Biomedical subjects

T S Kuo

Publications and source records attributed to T S Kuo.

At least 19 recordsLinked to original sources

PubMed1998

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.

Amino Acid Sequence↗

PubMed1997

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.

Animals↗

PubMed1997

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.

Adaptation, Physiological↗

PubMed1997

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.

Adult↗

PubMed1997

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.

Animals↗

PubMed1997

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.

Adult↗

PubMed1996

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.

Animals↗

PubMed1996

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%.

Adult↗

PubMed1996

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.

Case-Control Studies↗

PubMed1995

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.

Arteries↗

PubMed1995

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.

Electric Stimulation↗

PubMed1995

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.

Algorithms↗

PubMed1995

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.

Algorithms↗

PubMed1995

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%.

Adult↗

PubMed1994

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)

Animals↗

PubMed1994

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.

Animals↗

PubMed1994

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)

Arteries↗

PubMed1993

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)

Angiotensin II↗