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Biomedical subjects

T W Chow

Publications and source records attributed to T W Chow.

At least 37 records · Page 2Linked to original sources
PubMed2000

Antibody inhibitors to von Willebrand factor metalloproteinase and increased binding of von Willebrand factor to platelets in ticlopidine-associated thrombotic thrombocytopenic purpura.

BACKGROUND: Thrombotic thrombocytopenic purpura (TTP) affects 1 in 1600 to 1 in 5000 patients who receive ticlopidine, but little is known about the pathogenesis of this complication. OBJECTIVE: To investigate whether von Willebrand factor (vWF), which has been associated with idiopathic TTP, is involved in the pathogenesis of ticlopidine-associated TTP. DESIGN: Case series. SETTING: Three tertiary care, university-affiliated medical centers. PATIENTS: Seven patients who developed TTP 2 to 7 weeks after initiation of ticlopidine therapy. Controls were 7 consecutive patients without thrombocytopenia who had been receiving ticlopidine for 3 to 5 weeks and 10 randomly selected hospitalized patients. MEASUREMENTS: Platelet-bound vWF in patients' EDTA-anticoagulated whole blood samples; vWF proteinase activity in patients' plasma samples; inhibitory activity of IgG isolated from patients' plasma samples against the proteinase from the controls' plasma samples; and vWF multimeric patterns in patients' EDTA-anticoagulated plasma samples. RESULTS: Binding of vWF to single platelets was increased in the three patients tested during the most thrombocytopenic phase of TTP episodes. Initial plasma samples from all seven patients lacked the largest vWF multimers and were severely deficient in vWF metalloproteinase. IgG molecules, isolated from plasma samples of five patients, inhibited metalloproteinase in plasma samples from the controls. In patients examined, these abnormalities resolved upon the remission that accompanied plasma exchange and discontinuation of ticlopidine therapy. CONCLUSION: In the patients who developed ticlopidine-associated TTP, autoantibodies to the vWF metalloproteinase were formed; this led to the same type of vWF abnormalities observed in patients with idiopathic acute TTP. The findings suggest that failure to process large and unusually large vWF multimers in vivo caused binding of vWF to platelets, systemic platelet thrombosis, and TTP.

Aged↗
PubMed2000

Utilization of Alzheimer's disease community resources by Asian-Americans in California.

Alzheimer's disease is as prevalent among Asian ethnic minority groups as among Caucasians. We explored Asian groups' utilization of available Alzheimer's disease services in California, using a uniquely large sample of Asian-Americans. The Minimum Uniform Dataset includes data from nine California Alzheimer's Disease Diagnostic and Treatment Centers. Of the 9,451 cases included in the Minimum Utilizable Dataset, 4.2% were Asian (primarily Chinese), 0.8% Filipino, 0.3% Pacific Islander, and 75.9% Caucasian. In comparison to their numbers within the nine California countries served, Asian ethnic elders were underrepresented in enrollment by approximately 50%, except at one center where all staff were bilingual. The centers referred a significantly greater proportion of Asian than Caucasian patients for financial help (47.8 vs. 7.4%, P < 0.001), case management (47.8 vs. 22.3%, P < 0.001), and to Alzheimer's disease day care (41.3 vs. 28.4%, P < 0.05). A significantly greater proportion of Asian caregivers received referrals to caregiver resource centers (32.6 vs. 61.3%, P < 0.001) and financial help (29.6 vs. 4.7%, P < 0.001). A smaller proportion of Asian patients received referrals to home health services than Caucasians (4.3 vs. 14.9%, P < 0.05). Filipino patients were also referred more frequently to financial assistance than Caucasians (P < 0.05). Asians and Pacific Islanders under-enroll at centers specializing in AD care. Bilingual staff at centers specializing in dementia care, training for community physicians who treat these patients, and establishment of caregiver support groups within Asian and Pacific Islander communities may enhance the enrollment of these elders. AD care centers in areas supporting Asian and Filipino families may need to concentrate resources on providing financial assistance in case management.

Aged↗
PubMed2000

Personality in frontal lobe disorders.

Personality changes in frontal lobe disorders are easy to recognize, but their evolution can be hard to predict. Both focal lesions and diffuse neurodegenerative processes may produce personality change based on interruption of prefrontal cortex or subcortical structures that comprise the frontal-subcortical circuits. Observed changes in personality have been classified by behavioral neurologists into three frontal-subcortical circuit syndromes, yet a given patient may defy this classification system by manifesting only selective features of one or more syndromes simultaneously, based on the neuroanatomic distribution of pathology. The orbitofrontal syndrome is the most well known and consists of major antisocial behaviors such as disinhibition, emotional lability, and impulsivity. In some cases, changes are severe enough to lead to new onset of criminality. Apathy and amotivational state lie at the other end of the personality change spectrum. Many psychologic instruments can measure the degree of change in personality, but none of them can be used to extrapolate a patient's ability to function at home or at large in society. The psychopathy checklist by Hare may predict risk of violence but has been validated only for use in criminal populations.

Brain Diseases↗
PubMed2000

Thrombin receptor activating peptide (SFLLRN) potentiates shear-induced platelet microvesiculation.

Shear-induced activation of platelets plays a major role in vascular thrombosis. Shear stress tends to increase both platelet aggregation and procoagulant activity. One mechanism for increased procoagulant activity is promotion of the transbilayer movement of anionic phospholipids from the inner to the outer leaflet of the platelet membrane bilayer. This is accompanied by vesiculation of the platelet membrane, resulting in the formation of procoagulant membrane particles called microvesicles. In this study we have examined the effect of various platelet agonists on shear-induced platelet microvesiculation and the development of platelet procoagulant activity. Normal citrated whole blood was subjected to laminar shear rate up to 12,500 sec(-1) (shear stress approximately 375 dyne/cm2) in a cone-and-plate viscometer, and the formation of platelet microvesicles was measured by flow cytometry under different conditions. Elevated levels of shear stress induced significant microvesiculation. We investigated the effects of adenosine diphosphate, epinephrine, thromboxane A2 analog, collagen, and thrombin receptor activation peptide (SFLLRN) on shear-induced platelet microvesiculation. The thrombin peptide significantly increased shear-induced microvesicle formation. In contrast, under similar conditions, the other agonists had no significant effect on shear-induced microvesiculation. These studies suggest that thrombin formed in the vicinity of primary hemostatic plugs in areas of elevated shear stress may have a major role in the propagation of thrombi by potentiating shear-induced platelet microvesiculation.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed2000

Oral health status of patients 5-6 years after placement of cobalt-chromium removable partial dentures.

This study is a clinical survey of cobalt-chromium (Co-Cr) removable partial denture (RPD) wearers that aimed to investigate the effects of denture wearing on oral tissues. A random sample of patients who had received their dentures 5-6 years previously from a dental teaching hospital in Hong Kong was selected. Those who had been constantly wearing the RPDs were examined by one calibrated examiner under an optimal clinical setting. The patients' dental, periodontal and mucosal status were assessed. A total of 87 patients were examined. Mucosal lesions under the Co-Cr RPDs were uncommon in this study sample. However, there was a high prevalence of plaque, gingivitis and gingival recession, especially in dento-gingival surfaces in close proximity (within 3 mm) to the dentures. Thus, there is a special need for regular oral hygiene reinforcement, scaling and prophylaxis among RPD wearers. Despite a low caries incidence in the study sample, root caries were found to be associated with contact with the RPDs (P < 0.05) but coronal caries were not. It is recommended that coverage of the exposed root surfaces by RPD components should be avoided. Also, topical fluorides should be regularly applied onto exposed root surfaces as a preventive measure.

Adult↗
PubMed2000

Retrievable cement-retained implant-tooth-supported prosthesis: a new technique.

Clinicians often encounter difficulties with connecting natural teeth and osseointegrated implants. A new clinical technique with laboratory procedures are presented. The technique involves cementation of a two-part prosthesis over natural teeth and customized implant gold cylinders. This method achieved a passive-fit fixed bridge with retrievability maintained.

Adolescent↗
PubMed2000

A new prosthodontic technique for fabricating cement-retained implant-supported prostheses.

This article describes a new technique for fabricating cement-retained implant-supported prostheses. The technique involves cementation of the prostheses over customized gold cylinders. Access channels are incorporated in the prostheses to allow future access of the gold screws. This technique can be used in various clinical situations to achieve total passive fit of the framework without compromising retrievability. The technique overcomes the problems encountered with other previously advocated methods for constructing such prostheses. In addition, maintenance of the resulting prostheses is uncomplicated.

Cementation↗
PubMed1999

Inheritance of frontotemporal dementia.

BACKGROUND: Previous studies of families with fronto-temporal dementia (FTD) support an autosomal dominant inheritance pattern, but most studies have described genetic transmission in individual families specifically selected for the presence of multiple affected individuals. OBJECTIVE: To investigate the familial presentation and inheritance of FTD and related disorders among a large group of FTD index cases unselected for family history of dementia. DESIGN AND SETTING: We interviewed family members and reviewed medical records and autopsy reports at a university hospital and a university-affiliated hospital to determine the frequency of familial FTD and the most likely mode of inheritance. Characteristic families with the disorder are described, along with the history, clinical findings, and neuroimaging results in affected members of these families. PATIENTS AND PARTICIPANTS: The 42 index cases of FTD had a mean age of onset of 56.1 years (range, 40-69 years). Of these patients, 21 (50%) were women. All but one of the patients were white. Participants included male and female spouses and children of the index cases. family member with an FTD spectrum disorder and were considered familial cases. The majority (17 [89%]) of familial FTD cases showed a pattern consistent with dominant inheritance. If depression is excluded, familial cases decrease from 19 (45%) to 17 (40%), of which 15 (88%) showed a dominant transmission pattern. The initial presentations in the nonindex familial cases varied but most frequently consisted of personality and behavioral changes that preceded cognitive impairment (19 [43%]), followed by psychiatric illness (14 [33%]), dementia without behavioral change (5 [11%]), amyotrophic lateral sclerosis (5 [11%]), and parkinsonism (2[5%]). Two of the affected nonindex cases had dual presenting diagnoses. The average age of onset was 56.1 years and did not differ significantly between familial and nonfamilial cases. Onset of FTD-related symptoms occurred after the age of 65 years in only 4(10%) of 42 index cases and 3 (5%) of 60 affected relatives. CONCLUSIONS: Familial FTD is usually inherited in an autosomal dominant pattern. The initial onset is insidious, often consisting of mood and behavioral changes occurring in presenile years that are often erroneously attributed to other nonneurologic causes. Although the precise incidence of FTD in North America is not known, it is one of the most common presenile dementias.

Adult↗
PubMed1999

Effect of adhesive drying time on the bond strength of irreversible hydrocolloid to stainless steel.

STATEMENT OF PROBLEM: The efficacy of adhesive material is believed to be affected by the drying time allowed. However, there is no universal consensus on the drying time required for adhesive to achieve optimal bond strength for irreversible hydrocolloid impressions. PURPOSE: This study investigated the effect of drying time on the cleavage bond strength of irreversible hydrocolloid adhesive and determined optimal adhesive drying time. MATERIAL AND METHODS: In the cleavage test, the adhesive bond was stressed at the edge. An offset tensile force was applied to 1 side of the testing plates to split the bond. Cleavage testing plates were designed and machined in stainless steel. Adhesive material (Fix) was applied thinly to the plates and allowed to dry for 1, 3, 5, 7.5, 10, and 20 minutes before loading with an irreversible hydrocolloid (Blueprint). The irreversible hydrocolloid was then allowed to set for 5 minutes before testing. Twenty specimens were tested for each selected drying time. The force at failure was measured by an Instron machine with a crosshead speed of 50 mm/min applied to the edge of the bond. A nonadhesive group was included as a control. RESULTS: The calculated cleavage bond strength at 1-minute drying (32 kPa) improved moderately up to 5-minute drying (37 kPa), but decreased on further drying. When compared with specimens in the nonadhesive group, cleavage bond strength was 3 times greater when the adhesive was applied and dried for 5 minutes. CONCLUSIONS: Adhesive is effective in improving the cleavage bond strength of irreversible hydrocolloid to stainless steel, and drying of adhesive in excess of 5 minutes is not recommended.

2-Propanol↗
PubMed1999

Effect of processing method on the dimensional accuracy and water sorption of acrylic resin dentures.

STATEMENT OF PROBLEM: Acrylic resin complete dentures exhibit certain unavoidable dimensional changes. Processing shrinkage and expansion due to water uptake are 2 important aspects influencing dimensional accuracy. PURPOSE: This study investigated linear dimensional changes and water sorption of dentures processed by dry and wet heat with different rates of cooling. METHODS: Fine crosses marked on tinfoil inserts were placed at the incisive papilla and tuberosity regions of edentulous maxillary casts and incorporated into the dentures during polymerization by 3 processing techniques. A traveling microscope was used to measure the distances between the reference points to determine dimensional changes. Water uptake and content were determined by the mass changes of the dentures with an electronic balance. Data of linear dimensional change and water sorption were analyzed by multivariate analysis of variance and analysis of variance, respectively. Bonferroni simultaneous confidence intervals (95%) were applied for multiple comparison. RESULTS: Dry heat-processed and water bath-processed acrylic resin dentures did not exhibit significant differences in shrinkage (0.42% to 0.58%) at water saturation. Amounts of water sorption of dentures processed by dry and wet heat (0.50 and 0.48 mass%, respectively) were not significantly different, and their associated expansion did not entirely compensate for the processing shrinkage. The initial water content of dry heat-processed dentures (1.77 mass%) was unexpectedly slightly higher than that of wet heat-processed dentures (1.68 mass%). The rate at which the dentures cooled did not affect their initial water content and subsequent water uptake. CONCLUSIONS: Water uptake of dry and wet heat-processed acrylic resin dentures after deflasking was in both cases low, and the dentures did not reveal significant differences in shrinkage at water saturation. Air oven-processed and water bath-processed acrylic resin dentures show similar dimensional shrinkage at water saturation.

Acrylic Resins↗
PubMed1999

Chimeric 7E3 Fab (ReoPro) decreases detectable CD11b on neutrophils from patients undergoing coronary angioplasty.

OBJECTIVES: The purpose of this study was to monitor the effects of chimeric 7E3 Fab (ReoPro) on leukocyte and platelet activation and interaction during coronary angioplasty. BACKGROUND: Increased expression of CD11b on monocytes and neutrophils promotes their adhesion to endothelial cells, extracellular matrix and smooth muscle cells. Thrombin-activated platelets adhere via P-selectin to monocytes and neutrophils. These cell interactions may affect the outcome of coronary angioplasty. METHODS: During coronary angioplasty, venous blood was obtained for flow cytometric detection of leukocyte CD11b; platelet CD41a, CD61a and CD62P; the percentage of leukocytes with adherent platelets and the intensity of bound platelet fluorescence. RESULTS: Leukocyte CD11b expression increased after angioplasty in control patients (neutrophils 171+/-25 to 255+/-31 mean fluorescence intensity [MFI, mean+/-SEM], n=25, p < 0.0001; monocytes 200+/-40 to 248+/-36 MFI, n=17, p < 0.05) and decreased in the patients selected to receive chimeric 7E3 Fab (neutrophils 146+/-30 to 82+/-22 MFI, n=25, p < 0.0001; monocytes 256+/- 53 to 160+/-38 MFI, n= 17, p < 0.05). Neutrophil CD11b decreased after in vitro incubation of whole blood with chimeric 7E3 Fab (n=5, p=0.01), but fMLP-induced increases in CD11b were not prevented. The CD11b expression was unchanged and increased with fMLP stimulation after in vitro incubation of isolated neutrophils with chimeric 7E3 Fab. Direct-labeled chimeric 7E3 Fab was not detected bound to neutrophils in whole blood or isolated cells using flow cytometric techniques. Adhesion of isolated neutrophils to protein-coated glass was not prevented by in vitro incubation with chimeric 7E3 Fab. Platelet activation increased after angioplasty in control patients (CD62P 8.9+/-0.8 to 12.3+/-1.2 MFI, n=25, p < 0.05; CD41a 382+/-25 to 454+/-26 MFI, n=25, p < 0.05, CD61a 436+/-52 to 529+/-58 MFI, n=11, p < 0.05); it did not increase in the patients selected to receive chimeric 7E3 Fab (CD62P 13.2+/-1.0 to 9.0+/-0.9 MFI, n=25, p < 0.05; CD61a 398+/-32 to 410+/-38 MFI, n=7, p=NS). Leukocytes with adherent platelets tended to increase in the control group of patients and decrease after the procedure in patients selected to receive chimeric 7E3 Fab; individual and procedure-related variability were marked. CONCLUSIONS: Despite standard aspirin and heparin therapy, leukocyte and platelet activation with platelet adherence to leukocytes occurs after coronary angioplasty. Although chimeric 7E3 Fab does not bind to leukocytes directly, it influences CD11b expression in whole blood. Modulation of platelet and leukocyte activation and interaction by chimeric 7E3 Fab may contribute to an improved outcome after coronary angioplasty.

Abciximab↗
PubMed1999

Fabrication of complete denture bases reinforced with polyethylene woven fabric.

Incorporation of 5 layers of woven, high-modulus polyethylene fiber into acrylic resin denture bases produces substantial improvements in mechanical properties and dimensional changes. A modified split-pack technique has been developed using conventional dental-laboratory compression molding to accommodate multiple layers of woven fabric in complete denture bases. A recess formed in the resin by a spacer allows the reinforcement to be embedded in the denture base without exposing the fibers. Embedded fibers do not compromise the esthetics of complete dentures.

Acrylic Resins↗
PubMed1999

Custom-made titanium mandibular reconstruction tray.

Reconstruction of the mandible after ablative surgery can be achieved by using preformed trays or trays formed from models produced by computer-assisted modelling systems. The former presents difficulty in matching the required facial contour, jaw relationship and condylar position; while the latter is expensive. This paper presents a simple and inexpensive method of fabricating a custom-made titanium bone grafting tray. The dimensions of the patient's mandible are obtained by clinical measurement. Such measurements are used to construct a mandibular replica. The region to be reconstructed is carved to produce the ideal shape and dimensions of an edentulous segment. The tray is made either by casting or by swaging. Twenty-one custom-made titanium bone grafting trays have been fitted in patients with encouraging results. This method of bone grafting tray construction is a simple, inexpensive technique for achieving excellent facial contour and functional reconstruction after mandibulectomy.

Bone Transplantation↗
PubMed1998

Increased von Willebrand factor binding to platelets in single episode and recurrent types of thrombotic thrombocytopenic purpura.

Extensive microvascular platelet aggregation is characteristic of thrombotic thrombocytopenic purpura (TTP). Previous studies have indicated that abnormalities of von Willebrand factor (vWf) are often present in TTP patient plasma. There has not been previously any direct evidence linking these abnormalities to the process of intravascular platelet aggregation in TTP. We used flow cytometry to analyze the binding of vWf to single platelets, and the presence of platelet aggregates, in the blood of 4 children with chronic relapsing (CR) TTP and 5 adults with single episode or recurrent TTP. vWf on the single platelets of CRTTP patients at all time points studied was significantly increased compared to controls, and was increased further as platelet counts decreased to levels below 40,000/microl. The single episode and recurrent adult TTP patients had platelet aggregates in the blood, as well as increased vWf on single platelets, before therapy commenced and thereafter until recovery was in process. In the one unresponsive single episode TTP patient, vWf on single platelets remained elevated, and platelet aggregates persisted, until her death. The platelet alpha-granular protein, P-selectin, was not increased on the single platelets of most TTP blood samples, suggesting that it is vWf from plasma (rather than from alpha-granules) that attaches to platelet surfaces in association with platelet aggregation. These results suggest that vWf-platelet interactions are involved in the platelet clumping process that characterizes TTP.

Adenosine Diphosphate↗
PubMed1998

Increased von Willebrand factor (vWf) binding to platelets associated with impaired vWf breakdown in thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TTP) is a disorder of systemic platelet aggregation. Evidence has accumulated that the aggregating agonist in TTP of all types is likely to be von Willebrand factor (vWf), especially unusually large vWf multimers derived from endothelial cells. Recent evidence indicates that a metalloproteinase involved in vWf breakdown is produced in inadequate amounts in children with chronic relapsing TTP. Chronic relapsing TTP is, therefore, likely to be a congenital enzyme deficiency. In adults with single episode or intermittent types of TTP, the vWf metalloproteinase is inhibited by autoantibodies that are present either transiently or intermittently in patient blood. Single episode and intermittent types of TTP in adults are likely to be short-term or recurrent autoimmune processes, respectively.

Adult↗
PubMed1998

Linear dimensional change of heat-cured acrylic resin complete dentures after reline and rebase.

STATEMENT OF PROBLEM: Relining and rebasing of complete dentures are common procedures to improve the fit of the prostheses. After relining or rebasing, adjustments may be required because of dimensional change that occurs during reprocessing of the denture when new denture base material is polymerized. PURPOSE: This study analyzed the linear dimensional change of heat cured acrylic resin that occurs during reline and rebase procedures for complete dentures. MATERIAL AND METHODS: Twenty-two maxillary and mandibular complete denture bases with artificial teeth were saturated by immersion in distilled water at 37 degrees C +/- 1 degree C. Fine crosses were marked on the incisal edges of the central incisors and the supporting cusps of the second molar teeth. Distances between the marks were measured with a high resolution traveling microscope. Heat-cured acrylic resin was processed by a long curing cycle of 72 degrees C for 6.5 hours, then heated to 100 degrees C for over 30 minutes and kept at 100 degrees C for 1 hour. The relined or rebased denture was allowed to cool slowly in the water bath for 48 hours to reach ambient temperature. The reference-crosses were measured immediately after careful deflasking. RESULTS: In the relining procedure, all incisor-molar and intermolar distances exhibited shrinkage of 0.3%, despite different shapes of maxillary and mandibular dentures. Results of the rebasing procedure were similar to that of the reline expect that only 0.1% intermolar shrinkage was found on the maxillary denture. CONCLUSION: Shrinkage was approximately 0.15 mm for an interarch distance of 50 mm. This degree of change is both clinically undetectable and insignificant. Using this processing cycle for acrylic resin in reline or rebase procedures did not cause clinically significant dimensional changes to complete dentures.

Acrylic Resins↗
PubMed1998

Tensile, shear and cleavage bond strengths of alginate adhesive.

OBJECTIVES: This study determined the effect of alginate adhesive on various bond strengths of alginate to stainless steel. METHODS: Three test assemblies were designed and machined in stainless steel for tension, shear and cleavage tests. Alginate adhesive (Fix) was applied thinly and dried for 5 min. Alginate (Blueprint) was then loaded and allowed to set for 5 min before testing. The force at failure was measured by an Instron machine with a cross-head speed of 50 mm min(-1). RESULTS: Breaking stresses of alginate without adhesive were found to be 65 kPa (tension), 31 kPa (shear) and 10 kPa (cleavage). The bond strengths of Blueprint with Fix were 100 kPa (tension), 42 kPa (shear) and 37 kPa (cleavage) giving improvements of 53%, 37% and 270% respectively (p < 0.05). CONCLUSIONS: Alginate adhesive increases the bond strength of alginate, particularly cleavage, to stainless steel.

Adhesives↗