Kwang Suk Park

Seoul National University, Sŏul, Seoul, South Korea

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Publications (163)151.25 Total impact

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    ABSTRACT: Amyotrophic lateral sclerosis (ALS) patients can communicate via their residual capacity to voluntarily blink or move their eyes. Conventionally, electrooculography and video cameras have been used to detect blinks. However, these methods have several shortcomings for application to ALS patients. To overcome such weaknesses, a novel blink detection system that utilises transparent conductive films of indium tin oxide (ITO) is proposed. The ITO films, which are attached to the lenses of conventional glasses, detect blinks without obstructing the wearer's field of vision. The system was validated by a binary communication experiment conducted with six subjects. The results show that 100% of the blinks given by subjects correctly indicated their intended answers.
    Electronics Letters 03/2015; 51(5):382-384. DOI:10.1049/el.2014.3548 · 1.07 Impact Factor
  • 12/2014; 35(6):211-218. DOI:10.9718/JBER.2014.35.6.211
  • 12/2014; 35(6):203-210. DOI:10.9718/JBER.2014.35.6.203
  • 10/2014; 35(5):160-168. DOI:10.9718/JBER.2014.35.5.160
  • 10/2014; 35(5):169-176. DOI:10.9718/JBER.2014.35.5.169
  • 08/2014; 35(4):87-94. DOI:10.9718/JBER.2014.35.4.87
  • 08/2014; 35(4):95-98. DOI:10.9718/JBER.2014.35.4.95
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    ABSTRACT: This study proposes the use of flexible capacitive electrodes for reducing motion artifacts in a wearable electrocardiogram (ECG) device. The capacitive electrodes have conductive foam on their surface, a shield, an optimal input bias resistor, and guarding feedback. The electrodes are integrated in a chest belt, and the acquired signals are transmitted wirelessly for ambulatory heart rate monitoring. We experimentally validated the electrode performance with subjects standing and walking on a treadmill at speeds of up to 7 km/h. The results confirmed the highly accurate heart rate detection capacity of the developed system and its feasibility for daily-life ECG monitoring.
    Sensors 08/2014; 14(8):14732-14743. DOI:10.3390/s140814732 · 2.05 Impact Factor
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    ABSTRACT: Based on the its nonintrusive characteristics, ballistocardiography(BCG) has applied in the estimation of sleep structure without attaching any sensors to the subject's body. Loadcell or polyvinylidenefluoride (PVDF) film sensors are installed on the mattress for the monitoring of BCG. BCG peak was detected and heart rate variability parameters are derived. Parameters representing sleep structure and quality are estimated using these parameters. Sleep efficiency, four stages of sleep structure and sleep onset latency are estimated and results are compared with the results derived from polysomnographic recording.
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    ABSTRACT: The technology for measuring ECG using capacitive electrodes and its applications are reviewed. Capacitive electrodes are built with a high-input-impedance preamplifier and a shield on their rear side. Guarding and driving ground are used to reduce noise. An analysis of the intrinsic noise shows that the thermal noise caused by the resistance in the preamplifier is the dominant factor of the intrinsic noise. A fully non-contact capacitive measurement has been developed using capacitive grounding and applied to a non-intrusive ECG measurement in daily life. Many ongoing studies are examining how to enhance the quality and ease of applying electrodes, thus extending their applications in ubiquitous healthcare from attached-on-object measurements to wearable or EEG measurements.
    Annals of Biomedical Engineering 07/2014; 42(11). DOI:10.1007/s10439-014-1069-6 · 3.23 Impact Factor
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    ABSTRACT: Objective. Current electroencephalogram (EEG) monitoring systems typically require cumbersome electrodes that must be pasted on a scalp, making a private recording of an EEG in a public place difficult. We have developed a small, user friendly, biocompatible electrode with a good appearance for inconspicuous EEG monitoring. Approach. We fabricated carbon nanotube polydimethylsiloxane (CNT/PDMS)-based canal-type ear electrodes (CEE) for EEG recording. These electrodes have an additional function, triggering sound stimulation like earphones and recording EEG simultaneously for auditory brain-computer interface (BCI). The electrode performance was evaluated by a standard EEG measurement paradigm, including the detection of alpha rhythms and measurements of N100 auditory evoked potential (AEP), steady-state visual evoked potential (SSVEP) and auditory steady-state response (ASSR). Furthermore, the bio- and skin-compatibility of CNT/PDMS were tested. Main results. All feasibility studies were successfully recorded with the fabricated electrodes, and the biocompatibility of CNT/PDMS was also proved. Significance. These electrodes could be used to monitor EEG clinically, in ubiquitous health care and in brain-computer interfaces.
    Journal of Neural Engineering 06/2014; 11(4):046014. DOI:10.1088/1741-2560/11/4/046014 · 3.42 Impact Factor
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    ABSTRACT: Objective: A prospective, observational study to investigate how photoplethysmography (PPG) signals change during lumbar sympathetic blockade (LSB), and whether these changes can predict sympathetically mediated pain (SMP). Methods: Patients with unilateral lower extremity pain and self-reported cold hyperalgesia underwent LSB. Bilateral temperature and PPG signals (AC and DC) were recorded. Power spectrum analysis (PSA) was performed. Results: Of the total patient cohort (n=38), eight patients (22.1%) had excellent pain-relief after LSB and were determined to have SMP. In all patients, the PPG AC signal changed immediately after drug administration, before any temperature change. DC signals decreased slowly in a linear fashion. PSA of DC signals showed significantly lower low-frequency/ high-frequency (LF/HF) ratios in the SMP group than the sympathetically independent pain group, both before and after LSB. A cut-off value of 2.92 for LF/HF resulted in sensitivity, specificity and positive predictive values for SMP of 75.0%, 76.7% and 3.21 [1.5, 6.9], respectively. Conclusions: PPG may be used as an early indicator of a successful LSB and could also be helpful in diagnosing SMP.
    The Journal of international medical research 06/2014; 42(4). DOI:10.1177/0300060514532619 · 1.10 Impact Factor
  • Yun-Kyoung Yim, Kwang Suk Park
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    ABSTRACT: The objective of this study is to investigate the effects of short-term bed rest on the radial pulse in healthy subjects. Twenty-one healthy volunteers participated in this study. Their radial pulse was measured at different measuring positions using a multi-step tonometry system. The participants took 30 minutes of bed rest and their radial pulse was measured before and after the bed rest. The effects of bed rest on the radial pulse were analyzed. The pulse area, the amplitudes of h4 and h5, the pulse period, and the diastolic pulse proportion increased with short-term bed rest, whereas the proportions of systolic and hightension pulse and the fundamental frequency of the pulse wave decreased with short-term bed rest. All the changes were in the same direction in both male and female participants at all measuring positions; however, some parameters changed more in women than in men, and some changed more at the distal position than at the proximal position. In shortly, Short-term bed rest induces significant changes in the radial pulse of healthy subjects. The results of this study could be used as a control reference for clinical acupuncture studies with participants lying on a bed for acupuncture treatment.
    Journal of Acupuncture and Meridian Studies 06/2014; 7(3):133-139. DOI:10.1016/j.jams.2013.12.001
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    ABSTRACT: A high-frequency steady-state visual evoked potential (SSVEP) has been suggested for the reduction of eye fatigue for SSVEP-based brain-computer interfaces (BCIs). However, the poor performance of high-frequency SSVEP requires a novel stimulus of better performance even with low eye fatigue. As an alternative to the high-frequency SSVEP, we explore the SSVEP response to an amplitude-modulated stimulus (AM-SSVEP) to verify its availability for brain-computer interfaces (BCIs). An amplitude-modulated stimulus was generated as the product of two sine waves at a carrier frequency (fc) and a modulating frequency (fm). The carrier frequency was higher than 40Hz to reduce eye fatigue, and the modulating frequency ranged around the α-band (9-12Hz) to utilize low-frequency harmonic information. Four targets were used in combinations of three different modulating frequencies and two different carrier frequencies in the offline experiment, and two additional targets were added with one additional modulating and one carrier frequency in online experiments. In the AM-SSVEP spectra, seven harmonic components were identified at 2fc, 2fm, fc±fm, fc±3fm, and 2fc-4fm. Using an optimized combination of the harmonic frequencies, online experiments demonstrated that the accuracy of the AM-SSVEP was equivalent to that of the low-frequency SSVEP. Furthermore, subject evaluation indicated that an AM stimulus caused lower eye fatigue and less sensing of flickering than a low-frequency stimulus, in a manner similar to a high-frequency stimulus. The actual stimulus frequencies of AM-SSVEPs are in the high-frequency band, resulting in reduced eye fatigue. Furthermore, AM-SSVEPs can utilize both fundamental stimulus frequencies and non-integer harmonic frequencies including low frequencies for SSVEP recognition. The feasibility of AM-SSVEP with high BCI performance and low eye fatigue was confirmed through offline and online experiments. AM-SSVEPs combine the advantages of both low- and high-frequency SSVEPs - high power and low eye fatigue, respectively. AM-SSVEP-based BCI systems exploit these advantages, making them promising for application in practical BCI systems.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 12/2013; DOI:10.1016/j.clinph.2013.11.016 · 2.98 Impact Factor
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    ABSTRACT: We developed and tested a system for estimating body postures on a bed using unconstrained measurements of electrocardiogram (ECG) signals using 12 capacitively coupled electrodes and a conductive textile sheet. Thirteen healthy subjects participated in the experiment. After detecting the channels in contact with the body among the 12 electrodes, the features were extracted on the basis of the morphology of the QRS (Q wave, R wave, and S wave of ECG) complex using three main steps. The features were applied to linear discriminant analysis, support vector machines with linear and radial basis function (RBF) kernels, and artificial neural networks (one and two layers), respectively. SVM with RBF kernel had the highest performance with an accuracy of 98.4% for estimation of four body postures on the bed: supine, right lateral, prone, and left lateral. Overall, although ECG data were obtained from few sensors in an unconstrained manner, the performance was better than the results that have been reported to date. The developed system and algorithm can be applied to the obstructive apnea detection and analyses of sleep quality or sleep stages, as well as body posture detection for the management of bedsores.
    11/2013; 17(6):985-93. DOI:10.1109/JBHI.2013.2252911
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    ABSTRACT: Purpose Interest in brain computer interfaces (BCI) has recently increased due to the need for quality of life technologies for disabled people. While brain signal processing and its applications have been widely studied for many decades, BCI seldom requires attention to practical and efficient brain signal sensing methods. Noninvasive electroencephalogram (EEG) measurements using wet adhesive Ag/AgCl electrodes are universally employed for BCI, but have limitations in practical acceptability with regard to portability, comfort and aesthetic design. In order to translate the results of laboratory experiments into practical use, EEGs should be recorded easily without requiring scalp preparation and regardless of the presence of hair. Methods In this paper, general requirements for capacitive measurement of EEG are presented and four different frontends for capacitive EEG electrodes are evaluated: (a) basic voltage follower scheme with high value resistor bias network (Rb), (b) voltage follower scheme with active guarding (second op-amp), (c) reverse current of signal diodes to providing bias current, (d) electrode scheme without any external bias network. We explore the use of capacitively-coupled electrodes for BCI technologies through the use of current popular BCI paradigms such as steady state visual evoked potential, P300 and sensory motor rhythm. Results Our experimental results indicate that capacitive electrode technology allows the acquisition of spontaneous EEG signals through hair with average correlation coefficient of 0.7949, 0.7946, 0.6333, 0.6549 for each capacitive electrode at O2 and 0.8433, 0.7822, 0.6253, 0.5427 for each capacitive electrode at C4. Although signal quality is lower and the movement artifacts are larger than those of conventional electrodes, SSVEP was successfully recorded through hair without spectral difference between SSVEP peaks and stimulus peaks except low stimulus frequency (5.45 Hz). P300 responses was measured with significant coefficient of determination (>0.005) except electrode (d). Sensory motor rhythm was suppressed during right hand imagery movement with log ratio value less than zero for all electrodes. Conclusions Further studies are required to apply capacitive measurement technology to uses in diagnostic EEG, but the method can currently be used for simple BCI applications.
    09/2013; 3(3):158-169. DOI:10.1007/s13534-013-0099-6
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    ABSTRACT: Fragmented sleep due to frequent awakenings represents a major cause of impaired daytime performance and adverse health outcomes. Currently, the gold standard for studying and assessing sleep fragmentation is polysomnography. Here, we propose an alternative method for real-time detection of nocturnal awakening via ballistocardiography using an unobtrusive polyvinylidene fluoride (PVDF) film sensor on a bed mattress. From ballistocardiogram, heart rate and body movement information were extracted to develop an algorithm for classifying sleeping and awakening epochs. In total, 10 normal subjects (mean age 38.7 ± 14.6 years) and 10 patients with obstructive sleep apnea (OSA) (mean age 44.2 ± 16.5 years) of varying symptom severity participated in this study. Our study detected awakening epochs with an average sensitivity of 85.3% and 85.2%, specificity of 98.4% and 97.7%, accuracy of 97.4% and 96.5%, and Cohen's Kappa coefficient of 0.83 and 0.81 for normal subjects and OSA patients, respectively. Also, sleep efficiency was estimated using detected awakening epochs and then compared with polysomnography results. Mean absolute errors in sleep efficiency were 1.08% and 1.44% for normal subjects and OSA patients, respectively. The results presented here indicate that our suggested method could be reliably applied to real-time nocturnal awakening detection and sleep efficiency estimation. Furthermore, our method may ultimately be an effective tool for long-term, home monitoring of sleep-wake behavior.
    IEEE transactions on bio-medical engineering 08/2013; 61(1). DOI:10.1109/TBME.2013.2278020 · 2.23 Impact Factor
  • Min Hye Chang, Kwang Suk Park
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    ABSTRACT: Dual-frequency steady-state visual evoked potential (SSVEP) was suggested to generate more stimuli using a few flickering frequencies for brain-computer interface. Dual-frequency SSVEP peaks at more than two frequencies-both main and harmonic frequencies. However multi-frequency recognition strategy has not been investigated for dual-frequency SSVEP. In this paper, three modified power spectral density analysis (PSDA) methods and two modified canonical correlation analysis (CCA) methods were tested for dual-frequency SSVEP classification. Three methods among the five methods used conventional features or classification techniques, and the other two methods used modified features for harmonic frequencies. As a result, CCA with novel features showed the best BCI performance. Also the use of harmonic frequencies improved BCI performance of dual-frequency SSVEP.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 07/2013; 2013:2220-2223. DOI:10.1109/EMBC.2013.6609977
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    ABSTRACT: Sleep onset latency (SOL) is an objective indicator of sleepiness and is being used clinically as a diagnostic tool for sleep deprivation. This study proposes a new and less intrusive approach to estimate SOL based on the blood pressure (BP) regulatory reflex mechanism.We hypothesized that the arterial baroreflex, one kind of reflex mechanism for BP regulation, maintains the toning-down effect sleep has on BP. The arterial baroreflex is strongly activated after the time of sleep onset in order to maintain the lowered BP by leading to an increase in heart beat interval (HBI). This observation suggests that the arterial baroreflex has a marked influence on the HBI control with the onset of sleep. As a result, a positive correlation is expected between fluctuations of BP and those of subsequent HBI after sleep onset. To investigate our hypothesis, we determined the relationship between BP and HBI using the R-J and R-R intervals measured from an electrocardiogram and a ballistocardiogram.We estimated SOL using the correlation coefficients corresponding to the relationship between fluctuations of the R-J interval and those of the subsequent R-R interval. The SOLs of ten healthy subjects [age (mean ± SD): 28.72 ± 3.21 years] were estimated using our proposed method and compared with the polysomnography data. The mean absolute error was 0.25 ± 0.35 min, corresponding to a half epoch (15 s) on average. We expect our method will be applicable as a nonintrusive and automatic SOL estimation system that does not require the use of electroencephalogram sensors.
    05/2013; 17(3):534-44. DOI:10.1109/JBHI.2013.2257816
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    ABSTRACT: Objective. Long-term electroencephalogram (EEG) monitoring broadens EEG applications to various areas, but it requires cap-free recording of EEG signals. Our objective here is to develop a capacitive, small-sized, adhesive and biocompatible electrode for the cap-free and long-term EEG monitoring. Approach. We have developed an electrode made of polydimethylsiloxane (PDMS) and adhesive PDMS for EEG monitoring. This electrode can be attached to a hairy scalp and be completely hidden by the hair. We tested its electrical and mechanical (adhesive) properties by measuring voltage gain to frequency and adhesive force using 30 repeat cycles of the attachment and detachment test. Electrode performance on EEG was evaluated by alpha rhythm detection and measuring steady state visually evoked potential and N100 auditory evoked potential. Main results. We observed the successful recording of alpha rhythm and evoked signals to diverse stimuli with high signal quality. The biocompatibility of the electrode was verified and a survey found that the electrode was comfortable and convenient to wear. Significance. These results indicate that the proposed EEG electrode is suitable and convenient for long term EEG monitoring.
    Journal of Neural Engineering 04/2013; 10(3):036006. DOI:10.1088/1741-2560/10/3/036006 · 3.42 Impact Factor

Publication Stats

1k Citations
151.25 Total Impact Points

Institutions

  • 1997–2014
    • Seoul National University
      • Department of Biomedical Engineering
      Sŏul, Seoul, South Korea
  • 2007–2013
    • Sangji University
      • • College of Health Sciences
      • • Department of Oriental Medical Engineering
      Genshū, Gangwon, South Korea
  • 2001–2013
    • Seoul National University Hospital
      • • Department of Biomedical Engineering
      • • Department of Neurosurgery
      • • Department of Nuclear Medicine
      Sŏul, Seoul, South Korea