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Biomedical subjects

L Tan

Publications and source records attributed to L Tan.

At least 73 records · Page 4Linked to original sources
PubMed1999

Biomechanics of A-to-T flap design.

OBJECTIVES/HYPOTHESIS: The objective of this study was to determine the vertical height, horizontal incision width, and extent of undermining that correlated with the lowest closure tension. STUDY DESIGN: Prospective, cadaver study. METHODS: Forty "A-to-T" flaps were made on the torso and lower extremities of fresh cadavers. Ten flaps each were designed at heights of three, four, and five defect radii. Closing tensions were measured for each of these flaps initially, followed by serial base extensions. Based on the information from these first flaps, 10 additional flaps were made at the optimal height and base extensions. These flaps were then serially undermined and tension measurements taken. RESULTS: Our results suggest that making the vertical height of the "A" twice the height of the defect yields a significant decrease in tension of closure when compared with a vertical height one and a half times the defect (P < .01), while increasing the height to two and a half times the defect height provides only a minimal further reduction in closure tension. Extending the base (horizontal) incision one defect diameter in each direction offers the greatest reduction in closing tension. Undermining up to three times the diameter of the defect offers progressive improvement in the tension of closure, while further undermining confers little additional benefit. CONCLUSIONS: Our findings indicate that the ideal A-to-T flap is designed to be twice the height of the original defect, with base extensions one defect diameter in each direction, and undermined to three times the diameter of the defect.

Biomechanical Phenomena↗
PubMed1999

An integrated theory of the no-reflow phenomenon and the beneficial effect of vascular washout on no-reflow.

OBJECTIVES: No-reflow is failure of perfusion in free tissue transfer despite adequate arterial inflow. The objectives of this study were to construct a theory of interactive mechanisms of the no-reflow phenomenon and to determine whether preischemic vascular washout could increase flap ischemia tolerance. STUDY DESIGN: The evidence for the role of various mechanisms in the development of no-reflow is reviewed, and an integrated network proposed. A rat-groin free flap model is used to test preischemic vascular washout with normal saline, heparinized normal saline, lactated Ringer's solution, Tis-U-Sol, and Viaspan. METHODS: The mean ischemia tolerance of this flap without any therapeutic intervention was first determined, using 22 animals. An additional 50 animals were used to compare with the control group the ischemia tolerance of flaps washed out with the above fluids before their ischemic period. RESULTS: The critical ischemia time 50 (time after which half of the flaps are expected to survive and half, die) of the untreated flap is 23.4 hours in this model (P<.05). Flaps washed out with normal saline or lactated Ringer's solution have significantly worse ischemia tolerance (P<.0001). Flaps washed out with Tis-U-Sol or Viaspan behave similarly to the control group (P>.57). Flaps receiving preischemic washout with heparinized normal saline (4,000 units/L) had a significantly better outcome than the control group (P<.027). CONCLUSIONS: Preischemic washout with normal saline, lactated Ringer's solution, or heparinized Tis-U-Sol is detrimental for flap survival after ischemia, Tis-U-Sol- and Viaspan-treated flaps do have ischemia tolerance similar to the control group, and flaps washed out with heparinized normal saline have a survival advantage in this model.

Animals↗
PubMed1999

Interobserver variability in the measurement of internal carotid stenosis.

OBJECTIVE: To assess interobserver variability in the measurement of carotid stenoses from digital subtraction angiograms displayed in different ways (nonmagnified or magnified, white or black arteries); and to compare human readers with computer-generated densitometric measurements of vessel stenosis. METHODS: Digital subtraction angiograms of 20 proximal internal carotid artery stenoses were laser printed in the following ways: (1) Nonmagnified white artery on a black background; (2) Magnified white artery on a black background; (3) Nonmagnified black artery on a white background; (4) Magnified black artery on a white background. This resulted in 80 images of internal carotid artery stenoses. These stenoses were independently measured by 4 radiologists using the North American Symptomatic Carotid Endarterectomy Trial method. A computer-generated densitometric measurement of the black nonmagnified images was also obtained. RESULTS: The most reliable stenosis measurements were obtained from the nonmagnified black and white artery images. The interobserver variability in the measurement of internal carotid stenoses using these images was quite small. Variability increased with the use of magnification. The computer-generated stenosis measurements were consistently much higher than those of the radiologists. CONCLUSION: There was significant variability in measurements made from magnified images and between human readers and computer-generated measurements. This has great clinical significance. Readers of digital angiographic images must determine the most reliable, reproducible images generated by their equipment, as these measurements significantly affect treatment of patients with symptomatic internal carotid artery stenosis.

Absorptiometry, Photon↗
PubMed1999

Treatment of delayed partial bronchial rupture with expandable metallic stent.

Traumatic bronchial rupture is a rare entity. The severity of the trauma often causes lethal injury to other thoracic organs. The incidence in patients with blunt chest trauma admitted to the hospital ranges from 1.5% to 3%. As a rule, early diagnosis and surgical treatment are important to facilitate successful repair of the disruption. We describe an unusual case of bronchial rupture which was diagnosed 15 days after blunt chest trauma and was treated by bronchial stenting. The success of this case involving the left main bronchial rupture provides a feasible alternative to the repair of partial airway disruption and greatly reduces the morbidity.

Adult↗
PubMed1999

[Influence of nitric oxide upon cerebral infarction in 15 cases].

To study the role of the nitric oxide(NO) in patients with cerebral infarction, NO in cerebrospinal fluid was determined in cerebral infarction group(15 cases) and control group(10 cases). Infarct volume was determined by CT between the second and the 7th day after the onset of symptoms. The severity of neurological deficits was assessed with the stroke scale of Ministry of Public Healthy(China). The results showed that NO was higher in cerebral infarction group (3.12 +/- 1.60) than that in control group(1.19 +/- 1.01) (P < 0.01). The concentration of NO was positively correlated with infarction volume(r = 0.57, P < 0.05) and severity of neurological of deficits(r = 0.54, P < 0.05), respectively. The results support the conclusion that NO produced in large amounts in the postischemic tissue contributes to the progression of the brain damage, which was demonstrated in animal models of focal cerebral ischemia.

Adult↗
PubMed1999

[Survey of jugular bulb with MRA in sudden sensorineural hearing loss].

To evaluate the correlation between the size and position of the jugular bulb and the sudden sensorineural hearing loss(SSHL), the diameter and height of all jugular bulbs were measured with magnetic resonance angiography and analysed with statistics in 15 cases with SSHL and 35 cases without SSHL(as control). The ipsilateral and the contralateral bulbs of the SSHL were more asymmetrical than that of the control. The mean diameter and height of the ipsilateral bulbs of SSHL were larger than that of the dominant side bulbs of the control. It indicates that the heteroplasia of jugular bulbs which were greatly enlarged and bulgy upward might be related to SSHL.

Adult↗
PubMed1999

Feasibility study of an ultrasound contrast agent (levovist) in color Doppler imaging of liver neoplasms.

The purpose of this study was to determine the efficacy of using an ultrasound contrast agent (levovist) to enhance the color Doppler imaging of liver neoplasms. Thirty patients with hepatic tumors were enrolled in this study. After intravenous administration of levovist, the color Doppler signals of normal hepatic vessels were enhanced. In various hepatic tumors, the different patterns of tumor vascularity were observed, which had not been demonstrated in conventional non-contrast color Doppler imaging. In 11 of 16 patients with hepatocarcinoma, additional color Doppler signals were observed in the central part of the tumors. On the contrary, 3 patients with metastatic liver lesions the enhanced color Doppler signals appear only at the peripheral of tumors. A typical rim-like color enhancement was seen in 2 of the 3 cases. In six patients with hepatic hemangiomas contrast-enhanced color Doppler imaging demonstrated the blood vessels at the margin of the neoplasms. Contrast-enhanced color Doppler imaging improves the visualization of the hepatic neoplasm vascularity. This technique holds great promise for detecting small liver tumors and differentiating hepatic neoplasms.

Adult↗
PubMed1998

Tissue-specific up-regulation of B7-1 expression and function during the course of murine relapsing experimental autoimmune encephalomyelitis.

B7/CD28-mediated costimulation is a promising target for therapeutic intervention in autoimmune diseases. However, studies addressing the differential functional roles of B7-1 and B7-2 in several autoimmune models have resulted in conflicting data, perhaps due to the temporal dynamics of B7-1 and B7-2 surface expression on different cell types and/or at different sites during an autoimmune response. We examined the temporal expression of B7 costimulatory molecules in the CNS and in various lymphoid organs during the course of murine relapsing-remitting experimental autoimmune encephalomyelitis (R-EAE). Following immunization of SJL mice with the immunodominant proteolipid protein epitope, PLP139-151, surface expression of B7-1 was up-regulated on B cells, T cells, and macrophages, relative to B7-2, on CNS-infiltrating cells and on splenocytes. Similar enhancement in splenic B7-1 expression could be induced in SJL mice by the adoptive transfer of PLP139-151-specific cells or by immunization with CFA alone. These changes were not observed on lymph node cells, including those isolated from lymph nodes draining the immunization site, which maintained the predominant B7-2 expression pattern seen in naive mice. These phenotypic expression patterns correlated with the functional predominance of B7-1 in costimulating T cell activation when employing APCs from the spleen or CNS of mice with ongoing R-EAE, while B7-2 remained functionally predominant on lymph node APCs. Variation of phenotypic expression and functional dominance of costimulatory molecule expression in different lymphoid compartments during an active inflammatory autoimmune response has important implications in immune regulation, autoimmune pathogenesis, and therapeutic strategies.

Animals↗
PubMed1998

Direct visualization of antigen-specific CD8+ T cells during the primary immune response to Epstein-Barr virus In vivo.

Primary infection with virus can stimulate a vigorous cytotoxic T cell response. The magnitude of the antigen-specific component versus the bystander component of a primary T cell response remains controversial. In this study, we have used tetrameric major histocompatibility complex-peptide complexes to directly visualize antigen-specific cluster of differentration (CD)8+ T cells during the primary immune response to Epstein-Barr virus (EBV) infection in humans. We show that massive expansion of activated, antigen-specific T cells occurs during the primary response to this virus. In one individual, T cells specific for a single EBV epitope comprised 44% of the total CD8+ T cells within peripheral blood. The majority of the antigen-specific cells had an activated/memory phenotype, with expression of human histocompatibility leukocyte antigen (HLA) DR, CD38, and CD45RO, downregulation of CD62 leukocyte (CD62L), and low levels of expression of CD45RA. After recovery from AIM, the frequency of antigen-specific T cells fell in most donors studied, although populations of antigen-specific cells continued to be easily detectable for at least 3 yr.

Antigens, CD↗
PubMed1998

Presentation of proteolipid protein epitopes and B7-1-dependent activation of encephalitogenic T cells by IFN-gamma-activated SJL/J astrocytes.

There is controversy regarding the possible role of glial cells as APCs in the pathogenesis of central nervous system (CNS) demyelinating diseases such as multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). Microglia have been clearly shown to present Ag in the CNS, and due to the proximity of activated astroglial cells to infiltrating T cells and macrophages in demyelinating lesions, it is also possible that astrocytes positively or negatively regulate disease initiation and/or progression. We examined the capacity of IFN-gamma-treated astrocytes from EAE-susceptible SJL/J mice to process and present myelin epitopes. IFN-gamma activation up-regulated ICAM-1, VCAM-1, MHC class II, invariant chain, H2-M, CD40, and B7-1 as determined by FACS and/or RT-PCR analyses. B7-2 expression was only marginally enhanced on SJL/J astrocytes. Consistent with the expression of these accessory molecules, IFN-gamma-treated SJL/J astrocytes induced the B7-1-dependent activation of Th1 lines and lymph node T cells specific for the immunodominant encephalitogenic proteolipid protein (PLP) epitope (PLP139-151) as assessed by proliferation and activation for the adoptive transfer of EAE. Interestingly, IFN-gamma-activated astrocytes efficiently processed and presented PLP139-151, but not the subdominant PLP178-191, PLP56-70, or PLP104-117 epitopes, from intact PLP and a recombinant variant fusion protein of PLP (MP4). The data are consistent with the hypothesis that astrocytes in the proinflammatory CNS environment have the capability of activating CNS-infiltrating encephalitogenic T cells specific for immunodominant epitopes on various myelin proteins that may be involved in either the initial or the relapsing stages of EAE.

Adoptive Transfer↗
PubMed1998

T cell selection during the evolution of CD8+ T cell memory in vivo.

Memory T cell responses are frequently highly restricted in terms of receptor usage. How and when such clonotypic dominance is established remains poorly understood. Here we have investigated the evolution of the T cell responses to an epitope from Epstein-Barr virus (EBV), (FLRGRAYGL), by analyzing TCR use of clones specific for this epitope, derived from peripheral blood mononuclear cells taken from individuals early during primary EBV infection and up to 3 years later. We show that, in a given individual, particular T cell clonotypes are selected early during the primary response to this epitope and that the same clonotypes dominate the late memory response. In one individual direct analysis of HLA-B8-restricted FLRGRAYGL-specific T cells, isolated from peripheral blood lymphocytes taken during primary EBV infection using a tetrameric MHC-peptide complex, confirmed the early selection of the dominant clonotypes.

Amino Acid Sequence↗
PubMed1998

Arterial embolization for bleeding following hysterectomy for intractable postpartum hemorrhage.

Angiographic embolization is a well documented technique that has been utilized for controlling pelvic hemorrhage. A case is described of a 41-year-old para 3 woman with intractable bleeding following a cesarean hysterectomy for postpartum hemorrhage due to uterine atony and coagulopathy. On angiogram, no bleeding was seen from the uterine vessels. An injection of dye above the origin of the gonadal vessels showed persistent hemorrhage from the left ovarian artery. This report illustrates the importance of intensive resuscitation and supportive measures, and the value of angiographic embolization after failed surgery. It also emphasizes the need to locate the exact bleeding vessel on angiography for embolization to be successful.

Adult↗
PubMed1998

Role of corticotropin-releasing factor and substance P in pressor responses of nuclei controlling emotion and stress.

The wide distribution of corticotropin-releasing factor (CRF) and substance P (SP)-immunoreactive cell bodies, nerve terminals and corresponding receptors in pressor nuclei controlling emotion and stress implies that CRF and SP may play important roles in pressor responses of these nuclei; hence CRF or SP was microinjected into these nuclei respectively in Wistar male rats anesthetized with urethane to test this possibility. Microinjection of CRF into nucleus amygdaloideus centralis, nucleus paraventricularis, nucleus ventromedialis, lateral hypothalamus-perifornical region, periaqueductal gray matter, nucleus parabrachialis, locus coeruleus or rostral ventrolateral medulla respectively could evoke pressor responses (but CRF injection into nucleus dorsomedialis could not elicit significant pressor responses). Injection of substance P into all the above nuclei could also elicit hypertensive responses of different magnitudes, whereas normal saline injection into these nuclei had no effect. These results indicate that both CRF and SP in the above mentioned nuclei may play important roles in hypertension induced by prolonged emotional stress.

Animals↗
PubMed1998

PAK kinases are directly coupled to the PIX family of nucleotide exchange factors.

The PAK family of kinases are regulated through interaction with the small GTPases Cdc42 and Rac1, but little is known of the signaling components immediately upstream or downstream of these proteins. We have purified and cloned a new class of Rho-p21 guanine nucleotide exchange factor binding tightly through its N-terminal SH3 domain to a conserved proline-rich PAK sequence with a Kd of 24 nM. This PAK-interacting exchange factor (PIX), which is widely expressed and enriched in Cdc42- and Rac1-driven focal complexes, is required for PAK recruitment to these sites. PIX can induce membrane ruffling, with an associated activation of Rac1. Our results suggest a role for PIX in Cdc42-to-Rac1 signaling, involving the PIX/PAK complex.

3T3 Cells↗