Hyun Kyoon Lim

Functional activities characteristics of shoulder complex movements: Exploration with a 3-D electromagnetic measurement system.

The high prevalence of shoulder-related dysfunction has focused increased attention on functional activity assessment. This study (1) tested the reliability of three-dimensional shoulder complex movements during four functional tasks representing different levels of task difficulty, (2) characterized the four functional tasks, and (3) examined the relationships between age and shoulder movements. Twenty-five asymptomatic subjects, all veterans aged 30-82, performed the four functional tasks. Good within-session reliability was found (movement pattern: similarity index = 0.81 to 0.97, peak values: intraclass correlation coefficients = 0.88 to 0.99). The raising arm to overhead height task (hard task) placed the greatest demand on scapular motions and humeral elevation (p < 0.005). During the functional tasks, significant correlations existed between age and scapular tipping, humeral elevation, and scapular upward rotation (r = -0.62 to 0.50, p < 0.05). Correlation results indicated that elderly subjects have a greater potential for serratus anterior muscle weakness and shoulder capsule tightness.

Neurophysiological assessment of lower-limb voluntary control in incomplete spinal cord injury

Study design:Cross-sectional retrospective study of a neurophysiological method of voluntary motor control characterization.Objectives:This study was undertaken to validate the surface electromyography (sEMG)-based voluntary response index (VRI) as an objective, quantitative, laboratory measure of spinal cord injury severity in terms of voluntary motor control disruption.Setting:VA Medical Centers in Houston and Dallas Texas, USA.Methods:A total of 67 subjects with incomplete spinal cord injury (iSCI), American Spinal Injury Association Impairment Scale (AIS)-C (n=32) and -D (n=35) were studied. sEMG recorded during a standardized protocol including eight lower-limb voluntary motor tasks was analyzed using the VRI method that relates multi-muscle activation patterns of SCI persons to those of healthy-subject prototypes (n=15). The VRI is composed of a measure of the amount of the sEMG activity (magnitude) and the distribution of activity across muscle groups compared to that of healthy subjects for each motor task (similarity index, SI). These resulting VRI components, normalized magnitude and SI, were compared to AIS clinical findings in this study. Receiver operating characteristic analysis was performed to determine the SI values best separating AIS-C and AIS-D subjects.Results:Magnitude and SI for AIS-C subjects had mean values of 0.27±0.32 and 0.65±0.21, respectively. Both parameters were significantly larger in the AIS-D subjects (0.78±0.43 and 0.93±0.06), respectively (P<0.01). An SI value of 0.85 was found to separate AIS-C and AIS-D groups with a sensitivity of 0.89 and a specificity of 0.81. Further, the VRI of each leg strongly correlated with the respective AIS motor score (0.80, r<0.01).Conclusions:In the domains of voluntary motor control, the sEMG-based VRI demonstrated adequate face validity and sensitivity to injury severity as currently measured by the AIS.Sponsorship:Veterans Affairs Medical Center.

Usefulness of Magnetocardiogram to Detect Unstable Angina Pectoris and Non-ST Elevation Myocardial Infarction

Electrophysiologic information as well as anatomic information to detect coronary artery disease is important for accurate diagnosis. A diagnostic tool that can detect patients with unstable angina pectoris (UAP) or non-ST elevation myocardial infarction (NSTEMI) with severe stenosis would be beneficial for patients and clinicians. Magnetocardiography has been recognized as a noncontact, noninvasive, fast tool to detect ischemic coronary artery disease and provide direct electrophysiologic information from the heart. In this study, 10 magnetocardiographic (MCG) parameters from 4 groups, including 185 young controls, 19 age-matched controls (AMCs), 110 patients with UAP, and 83 patients with NSTEMIs, were analyzed. A 64-channel MCG system in a magnetically shielded room was used. All 10 parameters showed significant differences (p <0.001) between controls and patients with NSTEMIs, and 6 parameters showed significant differences (p <0.01) between AMCs and patients with UAP. MCG parameters significantly increased when ischemic heart conditions worsened. Of the 10 parameters, the magnetic field map was among the easiest ways to detect the severity of coronary artery disease. Abnormal magnetic field maps were observed frequently with worsening ischemic coronary artery disease (70% of patients with UAP and 92.5% of those with NSTEMIs had abnormal maps). The combination of the binary boundaries of the 10 parameters had 96.4% sensitivity and 85% specificity to detect NSTEMI. In conclusion, the MCG parameters and magnetic field maps may detect UAP and NSTEMI easily when they are considered together.

Reliability of surface electromyographic measurements from subjects with spinal cord injury during voluntary motor tasks

In this study, the reliability of surface electromyographic data (root-mean-square) for volitional motor tasks drawn from a standardized protocol was assessed. For each motor task, 5 s epochs of data were analyzed with a new method to generate a measure called the voluntary response index (VRI). The VRI consists of two components, magnitude and similarity index (SI), that were separately analyzed for repeatability. We examined three repetitions of each of 10 volitional motor tasks in 69 subjects with spinal cord injury (American Spinal Injury Association [ASIA] Impairment Scale [AIS], classifications C and D: 34 AIS-C and 35 AIS-D) for short-term (within-day) reliability. In 6 of the 69 subjects (3 each, AIS-C and AIS-D), the entire study was repeated after 1 week and results were assessed for intermediate-term (1 week apart) reliability. The reliability of the method for voluntary motor tasks was assessed by intraclass correlation coefficient (ICC), analysis of variance, coefficient of variance, and Pearsons correlation. Good reliability was found for magnitude (ICC = 0.71-0.99, Pearsons r = 0.77-0.99) and for SI (ICC = 0.65-0.96, Pearsons r = 0.72-0.93) for three repeated tests (within-day). Significant difference was found for studies completed 1 week apart for magnitude (p = 0.02) but not for SI (p = 0.57). In addition, SI showed less variation than magnitude (p < 0.001). No significant difference of magnitude and SI between tasks was observed.

Can magnetocardiography detect patients with non‐ST‐segment elevation myocardial infarction?

Background and aim. Magnetocardiography (MCG) has been proposed as a noninvasive diagnostic tool to risk‐stratify patients with myocardial infarction (MI) and ischemia. The purpose of this study is to find the MCG parameters that are sensitive enough to detect the non‐ST‐segment elevation myocardial infarction (NSTEMI) patients. Methods. MCG data were recorded and analyzed from 165 young controls (mean age = 27.2±9.0 years), 57 age‐matched controls (mean age = 55.9±10.5 years) and 83 NSTEMI patients (mean age = 59.7±11.1 years). The MCG recordings were obtained using a 64‐channel MCG system in a magnetically shielded room. Statistical analyses were performed for 24 parameters derived from QRS‐, R‐, T‐wave, and ST‐T period. Binary boundaries to detect NSTEMI patients out of control subjects were found using the receiver operating characteristic (ROC) curve for each parameter. Results. Fifteen parameters showed a significant difference (P<0.05 and P<0.01) between NSTEMI and both of the control groups. For detection of NSTEMI, the angle of the maximum current and the filed map angle on T‐wave peak showed the highest diagnostic performance from 75% to 92% including accuracy, sensitivity, specificity, positive predictive value, and negative predictive value (area under ROC curve = 0.87∼0.93). Conclusions. Our study showed that MCG has potential clinical application for detection of NSTEMI and should be further investigated.

Neurophysiological examination of the corticospinal system and voluntary motor control in motor-incomplete human spinal cord injury

This study employed neurophysiological methods to relate the condition of the corticospinal system with the voluntary control of lower-limb muscles in persons with motor-incomplete spinal cord injury. It consisted of two phases. In a group of ten healthy subjects, single and paired transcranial magnetic stimulation (TMS) of the motor cortex was used to study the behavior of the resulting motor evoked potentials (MEP) in lower-limb muscles. Interstimulus intervals (ISIs) of 15–100 ms were examined for augmentation of test MEPs by threshold or subthreshold conditioning stimuli. The second phase of this study examined eight incomplete spinal cord injured (iSCI) subjects, American Spinal Injury Association Impairment Scale C (n =5) and D (n =3) in whom voluntary motor control was quantified using the surface EMG (sEMG) based Voluntary Response Index (VRI). The VRI is calculated to characterize relative output patterns across ten lower-limb muscles recorded during a standard protocol of elementary voluntary motor tasks. VRI components were calculated by comparing the distribution of sEMG in iSCI subjects with prototype patterns collected from 15 healthy subjects using the same rigidly administered protocol, The resulting similarity index (SI) and magnitude values provided the measure of voluntary motor control. Corticospinal system connections were characterized by the thresholds for MEPs in key muscles. Key muscles were those that function as the prime-movers, or agonists for the voluntary movements from which the VRI data were calculated. Results include healthy-subject data that showed significant increases in conditioned MEP responses with paired stimuli of 15–50 ms ISI. Stimulus pairs of 75 and 100 ms showed no increase in MEP peak amplitude over that of the single-pulse conditioning stimulus alone, usually no response. For the iSCI subjects, 42% of the agonists responded to single-pulse TMS and 25% required paired-pulse TMS to produce an MEP. American Spinal Injury Association Impairment Scale component motor scores for agonist muscles, Quadriceps, Tibialis Anterior, and Triceps Surae, were significantly lower where MEPs could not be obtained (p <0.05). VRI values were also significantly lower for motor tasks with agonists that had no resting MEP (p <0.01). Therefore, the presence of a demonstrable connection between the motor cortex and spinal motor neurons in persons with SCI was related to the quality of post-injury voluntary motor control as assessed by the VRI.

Analysis of sEMG during voluntary movement-part II: voluntary response index sensitivity

In this paper, a method for analyzing surface electromyographic (sEMG) data recorded from the lower-limb muscles of incomplete spinal-cord injured (iSCI) subjects is evaluated. sEMG was recorded bilaterally from quadriceps, adductor, hamstring, tibialis anterior, and triceps surae muscles during voluntary ankle dorsiflexion performed in the supine position as part of a comprehensive motor control assessment protocol. Analysis of the sEMG centered on two features, the magnitude of activation and the degree of similarity [similarity index (SI)] of the sEMG distribution to that of healthy subjects performing the same maneuver (n=10). The analysis calculations resulted in response vectors (RV) that were compared to healthy-subject-derived prototype response vectors resulting in a voluntary response index (VRI) . Incomplete SCI subjects (n=9) were used to test the sensitivity of this analysis method. They were given supported-weight treadmill ambulation training, which is expected to improve or at least not cause a deterioration of voluntary motor control. The VRI provided evidence that the quantitative sEMG analysis method used was able to differentiate between healthy subjects and those with iSCI, characterize individual differences among iSCI subjects, and track motor control changes occurring over time.

Magnetocardiogram Difference Between Healthy Subjects and Ischemic Heart Disease Patients

Magnetocardiography (MCG) is a device to measure the weak magnetic fields generated from the heart using a superconducting quantum interference device sensor which converts magnetic flux to voltage and is the most sensitive sensor to detect magnetism. In the previous study, authors found that the values of MCG parameters of patients with non-ST-segment myocardial infarction were greater than those of age-matched controls (AMCs). In this study, we selected five different groups of patients considering their severity. We compared 10 MCG parameters recorded from 19 healthy young subjects (26.8plusmn13.4 years), 19 age-matched healthy subjects (55.4plusmn10.7), 23 stable angina patients (56.4plusmn7.6 years) with no stenosis (=0% on coronary angiogram) and normal echocardiogram, 24 unstable angina patients (61.9plusmn9.8 years) with severe stenosis (ges70%), and 20 Q-wave myocardial infarction (QMI) patients (57.3plusmn11.2 years) with severe stenosis (ges70%). To record the magnetic signals from a heart with minimal noise, a magnetically shielded room was used. The number of abnormal parameters was counted and magnetic field map (MFM) patterns were compared. As a result, young healthy subjects showed the smallest values in all 10 MCG parameters and QMI subjects showed the greatest values. Significant difference was found from dynamics parameters such as current angle, map angle, and distance dynamics between young healthy controls and AMC groups (p>0.05). No significant difference was found from AMC and stable angina groups even though parameter values of stable angina were slightly greater than those of AMC. Significant difference was found from five parameters between AMC and QMI subjects. These results are supportive to the previous analysis. In addition, the abnormal MCG parameters increased when the ischemic disease was worsened. Abnormal MFM patterns were easily found from QMI patients than stable angina pectoris. It is clear that abnormal MFM and parameters increase when the status of ischemic heart disease patients are getting worse.

Detection of non-ST-elevation myocardial infarction using magnetocardiogram: New information from spatiotemporal electrical activation map

Background and aim. Non-ST-segment elevation myocardial infarction (NSTEMI) cannot be easily detected in the emergency room. We evaluate a method to detect NSTEMI using 64-channel magnetocardiography (MCG). Methods. MCG recordings were made in 20 NSTEMI patients (aged 59.7±12.4 years), 15 young (aged 26.8±3.4 years), and 13 age-matched control subjects (aged 57.3±3.6). We evaluated three approaches to analysis, including 1) determination when individual subjects’ MCG results fell outside normal ranges for ten MCG parameters, 2) the magnetic field map at the T-wave peak (T-MFM), and 3) a pair of spatiotemporal activation graphs (STAGs) showing two projections of electrical excitation during repolarization. Results. Significant differences were found between normal controls and patients for all MCG parameters. None of the healthy controls had more than four MCG abnormal parameters, whereas 19 NSTEMI patients (95%) were abnormal in more than four parameters. STAGs and T-MFM also showed clear differences between healthy controls and NSTEMI patients. Conclusions. These results suggest that the MCG is sensitive to changes in the cardiac electrical pathway after myocardial infarction as described by these graphs and parameters, and therefore MCG may be a useful tool to detect severe ischemic patients.

Measurement of MCG in Unshielded Environment Using a Second-Order SQUID Gradiometer

In this paper, we fabricated a low-TC second-order superconducting quantum interference device gradiometer (SQUID) to measure magnetocardiography (MCG) in unshielded environment. The second-order gradiometer consists of the pickup coil and the SQUID. The pickup coil is formed with two single-turn coils and one double-turn coil. The three coils are connected in order of single-, double-, and single-turn coil. The coupling polarity of two single coils is opposite to the double-turn coil. The SQUID is based on double relaxation oscillation SQUID (DROS), which consists of a hysteretic signal SQUID, a reference junction, and shunted a relaxation circuit with a resistor and an inductor. The DROS has ten times larger flux-to-voltage transfer coefficient (~ 1 mV/Phi0) than that of the conventional SQUID. Therefore, DROS could be operated with a simple flux-locked loop circuit. The pickup coil and the SQUID were fabricated on the independent wafers and connected superconductively using an Nb wire. The overall size of the second-order gradiometer is 94 times 12 mm2 with a baseline of 35 mm. The average field noise was about 8 fT /radicHz at 100 Hz with the second-order gradiometer in shielded or unshielded environment. The noise level is low enough to measure MCG signals in the unshielded environment. Finally, we measure the MCG in shielded and unshielded environments by using the second-order gradiometer and compared the signal characteristics measured in both environments.