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Biomedical subjects

D Wei

Publications and source records attributed to D Wei.

At least 109 records · Page 6Linked to original sources
PubMed1993

Validation of continuous thermal measurement of cerebral blood flow by arterial pressure change.

A thermal measurement system to monitor cerebral blood flow (CBF) continuously from the cortical surface is evaluated in vivo. It has a temperature resolution of better than 0.001 degrees C (1 m degrees C) and can compensate for baseline temperature fluctuations in the brain tissue. A new approach has been developed to test the capability of monitoring dynamic CBF response. Transient CBF changes associated with changes in mean arterial blood pressure (MABP) caused by repeated bolus norepinephrine injections are used to examine the response of the measurement system in both the heated mode, sensitive to flow, and the unheated mode, sensitive only to temperature. Experiments on 13 rats demonstrate that changes in the MABP are closely correlated with those of temperature difference in the heated mode. Regression analysis shows a mean slope of 0.9 m degrees C/mm Hg in the heated mode, which is significantly different from zero (p < 0.002) and from the mean slope in the unheated mode (p < 0.002). This indicates that flow signal in the system output can be distinguished from the baseline thermal fluctuations. Thus, the system can be used to detect and study dynamic perfusion changes from the brain surface with minimal tissue damage. Furthermore, analysis of the data shows that the transient flow signal before autoregulation is linearly correlated with changes in MABP.

Animals↗
PubMed1993

Extended Kalman filter (EKF) application in vitamin C two-step fermentation process.

Based on kinetic model study of vitamin C two-step fermentation, the extended Kalman filter (EKF) theory is conducted for studying the process which is disturbed by white noise to some extent caused by the model, the fermentation system and operation fluctuation. EKF shows that calculated results from estimated process parameters agree with the experimental results considerably better than model prediction without using estimated parameters. Parameter analysis gives a better understanding of the kinetics and provides a basis for state estimation and state prediction.

Ascorbic Acid↗
PubMed1993

Soft X-ray microimages of immunogold-labelled tumor cell surface antigens.

After successfully introducing the colloidal immunogold labelling technique to soft X-ray contact microscopy (SXCM), SXCM replica microimages of immunogold labelled tumor cell HLA-A2 surface antigens have been acquired for the first time. A biological sample preparation method using immunocytochemical staining techniques suitable for SXCM has also been established.

Antibodies, Monoclonal↗
PubMed1992

Studies on kinetic model of vitamin C two-step fermentation process.

This paper aims at analyzing the bioconversion process from L-sorbose to 2-Keto-L-gulonic acid with the aid of the growth factor assumption. Fermentation mechanism is discussed after making necessary simplifications. A model is established for this second step fermentation process. Nonlinear optimization together with Runge-Kutta method, are used to obtain model parameters. Results of computer simulation agree with experimental data to show the reliability of the kinetic model.

Ascorbic Acid↗
PubMed1991

Study on the genesis of giant negative T wave in apical hypertrophic cardiomyopathy using a three-dimensional computer model.

Apical hypertrophic cardiomyopathy is characterized by a spade-like left ventricular cavity and by both giant negative T waves and tall R waves in the electrocardiogram. However, the mechanisms of these ECG abnormalities have not been satisfactorily clarified. We have recently developed a three-dimensional computer model of ventricular depolarization and repolarization processes. This model has successfully simulated normal QRST waves and changes characterizing some abnormal conditions. A model of apical hypertrophic cardiomyopathy was constructed by adding model units to the endocardium of the left ventricular apex. The surface ECG was then calculated by assuming different gradients of action potential durations and different proportions of the hypertrophic cells in the apical segment. A negative T wave of -1.45 mV in lead V4, similar to the clinically reported ECG, was obtained by assuming: (1) diffusely distributed hypertrophic cells at the apex and (2) uniform, long action potential durations of hypertrophic cells. It is suggested that these properties may account for the distinctive ECG abnormalities in apical hypertrophic cardiomyopathy.

Cardiomyopathy, Hypertrophic↗
PubMed1991

[Different effects on dopamine receptors D1 and D2 following long-term usage of L-dopa].

Different effects on D1 and D2 receptor subtypes were studied through observation of animal behavior, striatal receptor binding, and micro-electrode recording of cell activity in substantia nigra pars compacta of rats. The authors investigated the relation between dynamic changes of D1 and D2 receptor subtypes and the animal behavior, and speculate on the possible mechanisms of deterioration of drug effect and appearance of AIM induced by DA agonists during the treatment of Parkinson's disease.

Animals↗
PubMed1991

Correction of anemia in patients on continuous ambulatory peritoneal dialysis with subcutaneous recombinant erythropoietin twice a week: a long-term study.

Subcutaneous recombinant human erythropoietin (rHuEPO) was given for 12 months twice weekly to 10 patients on continuous ambulatory peritoneal dialysis (CAPD) with anemia (hemoglobin less than 9.0 mg/dl). All patients responded to a median weekly dose of between 37.5 to 100 (mean 55 to 105) units/kg and reached a target hemoglobin of 10-12 mg/dl in a mean of 11.7 weeks (range 5-24). Serum iron, iron saturation and ferritin were significantly lower and serum potassium was significantly higher than the pre-treatment level from 1 month onwards. Five patients without pre-treatment iron overload required oral iron supplement and 3 required oral potassium-binding resin. No significant change in other serum biochemical parameters was observed. Blood pressure remained stable during the treatment period but additional or increased dosage of antihypertensive drugs was required in 5 patients. Peritoneal small solute clearance and ultrafiltration and residual renal clearance did not change significantly after correction of anemia. The incidence of peritonitis and exit site infection was similarly unaffected. One patient developed a severe headache which was not associated with hypertension and responded to withdrawal of rHuEPO treatment. Most of the remaining patients showed improvement in subjective well-being. It was concluded that the subcutaneous route twice a week is a safe, convenient and cost-effective way to administer rHuEPO to patients on CAPD.

Adult↗
PubMed1990

Heterogeneity of hepatitis delta antigen.

Hepatitis delta antigen (HDAg) is the only known protein encoded by the hepatitis delta virus (HDV). Two HDAg species of different sizes have been detected in the sera and livers of the infected humans, chimpanzees, and woodchucks, even though only one RNA species was previously identified in most of the HDV strains. To study HDAg heterogeneity, we took advantage of the fact that a single base mutation at nucleotide 1015 (C to U), which results in an amber termination codon in the HDAg open reading frame (ORF), eliminates a unique Ncol restriction enzyme site. We screened various HDV cDNA clones and detected sequence heterogeneity of the HDAg-coding region on the basis of the presence or absence of the Ncol site. Five delta hepatitis patients were examined. In every patient, two types of HDAg-coding sequence were detected at nucleotide 1015: one which contains a C and results in an ORF encoding a delta antigen of 214 amino acids, and the other which possesses a U and results in an amber termination codon and a truncated HDAg species of 195 amino acids. The in vitro translation products of these two ORFs comigrated with the two HDAg species from the patient's plasma on SDS polyacrylamide gels. Polymerase chain reaction (PCR) amplification of the HDV RNA from some patients' sera and subsequent sequencing showed several additional mutations in the HDAg-coding region. These mutations are independent of the C or U nucleotide change at the site of the amber termination codon.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigens, Viral↗
PubMed1990

[Synthesis of analogs of cephalotaxine esters and their antitumor activities].

Four analogs of cephalotaxine esters (C1Z, C2E, C3E, C4E) were synthesized. The ratio of the Z, E isomers of the side chain alpha, beta-unsaturated ester carboxylic acids is reported. The Z isomer was easy to transform to the E isomer. Compound C1Z showed significant activity of inducing cancer cell HL-60 differentiation. It also showed inhibitory activity on Leukemia L1210.

Animals↗
PubMed1990

[The correlation of central projection of the acupoints riyue, qimen with correlative viscera, in the rabbit].

Twenty two rabbits were selected for the experiment and were divided into three groups. CT-HRP or CB-HRP was injected respectively into the ampulla wall (group 1) or acupoint area Riyue (group 2) or Qimen (group 3). The results obtained are as follows: Group 1. The labelled cells appeared in the spinal ganglia from T3 to T11 on the left side and T2 to T10 on the right side, and a lot appeared in the nodose ganglion of the vagus nerve on both sides. The transganglionic labeled terminals were found in the region of the solitary nucleus on both sides. A lot of labelled cells appeared in the celiae ganglia on both sides, a few dorsal motor nucleus of the vagus nerve on both sides. Group 2. The labelled cells appeared in the spinal ganglia from T4 to T10 and C6 to C8 on the same side, the anterior horn of the spinal cord from T5 to T10 segments on the same side, and a lot appeared in the ganglia of the sympathetic trunk from T3 to T10 on the same side. Group 3. The labelled cells appeared in the spinal ganglia from T4 to T8 on the same side, the anterior horn of the spinal cord from T5 to T7 segments on the same side, and a lot appeared in the ganglia of the sympathetic trunk from T4 to T8 on the same side. The results of experiment shows: 1. There are 5-7 overlapping segments of sensory nerve projection between Riyue, Qimen acupoint area and ductus choledochus ampulla.(ABSTRACT TRUNCATED AT 250 WORDS)

Acupuncture Points↗
PubMed1989

Clinical application of electrocardiographic computer model.

A three-dimensional computer model was developed to stimulate the ventricular depolarization and repolarization in a clinical setting. The ventricle is composed of approximately 50,000 units arranged in a cubic close-packed structure and the specialized conduction system is distributed so as to obtain the excitation sequence resembling normal ventricular depolarization. The normal distribution of action potential waveforms with the longest duration on the endocardium and the shortest on the epicardium is used in the model. The heart model is mounted in a homogeneous torso model, and the body surface potential distribution generated by the electric dipoles is calculated using the boundary element method. The QRST waveforms corresponding to the normal and some abnormal heart conditions, such as bundle branch block, myocardial infarction, apical hypertrophic cardiomyopathy, and Wolff-Parkinson-White syndrome, is obtained by assuming the abnormal area with altered electrical properties. Thus the three-dimensional computer model may provide further insight into the genesis of the clinical electrocardiogram.

Bundle-Branch Block↗
PubMed1989

[Mechanisms underlying depressor and bradycardia effects of A1-excitation in rats].

In chloral hydrate-anesthetized, tubocurarine-immobilized and artificially ventilated rats, the following results were observed: (1) Microinjection of sodium L-glutamate (Glu) into A1 area induced a significant fall in blood pressure and heart rate. (2) Bilateral vagotomy markedly reduced the magnitude of the depressor and bradycardia effects of Glu-injection into A1. (3) Injection of phentolamine or propranolol into bilateral RVL reduced the depressor effect of Glu-injection into A1. Naloxone-injection into RVL had no significant influence on cardiovascular effects of A1-excitation, but injecting bicuculline into RVL could reverse both depressor and bradycardia effects of A1 area. The results suggest that A1 exerts its cardiovascular effects mainly via RVL, and the alpha-, beta- and GABA-receptors within RVL (but not opiate receptors) mediate the hypotension effect of A1 area, while GABA-receptors play an important role in mediating the bradycardia effect of the A1 area.

Animals↗
PubMed1989

[Mechanisms underlying depressor and bradycardia effects of A5-excitation (compared with that of A1-excitation) in rats].

Experiments were performed under the same condition described in the accompanying paper. (1) Injection of sodium L-glutamate (Glu) into A5 area of rat induced depressor and bradycardia responses, as Glu-injection into A1 area did. (2) Bilateral vagotomy also markedly attenuated the cardiovascular effect of Glu-injection into A5. (3) Influences of the receptor blockers injected into rostral ventrolateral medulla (RVL) on the depressor and bradycardia responses of Glu-injection into A5 were slightly different from those of the same receptor blockers administered into RVL: phentolamine, propranolol, naloxone and bicuculline all markedly reduced the depressor and bradycardia effects of A5-excitation (propranolol and bicuculline even reversed these effects). These results indicate that not only alpha-, beta-, GABA receptors, but also opiate receptors mediate the depressor and bradycardia effects of A5.

Animals↗