[Show abstract][Hide abstract] 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. · 3.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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).
The Journal of international medical research. 06/2014;
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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; · 3.12 Impact Factor
[Show abstract][Hide abstract] 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.
IEEE journal of biomedical and health informatics. 11/2013; 17(6):985-93.
[Show abstract][Hide abstract] 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; · 2.15 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
IEEE journal of biomedical and health informatics. 05/2013; 17(3):534-44.
[Show abstract][Hide abstract] 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. · 3.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Objective. Brain-computer interface (BCI) technologies have been intensely studied to provide alternative communication tools entirely independent of neuromuscular activities. Current BCI technologies use electroencephalogram (EEG) acquisition methods that require unpleasant gel injections, impractical preparations and clean-up procedures. The next generation of BCI technologies requires practical, user-friendly, nonintrusive EEG platforms in order to facilitate the application of laboratory work in real-world settings. Approach. A capacitive electrode that does not require an electrolytic gel or direct electrode-scalp contact is a potential alternative to the conventional wet electrode in future BCI systems. We have proposed a new capacitive EEG electrode that contains a conductive polymer-sensing surface, which enhances electrode performance. This paper presents results from five subjects who exhibited visual or auditory steady-state responses according to BCI using these new capacitive electrodes. The steady-state visual evoked potential (SSVEP) spelling system and the auditory steady-state response (ASSR) binary decision system were employed. Main results. Offline tests demonstrated BCI performance high enough to be used in a BCI system (accuracy: 95.2%, ITR: 19.91 bpm for SSVEP BCI (6 s), accuracy: 82.6%, ITR: 1.48 bpm for ASSR BCI (14 s)) with the analysis time being slightly longer than that when wet electrodes were employed with the same BCI system (accuracy: 91.2%, ITR: 25.79 bpm for SSVEP BCI (4 s), accuracy: 81.3%, ITR: 1.57 bpm for ASSR BCI (12 s)). Subjects performed online BCI under the SSVEP paradigm in copy spelling mode and under the ASSR paradigm in selective attention mode with a mean information transfer rate (ITR) of 17.78 ± 2.08 and 0.7 ± 0.24 bpm, respectively. Significance. The results of these experiments demonstrate the feasibility of using our capacitive EEG electrode in BCI systems. This capacitive electrode may become a flexible and non-intrusive tool fit for various applications in the next generation of BCI technologies.
Journal of Neural Engineering 02/2013; 10(2):024001. · 3.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Motor imagery brain-computer interface (BCI) is a system that sends commands from human to external devices using brain activity patterns of imagination of a motor action without an actual movement. In this paper, we compared classification performance among the various combinations of motor imagery tasks, toward the multi-dimensional control of motor imagery BCI. We used EEG motor imagery dataset of 99 subjects. Common spatial patterns (CSP) and linear discriminant analysis (LDA) were applied to extract features and to classify motor imagery tasks. 10×10 fold cross validation was used to evaluate classification accuracies through large dataset. For two-class discrimination, we compared the classification accuracy of the results between combinations: both feet and one hand, and both hand and one hand. From these results, using both feet motor imagery task showed 3% higher accuracy than using both hand motor imagery task (p
Neural Engineering (NER), 2013 6th International IEEE/EMBS Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Objectives
This study was conducted 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 high-tension 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.
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 01/2013;
[Show abstract][Hide abstract] ABSTRACT: This paper introduced a method for biometric authentication using EEG signals. Especially, we focused on the performance of reproducibility for personal authentication. Four healthy subjects participated in the experiment. EEG was measured from only one bipolar channel (O1A2) during resting state with closed eyes. EEG was also recorded with same protocol from same subjects on different days to verify reproducibility (the interval between 1st and 2nd recording: 10 days or 5 months). Three features were extracted: the spectral power, the maximum power, and the frequency of maximum power in alpha band. Linear discriminant analysis was used as a classifier. The authentication accuracy for reproducibility was 98.33% with 20s data length and 100% with 50s data length.
Neural Engineering (NER), 2013 6th International IEEE/EMBS Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: As a smartphone is becoming very popular and its performance is being improved fast, a smartphone shows its potential as a low-cost physiological measurement solution which is accurate and can be used beyond the clinical environment.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:2174-7.
[Show abstract][Hide abstract] ABSTRACT: Using the Ballistocardiogram(BCG) measured on weighing scale, heart rate variability(HRV) and blood pressure were estimated. BCG was measured while subjects were on weighing scale in resting state and under the Valsalva maneuver and static exercise condition to induce the change in cardiac autonomic rhythm. Time domain, frequency domain and nonlinear HRV parameters were estimated from the measured BCG and compared with the ones calculated from ECG measured simultaneously. For blood pressure(BP) estimation, ECG was measured additionally on the feet using dry electrodes simultaneously installed on weighing scale and R-J intervals were extracted as a BP correlated parameter at every beat cycle. HRV estimation results shows the correlation higher than 0.97, and the estimated BP was similar to the measured BP with a reliable correlations.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:3789-92.
[Show abstract][Hide abstract] ABSTRACT: We propose a new method that measures skin conductance over clothes to nonintrusively monitor the changes in physiological conditions affecting skin conductance during daily activities. We selected the thigh-to-thigh current path and used an indirectly coupled 5-kHz AC current for the measurement. While varying the skin conductance by the Valsalva maneuver method, the results were compared with the traditional galvanic skin response (GSR) measured directly from the fingers. Skin conductance measured using a 5-kHz current displayed a highly negative correlation with the traditional GSR and the current measured over clothes reflected the rate of change of the conductance of the skin beneath.
Medical & Biological Engineering 07/2012; · 1.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: With the development of an implantable radio transmitter system, direct measurement of cardiac autonomic nervous activities (CANAs) became possible for ambulatory animals for a couple of months. However, measured CANAs include not only CANA but also cardiac electric activity (CEA) that can affect the quantification of CANAs. In this study, we propose a novel CEA removal method using moving standard deviation and cubic smoothing spline. This method consisted of two steps of detecting CEA segments and eliminating CEAs in detected segments. Using implanted devices, we recorded stellate ganglion nerve activity (SGNA), vagal nerve activity (VNA) and superior left ganglionated plexi nerve activity (SLGPNA) directly from four ambulatory dogs. The CEA-removal performance of the proposed method was evaluated and compared with commonly used high-pass filtration (HPF) for various heart rates and CANA amplitudes. Results tested with simulated CEA and simulated true CANA revealed stable and excellent performance of the suggested method compared to the HPF method. The averaged relative error percentages of the proposed method were less than 0.67%, 0.65% and 1.76% for SGNA, VNA and SLGPNA, respectively.
[Show abstract][Hide abstract] ABSTRACT: Sleep onset latency (SOL) provides an objective assessment of sleepiness and it also clinically useful as a sleep deprivation diagnostic tool. In this study, we suggest a new approach to estimate SOL based on the correlation between blood pressure (BP) and heart beat interval (HBI). This approach facilitates less intrusive finding of SOL as compared with currently using polysomnographic method. We hypothesized that the arterial baroreflex, one kind of reflex mechanism to regulate BP, takes a role of maintaining sleep's toning-down effect on BP. At the time of transition from full wakefulness to sleep, the toning-down effect starts to drop the BP and the arterial baroreflex is activated to maintain lowered BP by leading to increase in HBI for the elevated BP. Consequently, there is a great contribution of arterial baroreflex to HBI control. With a quantitative evaluation of the contribution, we tried to estimate SOL. For six healthy subjects (27.5 ± 3.15 years), the mean absolute error (MAE) was 0.3 ± 0.42 minutes. We expect our method can be applicable to non-intrusive and automatic SOL estimation system by not using electroencephalogram (EEG) sensors.
Biomedical and Health Informatics (BHI), 2012 IEEE-EMBS International Conference on; 01/2012
[Show abstract][Hide abstract] ABSTRACT: In this paper, the preliminary investigation for application of capacitive electroencephalogram (EEG) measurement for brain-computer interface (BCI) is described. EEG was obtained by active electrodes that very high input impedance pre-amplifier circuit was mounted on the electrodes. This method enabled EEG measurements through hair without direct contact with scalp and conductive gel applications. The presented electrode was attached to the normal usual baseball cap for nonintrusive daily or long-term use. Subject wore electrode installed baseball cap and EEG signal was measured under experimental BCI paradigms such as alpha wave, steady-state visual evoked potential, P300, auditory steady-state response and motor imagery. The results showed that further studies are still required to apply capacitive sensing methods to clinical neurosciences, however, it can be concluded that steady of the art capacitive electrode technology can be used for engineering applications using current popular BCI paradigms.
Systems, Man, and Cybernetics (SMC), 2012 IEEE International Conference on; 01/2012
[Show abstract][Hide abstract] ABSTRACT: Heart sounds are generated by the fluctuations of blood velocity and the vibrations of cardiac structure. The auscultation of heart sounds is one of the basic tools for patient diagnosis and provides a lot of information associated with cardiovascular systems. For converting mechanical sound waves into electronic signals, PVDF (polyvinylidene fluoride) film sensor was used as heart sounds measurement device. After suited filtering process, the first (S1) and the second (S2) heart sounds components were plainly distinguished and their peak timings were closely corresponded to reference heart sounds signals measured by microphone. Lastly, there was high correlation between S1 intervals (from PVDF signals) and RR intervals (from ECG signals). So it is expected that S1 intervals can replace RR intervals. In future application, these methods have possibilities for non-intrusive heart rate estimation.