features existed between the two stages. Our results indicated that ultra short term analysis of heart rate and RR intervals within 10 s, RMSSD and PNN50 within 30 s, HF within 40 s, LF/HF, normalized LF, and normalized HF within 50 s could be reliably performed for monitoring mental stress in mobile settings.

Electron-Transfer Mediator for a NAD-Glucose Dehydrogenase-Based Glucose Sensor

A new electron-transfer mediator, 5-[2,5-di (thiophen-2-yl)-1H-pyrrol-1-yl]-1,10-phenanthroline iron(III) chloride (FePhenTPy) oriented to the nicotinamide adenine dinucleotide-dependent-glucose dehydrogenase (NAD-GDH) system was synthesized through a Paal-Knorr condensation reaction. The structure of the mediator was confirmed by Fourier-transform infrared spectroscopy, proton and carbon nucler magnetic resonance spectroscopy, and mass spectroscopy, and its electron-transfer characteristic for a glucose sensor was investigated using voltammetry and impedance spectroscopy. A disposable amperometric glucose sensor with NAD-GDH was constructed with FePhenTPy as an electron-transfer mediator on a screen printed carbon electrode (SPCE) and its performance was evaluated, where the addition of reduces graphene oxide (RGO) to the mediator showed the enhanced sensor performance. The experimental parameters to affect the analytical performance and the stability of the proposed glucose sensor were optimized, and the sensor exhibited a dynamic range between 30 mg/dL and 600 mg/dL with the detection limit of 12.02 ± 0.6 mg/dL. In the real sample experiments, the interference effects by acetaminophen, ascorbic acid, dopamine, uric acid, caffeine, and other monosaccharides (fructose, lactose, mannose, and xylose) were completely avoided through coating the sensor surface with the Nafion film containing lead(IV) acetate. The reliability of proposed glucose sensor was evaluated by the determination of glucose in artificial blood and human whole blood samples.

Bragg grating-assisted WDM filter for integrated optical triplexer transceivers

We designed and experimentally demonstrated a Bragg grating-assisted wavelength-division-multiplexing filter for the three-wavelength multiplexing on a planar-lightwave-circuit platform. The 1310- and 1550-nm lights were designed to be separated after passing the directional coupler by a half-cycle and a full-cycle coupling actions with losses of 0.07 and 0.19 dB, respectively. The 1492-nm light was reflected back by a Bragg grating fabricated on the directional coupler and its loss was less than 2.0 dB. We also introduced and discussed the new concept of an integrated optical triplexer transceiver using this filter.

Thin film filter-embedded triplexing-filters based on directional couplers for FTTH networks

We designed and experimentally demonstrated a thin film filter (TFF)-embedded directional coupler-type triplexing-filter on the planar-lightwave-circuit platform. The triple-play multiplexing was significantly simplified by using one TFF. The 1.31- and 1.55-/spl mu/m lights were designed to be divided after passing the directional coupler by half-cycle and full-cycle coupling actions, respectively. The 1.49-/spl mu/m light was reflected by a TFF inserted in a trench on the directional coupler. The insertion losses of fabricated triplexing-filters were less than 2.0 dB with bandwidths of 20 nm. The newly proposed triplexing-filter provides a cost-effective high-performance solution for fiber-to-the-home networks.

Detection of subjects with higher self-reporting stress scores using heart rate variability patterns during the day

Heart rate variability (HRV) has been well established to measure instantaneous levels of mental stress. Circadian patterns of HRV features have been reported but their use to estimate levels of mental stress were not studied thoroughly. In this study, we investigated time dependent variations of HRV features to detect subjects under chronic mental stress. Sixty eight subjects were divided into high (n=10) and low stress group (n=43) depending on their self-reporting stress scores. HRV features were calculated during three different time periods of the day. High stress group showed decreased patterns of HRV features compared to low stress group. When logistic regression analysis was performed with raw multiple HRV features, the classification was 63.2% accurate. A new % deviance score reflecting the degree of difference from normal reference patterns increased the accuracy to 66.1%. Our data suggested that HRV patterns obtained at multiple time points of the day could provide useful data to monitor subjects under chronic stress.

Unconstrained snoring detection using a smartphone during ordinary sleep

BackgroundSnoring can be a representative symptom of a sleep disorder, and thus snoring detection is quite important to improving the quality of an individual’s daily life. The purpose of this research is to develop an unconstrained snoring detection technique that can be integrated into a smartphone application. In contrast with previous studies, we developed a practical technique for snoring detection during ordinary sleep by using the built-in sound recording system of a smartphone, and the recording was carried out in a standard private bedroom.MethodThe experimental protocol was designed to include a variety of actions that frequently produce noise (including coughing, playing music, talking, rining an alarm, opening/closing doors, running a fan, playing the radio, and walking) in order to accurately recreate the actual circumstances during sleep. The sound data were recorded for 10 individuals during actual sleep. In total, 44 snoring data sets and 75 noise datasets were acquired. The algorithm uses formant analysis to examine sound features according to the frequency and magnitude. Then, a quadratic classifier is used to distinguish snoring from non-snoring noises. Ten-fold cross validation was used to evaluate the developed snoring detection methods, and validation was repeated 100 times randomly to improve statistical effectiveness.ResultsThe overall results showed that the proposed method is competitive with those from previous research. The proposed method presented 95.07% accuracy, 98.58% sensitivity, 94.62% specificity, and 70.38% positive predictivity.ConclusionThough there was a relatively high false positive rate, the results show the possibility for ubiquitous personal snoring detection through a smartphone application that takes into account data from normally occurring noises without training using preexisting data.

A framework for personalized Healthcare Service Recommendation

Development of the Internet enables numerous healthcare services to be available to many service consumers. As a result, many brokering web sites such as healthcare service portals and search engines are deployed to support userspsila choice. However, to provide better healthcare to the novice users, systems need more sophisticated mechanism for healthcare recommendation. In this paper, we propose healthcare service recommendation framework (HSRF) that considers health status and various contexts of each user. HSRF arranges healthcare services based on medical similarities between user and services. We successfully implemented the framework and confirmed its functionality and feasibility.

Robust Sleep Quality Quantification Method for a Personal Handheld Device

OBJECTIVE The purpose of this study was to develop and validate a novel method for sleep quality quantification using personal handheld devices. MATERIALS AND METHODS The proposed method used 3- or 6-axes signals, including acceleration and angular velocity, obtained from built-in sensors in a smartphone and applied a real-time wavelet denoising technique to minimize the nonstationary noise. Sleep or wake status was decided on each axis, and the totals were finally summed to calculate sleep efficiency (SE), regarded as sleep quality in general. The sleep experiment was carried out for performance evaluation of the proposed method, and 14 subjects participated. An experimental protocol was designed for comparative analysis. The activity during sleep was recorded not only by the proposed method but also by well-known commercial applications simultaneously; moreover, activity was recorded on different mattresses and locations to verify the reliability in practical use. Every calculated SE was compared with the SE of a clinically certified medical device, the Philips (Amsterdam, The Netherlands) Actiwatch. RESULTS In these experiments, the proposed method proved its reliability in quantifying sleep quality. Compared with the Actiwatch, accuracy and average bias error of SE calculated by the proposed method were 96.50% and -1.91%, respectively. CONCLUSIONS The proposed method was vastly superior to other comparative applications with at least 11.41% in average accuracy and at least 6.10% in average bias; average accuracy and average absolute bias error of comparative applications were 76.33% and 17.52%, respectively.

Reduction of insertion loss of thin film filters embedded in PLC platforms

We propose and experimentally demonstrate a method of reducing insertion loss of a thin-film-filter-embedded planar-lightwave-circuit platform for a triplexer transceiver module. Significant loss reduction was achieved by adding horn waveguide elements at the interfaces between the thin film filter and the output-port (transmission and reflection) waveguides.

Activation of pluripotency genes by a nanotube-mediated protein delivery system

The overexpression of cell reprogramming factors (Oct4, Sox2, Klf4, Nanog, and c‐Myc) allows differentiated cells to revertto an earlier developmental stage. Differentiated cells can also be reprogrammed by directly delivering reprogramming proteins tagged with cell‐penetrating peptides, which allow the proteins to pass through the cell membrane and into the cytoplasm–although this method has been an inefficient process. Here, we describe a novel technique for delivering reprogramming proteins into cells using titanium oxide (TiO2) nanotubes, which show no cytotoxic effects and do not affect cell proliferation. TiO2 nanotubes successfully transferred the above‐mentioned reprogramming factors into differentiated somatic cells. After 3 weeks of treatment with protein‐conjugated nanotubes, the somatic cells adopted an embryonic stem cell‐like morphology and expressed activated Oct4‐green fluorescent protein, a pluripotency biomarker. Our results indicate that TiO2 nanotubes can be used to directly deliver reprogramming factors into somatic cells to induce pluripotency. Mol. Reprod. Dev. 80: 1000–1008, 2013.