PubMed Health⌕ Search

Biomedical subjects

Y T Zhang

Publications and source records attributed to Y T Zhang.

At least 19 recordsLinked to original sources
PubMed2004

The effect of contacting force on photoplethysmographic signals.

Photoplethysmography (PPG) has been used in oxygen saturation measurement, heart rate monitoring, and the assessment of peripheral circulation and large artery compliance. However, the waveform of the photoplethysmographic signal may be affected by the contacting force between the sensor and the measurement site. The aim of this study is to investigate the change in pulse amplitude (AC), DC amplitude, ratio of AC/DC and normalized pulse area of the reflective photoplethysmographic signals with increasing contacting force, from 0.2 N to 1.8 N. Signals were recorded from the fingers of fifteen healthy subjects. With increasing contacting force, the DC amplitude increased and the normalized pulse area decreased, whereas the pulse amplitude and the ratio of AC/DC increased first and then decreased. For different subjects, the pulse amplitude and the ratio of AC/DC peaked at different contacting forces, from 0.2 N to 1.0 N, and most of the subjects achieved their maximum pulse amplitude within 0.2-0.4 N. Over the range of contacting force between 0.2 N and 0.8 N, the DC amplitude and the normalized pulse area had significant changes (p < 0.001). The results suggest that the effects of contacting force should be carefully examined in the design of photoplethysmography-based health care devices.

Adult↗
PubMed2002

Neuroengineering modeling of single neuron and neural interface.

The single neuron has attracted widespread attention as an elementary unit for understanding the electrophysiological mechanisms of nervous systems and for exploring the functions of biological neural networks. Over the past decades, much modeling work on neural interface has been presented in support of experimental findings in neural engineering. This article reviews the recent research results on modeling electrical activities of the single neuron, electrical synapse, neuromuscular junction, and neural interfaces at cochlea. Single neuron models vary form to illustrate how neurons fire and what the firing patterns mean. Focusing on these two questions, recent modeling work on single neurons is discussed. The modeling of neural receptors at inner and outer hair cells is examined to explain the transforming procedure from sounds to electrical signals. The low-pass characteristics of electrical synapse and neuromuscular junction are also discussed in an attempt to understand the mechanism of electrical transmission across the interfaces.

Action Potentials↗
PubMed2002

Ascorbic acid induces redifferentiation and growth inhibition in human hepatoma cells by increasing endogenous hydrogen peroxide.

The mechanisms of redifferentiation and growth inhibition induced in human hepatoma cells by ascorbic acid (AA) were studied. After treatment with AA, the content of hydrogen peroxide (H2O2) and the activity of superoxide dismutase (SOD) increased in a concentration- and time-dependent manner, while the activity of catalase (CAT) decreased in a concentration- and time-dependent manner. Using 6 mM AA as a positive control, after treatment by 50 microM hydrogen peroxide, the malignant characteristics of human hepatoma cells were alleviated; for example as cell surface charge markedly decreased, the electrophoresis rate dropped from 1.68 microns.s-1.V-1.cm-1 to 0.97, the average of alpha-fetoprotein content decreased from 327 micrograms.g-1 protein to 193, and gamma-glutamyl-transpeptidase activity fell from 0.84 U.g-1 protein to 0.30. The indexes related to cell differentiation were promoted, such as tyrosine-alpha-ketoglutarate transaminase activity increased from 17.1 mumol.g-1 protein to 33.1, and the colonogenic potential decreased by 79.3%. SOD and 3-amino-1,2,4-triazole (AT) exhibited some effects, but there were statistically significant differences between the SOD, AT and H2O2 or AA groups. AA induced growth inhibition and redifferentiation of human hepatoma cells through the production of hydrogen peroxide, since addition of SOD (200 units/ml), an enzyme that dismutates superoxide and generates hydrogen peroxide, and AT (1.5 mM), a CAT inhibitor that inhibits the activity of CAT and leads to an increase in H2O2 content, showed some inducing changes emphasizing the involvement of reactive oxygen species (ROS) in redifferentiation of hepatoma cells. AA can cause the content of H2O2 to increase, and the factor H2O2 showed a similar effect to AA on growth and redifferentiation suggests that H2O2 is involved in hepatoma cell redifferentiation. In conclusion, these results suggest that AA inhibits tumor growth and induces tumor redifferentiation by virtue of producing H2O2.

Amitrole↗
PubMed2001

Bionic wavelet transform: a new time-frequency method based on an auditory model.

In this paper, a new adaptive wavelet transform, named bionic wavelet transform (BWT), is developed based on a model of the active auditory system. The most distinguishing characteristic of BWT is that its resolution in the time-frequency domain can be adaptively adjusted not only by the signal frequency but also by the signal instantaneous amplitude and its first-order differential. The automatically adjusted resolution, even in a fixed frequency along the time-axis, is achieved by introducing the active control of the auditory system into the wavelet transform (WT). Other properties of BWT include that: 1) BWT is a nonlinear transform that has high sensitivity and frequency selectivity; 2) BWT represents the signal with a concentrated energy distribution; and 3) the inverse BWT can reconstruct the original signal from its time-frequency representation. In order to compare these three properties between BWT and WT, experiments were conducted on both constructed signals and real speech signals. The results show that BWT performs better than WT in these three aspects, and that BWT is appropriate for speech signal processing, especially for cochlear implants.

Algorithms↗
PubMed2001

A new method for experimental simulation of EMG using multi-channel independent stimulation of small groups of motor units.

The experimental simulation method was based upon the separate activation of up to 10 small groups of motor units (MU) in an acute nerve-muscle preparation. The investigator was able to precisely control and systematically alter the features of MU pool activation strategies. No implicit assumptions were made regarding MU properties. The purpose of this study was to evaluate the validity of this method. Three criteria were formulated and found to be satisfied: First, in the time domain, visual and audio displays of simulated EMG were indistinguishable from physiological EMG. Secondly, in the frequency domain, power spectra of simulated EMG revealed the typical features of EMG recorded during voluntary activation in the cat. Thirdly, the well-known monotonic relationship between EMG magnitude and force was readily reproduced, although strictly linear relations were not found. In addition, the relationship between the pool's ensemble activation rate and EMG magnitude showed distinct gain compression, mostly attributable to signal cancellation.

Animals↗
PubMed2000

Fuzzy EMG classification for prosthesis control.

This paper proposes a fuzzy approach to classify single-site electromyograph (EMG) signals for multifunctional prosthesis control. While the classification problem is the focus of this paper, the ultimate goal is to improve myoelectric system control performance, and classification is an essential step in the control. Time segmented features are fed to a fuzzy system for training and classification. In order to obtain acceptable training speed and realistic fuzzy system structure, these features are clustered without supervision using the Basic Isodata algorithm at the beginning of the training phase, and the clustering results are used in initializing the fuzzy system parameters. Afterwards, fuzzy rules in the system are trained with the back-propagation algorithm. The fuzzy approach was compared with an artificial neural network (ANN) method on four subjects, and very similar classification results were obtained. It is superior to the latter in at least three points: slightly higher recognition rate; insensitivity to overtraining; and consistent outputs demonstrating higher reliability. Some potential advantages of the fuzzy approach over the ANN approach are also discussed.

Algorithms↗
PubMed2000

Theoretical analysis of a rectifying gap junction model.

Based on the experimental observations, an electrical circuitry model for a rectifying gap junction was developed in previous work. In order to show the physiological function for each element in the model, a theoretical analysis is carried out in this report. The results indicate that the gap junctional capacitance Cj newly introduced into the model plays a major role in determining the duration increase, the peak attenuation, and the peak delay on the postmembrane action potential. Also, a comparison between the newly proposed model and the widely accepted kinetic model by Giaume is made. The results show that the electrical circuitry model can not only describe the characteristics of Giaume's model but also allow the interpretation of some experimental phenomena that were not reflected in other gap junctional models.

Animals↗
PubMed1999

A fast recursive-least-squares adaptive notch filter and its applications to biomedical signals.

A fast recursive-least-squares (FRLS) adaptive notch filter (ANF) for cancellation of sinusoidal interference from recorded biomedical signals is investigated. The FRLS ANF is derived by making an approximation to the conventional recursive-least-squares (RLS) ANF for computation economy. It outperforms the commonly adopted least-mean-squares (LMS) ANF, demonstrating a rapid and bandwidth-insensitive initial convergence. A novel application of the FRLS ANF is for the elimination of the tonal artefact in distortion product otoacoustic emission (DPOAE) signals.

Electronics, Medical↗
PubMed1999

Synthesis and decomposition of transient-evoked otoacoustic emissions based on an active auditory model.

In this paper, transient-evoked otoacoustic emissions (TEOAE's) are synthesized by an active auditory model, and decomposed by continuous wavelet transform (CWT) to study the frequency-latency relationship and the generation of TEOAE signals. The controlled voltage sources that relate to the mobile mechanism of the outer hair cells (OHC's) are proposed to serve as the generation sources of TEOAE signals. The state-variable method is adopted to calculate the auditory model. The mother wavelet used in CWT is selected on basis of the model. The results of this study show that the simulated TEOAE signal is similar to the clinically detected ones not only in the time-domain waveform, but also in the frequency-latency relationship. It seems to be clear that the generation of TEOAE signals is related to the same active mechanism as the cochlear sharp frequency selectivity.

Adult↗
PubMed1999

Estimation of distortion product otoacoustic emissions.

Distortion product otoacoustic emissions (DPOAE's) are acoustic signals generated from the cochlea when stimulated by dual tone stimulus. The measurement of the DPOAE's is useful in objectively assessing the hearing functionality of humans. The parameter estimation of the DPOAE's has been based on the fast Fourier transform (FFT) technique, which may not guarantee optimum performance in general. In this paper, we investigate the optimal maximum-likelihood estimator (MLE) for the DPOAE's. Experiments showed that the performance of the MLE is superior to those of the conventional FFT estimators. Furthermore, it is proven that the unwindowed FFT estimator is essentially the MLE when the stimulus tones are constrained to exhibit complete cycle within the data frame.

Acoustic Stimulation↗
PubMed1998

The latex allergen Hev b 5 transcript is widely distributed after subcutaneous injection in BALB/c mice of its DNA vaccine.

BACKGROUND: DNA vaccines reduce IgE responses to selected allergens, but severe reactions to the expressed antigen may limit the usefulness of the technique in allergen immunotherapy. OBJECTIVE: We sought to determine the extent of spread of an injected DNA vaccine in mice. METHODS: We placed the gene encoding the potent Hevea latex allergen Hev b 5 in a mammalian expression vector and injected this DNA vaccine subcutaneously into BALB/c mice. At several times after injection, the presence of Hev b 5 transcript was determined in multiple tissues by RT-PCR. The identity of the amplification product was confirmed by Southern hybridization and restriction analyses. RESULTS: Hev b 5 RNA appeared at the injection site and in the lymph nodes, spleen, and lungs within 1 day after injection and persisted for at least 14 days. Hev b 5 RNA was also identified in the blood and tongue 14 days after injection. Antibody and cell-mediated responses to Hev b 5 were also noted in the immunized animals at later time points. As expected, animals injected with the identical plasmid containing the Hev b 5 DNA in the antisense orientation mounted no immune response to Hev b 5. CONCLUSIONS: The rapid and widespread appearance of the Hev b 5 transcript in the injected mice confirms that DNA is translocated from the injection site, transcribed, and expressed in immune and nonimmune tissues after injection. Controlling the extent and degree of expression in specific target tissues may allow therapeutic DNA vaccination with plasmids that encode potentially toxic allergens.

Allergens↗
PubMed1998

EMG-force relation in dynamically contracting cat plantaris muscle.

The purpose of this study was to revisit the electromyographical (EMG)-force relationship of dynamically contracting muscles using direct measurements of EMG and force in cat hindlimb muscles during locomotion. EMG signals were recorded from the plantaris muscle using bipolar indwelling wire electrodes, and the corresponding forces were measured using a tendon force transducer. Force-time histories of cat plantaris muscle were predicted by estimating selected force parameters from EMG and timing parameters, and then constructing two smoothly fitting quintic spline functions from the estimated force parameters. The force predictions did not contain information on force-length or force-velocity properties of the cat plantaris and did not use instantaneous contractile conditions as input. It was found that two smoothly fitting quintic spline functions provided the required properties to approximate plantaris force-time histories accurately, and approximations of the force-time histories using EMG and timing parameters as input for the quintic splines were good. The root mean square errors (RMS) of the predicted compared to the actual plantaris forces were smaller than corresponding results reported in the literature, even though the prediction model did not require the force-length-velocity properties or the instantaneous contractile conditions of the target muscles as input. From the results obtained in this study, it appears that force-time histories of the cat plantaris muscle during locomotion can be predicted adequately from information obtained using EMG and video records, without information on either the force-length and force-velocity properties, or the instantaneous contractile conditions of the muscle.

Algorithms↗
PubMed1997

[Multivariate analysis on prognostic factors of non-Hodgkin's lymphoma].

OBJECTIVE: To predict the prognostic factors and to improve the response and survival in intermediate-grade and high-grade non-Hodgkin lymphoma (NHL). METHODS: 200 patients with intermediate-grade and high-grade NHL were treated with chemotherapy. A multivariate Cox model was used to analyse the prognostic factors that significantly affect the treatment outcome. The variables examined included: sex, age, clinic stage of disease, B symptoms, extranodal sites, bone marrow involvement, tumor bulk, performance status (ECOG) and malignancy grades. RESULTS: Multivariate analysis showed that performance status, the number of extranodal sites, pathologic malignancy grade and tumor bulk were significantly independent prognostic factors. These factors were put together to construct a prognostic index formula. The index partitioned the patients into low risk group (PI -2.43(-)-1.30), intermediate risk group (PI -1.29-1.0) and high risk group (PI > 1.0) giving 5-year survival rates of 76.0%, 21.6% and 7.4%, respectively. CONCLUSION: The prognostic index formula and subgroups could serve as a reference to distinguish patients requiring more intensive chemotherapy and autologous stem cell transplantation from those who should be treated with standard regimens in order to improve the prognosis.

Adolescent↗
PubMed1997

Movements of vertebrae during manipulative thrusts to unembalmed human cadavers.

OBJECTIVE: The purpose of this study was to measure the relative movements of vertebrae during manipulative thrusts to unembalmed post-rigor mortis human cadavers. SETTING: The investigation was conducted in the gross anatomy laboratory at the University of Calgary. SUBJECTS: Two 77-yr-old, unembalmed, post-rigor mortis, male cadavers were used. INTERVENTIONS: The movements of vertebrae were investigated by using high-speed cinematography to record the movements of bone pins threaded into T10, T11 and T12 during spinal manipulative therapy to unembalmed post-rigor human cadavers. A single clinician delivered a series of posterior-to-anterior (p-to-a) thrusts to the right transverse process of either T10, T11 or T12, using a reinforced hypothenar contact. Relative p-to-a and lateral translations, as well as axial and sagittal rotations, in T10-T11 and T11-T12 were calculated. Corresponding p-to-a forces exerted by the clinician onto the cadaver were recorded using a pressure pad. MAIN RESULTS: Significant relative movements were measured primarily between the targeted and immediately adjacent vertebrae during the thrusts. Vertebral pairs remained slightly 'hyper-extended' after the rapid thrusts to T11, when the p-to-a forces returned to preload levels. CONCLUSIONS: These findings may be useful for the understanding of the deformation behavior of the vertebral column during therapeutic manipulation. A fully three-dimensional analysis of all six degrees of freedom, using a larger number of unembalmed cadavers, would be useful in clarifying the relationship between the externally applied forces and the observed relative movement patterns of the vertebrae.

Aged↗
PubMed1997

Vibromyography as a quantitative measure of muscle force production.

This study was undertaken to investigate the use of vibromyography (VMG) as a tool for quantifying skeletal muscle force production. Fourteen healthy volunteers were pretested using a Cybex isokinetic dynamometer to determine their isometric quadricep maximum voluntary contraction (MVC) values. On the basis of these results, the subjects were separated into two groups: high-force ("HF" MVC mean = 289 ft.lb., range 254-330) and low-force ("LF" MVC mean = 154 ft.lb., range 101-198). A vibromyographic piezoelectric accelerometer (Dytran 3115A) and electromyographic (EMG) surface electrodes were affixed to the rectus femoris muscle and recordings were obtained at 20, 40, 60, 80, and 100% MVC. Root mean squares, median and mean values were computed from digitized data in the time domain while peak values were calculated from a fast Fourier transform for both the VMG and EMG data. A two-way repeated measures MANOVA using relative values and a linear regression model using absolute values were studied using BMDP and MiniTab software. Linear correlations were found between quadricept force and all EMG variables (R2 range 0.71-0.90) except peak (R2 = 0.39). The relationship between VMG and force was less linear (R2 range 0.19-0.69) because VMG values reach a plateau or even drop at 80% and 100% MVC. The HF-LF group differences were significant (p < 0.05), for all VMG values with the exception of root mean squares, but were not significant (p > 0.05) for all four EMG values. This study shows that, while EMG can discriminate force production within a given subject, VMG is a better discriminator of absolute muscle force values between subjects, particularly up to 60% MVC.

Adult↗