Kun-soo Shin

Autonomic differences between athletes and nonathletes: spectral analysis approach

The purpose of this study was to assess the adaptive effects of endurance training on autonomic function in athletes with spectral analysis of cardiovascular variability signals. Continuous ECG, arterial blood pressure (ABP), and respiratory signals were recorded from 15 athletes (VO2max > 55 mL.min-1.kg-1) and 15 nonathletes (VO2max < 45 mL.min-1.kg-1) during 10 min at sitting position. Autonomic function was assessed by low frequency power (LF power: 0.06-0.14 Hz) and high frequency power (HF power: the region of the respiratory frequency based on respiratory spectrum) obtained from the autospectra of RR interval, systolic arterial pressure (SAP), and diastolic arterial pressure (DAP) variability signals. The spontaneous baroreflex sensitivity was evaluated by the moduli, BRSLF and BRSHF, of the transfer function between RR interval and SAP variability in LF and HF bands. The resting HR in athletes was significantly lower than that in nonathletes. The HF power, an index of parasympathetic activity, in RR interval spectra were significantly higher in athletes than in nonathletes. Meanwhile, the LF power (an indicator of sympathetic activities contributing to RR interval and of ABP variabilities) showed no significant difference between both groups, although that of athletes was slightly less than that of nonathletes. Also, BRSLF and BRSHF were not significantly different between athletes and nonathletes. These results indicate that endurance training results in the enhanced vagal activities in athletes, which may contribute in part to the resting bradycardia.

Estimation of Activity Energy Expenditure: Accelerometer Approach

A novel algorithm estimating the calorie expenditure during physical activities is introduced. The physical activity is quantified by the integration of the accelerometer signals obtained from the 3D accelerometer fixed at the waist level of the human body. Simultaneous measurements of activity and calorie expenditure using 3D accelerometer and gas analyzer show the activity calorie expenditure increases as the activity increases with different rates depending on the type of activities (e.g., walking, running) as well as the physical characteristics of the subjects (e.g., gender, age, mass, and height). Based on the experimental data gathered from 94 subjects, we suggest a new algorithm estimating the activity calorie expenditure dependent on the demographic data of the subjects and the types of the activity

Motion artifact reduction in electrocardiogram using adaptive filtering based on half cell potential monitoring

The electrocardiogram (ECG) is the main measurement parameter for effectively diagnosing chronic disease and guiding cardio-fitness therapy. ECGs contaminated by noise or artifacts disrupt the normal functioning of the automatic analysis algorithm. The objective of this study is to evaluate a method of measuring the HCP variation in motion artifacts through direct monitoring. The proposed wearable sensing device has two channels. One channel is used to measure the ECG through a differential amplifier. The other is for monitoring motion artifacts using the modified electrode and the same differential amplifier. Noise reduction was performed using adaptive filtering, based on a reference signal highly correlated with it. Direct measurement of HCP variations can eliminate the need for additional sensors.

Gravimetric Method for in Vitro Calibration of Skin Hydration Measurements

A novel method for in vitro calibration of skin hydration measurements is presented. The method combines gravimetric and electrical measurements and reveals an exponential dependency of measured electrical susceptance to absolute water content in the epidermal stratum corneum. The results also show that absorption of water into the stratum corneum exhibits three different phases with significant differences in absorption time constant. These phases probably correspond to bound, loosely bound, and bulk water.

Statistical Approach to Quantify the Presence of Phase Coupling Using the Bispectrum

The bispectrum is a method to detect the presence of phase coupling between different components in a signal. The traditional way to quantify phase coupling is by means of the bicoherence index, which is essentially a normalized bispectrum. The major drawback of the bicoherence index (BCI) is that determination of significant phase coupling becomes compromised with noise and low coupling strength. To overcome this limitation, a statistical approach that combines the bispectrum with a surrogate data method to determine the statistical significance of the phase coupling is introduced. Our method does not rely on the use of the BCI, where the normalization procedure of the BCI is the major culprit in its poor specificity. We demonstrate the accuracy of the proposed approach using simulation examples that are designed to test its robustness against noise contamination as well as varying levels of phase coupling. Our results show that the proposed approach outperforms the bicoherence index in both sensitivity and specificity and provides an unbiased and statistical approach to determining the presence of quadratic phase coupling. Application of this new method to renal hemodynamic data was applied to renal stop flow pressure data obtained from normotensive (N = 7) and hypertensive (N = 7) rats. We found significant nonlinear interactions in both strains of rats with a greater magnitude of coupling and smaller number of interaction peaks in normotensive rats than hypertensive rats.

Evaluation of Chip LED Sensor Module for Fat Thickness Measurement using Tissue Phantoms

We tested the feasibility of noninvasive fat thickness measurements by using a diffuse optical method with variable source-detector pairs. A light source module composed of 770 nm low-power chip LEDs and a photodetector were used in this study. The tissue phantoms are composed of a fat and a muscle layer made with gels with appropriate absorption/scattering coefficients. The fat thickness was varied from several to 30 mm. Based on this preliminary study, it is concluded that the noninvasive fat thickness measurement is possible with proper curve fitting procedure

Extremely Low-Profile Antenna for Attachable Bio-Sensors

In this paper, an extremely low-profile patch-type slot antenna for on-body wireless bio-sensor is presented in the medical body area network (MBAN) band. By locating the proposed antenna at the top of the sensor as a sensor cover layer, it is able to maintain compact and flexible sensor structure as well as to enhance its radiation efficiency. The proposed antenna consists of a rectangular loop for balanced feeding and patch with slots for radiating element, and it is designed on flexible printed circuit board (FPCB). To further improve the performance of the antenna with extremely low-profile sensor, air substrate is employed to satisfy the bandwidth, gain, and efficiency requirements. The proposed antenna is measured on a human phantom model with permittivity and conductivity close to those of a human body. From the measured results, it is found that the 3-dB bandwidth of the antenna is sufficient to cover the entire MBAN band (2.36-2.39 GHz) and has a relatively reasonable peak gain of -04 dBi on the human body model.

A PD control-based QRS detection algorithm for wearable ECG applications

We present a QRS detection algorithm for wearable ECG applications using a proportional-derivative (PD) control. ECG data of arrhythmia have irregular intervals and magnitudes of QRS waves that impede correct QRS detection. To resolve the problem, PD control is applied to avoid missing a small QRS wave followed from a large QRS wave and to avoid falsely detecting noise as QRS waves when an interval between two adjacent QRS waves is large (e.g. bradycardia, pause, and arioventricular block). ECG data was obtained from 78 patients with various cardiovascular diseases and tested for the performance evaluation of the proposed algorithm. The overall sensitivity and positive predictive value were 99.28% and 99.26%, respectively. The proposed algorithm has low computational complexity, so that it can be suitable to apply mobile ECG monitoring system in real time.

Optical Skin-fat Thickness Measurement Using Miniaturized Chip LEDs: A Preliminary Human Study

We tested the feasibility of measuring fat thickness using a miniaturized chip LED sensor module, testing 12 healthy female subjects. The module consisted of a single detector and four sources at four different source-detector distances (SD). A segmental curve-fitting procedure was applied, using an empirical algorithm obtained by Monte-Carlo simulation, and fat thicknesses were estimated. These thicknesses were compared to computed-tomography (CT) results; the correlation coefficient between CT and optical measurements was 0.932 for bicep sites. The mean percentage error between the two measurements was 13.12%. We conclude that fat thickness can be efficiently measured using the simple sensor module.

Fat thickness measurement using optical technique with miniaturized chip LEDs: A preliminary human study

In this study, we present the possibility of the fat thickness measurement using the miniaturized chip LEDs sensor module for the twelve healthy women. The newly developed sensor module consisted of four different source-detector distances. The measurement sites are the five parts of biceps, triceps, upper abdomen, front thigh, and calf and the range of fat thickness is from 3.5 mm to 39.0 mm. The fitting curve for each measurement sites is separately obtained. We obtained the correlation coefficient of 0.932 compared with the fat thickness of CT measurement for biceps site. For the three measurement sites of biceps, front thigh, and calf of twelve persons and namely 36 data points, the mean absolute difference thickness and % error for the measured thickness compared with that of reference CT thickness are 1.08 mm and 11.49%, respectively. Based on this preliminary experiment, it is confirmed that the fat thickness measurement is possible with proper curve fitting procedure using slope analysis.