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Biomedical subjects

H H Sun

Publications and source records attributed to H H Sun.

At least 19 recordsLinked to original sources
PubMed1999

Time-frequency methods for detecting spike activity of stomach.

It has been hypothesised by many researchers that the spike activity signals of the stomach are responsible for triggering peristaltic contractions. Since most gastric motility disorders include an abnormality in the contraction pattern, it is very important to access this information non-invasively. The aim in this study is to use abdominal electrogastrogram (EGG) signals to detect the spike activity signals generated by the serosa of the stomach, and hence provide clinicians with a better method to monitor the motility state of the stomach. Through second and third-order spectral estimations performed on the serosal data obtained from canine experiments, it was concluded that the spike activity in serosal signals occupies a frequency range of 50-80 cycles per minute. An increase in this frequency range during strong antral contractions was observed both in the serosal and cutaneous power spectra. By using the 'continuous wavelet transform' with respect to a modified Morlet wavelet, the spike activity signals generated from the serosa of the stomach can be detected and quantified in time from the cutaneous EGG records. During phase III contraction episodes, a detection accuracy of up to 96% from the cutaneous EGG recordings was calculated based on the scored serosal spike activities simultaneously recorded.

Animals↗
PubMed1999

Enhanced responsiveness to photodynamic therapy-induced apoptosis after mitochondrial DNA depletion.

Several lines of evidence indicate that mitochondria are an especially sensitive target for photodamage. Reports of cross resistance between photodynamic therapy (PDT) and the drug cisplatin, along with evidence that depletion of mitochondrial DNA (mtDNA) sensitized cells to cisplatin suggested a study of the photodynamic responsiveness of murine leukemia control L1210 cells versus cells depleted of mtDNA. Loss of mtDNA led to an increased sensitivity to mitochondrial photodamage, while the cytotoxic effects of lysosomal photodamage were not affected. Cells depleted of mtDNA showed an enhanced apoptotic response to PDT involving a mitochondrial target, compared with control cells.

Animals↗
PubMed1997

Antimycins, inhibitors of ATP-citrate lyase, from a Streptomyces sp.

A related group of compounds belonging to the antimycin class of antibiotics was found in culture broth produced by a Streptomyces species. The group includes known antimycins A1, A2, A3 and A4, and new antimycins A7 and A8. These compounds inhibit ATP-citrate lyase with Ki values of 4 to 60 microM against the substrate magnesium citrate. The structures of the new antimycins were determined by spectroscopic analyses.

ATP Citrate (pro-S)-Lyase↗
PubMed1995

An advanced signal processing technique for impedance cardiography.

A new design using the latest technique in signal processing, the time-frequency analysis method, was developed to process impedance cardiography signals. This technique, when used to determine the relevant calculation parameters, was found to be more accurate than conventional methods. It was shown to be advantageous in reducing ventilation artifacts and motion noise, resulting in greater accuracy. Its cardiac output values had a much better correlation coefficient when compared in the clinical setting to the standard thermodilution technique than did the values from conventional impedance cardiography devices.

Cardiography, Impedance↗
PubMed1994

Harmonic distortion caused by electrode polarisation.

Steady-state measurements of the electrical properties of electrodes immersed in physiological saline were taken with small- and large-amplitude sinusoidal voltages (30 m V-1 V) in the frequency range 0.2 mHz-2 Hz. Impedance magnitude and phase, and the first four Fourier series coefficients of the polarised current were measured. The dependence of the polarisation admittance on input current intensity was modelled with the linear relationship proposed by Schwan. This model predicts harmonics in the non-linear range for AC overpotentials up to several hundred millivolts. Observed values deviated from theoretical values. Reasons for such deviations are discussed. The study of harmonic distortion appears to be a useful tool to monitor and predict the non-linear behaviour of the interface and other dielectric phenomena.

Electric Impedance↗
PubMed1994

Spiroquinazoline, a novel substance P inhibitor with a new carbon skeleton, isolated from Aspergillus flavipes.

A novel substance P inhibitor, spiroquinazoline [1], was isolated from the fungus Aspergillus flavipes, which was originally obtained from soil. The structure of 1 was determined by analysis of spectroscopic data and 1 was shown to contain a new carbon skeleton containing a spiro-carbon center. Also isolated from the same culture extract were the new natural product, benzodiazepiedione [3], and the known compounds, acyl aszonalenin [4], N-benzoyl-L-phenylalaninol, and seven diketopiperazines.

Antineoplastic Agents↗
PubMed1994

WIN 66306, a new neurokinin antagonist produced by an Aspergillus species: fermentation, isolation and physico-chemical properties.

WIN 66306 (1a), a cyclic peptide containing a novel amino acid, was isolated as a neurokinin antagonist from an Aspergillus species, labelled SC230. Conditions that maximized the production of 1a were developed, leading also to production of the related compound WIN 68577 (2) and rosellichalasin (3). Both 2 and 3 were more active in the rat NK1 than in the human NK1 receptor binding assay, while 1a was more active at the human receptor with an inhibitor affinity constant of 7 microM.

Amino Acid Sequence↗
PubMed1994

Isolation and structure elucidation of two new calpain inhibitors from Streptomyces griseus.

Two new peptides, a diketopiperazine of N-methyltyrosine (1) and a tetrapeptide containing N-methyltyrosine (2), were isolated from an actinomycete strain Streptomyces griseus. These compounds inhibit the enzyme calpain in the micromolar range and were characterized on the basis of spectroscopic analysis, amino acid analysis and sequencing. The structure of the tetrapeptide N-methyltyrosyl-N-methyltyrosyl-leucyl-alanine (2), was also confirmed by total synthesis.

Calpain↗
PubMed1994

Benzomalvins, new substance P inhibitors from a Penicillium sp.

In the course of screening microbial broths for neurokinin receptor antagonists, a series of new benzodiazepines, benzomalvins A (1), B (2) and C (3), has been isolated from the culture broth of a fungus identified as a Penicillium sp. Benzomalvin A (1) showed inhibitory activity against substance P with Ki values of 12, 42 and 43 microM at the guinea pig, rat and human neurokinin NK1 receptors, respectively. Benzomalvins B (2) and C (3) were only weakly active. The structures of these compounds were determined by spectroscopic methods including MS measurements and NMR analysis.

Animals↗
PubMed1994

[Drug resistance and plasmid analysis in Pseudomonas aeruginosa].

One hundred and ninety seven strains of Pseudomonas aeruginosa were isolated from urine (59 strains), wound pus (60 strains), sputum (30 strains), stool (30 strains) and eye discharge (18 strains) at Kaohsiung medical College Hospital. These strains were serotyped with antisera against O antigens and tested with twelve different antimicrobial agents. The results showed that the most frequently isolated strains were serotype E (41.1%), followed by serotype B (20.3%), serotype F (10.7%) and serotype L (9.1%). In in vitro susceptibility testing, all isolated strains were resistant to chloramphenicol and tetracycline. Otherwise, these isolates were highly susceptible to ceftazidime (95.4%), enoxacin (89.3%) and piperacillin (87.8%). The isolates from urine exhibited more multiple drug resistance patterns than those of other specimens. When plasmid content was analysed from pseudomonas aeruginosa, only 15.2% (30/197) of isolates carried plasmids. By conjugation, transformation and mobilization experiments, it was shown that 13.3% (4/30) of plasmid carrying strains contained R plasmids.

Chloramphenicol↗
PubMed1991

Decomposition of nonlinear non-Gaussian process and its application to nonlinear filter and predictor design.

An approach for decomposing of a Nonlinear Non-Gaussian Process (NNGP) is presented. A set of adjoin processes alpha's are first constructed based on the orthogonal principle so that the linear and nonlinear part of the process can be completely separated by a correlation operation without the statistical assumption on the process (i.e., it is not necessarily a Gaussian Process). The linear and nonlinear filters or predictors can then be designed and implemented independently and the consistency of parameters is guaranteed. An algorithm is given for a second order nonlinear process, and it can easily be extended to higher order cases if necessary. The method is first demonstrated by applying it to a nonlinear filter design problem, i.e., system identification. Finally, the necessity of a proposed decomposition procedure is proven by applying it to an example in which the parameters of a signal model are extracted from a version which is distorted due to the nonlinearity of the channel.

Algorithms↗
PubMed1990

Nonlinear phenomenon of interfacial polarization immittance of a Pt electrode.

Description of a computerized, automated method to measure the interfacial polarization immittance of a Pt electrode in nonlinear range is presented. The classical three-electrode setup is used for measurements in conjunction with a special purpose software implemented on a Unix computer using C language. A collection of data at very low frequencies (below 2 Hz) and at high input intensities with various dc biases imposed on the input are presented to show the behavior of the interface in nonlinear range. The instrument also provides on-line harmonic analysis of the output signal, by calculating the first four Fourier series coefficients, in response to a pure sinusoidal input.

Electrodes↗
PubMed1990

Fractal system--a time domain approach.

A method to analyze the fractal system in the time domain is presented so that the dynamic behavior of the system can be studied. The fractal system is represented by a set of linear time-varying differential equations whose order depends on the order of the system under non-fractal condition. Four different types of fractal system are considered and their solutions in the time domain are presented. These analyses show that the fractal system is dynamically more stable with smooth changes of magnitude and less oscillatory than the non-fractal system. Examples of the physiological system of the conduction pathways in the heart and also the polarization phenomena of noble metal are presented to illustrate the phenomena.

Bundle of His↗
PubMed1990

Nonlinear system identification for cascaded block model: an application to electrode polarization impedance.

A new algorithm has been developed to identify a system divided into cascaded blocks of dynamic linear (L), static nonlinear (N), and dynamic linear (L) subsystems based strictly on the input-output relationship. The nonlinear element is assumed to be equicontinuous, or must be satisfied by the Weierstrass criterion. Therefore, it could either be continuous type as represented by polynomial approximation or abrupt type as represented by piecewise-linear segments. The process uses a series of multilevel input to decouple the two linear subsystems from the nonlinear subsystem and then applies the predictor-corrector algorithm to minimize a cost function to obtain the parameter of the subsystem. The method does not restrict the type of input signal and no prior knowledge of the subsystems is necessary. Numerical example for a prescribed system is given and the results show almost identical values by any one of the three types of input, namely: step, sinusoidal, or white noise. Three computer programs have been developed for the identification of the system with odd, even, and piecewise abrupt types of nonlinearity. The method is applied to model the interfacial phenomenon of noble metal electrode (Pt) at the nonlinear range and the algorithm is verified by comparison with the result developed previously.

Algorithms↗
PubMed1989

An impedance cardiography system: a new design.

An IBM compatible impedance cardiac output monitoring prototype system has been developed for use at the bedside on patients in the ICU, CCU, ER, Cath. Lab, and OR, etc. This impedance cardiographic (ICG) system, whose operation is completely technician-free, provides a continuous display with digital results and four channel color waveforms on an Enhanced Graphics Display screen. The software is written in C language with several special segments in assembly code where speed is essential. In this prototype system, a real-time algorithm was introduced to modify the ensemble averaging technique so that it averages nonperiodic signals such as: ECG, dZ/dT, delta Z, etc. Also, a real-time algorithm was developed to adaptively detect R spikes from conventional ECG signals. A signal preprocessor was developed to process signals digitally before any further work is done. This procedure reduces muscle noise, 60 Hz interference, and ventilatory movement. A special digital filter was designed to cope with the cases in which pacemakers are used. A special algorithm was also developed to further reduce the ventilation artifacts so that a period of apnea is unnecessary during the performance of the measurements. An anatomically specified electrode configuration has been defined enabling precise and reproducible positioning of the electrodes--hopefully leading to electrode standardization. At the present time, this prototype system has been compared with standard hand calculation and correlated with the clinical "gold standard," the Swan-Ganz thermodilution cardiac output. Using 144 sets of data from 10 healthy volunteers, 4 critically ill patients, and 8 healthy exercising volunteers, calculations of cardiac output were made using our system and the standard hand calculation of stroke volume, based upon Kubicek's equation; there was a relatively high and stable correlation: r = 0.93, p less than 0.005 (healthy); r = 0.94, p less than 0.002 (ill), r = 0.95, p less than 0.002 (exercise). From 20 patients at two different hospitals all with Swan-Ganz catheters in their hearts, 65 correlation studies between our system and the standard thermodilution technique were performed; the results were encouraging in terms of accuracy and consistency (r1 = 0.84, p less than 0.01, n = 10 CCU patients), and (r2 = 0.93, p less than 0.01, n = ICU patients). These results along with a growing body of data from other investigators indicate that this noninvasive and technician-free system for measuring cardiac output could have a significant role in patient care.

Cardiography, Impedance↗