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Biomedical subjects

M Lei

Publications and source records attributed to M Lei.

At least 73 records · Page 4Linked to original sources
PubMed1996

Geometric design improvements for femoral graft-artery junctions mitigating restenosis.

The present study is based on the hypothesis that nonuniform hemodynamics, represented by large time-averaged wall shear stress gradients, trigger abnormal biological processes leading to rapid restenosis, i.e. excessive tissue overgrowth and renewed plaque formation, and hence early graft failure. It implies that this problem may be significantly mitigated by finding graft-artery bypass configurations for which the wall shear stress gradient is approximately zero and hence nearly uniform hemodynamics is achieved. These fluid flow and geometric design considerations are applied to four different end-to-side anastomoses for the distal end of a femoral artery bypass with an appropriate test input pulse and a typical 20-80 flow division. A validated finite-volume code has been used to compute the transient three-dimensional velocity vector fields, wall shear stress distributions and surface contours of the wall shear stress gradients. It is shown that large anastomotic flow areas, small continuously changing bifurcation angles, and smooth junction wall curvatures reduce local time-averaged wall shear stress gradients significantly and hence should mitigate restenosis.

Algorithms↗
PubMed1995

Rescue of adult mouse motoneurons from injury-induced cell death by glial cell line-derived neurotrophic factor.

Glial cell line-derived neurotrophic factor (GDNF) has been shown to rescue developing motoneurons in vivo and in vitro from both naturally occurring and axotomy-induced cell death. To test whether GDNF has trophic effects on adult motoneurons, we used a mouse model of injury-induced adult motoneuron degeneration. Injuring adult motoneuron axons at the exit point of the nerve from the spinal cord (avulsion) resulted in a 70% loss of motoneurons by 3 weeks following surgery and a complete loss by 6 weeks. Half of the loss was prevented by GDNF treatment. GDNF also induced an increase (hypertrophy) in the size of surviving motoneurons. These data provide strong evidence that the survival of injured adult mammalian motoneurons can be promoted by a known neurotrophic factor, suggesting the potential use of GDNF in therapeutic approaches to adult-onset motoneuron diseases such as amyotrophic lateral sclerosis.

Animals↗
PubMed1995

Expression of the rice Osgrp1 promoter-Gus reporter gene is specifically associated with cell elongation/expansion and differentiation.

To study the expression and regulation of a rice glycine-rich cell wall protein gene, Osgrp1, transgenic rice plants were regenerated that contain the Osgrp1 promoter or its 5' deletions fused with the bacterial beta-glucuronidase (GUS) reporter gene. We report here a detailed histochemical analysis of the Osgrp1-Gus expression patterns in transgenic rice plants. In roots of transgenic rice plants, GUS expression was specifically located in cell elongation and differentiation regions, and no GUS expression was detectable in the apical meristem and the mature region. In shoots, GUS activity was expressed only in young leaves or in the growing basal parts of developing leaves, and little GUS activity was expressed in mature leaves or mature parts of developing leaves. In shoot apices, GUS activity was detected only in those leaf cells which were starting to expand and differentiate, and GUS expression was not detected in the apical meristem and the young meristematic leaf primordia. GUS activity was highly expressed in the young stem tissue, particularly in the developing vascular bundles and epidermis. Thus, the expression of the Osgrp1 gene is closely associated with cell elongation/expansion during the post-mitotic cell differentiation process. The Osgrp1-Gus gene was also expressed in response to wounding and down-regulated by water-stress conditions in the elongation region of roots. Promoter deletion analysis indicates that both positive and negative mechanisms are involved in regulating the specific expression patterns. We propose a simple model for the developmental regulation of the Osgrp1 gene expression.

Base Sequence↗
PubMed1995

Numerical investigation and prediction of atherogenic sites in branching arteries.

Atherosclerosis, a disease of large- and medium-size arteries, is the chief cause of death in the US and most of the western world. It is widely accepted that the focal nature of the disease in arterial bends, junctions, and bifurcations is directly related to locally abnormal hemodynamics, often labeled "disturbed flows." Employing the aorto-celiac junction of rabbits as a representative atherosclerotic model and considering other branching blood vessels with their distinctive input wave forms, it is suggested that the local wall shear stress gradient (WSSG) is the single best indicator of nonuniform flow fields leading to atherogenesis. Alternative predictors of susceptible sites are briefly evaluated. The results discussed include transient velocity vector fields, wall shear stress gradient distributions, and a new dimensionless parameter for the prediction of the probable sites of stenotic developments in branching blood vessels. Some of the possible underlying biological aspects of atherogenesis due to locally significant /WSSG/-magnitudes are briefly discussed.

Animals↗
PubMed1994

Neurotrophic agents prevent motoneuron death following sciatic nerve section in the neonatal mouse.

We have examined the ability of different neurotrophic and growth factors to prevent axotomy-induced motoneuron cell death in the developing mouse spinal cord. After postnatal unilateral section of the mouse sciatic nerve, most motoneuron (MN) loss occurs in the lateral motor column of the fourth lumbar segment (L4). Significant axotomy-induced cell death occurred after surgery performed on or before postnatal day (PN) 5. In contrast, no significant cell loss was found when axotomy was performed after PN10. Axotomy on PN2 or PN5 resulted in a 44% loss of L4 motoneurons by 7 days, and a 66% loss of motoneurons by 10 days postsurgery. Implantation of gelfoam presoaked in various neurotrophic factors at the lesion site rescued axotomized motoneurons. Nerve growth factor (NGF), neurotrophin-4/5 (NT-4/5) and ciliary neurotrophic factor (CNTF) rescued 20%-30% of motoneurons, whereas brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and insulin-like growth factor 1 (IGF-1) rescued virtually all motoneurons from axotomy-induced death. By contrast, platelet-derived growth factor (PDGF)-AA, PDGF-AB, basic fibroblast growth factor (bFGF), and interleukin (IL-6) were ineffective on motoneuron survival following axotomy. NGF, BDNF, NT-3, IGF-1, and CNTF also prevented axotomy-induced atrophy of surviving motoneurons. These data show that mouse lumbar motoneurons continue to be vulnerable to axotomy up to about 1 week after birth and that a number of trophic agents, including the neurotrophins, CNTF, and IGF-1, can prevent the death of these neurons following axotomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

A direct sensitivity matrix approach for fast reconstruction in electrical impedance tomography.

In electrical impedance imaging, several proposed reconstruction algorithms have employed the concept of a sensitivity matrix, which can be used to relate the magnitude of a boundary voltage change of a 2D object to the change in conductivity inside the object that has given rise to it. The search for an appropriate inversion of the sensitivity matrix is the key to these algorithms. In this work, a method called the direct sensitivity matrix (DSM) approach for fast image reconstruction is proposed. Both theoretical and experimental results showing the efficiency of this proposed method are also presented.

Algorithms↗
PubMed1993

Airway hyperresponsiveness in cigarette smoke-exposed rats.

To investigate the possibility that altered airway-parenchymal interaction may account for bronchial hyperresponsiveness induced by cigarette smoke exposure, we tested the effect of administration of cigarette smoke (SM), elastase (EL), and both SM and EL on airway responsiveness in 41 Long-Evans male rats. Twelve were exposed to 30 puffs of SM for 15 weeks; 8 received a single intratracheal injection of EL (250 IU/kg); 9 received both EL and SM exposure (SE); 12 control rats were exposed to room air (CO). After 15 weeks, animals were anesthetized and mechanically ventilated (Vt = 2.5 ml, f = 80/min). Methacholine (MCh) dose-response curves (DRCs) were constructed by calculating pulmonary resistance (RL) after ultrasonic nebulization of saline followed by doubling concentrations of MCh (0.0625-256 mg/ml). Exposure to cigarette smoking, with or without elastase, led to a significant reduction in body weight and increased total lung capacity (TLC) compared to exposure to CO. However, there was no significant change in static compliance in the experimental groups, despite increased lung volume. The concentration resulting in a doubling of RL (EC200RL) was significantly lower in rats treated with SM (n = 7) than CO (n = 8) (3.3 vs. 56.1 mg/ml, geometric mean, p < 0.01). The concentration at which a maximal RL was achieved was lower in SM than CO, EL, and SE (p < 0.05). To assess the possible influence of airway-parenchymal interaction on responsiveness, we measured RL both at functional residual capacity (FRC) and at a volume above FRC equivalent to 1 tidal volume. RL changed similarly in all groups. Despite similar effects on mechanics of both cigarette smoke exposure and elastase administration, only cigarette smoke-exposed animals exhibited evidence of hyperresponsiveness. In this model cigarette smoke-induced hyperresponsiveness is unrelated to changes in either lung elasticity or airway-parenchymal interaction.

Airway Resistance↗
PubMed1993

Morphometry of methacholine-induced bronchoconstriction in the rat.

It has been suggested that parenchymal viscoelasticity accounts for a large proportion of resistive pressure losses induced by smooth muscle agonists. We used morphometric methods to evaluate the relative contributions of parenchyma and airways to mechanical changes during methacholine- (MCh) induced bronchoconstriction. We measured tracheal pressure and tidal volume in 17 open-chest mechanically ventilated Sprague-Dawley rats (frequency = 1.5 Hz, tidal volume = 2 ml, positive end-expiratory pressure = 5 cmH2O) after saline (n = 7, C), 16 mg/ml MCh (n = 5, L), and 256 mg/ml MCh (n = 5, H) aerosols. We calculated pulmonary resistance (RL) and elastance (EL) by fitting the equation PL = VRL + VEL + K, where PL is transpulmonary pressure, V is flow, and V is volume. V was obtained numerically from V. Lungs were rapidly frozen in liquid N2 30 s after aerosolization and processed with freeze substitution. Using midsagittal slices of left lung, we measured airway narrowing as the ratio of lumen area (aBM) subtended by the basement membrane perimeter (LBM) to predicted maximal lumen area (ABM = LBM2/4 pi). Air space size was estimated as mean linear intercept (Lm) and parenchymal distortion as standard deviation of linear intercepts (SDi). Lm was increased in L and H animals, reflecting hyperinflation; aBM/ABM in 0.17- to 0.43-mm-diam airways decreased progressively from C to L to H animals, reflecting bronchoconstriction. By use of stepwise multiple linear regression, the contribution of Lm to variance in mechanics was found to consistently exceed or equal that of aBM/ABM. SDi contributed little once Lm was taken into account.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosols↗
PubMed1993

[Rotundium in the treatment of atrial fibrillation].

L-tetrahydropalmatine (Rotundium) is an alkaloid of Corydalis turtschaninovii. Some animal experiments had demonstrated that Rotundium had a good antiarrhythmic effect in blocking the calcium channel and that it was a class IV antiarrhythmic agent, similar to that of Bepridil in literatures. This is a clinical report of Rotundium (oral given) on an atrial fibrillation (AF) patients. The therapeutical results were evaluated by 24 hours ambulatory electrocardiographic monitoring and ECG. The results showed that the effective rate of Rotundium on paroxysmal atrial fibrillation and sustained atrial fibrillation of 45 mm (left atrium diameter) or more was 30%, while LAD of less than 45 mm was 80% (P < 0.01). Among 8 cases' duration of AF were 6 months or more, 3 cases were effective, the effective rate 37.5%, while among 10 cases' duration of AF were less than 3 weeks, 3 cases were converted to sinus rhythm, 5 cases were effective. There was a significant difference between two groups. Age and sex exerted no effect on efficacy. During taking Rotundium, blood pressure had no apparent changes and no severe side effects were found. The results showed that Rotundium is an effective, safe new drug to treat AF, especially in paroxysmal atrial fibrillation. The antiarrhythmic mechanism of Rotundium might be related to its prolonging of the effective refractory period of atrial and atrioventricular node.

Adult↗
PubMed1992

Experimental and numerical analyses of the steady flow field around an aortic Björk-Shiley standard valve prosthesis.

To develop a numerical method for the description of the flow field around a Björk-Shiley (BS) standard valve prosthesis in aortic position, detailed experimental measurements and numerical calculations are performed under steady flow conditions. The experiment was conducted at Reynolds numbers up to 800. In order to perform LDA measurement of velocity in the vicinity of the valve with a curved sinus boundary, a mixture of oil and kerosine was used as the fluid which exactly matches the refractive index of the perspex aortic model. The velocity profiles at six positions in the vicinity and downstream of the valve were measured, including both axial and radial velocity components. The results show very clearly the existence of two nearly symmetric spiral vortex streams downstream of the valve. There is no recirculation area in the aorta downstream and also no obvious stagnation area in the minor orifice region near the valve when Re less than or equal to 800. Theoretically, the flow field of a BS valve is simulated by the flow pattern around a circular plate with an angle of incidence to the approaching stream. The numerical calculations were carried out by means of a 2-D model using the FEM together with the penalty function method. The maximum Reynolds number is 700. The results agree with the experimental results in the plane of symmetry when the Reynolds number is small. However, as the Reynolds number increases, the difference becomes evident. Our conclusion is that the steady flow field of a BS valve is completely 3-dimensional, featured by two spiral vortices. It cannot be simulated exactly by 2-D numerical calculations. To get more detailed and complete information about the flow field of this valve, 3-D numerical calculations are needed.

Aorta↗
PubMed1992

Tissue viscance during induced constriction in rabbit lungs: morphological-physiological correlations.

Tissue viscance (Vti), the pressure drop across the lung tissues in phase with flow, increases after induced constriction. To gain information about the possible site of response, we induced increases in Vti with methacholine (MCh) and attempted to correlate these changes with alterations in lung morphology. We measured tracheal (Ptr) and alveolar pressure (PA) in open-chest rabbits during mechanical ventilation [frequency = 1 Hz, tidal volume = 5 ml/kg, positive end-expiratory pressure (PEEP) = 5 cmH2O] under control conditions and after administration of saline or MCh (32 or 128 mg/ml) aerosols. We calculated lung elastance (EL), lung resistance (RL), Vti, and airway resistance (Raw) by fitting the equation of motion to changes in Ptr and PA. The lungs were then frozen in situ with liquid nitrogen (PEEP = 5 cmH2O), excised, and processed using freeze substitution techniques. Airway constriction was assessed by measuring the ratio of the airway lumen (A) to the ideally relaxed area (Ar). Tissue distortion was assessed by measuring the mean linear intercept between alveolar walls (Lm), the standard deviation of Lm (SDLm), and an atelectasis index (ATI) derived by calculating the ratio of tissue to air space using computer image analysis. RL, Vti, and EL were significantly increased after MCh, and Raw was unchanged. A/Ar, Lm, SDLm, and ATI all changed significantly with MCh. Log-normalized change (% of baseline) in Vti significantly correlated with A/Ar (r = -0.693), Lm (r = 0.691), SDLm (r = 0.648), and ATI (r = 0.656). Hence, changes in lung tissue mechanics correlated with changes in morphometric indexes of parenchymal distortion and airway constriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosols↗
PubMed1992

Morphometric changes during the early airway response to allergen challenge in the rat.

The purpose of this study was to determine the relative contributions of airway wall edema and smooth muscle contraction to the early response (ER) of allergic bronchoconstriction. Brown Norway rats, 6 to 7 wk old, were sensitized with ovalbumin (OA). Anesthetized rats were challenged with either OA or saline 2 wk later. Pulmonary resistance (RL) was measured every minute until either it increased to 150% of the baseline, defined as a significant ER, or until 15 min elapsed. Eight OA-challenged test rats with a significant ER and eight saline-challenged control rats were used for morphometric studies. The lungs were quick-frozen with liquid nitrogen, processed with freeze substitution, and sagittal sections (5 microns) were stained with hematoxylin and eosin. The airway lumen subtended by the epithelial basement membrane (LuB) and cross sectional airway wall area (AW) of all airways were measured by camera lucida and digitization. The LuB and AW of each airway was standardized for size by dividing by the ideal airway lumen (LuBideal), which was calculated from the length of basement membrane, assuming a perfect circle in the unconstricted state. The cumulative frequency distribution of the LuB/LuBideal for the airways from test rats was shifted to the left compared with the control rats (p less than 0.01), indicating airway narrowing after challenge. Airway narrowing increased as a function of airway size. Cumulative frequency distributions of AW/LuBideal showed that there was a significant increase in the wall thickness of only the small airways of test animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Allergens↗
PubMed1991

A novel glycine-rich cell wall protein gene in rice.

A genomic clone isolated from rice (Oryza sativa var. IR 36) contains a gene that encodes a glycine-rich cell wall protein. This gene is a member of a multi-gene family. Two transcripts with different 5' termini are encoded by this gene and the expression of these two transcripts is differentially regulated. The amino acid sequence derived from the DNA sequence of this gene has a putative amino terminal signal peptide, and a highly repetitive structure in the putative mature protein. A model is proposed which describes the potential monomeric structure of this glycine-rich protein and how these monomers may be covalently linked to produce a network-like structure.

Amino Acid Sequence↗
PubMed1991

Structure and molecular evolutionary analysis of a plant cytochrome c gene: surprising implications for Arabidopsis thaliana.

We have isolated a cytochrome c gene from Arabidopsis thaliana (cv. Columbia), which is the first cytochrome c gene to be cloned from a higher plant. Genomic DNA blot analysis indicates that there is only one copy of cytochrome c in Arabidopsis. The gene consists of three exons separated by two introns. Gene features such as regulatory regions, codon usage, and conserved splicing-specific sequences are all present and typical of dicotyledonous plant nuclear genes. We have constructed phenograms and cladograms for cytochrome c amino acid sequences and histone H3, alcohol dehydrogenase, and actin DNA sequences. For both cytochrome c and histone H3, Arabidopsis clusters poorly with other higher plants. Instead, it clusters with Neurospora and/or the yeasts. We suggest that perhaps this observation should be considered when using Arabidopsis as a model system for higher plants.

Actins↗