Patient-driven loop control for ambulation function restoration in a non-invasive functional electrical stimulation system

PURPOSE

In this study, a patient-driven loop control in a non-invasive functional electrical stimulation (FES) system was designed to restore ambulation function of patients with stroke with their residual capabilities.

METHOD

With this patient-driven loop control, patients use the electromyographic (EMG) signals from their voluntary controlled muscles in affected extremity to adjust stimulus parameters of the system. A special designed FES system generated electrical stimuli to excite the paralysed muscles through surface electrodes on the basis of the control command from the residual myoelectric signals. The EMG signals were also served as the trigger and the adjustment of stimulus parameters and thereby adding versatility of the FES system. One patient with hemiplegia was recruited to conduct clinical evaluation and treated by using the new closed-loop FES system.

RESULTS

The experimental results showed that hemiplegic could successfully control the system to restore their lost ambulation functions with the strategy of patient-driven loop control. It is revealed that the mean velocity, cadence, stride length, active ankle motion range and functional ambulation category have improved significantly from 0.22 + or - 0.17 m/s, 37.3 + or - 15.5 steps/min, 0.32 + or - 0.11 m, 10 degrees , level 2 to 0.46 + or - 0.23 m/s, 58.2 + or - 19.1 steps/min, 0.73 + or - 0.22 m, 35 degrees , level 4 respectively for the patient. A paired t-test indicated that differences in the EMG of the tibialis anterior and the gastrocnemius muscles between patient's disabled (affected-side) foot and normal (unaffected-side) foot are not significant (p > 0.05) after 12 weeks of training.

CONCLUSIONS

According to the experiment results, this patient-driven loop control can be beneficial for patient with hemiplegia to restore their ambulation functions such as dorsi-flexion and plantar-flexion. The control strategy of this study has the potential to be employed not only in the FES system but also in other assistive devices.

Dynamic evaluation of [18F]-FDG uptake in the rat brain by microPET imaging

This study aims to acquire the functional image of the rat brain, small animal positron emission tomography (microPET) with high resolution and sensitivity is adopted to assess the metabolic activity corresponding to the neuronal activity induced by the electrical stimulation of the rat tail using [18F] fluorodeoxyglucose (FDG) as the radiotracer. The microPET imaging technology can provide anatomical and functional information on neuronal activity used to analyze responses in pathway sequence relationships between the thalamus and the cerebral cortex.

Effects of noise on transient-evoked oto-acoustic emission pass/fail criteria

This study investigated the effects of noise on typical transient-evoked oto-acoustic emission (TEOAE) pass/fail criteria. Different levels of synthesised noise were added to one TEOAE signal, to determine the relationship between the signal-to-noise ratio (SNR) and typical TEOAE parameters: reproducibility, TEOAE level and corrected TEOAE level. Results showed that, with the same TEOAE signal, if the SNR decreased from 19 dB to -7 dB, the means of estimated reproducibility decreased from 97% to 7%, and the means of estimated TEOAE levels were doubled. Only the means of estimated corrected TEOAE levels were relatively insensitive to SNR. The standard deviations of all TEOAE parameter estimators increased with decreasing SNR. With these results, this study proposed that each typical TEOAE parameter alone should not be taken as the absolute pass/fail criterion. A combination of the corrected TEOAE level and the reproducibility would be better.

Electrogastrographic characteristics in patients of stomach cancer

Using a homemade electrogastrography (EGG) system, we studied the characteristics of myoelectrical rhythm in gastric cancer (GC) patients. Based on a short-term Fourier transform, recorded slow waves could be automatically analyzed to obtain the following parameters: dominant frequency/power, percent of normal rhythm (2.4-3.7 cpm), power ratio, etc. Fifty histologically confirmed GC patients (34 men, 16 women) were enrolled before surgical intervention to measure their fasting and postprandial EGG parameters for 30 min. The cancerous parameters of GC patients were then obtained postoperatively. In addition, 46 healthy subjects were enrolled for comparison. When compared to controls, GC patients had the following characteristics: absence of postprandial increase in dominant frequency (GC: 3.04 +/- 0.47 vs 3.07 +/- 0.44 cpm, NS; controls: 3.02 +/- 0.31 vs 3.21 +/- 0.25 cpm, P < 0.001), marked power response after meal (P < 0.05), and obvious power ratio (4.58 +/- 7.38 vs 2.27 +/- 2.05, P < 0.05). Multivariate analysis indicated that advanced GC was the factor responsible for the obvious dominant power enhancement after meal (P < 0.05). Other demographic, clinical, and cancerous factors did not influence EGG parameters. We conclude that apparent arrhythmia is not encountered in GC patients, although they mainly exhibit obvious postprandial power response. Advanced GC is likely responsible for this power enhancement on EGG recording.

Review of telemedicine projects in Taiwan

Taiwan is a heavily populated country, with a small land area and many mountains and isolated islands. Because medical resources are unequally distributed, high quality accessible medical care is a major problem in rural areas. Medical personnel are unwilling to practice in rural areas because of fear of isolation from peers and lack of continuing medical education (CME) in those areas. Telemedicine provides a timeless and spaceless measure for teleconsultation and education. The development of telemedicine in Taiwan began under the National Information Infrastructure (NII) Project. Distance education and teleconsultation were the first experimental projects during the initiation research stage. The cost and effectiveness of the hardware and network bandwidth were evaluated. In the promotion research stage, applications in different medical disciplines were tested to promote multipoint videoconference, electronic journals and VOD. Investigation of user satisfaction put on more emphasis on improving application functions. In 1998, a new Cyber Medical Center (CMC) international collaboration project was begun, integrating technologies of multimedia, networking, database management, and the World Wide Web. The aim of the CMC is to create a multimedia network system for the management of electronic patient records, teleconsultation, online continuing medical education, and information services on the web. A Taiwan mirror site of Virtual Hospital and two international telemedicine trials through Next Generation Internet (NGI) were done at the end of 1998. In the future, telemedicine systems in Taiwan are expected to combine the Internet and broadband CATV, ADSL, and DBS networking to connect clinics, hospitals, insurance organizations, and public health administrations; and, finally, to extend to every household.

A radio controller using speech for the blind

This article describes a low-cost, portable real-time DSP-based speech controller system to provide radio interface control command applications for the blind. The system recognizes spoken Mandarin Chinese words on a DSP chip (TMS320C31) using a hidden Markov model. The function of the radio set, which includes a tuner, tape, and compact disc, were evaluated under both noisy and noiseless environments. Four subjects took part in the experiment and achieved 83 and 90% mean recognition rates under noisy and noiseless conditions, respectively. In addition, because this system is based on a DSP chip, it can easily be programmed to execute speaker-independent algorithms.

The development of a closed-loop controlled functional electrical stimulation (FES) in gait training

A closed-loop functional electrical stimulation (FES) system is developed to provide hemiplegic patients with a real-time stimulation to their muscles to prevent the drop-foot and the quadriceps weakness from happening during gait training. The FES is controlled by position sensors (ps) and triggered by footswitches (f) with real-time feedback. As the FES receives the signals from these sensors, it adjusts and outputs an optimum set of stimulation parameters automatically. One hemiplegic patient was recruited to conduct clinical evaluation and treated by using the new closed-loop FES system. It was revealed that the mean velocity, cadence, stride length, active ankle motion range, and functional ambulation category (FAC) improved significantly from 0.12 +/- 0.07 ms-1, 40.3 +/- 18.3 steps min-1, 0.35 +/- 0.10 m, 15 degrees, level 2 to 0.42 +/- 0.23 ms-1, 68.2 +/- 19.0 steps min-1, 0.70 +/- 0.22 m, 40 degrees, level 4 respectively for the patient. A paired t-test indicated that differences in the electromyography (EMG) of the tibialis anterior and the quadriceps muscles between the patient's disabled (affected side) foot and normal (unaffected side) foot are not significant (p > 0.05) after 12 weeks of training. It is concluded that this new closed-loop FES system is capable of providing this hemiplegic patient with restoration to regular walking after appropriate gait training. Future studies, including randomized-controlled study, should be implemented to document the efficacy of this system.

Impaired postprandial gastric myoelectrical activity in Chinese patients with nonulcer dyspepsia

Using a homemade electrogastrography (EGG) system, we studied the characteristics of the myoelectrical rhythm in Chinese patients with nonulcer dyspepsia (NUD). Based on short-term Fourier transformation, recorded slow waves could be automatically analyzed to obtain the following parameters: dominant frequency/power, percent of normal frequency (2-4 cpm), power ratio, etc. EGG parameters, Helicobacter pylori status, histological examination of gastric mucosa, and dyspeptic symptoms were recorded in 27 NUD patients. Compared to 32 healthy controls, the Chinese NUD patients had abnormal postprandial EGG parameters including a lower percentage of regular 2-4 cpm slow waves (70.10 +/- 2.97% vs 79.08 +/- 2.95%, P < 0.05), a lower level of increment of dominant power (0.62, +/- 0.91 vs 3.76 +/- 0.58 dB, P < 0.05), lower power ratio (1.42 +/- 0.28 vs 2.79 +/- 0.39, P < 0.05) and a higher instability coefficient (0.36 +/- 0.03 vs 0.26 +/- 0.03, P < 0.05). However, Helicobacter pylori infection and its associated gastritis did not influence any EGG parameters in NUD patients. Six main dyspeptic symptoms and total symptom score had no correlation with any EGG parameters. In conclusion, Chinese NUD patients may have abnormal postprandial stomach myoelectrical activity, but these EGG abnormalities are not a direct result of Helicobacter pylori infection and its related gastritis and do not contribution to the dyspeptic symptoms.

Real-time display of the stomach slow wave and its parameters in a newly designed electrogastrographic system

We designed a new three-channel electrogastrographic (EGG) system, which was easily operated on the Windows 95 platform and could automatically provide slow wave parameters. The purpose of the present study was to test its reliability and accuracy in clinical recording. The system included a signal acquisition device assembled on a printed circuit board. Recorded myoelectrical signals were filtered, amplified, digitized, and transmitted via this device into a notebook personal computer (PC). Based on the short-term Fourier transform the software could transfer the time domain of the signal into the frequency domain. Real-time displayed slow wave parameters, including dominant frequency/power, percent of normal frequency (2-4 cpm), instability coefficient in frequency/power, and power ratio, were automatically renewed every 64s. Twenty healthy subjects (M/F, 12/8; age, 23-51 years) were enrolled to measure both fast and postprandial myoelectrical activities for each 30-min recording. Our results indicated that meal ingestion significantly increased dominant frequency (3.15+/-0.20 vs 3.23+/-0.23 cpm; P < 0.05) and power (26.1+/-3.8 vs 28.4+/-3.9 dB; P < 0.05). The power ratio of the meal effect was 2.02+/-2.07. Other parameters, including instability coefficient and percent of normal frequency, remained similar despite food ingestion. This newly designed EGG system is acceptable for clinically measuring gastric myoelectrical activity; the real-time display of many EGG parameters is an advantage with this new system.

Theoretical study of convergent ultrasound hyperthermia for treating bone tumors

This study investigates the optimal external parameters for using an ultrasound applicator for treating bone tumors. This system utilized spherically arranged applicators such as scanned focused ultrasound, and spherically focused multielement applicators. The power deposition pattern is modeled as geometric gain with exponential attenuation. The specific absorption rate ratio (SARR) criteria have been used to determine the proper heating domain of ultrasound driving frequency and therapeutic tumor diameter. The results demonstrate that the optimal driving frequency depends on tumor depth, ultrasound absorption of bone marrow, and diameter of bone, but it is independent of the acoustic window area and SARR. The treatable diameter of bone tumor increased when the absorption ratio of bone marrow to tumor, acoustic window of surface skin, and diameter of bone were elevated. However, the treatable diameter of bone tumor decreased when muscle thickness, SARR of bone tumor site to the surface skin, bone marrow, and bone declined. To deliver the ultrasound energy into the tumor site and to avoid the potential damage to the normal tissue as much as possible, the specific absorption rate (SAR) in the bone tumor site has to be three times higher than that in the surface skin, tumor/marrow, and marrow/bone interfaces. The temperature distributions can verify the SARR criteria in this model. This study provides the information for choosing the optimal operating frequency of the ultrasound transducer and the acoustic window on the skin surface, and for designing the ultrasound applicator for clinical implementation.

A novel speech controller for radio amateurs with a vision impairment

This paper describes a portable speech controller system for persons with a vision impairment to adjust the channel frequency of a radio set via speech commands. The speech commands are recognized on a general-purpose digital signal processor using a hidden Markov model (HMM), and are used to remotely control radio channel changes.

The new design of an infrared-controlled human-computer interface for the disabled

This paper reports on the development of an eyeglass- type infrared (IR)-controlled computer interface for the disabled. This system may serve to assist those who suffer from spinal cord injuries or other handicaps to operate a computer. This system is comprised of three major components: 1) an infrared transmitting module, 2) an infrared receiving/signal-processing module, and 3) a main controller, the Intel-8951 microprocessor. The infrared transmitting module utilizes tongue-touch circuitry which is converted to an infrared beam and a low power laser (<0.1 mW) beam. The infrared receiving/signal-processing module, receives the infrared beam and fine tunes the unstable infrared beam into standard pulses which are used as control signals. The main controller is responsible for detecting the input signals from the infrared receiving/signal-processing module and verifying these signals with the mapping table in its memory. After the signal is verified, it is released to control the keys of the computer keyboard and mouse interface. This design concept was mainly based on the idea that the use of an infrared remote module fastened to the eyeglasses could allow the convenient control of the input motion on the keys of a computer keyboard and mouse which are all modified with infrared receiving/signal-processing modules. The system is designed for individuals with spinal cord injuries and disabled in which the subjects' movement are severely restricted. The infrared transmitting module can be easily mounted on eyeglasses or artificial limbs.

Recent advances in telemedicine

With continuing advances in information technology, the applications of computers in medicine are increasing rapidly. Modern information technology not only affects the delivery of health care, but also significantly influences the doctor-patient relationship. Since the 1990s, technologic developments in high-bandwidth telecommunications systems and digitizing devices have led to a surge of interest in telemedicine. In recent years, the Internet, with its powerful penetration and scalability, has become an increasingly popular medical information resource and a new platform for telemedicine. The impact of modern technology on the advancement of telemedicine in Taiwan started with the 1995 National Information Infrastructure project, which uses networks of different bandwidths for teleconsultation and distance education programs. In 1998, National Taiwan University and Taipei Medical College in Taiwan, and the University of Pittsburgh and the University of Iowa in the USA, began cooperation on a new Cyber Medical Center (CMC) project that integrates the technologies of multimedia, database management, a multiple-site videoconferencing system, and the World Wide Web. The aim of the CMC is to create a multimedia network system for the management of electronic patient records, teleconsultation, online continuing medical education, and information services on the Web. In the future, telemedicine systems in Taiwan are expected to combine the Internet and cable television to connect clinics, hospitals, insurance organizations, and public health administrations; and, finally, to extend health services to every household.

Optimal configuration of multiple-focused ultrasound transducers for external hyperthermia

External ultrasound hyperthermia is considered to be a very flexible modality for heating deep-seated tumors owing to its penetration and focusing ability. However, using this flexibility requires that many complicated, interacting decisions be made to obtain optimal treatment. This paper presents the feasibility of arranging multiple-focused ultrasound transducers to produce an appropriate heating pattern for a specific treatment, based on the optimal scan parameters obtained from an optimization algorithm. The variable scan parameters of the heating system optimized are the transducer tilt and rotation angles, focal depth, scan radius, and output acoustical power. After obtaining the optimal scan parameters, multiple transducers are systematically arranged according to these scan parameters. Three-dimensional ultrasound power deposition and temperature distribution for a specific treatment are calculated for this multiple ultrasound transducer system. A more uniform temperature distribution in the treatment region for a large, highly perfused tumor can be achieved by scanning the system with respect to the central scan axis and/or swinging the transducers inwards and outwards. The maximum heating depth of focused ultrasound transducers used in this heating system is also studied. Simulation results demonstrate that the optimal arrangement of this multiple-focused ultrasound transducer system is highly promising for heating deep, large, and highly perfused tumors.

Isokinetic elbow joint torques estimation from surface EMG and joint kinematic data: using an artificial neural network model

Because the relations between electromyographic signal (EMG) and anisometric joint torque remain unpredictable, the aim of this study was to determine the relations between the EMG activity and the isokinetic elbow joint torque via an artificial neural network (ANN) model. This 3-layer feed-forward network was constructed using an error back-propagation algorithm with an adaptive learning rate. The experimental validation was achieved by rectified, low-pass filtered EMG signals from the representative muscles, joint angle and joint angular velocity and measured torque. Learning with a limited set of examples allowed accurate prediction of isokinetic joint torque from novel EMG activities, joint position, joint angular velocity. Sensitivity analysis of the hidden node numbers during the learning and testing phases demonstrated that the choice of numbers of hidden node was not critical except at extreme values of those parameters. Model predictions were well correlated with the experimental data (the mean root-mean-square-difference and correlation coefficient gamma in learning were 0.0290 and 0.998, respectively, and in three different speed testings were 0.1413 and 0.900, respectively). These results suggested that an ANN model can represent the relations between EMG and joint torque/moment in human isokinetic movements. The effect of different adjacent electrode sites was also evaluated and showed the location of electrodes was very important to produce errors in the ANN model.

The Homothorax homeoprotein activates the nuclear localization of another homeoprotein, extradenticle, and suppresses eye development in Drosophila

The Extradenticle (Exd) protein in Drosophila acts as a cofactor to homeotic proteins. Its nuclear localization is regulated. We report the cloning of the Drosophila homothorax (hth) gene, a homolog of the mouse Meis1 proto-oncogene that has a homeobox related to that of exd. Comparison with Meis1 finds two regions of high homology: a novel MH domain and the homeodomain. In imaginal discs, hth expression coincides with nuclear Exd. hth and exd also have virtually identical, mutant clonal phenotypes in adults. These results suggest that hth and exd function in the same pathway. We show that hth acts upstream of exd and is required and sufficient for Exd protein nuclear localization. We also show that hth and exd are both negative regulators of eye development; their mutant clones caused ectopic eye formation. Targeted expression of hth, but not of exd, in the eye disc abolished eye development completely. We suggest that hth acts with exd to delimit the eye field and prevent inappropriate eye development.

Single-beat estimation of the ventricular pumping mechanics in terms of the systolic elastance and resistance

An elastance-resistance model has long been used to assess the systolic mechanical behavior of the ventricular pump under an in situ, open-chest experiment. However, there is difficulty in the clinical application of such a model because of the required isovolumetric signal that is obtained by occluding the ascending aorta in diastole. In this study, we determine the characteristics of an elastance-resistance model in the absence of isovolumeric measurement to quantify the physical properties of the left ventricle. A high-fidelity multisensor catheter was used to record the left ventricular pressure and ascending aortic flow in nine anesthetized, closed-chest dogs. The isovolumetric pressure was estimated from the instantaneous pressure of an ejecting contraction by a curve-fitting technique. Thus, the parameters in the characterization of systolic pumping mechanics could be inferred by the use of fitting this elastance-resistance model. The results showed that the maximal systolic elastance was 7.3 +/- 2.8 mmHg and theoretical maximum flow was 494 +/- 194 ml s-1. These data were compatible with other reports in the literature. Moreover, in every dog studied the maximal systolic elastance was smaller than the end-systolic elastance which was determined by using the end-systolic pressure-volume relation. We suggested that an elastance-resistance model with the estimated isovolumetric pressure has the potential to measure the intrinsic systolic mechanics of the left ventricle in a closed-chest cardiovascular system.

The effect of electrode arrangement on spectral distance measures for discrimination of EMG signals

The proper electrode placement in applying cepstral coefficients for electromyogram (EMG) signature discrimination was investigated. We measured EMG signals of different motions with two electrode arrangements simultaneously. Electrode pairs were located separately on dominant muscles (S-type arrangement) and closely in the region between muscles (C-type arrangement). The application of the cepstral method to signals derived from a C-type arrangement did not achieve the same discrimination as with a S-type arrangement. We used a simplified model to elucidate the poor performance in C-type signals. The bandwidth of signals obtained from S-type placement is wider than that from C-type. Narrower bandwidth decreases the importance of the more discriminative parts for both autoregressive (AR) and cepstral methods. The cepstral method is more sensitive to such variation, so the degradation in performance is more serious for the cepstral method. Second, the amplitude of C-type signal is lower than the S-type; therefore, the C-type signal is more sensitive to the disturbance of noise, especially in the high-frequency band. As high-frequency noise increases, the spectral difference between different EMG signals is gradually dominated by the low-frequency part, which is more informative. Thus, the performances of both methods are improved with increasing high-frequency noise. The improving rate of the AR method is faster than the cepstral method; therefore, its discriminative efficiency may exceed the cepstral method with C-type arrangement.

Adaptive control of arterial blood pressure with a learning controller based on multilayer neural networks

We discuss a two-model multilayer neural network controller for adaptive control of mean arterial blood pressure (MABP) using sodium nitroprusside. A model with an autoregressive moving average (ARMA), representing the dynamics of the system, and a modified back-propagation training algorithm are used to design the control system to meet specified objectives of design (settling time and undershoot/overshoot) and clinical constraints. The controller is associated with a weighting-determinant unit (WDU) to determine and update the output weighting factor of the parallel two-model neural network for adequate control action and a control-signal modification unit (CMU) to comply with clinical constraints and to suppress the effect of adverse noise and to improve the WDU performance. Extensive computer simulations indicate satisfactory performance and robustness of the proposed controller in the presence of much noise, over the full range of plant parameters, uncertainties, and large variations of parameters.

Dynamic aspects for interislet synchronization of oscillatory insulin secretions

How are the oscillatory insulin secretions from numerous islets synchronized to result in an identifiable oscillation? We postulated that a sudden increase in glucose concentration could best account for the interislet synchronization. The perifusion with two parallel chambers each containing 100 islets from the same rat was performed. The glucose concentrations of two chambers were simultaneously increased from 100 to 300 mg/dl in step function to examine the synchronizing efficacy. Synchrony and regularity of insulin oscillation were evaluated by cross-correlation and/or power spectral analysis. Although the insulin had been in stable oscillation, we found that the synchrony between two chambers and the regularity of each chamber were still significantly improved after a sudden increase in glucose level. However, the improved synchrony and regularity were transient. They gradually slid toward a less rigorous condition in a 15-h long-term perifusion. We suggested that the interislet synchronization of oscillatory insulin secretions could be improved by a sudden increase in glucose level. The insulin pulses were therefore enhanced to present their physiological effects.

A neuro-control system for the knee joint position control with quadriceps stimulation

A neuro-control system was designed to control the knee joint to move in accordance with the desired trajectory of movement through stimulation of quadriceps muscle. This control system consisted of a neural controller and a fixed parameter proportional-integral-derivative (PID) feedback controller, which was designated as a neuro-PID controller. A multilayer feedforward time-delay neural network was used and trained as an inverse model of the functional electrical stimulation (FES)-induced quadriceps-lower leg system for direct feedforward control. The training signals for neural network learning were obtained from experimentation using a low-pass filtered random sequence to reveal the plant characteristics. The Nguyen-Widrow method was used to initialize the neural connection weights. The conjugate gradient descent algorithm was then used to modify these connection weights so as to minimize the errors between the desired outputs and the network outputs. The knee joint angle was controlled with only small deviations along the desired trajectory with the aid of the neural controller. In addition, the PID feedback controller was utilized to compensate for the residual tracking errors caused by disturbances and modeling errors. This control strategy was evaluated on one able-bodied and one paraplegic subject. The neuro-PID controller showed promise as a position controller of knee joint angle with quadriceps stimulation.

Exponentially tapered T-tube model in the characterization of arterial non-uniformity

There is no question that geometric and elastic tapering is the rule of the nature of the mammalian arterial system. In this investigation, we determine the role of an exponentially tapered T-tube model to characterize the non-uniform nature and physical properties of the vasculature. The tapering feature could be inferred to show a connection between characteristic impedance at the distal of the tube and that at the entrance of the tube. Pulsatile pressure and flow signals of the ascending aorta were measured in 12 closed-chest, anesthetized dogs. This non-uniform T-tube model fits the measured aortic pressure waveform well. The mathematical and experimental model impedance spectra are similar. In the basal state, the distal characteristic impedance is 9.5% higher than the input characteristic impedance. The input characteristic impedance estimated in the model is compatible with that calculated by averaging high-frequency moduli of impedance data points obtained from the ratio of the corresponding harmonics of pressure and flow. Furthermore, the exponentially tapered T-tube model has a close estimate in wave transit time when compared with that computed by the impulse response of the filtered aortic input impedance. These data suggest that inclusion of tube tapering improves the mathematical model so that it is capable of characterizing the non-uniform nature of the arterial system. We conclude that the non-uniform properties of wave-transmission paths play an important role in governing the behavior of an asymmetric T-tube for the representation of the arterial system.

Real-time implementation of electromyogram pattern recognition as a control command of man-machine interface

The purpose of this study was to develop a real-time electromyogram (EMG) discrimination system to provide control commands for man-machine interface applications. A host computer with a plug-in data acquisition and processing board containing a TMS320 C31 floating-point digital signal processor was used to attain real-time EMG classification. Two-channel EMG signals were collected by two pairs of surface electrodes located bilaterally between the sternocleidomastoid and the upper trapezius. Five motions of the neck and shoulders were discriminated for each subject. The zero-crossing rate was employed to detect the onset of muscle contraction. The cepstral coefficients, derived from autoregressive coefficients and estimated by a recursive least square algorithm, were used as the recognition features. These features were then discriminated using a modified maximum likelihood distance classifier. The total response time of this EMG discrimination system was achieved about within 0.17 s. Four able bodied and two C5/6 quadriplegic subjects took part in the experiment, and achieved 95% mean recognition rate in discrimination between the five specific motions. The response time and the reliability of recognition indicate that this system has the potential to discriminate body motions for man-machine interface applications.

A comparative analysis of various EMG pattern recognition methods

Identification of motions of the neck and shoulders using the electromyographic (EMG) signal was investigated in this study. Three discrimination methods, the Euclidean distance measure (EDM), the weighted distance measure (WDM) and the modified maximum likelihood method (MMLM), were used to compare the conventional autoregressive (AR) and cepstral coefficients with closely positioned (C-type) and separately located (S-type) electrode arrangements. Surface electrodes were bilaterally located on and between the sternocleidomastoid and the upper trapezius muscles. The EMG signals obtained during 20 repetitions of 10 motions were analyzed for each subject. Results from nine subjects showed that the mean recognition rate of the cepstral coefficients was at least 5% better than that of the AR coefficients for the S-type signals, while the improvement was less obvious for the C-type signals. The MMLM obtained the best discrimination results of the three discrimination methods. The S-type signals achieved higher recognition rates than the C-type signals in most cases. Among the various combinations of feature sets, classifiers and electrode arrangements proposed in this study, the combination of the cepstral coefficients and the MMLM with the S-type arrangement achieved the best discrimination efficiency. The proper choice of five of 10 motions raised the recognition rate to more than 97%.

Microcomputer-based pulse stimulator

A low-cost PC-based 2-channel stimulator was designed. This device can generate regular current pulses for many neuroscience experiments. It can also generate irregular pulses for nerve stimulation, thus could possibly avoid the problem of sensitization or habituation in the central nervous system. The stimulation frequency (can be < 0.0005 Hz) and pulse duration (5 microseconds to 65 ms) of this device can be programmed by an interactive user interface. Furthermore, the output current (0-10 mA) can be continuously varied and was optically isolated to minimize stimulus artifact. Moreover, features such as low-power consumption (0.2 mA of a 9 V battery) and high-compliance output (> 120 V) could accommodate the stimulator for widespread applications. A trial of nerve stimulation was illustrated besides the electrical specifications of the stimulator.

Impedance and wave reflection in arterial system: simulation with geometrically tapered T-tubes

The aortic input impedance is simulated by an asymmetric T-tube model loaded with complex loads. A geometric tapering is incorporated to represent the vasculature, assuming a triangular distribution of the wave transmission paths. Parametric analyses using physiological data demonstrate that the predicted impedance and reflection coefficient spectrum (RCS) closely mimic the experimental data. The simulation also reveals several significant features. As diameter tapering can minimise the presence and influence of wave reflections, the impedance modulus stays relatively constant with two distinct minima. The frequency of first minimum of impedance modulus is evidence of the tube elasticity and load compliance in the lower extremity, and the frequency of second minimum is evidence of those in the upper extremity. The high-frequency portion of the impedance modulus is affected by the tube elasticity, but not by the load compliance. The impedance spectrum at higher frequencies shows no notable fluctuations corresponding to a decrease in blood or wall viscosity. Furthermore, the low-frequency range in RCS is dominated by the longer lower body tube, and the high-frequency range by the shorter upper body tube. This geometrically tapered T-tube is considered a more natural model for the description of the systemic arterial system.

The application of cepstral coefficients and maximum likelihood method in EMG pattern recognition

A new technique for classifying patterns of movement via electromyographic (EMG) signals is presented. Two methods (conventional autoregressive (AR) coefficients and cepstral coefficients) for extracting features from EMG signals and three classification algorithms (Euclidean Distance Measure (EDM), Weighted Distance Measure (WDM), and Maximum Likelihood Method (MLM)) for discriminating signals representative of broad classes of movements are described and compared. These three classifiers are derived from Bayes classifier with some assumptions, the relationship among them is discussed. The conventional MLM is modified to avoid heavy matrix inversion. Six able-bodied subjects with two pairs of surface electrodes located on bilateral sternocleidomastoid and upper trapezius muscles were studied in the experiment. The EMG signals of 20 repetitions of 10 motions were analyzed for each subject. Experimental results showed that mean recognition rate of the cepstral coefficients was at least 5% superior to that of the AR coefficients. The improvement achieved by the cepstral method was statistically significant for all the three classifiers. Reasons for the superiority of cepstral features were investigated from the feature space and frequency domain, respectively. The cepstral coefficients owned better cluster separability in feature space and they emphasized the more informative part in the frequency domain. The discrimination rate of the MLM was the highest among three classifiers. Incorporation of the cepstral features with the MLM could reduce the misclassification rate by 10.6% when compared with the combination of AR coefficients and EDM. Proper choice of five of ten motions could further raise the recognition rate to more than 95%.

Source localization of averaged and single EEG spikes using the electric dipole model

A scheme for localizing the epileptic focus is proposed. The scheme is on the basis of a model with an electric dipole inside a four-layer inhomogeneous spherical model of head and utilizes a nonlinear programming algorithm applying the gradient projection method. Various initial estimates are used to prove the stability of the implemented dipole model. Fourteen single spike data and the averaged spike data are used to localize the epileptic focus. The results of the usage of the averaged spike data show that the dipole position is compatible with visual inspection of experienced clinical physicians. The results of the usage of the single spike show that 11 of the 14 single spikes have dipole locations near the result of the averaged spike but the estimated dipole moments differ markedly from one another. The localization results of the other three single spikes show that the dipole position is strongly affected by the background EEG. This kind of interference generally causes the eccentricity of the dipole to deviate from its anatomically meaningful value. According to our results, the electric dipole model is concluded to be valuable for the clinical application of localizing epileptic foci.

Evaluation of parametric methods in EEG signal analysis

In this paper, a well designed database, considering statistical characteristics and including all types of Electroencephalogram (EEG) is built. 900 EEG segments, each with a short interval (1.024 sec) in this database are clustered into eight classes. Three tests of white noise for evaluating the efficiency of autoregressive (AR) and autoregressive-moving average (ARMA) models are proposed. The Akaike information criterion (AIC) is used for determining orders of AR and ARMA models. The AR model requires a higher model order (8.67 on the average) than the ARMA model (6.17 on the average). However, it is found that about 96% of the 900 segments can be efficiently represented by the AR model, and only about 78% of them can be efficiently represented by ARMA model. We therefore conclude that the AR model is preferred for estimating EEG signals.

Impaired left ventricular relaxation and arterial stiffness in patients with essential hypertension

1. This study was designed to determine how left ventricular relaxation function in patients with essential hypertension is impaired by arterial haemodynamic load that is increased in early ejection phase. These patients did not suffer from cardiac hypertrophy or disturbed coronary perfusion. We used a high-fidelity multisensor catheter to record pressure and flow signals in the ascending aorta. The timing and magnitude of wave reflection were obtained by decomposing the measured waves into their forward and backward components. Radionuclide angiography was employed to obtain the time-activity curve. The left ventricular relaxation function was assessed by analysing the time-activity curve, which was filtered using Fourier expansion with the number of harmonics for minimum error. 2. In comparison with age-matched normotensive subjects (seven subjects with mean blood pressure 97 mmHg), hypertensive subjects (seven subjects with mean blood pressure 138 mmHg) had a shorter backward wave arrival time (193 +/- 26 versus 258 +/- 35 ms) and a higher reflection factor (0.58 +/- 0.12 versus 0.42 +/- 0.07). Isovolumic relaxation period was prolonged in hypertensive subjects (118 +/- 19 versus 90 +/- 19 ms). There was an inverse correlation between isovolumic relaxation period and backward wave arrival time in all 14 subjects (r = -0.67, P < 0.05). In contrast, there were no significant differences in cardiac output and time to peak ejection rate between the two groups. 3. Our analyses revealed that early return of the enhanced wave reflection may profoundly impair left ventricular relaxation function in patients with hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

The correlation of cardiac mass with arterial haemodynamics of resistive and capacitive load in rats with normotension and established hypertension

In hypertensive animals and humans, cardiac hypertrophy may occur as a consequence of an external load on the heart. Several studies have suggested that the non-pulsatile components of arterial haemodynamics, such as arterial pressure and vascular resistance, do not adequately represent the ventricular afterload and are not well correlated with the degree of cardiac hypertrophy (CH). The present study was undertaken to analyse the correlation between the degree of CH and various haemodynamic parameters in the spontaneously hypertensive rat (SHR) with established hypertension. A total of 36 SHRs (6-8 months) with a tail-cuff pressure above 190 mm Hg were used. Control data were obtained from 32 age-matched normotensive Wistar Kyoto rats (WKY). Animals were anaesthetized with pentobarbitone sodium (40 mg/kg i.p.) and artificially ventilated with a respirator. A Millar catheter with a high-fidelity pressure sensor was used to record the aortic pressure and an electromagnetic flow transducer to monitor the aortic flow. The pressure and flow signals were subjected to Fourier transformation for the analysis of the arterial impedance spectrum. The left ventricular weight-to-body weight ratio (LVW/BW) was taken as a measure of the degree of CH. The measured haemodynamic parameters in these anaesthetized, open-chest SHRs were systolic pressure (SP) (mean +/- SE) 172 +/- 4 mm Hg, diastolic pressure (DP), 120 +/- 3 mm Hg, pulse pressure (PP) 52 +/- 2 mm Hg, peripheral resistance (Rp) 344,032 +/- 8,012 dyne.s.cm-5, characteristic impedance (Zc) 6,442 +/- 313 dyne.s.cm-5, the impedance modulus at the first harmonic (Z1) 26,611 +/- 1,061 dyne.s.cm-5, mean arterial compliance (Cm) 0.87 +/- 0.04 microliter/mm Hg and LVW/BW 3.092 +/- 0.026 mg/g.(ABSTRACT TRUNCATED AT 250 WORDS)

Exponentially tapered t-tube model of systemic arterial system in dogs

This study determines the role of an asymmetric T-tube model as a representation of arterial mechanical properties. The model consists of two non-uniform tubes connected in parallel. The non-uniform properties of each tube include geometric and elastic tapering and each tube terminates in a complex load. Pulsatile pressure and flow velocity of the ascending aorta were measured in 10 closed-chest, anaesthetized dogs. An exponentially tapered transmission line is used to describe the non-uniform properties of the vasculature. The phase constant is a function of position along the path length due to geometric and elastic tapers. This non-uniform T-tube model makes it possible to fit the measured pressure waveform in the ascending aorta. Model parameters could be estimated and used to interpret the physical properties of the arterial system. The mathematical and experimental model impedance spectra are similar. There is a close correspondence between the impedance parameters derived from the non-uniform T-tube model and values computed from measurements on dogs. The results suggest that inclusion of tube tapering improves the mathematical model so that it closely represents the experimentally derived arterial impedance in closed-chest dogs. We conclude that the non-uniform properties of wave-transmission paths may play an important role in governing the behaviour of an asymmetric T-tube for the description of the arterial system.

Evaluation of left ventricular functional status using thermodynamic indices

Conventional methods to assess cardiac contractility have been focused on the mechanical properties of the myocardium. Many of these have suffered from theoretical and practical drawbacks. In this study, we have attempted to evaluate the left ventricular contractile status using the thermodynamic principle and compared these indices with the conventional index (dP/dt). A total of 8 mongrel dogs were anesthetized and artificially ventilated. A Millar catheter with high-fidelity multiple sensors was inserted into the aorta to record the simultaneous changes in aortic flow and pressure waves. Cardiac inotropy was increased by graded doses (2-32 micrograms/kg/min) of dobutamine. Angiotensin injection (100-300 micrograms) to achieve a blood pressure elevation of 30 mmHg was employed for afterload augmentation. Preload was increased by rapid infusion of 6% dextran solution (20 ml/kg). Several thermodynamic parameters were calculated at steady state during the control period and after drug interventions. These included power-averaged rate of power density generation (ARPD), peak ejection rate of change of power (PREP), energy-averaged power density (APD) and frequency-normalized ARPD (FARPD). PREP and APD were unchanged by afterload increment while FARPD, ARPD and dP/dt decreased significantly with an increase in afterload, ARPD was highly sensitive to an increased preload (p < 0.001), and PREP was also changed significantly by an increase in preload. dP/dt was boarderlinely affected by Dextran infusion (p = 0.05), and APD was independent of preload (P > 0.05). Inotropic stimulation increased ARPD, PREP, APD, FARPD and dP/dt by 139.0 +/- 48.0%, 98.0 +/- 51.4%, 74.0 +/- 49.7%, 60.0 +/- 30.4% and 44.6 +/- 10.4%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The filter properties of the arterial beds of organs in rats

The frequency properties of arterial beds in organs were studied by temporarily ligating the renal, the gastric, the splenic or the superior mesenteric arteries of rats. Blood-pressure waves of the tail arteries were recorded before and during the ligations, and were analysed by Fourier's transformation. Their frequency spectra have been found to change profiles following specific patterns with the ligations of different arteries. The results were significant with regard to the frequency selectivities of the organic arterial beds. Such frequency properties can be clearly explained when the circulation system is viewed as an electrical circuit network in which the organic arterial beds work as filters.

Effects of nifedipine on systemic hydraulic vascular load in patients with hypertension

STUDY OBJECTIVE

The aim of the study was (1) to determine the difference in aortic input impedance and derived parameters between hypertensives and normotensives; and (2) to assess the acute effects of nifedipine on the aortic impedance, compliance, and resistance in patients with hypertension.

DESIGN

A high fidelity multisensor catheter (Millar) was used to obtain the aortic pressure and flow signals for impedance analysis. The acute effects of nifedipine on the impedance parameters were evaluated at steady state before and after (10-30 min) a sublingual dose of 10 mg.

PATIENTS

The patients included seven normotensive (mean blood pressure, 97 mm Hg) and nine hypertensive (mean blood pressure, 135 mm Hg), age matched, ethnic Chinese. Patients with clinical evidence of heart failure and valvular or congenital heart diseases were excluded.

MEASUREMENTS AND MAIN RESULTS

Pulsatile aortic flow and pressure were measured by Millar catheter inserted into the ascending aorta. Cross sectional area of aorta was estimated by echocardiograms. Cardiac output was determined by Fick principle with an oximeter. These data were subjected to Fourier analysis for impedance spectra. In comparison with normotensives, hypertensives had increased peripheral vascular resistance R, at 2751(705) v 1651(363) dyne.s.cm-5; increased characteristic impedance Zc, at 193(64) v 122(27) dyne.s.cm-5; and increased first zero crossing frequency of impedance phase angle fo, at 4.8(0.9) v 3.4(0.7) Hz. Arterial compliances corresponding to peak systolic pressure Cs were lower, at 0.32(0.19) v 0.90(0.32) ml.mm Hg-1, as was mean pressure Cm, at 0.55(0.25) v 1.24(0.38) ml.mm Hg-1, and end diastolic pressure Cd, at 0.83(0.29) v 1.65(0.44) ml.mm Hg-1. Although the values of external ventricular hydraulic power were higher in hypertensive subjects, the difference was not statistically significant. Nifedipine administration in 7/9 hypertensives significantly reduced R, from 2806(721) to 2433(664) dyne.s.cm-5; mean aortic pressure Pm, from 138(22) to 112(12) mm Hg; total external ventricular power Wt, from 1452(306) to 1121(135) mW; and steady external power Ws, from 1251(310) to 939(119) mW; but did not reduce Zc, fo, Cs, Cm, Cd, and oscillatory external power Wo.

CONCLUSIONS

The results indicate that (1) the stiffness of proximal aorta and vascular tone of peripheral arterioles are higher in hypertensives than in normotensives; (2) in hypertensive subjects, sublingual administration of nifedipine reduces the arterial pressure and peripheral arteriolar tone, but not the stiffness of proximal aorta; (3) the decrease in total external ventricular power in hypertensives treated with nifedipine results from a reduction in the steady, but not the oscillatory, component of hydraulic external ventricular power.

Suppressor T cells induced by epidermally applied hapten are located in bone marrow

Mice painted epidermally with trinitrochlorobenzene (TNCB) develop delayed type dermal hypersensitivity within five days, however, subsequent immunization with TNP-syngeneic antigens (TNP-H2k) does not generate CTLs to the same antigens. These studies were undertaken to determine what prevents development of the CTL. We report here, that a suppressor cell for CTL generation is found in the bone marrow (BM) of TNCB-painted mice. This suppressor cell is not present in spleens or lymph nodes, but is readily detected by adoptive transfer of BM cells. The cell responsible for suppression is an Lyt2+ (CD8+) T cell. Further studies with two monoclonal antibodies (one directed to a T cell suppressor factor [mAb 14-12], and the other directed to a suppressor T cell inducer factor [mAb 14-30]), demonstrated that the suppression could be reversed by either antibody when they were given prior to epidermal hapten painting. However, when each mAb was administered to recipients of BM cells from hapten painted donors, only mAb 14-12 reversed suppression of CTL generation. Examination of the number of resident BM cells revealed that TNCB-sensitized mice had 35% more cells than normal controls. When cultured in vitro with inactivated, syngeneic TNP-thymocytes, BM from normal mice readily developed TNP-self specific CTL, whereas whole BM from hapten-painted mice did not. The inability to generate CTLs was found to be attributable to suppressor cells, since BM cells from hapten-painted mice prevented CTL development by splenic T cells in culture. BM cells from normal mice did not suppress CTL generation. Suppression in vitro was not overcome by the presence of exogenous IL-2.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific frequency properties of renal and superior mesenteric arterial beds in rats

In order to investigate the effects of arterial beds on pressure waveforms in arteries, the pressure waves observed in the rat tail artery were resolved into their Fourier moduli before and during ligation of the left renal artery and the superior mesenteric artery. Consistently different patterns of waveform changes in the tail artery were seen on occlusion of these vessels. Ligation of the renal artery reduced, and of the superior mesenteric artery increased, the pressure harmonics over most of the spectra. These results imply that to study the changes in the pressure contours as the observation point is moved downstream, one may have to account separately for the contributions of individual arterial beds. This is relevant in considering the degree to which it is appropriate for data to be amalgamated in models of the systemic arterial bed.