Biomedical subjects

M C Yang

Publications and source records attributed to M C Yang.

131 records · Page 8Linked to original sources

PubMedDate not supplied

In vitro characterization of the occurrence of hemolysis during extracorporeal blood circulation using a mini hemodialyzer.

A minimodule dialyzer was made of polyacrylonitrile (PAN) hollow fibers and tested in an in vitro circuit under varying flow rates and blood volumes. Hemolysis occurred in the open circuit in the inlet and outlet chambers. The module was measured to investigate the hemolysis effect during dialysis. The results show that hemolysis ratio (HR) increased with blood flow rate. When the blood speed was increased from 27 to 70 cm/sec, the damaged fraction of red blood cells increased from 0.8% to 1.5%. Shearing in the hollow fiber contributed approximately 13% of the overall HR. Approximately 55% of the overall HR occurred at the inlet and outlet chambers. With increasing blood volume, the contacting surface area per unit blood volume (S/V) and the frequency of pump squeezing of red cells were decreased; hence the damage to the red blood cells and thus reduction of HR. When S/V was 2 cm(-1), the damaged fraction of red cells was approximately 0.7%. In addition, the tubing and connectors of the circuit caused further damage to the red blood cells. By referring to the linear velocity and blood volume, we can predict the HR in an actual protocol from the results of this experiment. This should improve the quality of hemodialysis and benefit the patient.

Acrylic Resins↗

PubMedDate not supplied

Influence of design of the hemodialyzer inlet chamber on red blood cell damage during hemodialysis.

Red blood cell damage occurring in the inlet chamber of a hollow fiber dialyzer was investigated by using a simplified model assembly. To vary the geometry of the inlet chamber, four parameters were used in this study, including the entrance angle, the chamber length, the convergence ratio, and the number of holes. The degree of red blood cell damage was represented by the hemolysis ratio. The results show that the hemolysis ratio was affected mostly by the chamber length and the convergence ratio, and less affected by the entrance angle and number of holes. The hemolysis ratio was the lowest when the chamber length was 2 mm and the entrance angle was 15 degrees. In addition, the hemolysis ratio decreased with the convergence ratio. Because the hemolysis ratio was only slightly affected by the number of holes and the flow channel length, the experimental results of this simplified assembly can be used to improve the design of an actual inlet chamber.

Blood Flow Velocity↗

PubMedDate not supplied

Haemodynamic effects of a combination of propranolol and clonidine in patients with post-hepatitic cirrhosis.

The haemodynamic effects of a combination of propranolol and clonidine were evaluated in 20 patients with post-hepatitic cirrhosis. Haemodynamic measurements were taken before and 30 min after an intravenous injection of 0.1 mg/kg of propranolol. Thereafter, each patient was given an oral dose of 150 micrograms of clonidine and re-measured 60 min later. In this series, eight patients were defined as 'non-responders' (a decrease in hepatic venous pressure gradient of < 10%) after propranolol treatment. Of both the responders and non-responders, propranolol caused expected decreases in the cardiac index and heart rate while mean arterial pressure remained unchanged. Of the propranolol responders, a significant decrease in hepatic venous pressure gradient was observed. After the addition of clonidine, in both the responders and non-responders there was a further decrease in hepatic venous pressure gradient with a concurrent drop in mean arterial pressure, but cardiac index and heart rate remained unaltered. In conclusion, the combination of propranolol and clonidine in post-hepatitic cirrhotic patients enhanced the reduction of portal pressure achieved by propranolol alone. The beneficial effects of the combination of the two in the reduction of portal pressure appeared to be similar in both the propranolol responders and non-responders. However, the drop in mean arterial pressure following the addition of clonidine may be hazardous to cirrhotic patients.

Adrenergic alpha-Agonists↗

PubMedDate not supplied

Fracture resistance of all-ceramic and metal-ceramic inlays.

PURPOSE: Metal-ceramic inlay designs were developed to determine if the esthetic qualities of all-ceramic inlays could be duplicated and at the same time improve their strength and stability. The objectives of this study were to: (1) compare the fracture resistance of metal-ceramic inlays with that of all-ceramic inlays; (2) determine the correlation between the degree of preparation taper and fracture resistance; and (3) determine the correlation between marginal gap width and fracture resistance. MATERIALS AND METHODS: Inlay preparations were made on 60 Dentoform teeth, with 30 teeth allocated for metal-ceramic inlays and 30 teeth for all-ceramic inlays. Each group was further subdivided into 5-, 10-, and 20-degree taper preparations. Metal-ceramic inlays were fabricated using Goldtech Bio 2000 metal and Ceramco porcelain extending to the margin, while all-ceramic inlays were made from Empress II ceramic. Marginal gap widths were measured at six critical areas after fabrication. The load at failure was measured using an Instron Universal Testing Machine. RESULTS: The mean fracture load for all-ceramic inlays and metal-ceramic inlays at 5, 10, and 20 degrees was 70+/-40 N, 48+/-37 N, 33+/-7 N, and 40+/-23 N, 29+/-22 N, and 14+/-4 N, respectively. The mean gap width was 105 microm and 126 microm for all-ceramic and metal-ceramic inlays, respectively. CONCLUSION: The mean fracture load for Empress inlays was significantly higher than that for metal-ceramic inlays. Inlays with a 5-degree taper were significantly more fracture resistant than those with a 20-degree taper. There was no relation between marginal gap width and fracture resistance.

Aluminum Silicates↗

PubMedDate not supplied

Influence of glass-ceramic thickness on Hertzian and bulk fracture mechanisms.

PURPOSE: The objective of this study was to test the hypothesis that bulk fracture of glass-ceramic disks of variable thickness originates at the inner, resin-bonded surface and is dominant over Hertzian fracture at the lower range of thickness values. MATERIALS AND METHODS: Eight groups of seven glass-ceramic disks (Dicor, Dentsply), 12 mm in diameter with thicknesses ranging from 0.4 to 2.4 mm, were cast, cerammed (to produce approximately 55 vol% of tetrasilicic fluormica crystals), air abraded, etched, and silane coated according to the manufacturer's instructions. The disks were bonded to an epoxy die substrate (with an elastic modulus comparable to that of dentin) using a light-activated resin cement. The bonded samples were supported on a flat surface and loaded at the top center of each disk until crack initiation occurred. All disks exhibited an initial crack within the bonded surface. Three randomly selected samples for each thickness were loaded beyond the point of crack initiation until Hertzian failure occurred. RESULTS: Although the crack-initiation force increased with increasing thickness, the failure stress approached a maximum level at a thickness of approximately 1.6 mm. These results suggest that the estimated maximum occlusal load for each patient should be used to select the minimum thickness of ceramic crowns rather than using the arbitrary traditional selection of a 1.5-mm thickness. CONCLUSIONS: The authors conclude that bulk fracture is initiated within the bonded surface of a glass-ceramic specimen (for samples 0.4 to 2.4 mm in thickness) when the glass-ceramic is supported by a substrate with an elastic modulus similar to that of dentin. Furthermore, a Hertzian failure mechanism is unlikely to cause bulk fracture for these conditions.

Dental Porcelain↗