Effect of ultrasonic vibration on forming force and forming quality in micro-punching with a flexible punch.

In this paper, a special ultrasonic microforming method, Micro Ultrasonic thin Sheetmetal Forming using molten plastic as a flexible punch (short as Micro-USF), was used to conduct micro-punching experiments on stainless steel sheet with thickness of 10 µm and 20 µm. The influence of ultrasonic vibration on forming force and forming quality were investigated. The experimental results showed that the forming force required for punching thin sheet metal decreased gradually as the ultrasonic time or ultrasonic power increased. By applying the ultrasonic vibration effect, the forming force could be decreased dramatically and the maximum value of forming force drop could reach 86%. Moreover, with the application of ultrasonic vibration, the size accuracy and shape accuracy of micro-holes could be increased by 36.92% and 22.65%, but the cross-section quality of micro-holes were not significantly improved.

[Cerebral uptake and regional cerebral distribution of propofol under concentration equilibrium condition in the internal carotid artery and internal jugular vein in dogs].

OBJECTIVE: To investigate the cerebral uptake and regional distribution of propofol when plasma propofol concentration reaches equilibrium in the internal carotid artery and internal jugular vein in dogs. METHODS: Eight male hybrid dogs aged 12-18 months weighing 10-12 kg were anesthetized with propofol at a single bolus (7 mg/kg) in 15 s followed by propofol infusion at a constant rate of 70 mg.kg(-1).h(-1) via the great saphenous vein of the right posterior limb. Blood samples were taken from the internal carotid artery and internal jugular vein at 30 min (T30) after propofol infusion for measurement of plasma propofol concentrations by high-pressure liquid chromatography (HPLC). The thalamus, epithalamus, metathalamus, hypothalamus, subthalamus, frontal lobe, parietal lobe, temporal lobe, hippocampus, cingulate gyrus, cerebellum, midbrain, pons, medulla oblongata and cervical cord were then dissected to determine propofol concentrations in these tissues by HPLC. RESULTS: The propofol concentrations in the internal carotid artery and internal jugular vein blood plasma were comparable at T30 (6.16-/+1.02 vs 6.17-/+1.00 microg/ml, P>0.05). The propofol concentration was 6.11-/+1.07 microg/g in the epithalamus, 6.14-/+0.98 microg/g in the metathalamus, 6.12-/+1.02 microg/g in the hypothalamus, 6.15-/+1.00 microg/g in the subthalamus, 6.20-/+1.03 microg/g in the frontal lobe, 6.18-/+1.02 microg/g in the parietal lobe, 6.13-/+1.00 microg/g in the temporal lobe, 6.07-/+0.99 microg/g in the hippocampus, 6.14-/+1.06 microg/g in the cingulate gyrus, 6.15-/+1.00 microg/g in the cerebellum, 6.13-/+1.05 microg/g in the midbrain, 6.18-/+1.01 microg/g in the pons, 6.15-/+0.93 microg/g in the medulla oblongata, and 6.13-/+1.00 microg/g in the cervical cord, showing no significant differences in the distributions (P>0.05). Propofol concentration in the thalamus (8.68-/+0.88 microg/g) was significantly higher than those in the other brain tissues (P<0.05). CONCLUSIONS: At the constant intravenous propofol injection rate of 70 mg.kg(-1).h(-1), plasma propofol concentration reaches equilibrium 30 min after the injection in the internal carotid artery and internal jugular vein with even distribution in the cerebral tissues in dogs, but the thalamus contains high propofol concentration.

[Cerebral distribution of propofol at cerebral propofol uptake equilibrium in dogs].

OBJECTIVE: To investigate the cerebral distribution of propofol during continued infusion at a constant rate when the cerebral propofol uptake reaches equilibrium in dogs. METHODS: Six healthy 1-year-old male dogs were used in this study. The venous channel was established in the great saphenous vein of the right posterior limb. Anesthesia was induced with a single bolus injection of propofol (7 mg/kg), followed by propofol infusion at a constant rate of 70 mg/(kg.h) using a microinfusion pump. The blood samples were taken from the right internal carotid and internal jugular vein at 30 min (T30) and 50 min (T50) during propofol infusion for measurement of plasma propofol concentrations with high performance liquid chromatography (HPLC). At T50, the frontal lobe, parietal lobe, temporal lobe, hippocampus, cingulate gyrus, thalamus, midbrain, pons, and cerebellum were dissected respectively for determination of propofol concentrations. RESULTS: Propofol concentrations in the internal carotid artery and internal jugular vein blood plasma were 3.107-/+1.067, 3.095-/+1.085 microg/ml at T30 and 3.091-/+1.101, 3.117-/+1.091 microg/ml at T50, respectively, showing no significant differences (P>0.05). Propofol concentrations in the frontal lobe, parietal lobe, temporal lobe, hippocampus, cingulate gyrus, thalamus, midbrain, pons, cerebellum at T50 were 3.085-/+1.123, 3.116-/+1.125, 3.073-/+1.159, 3.117-/+1.090, 3.075-/+1.178, 3.073-/+1.146, 3.075-/+1.151, 3.102-/+1.174, and 3.072-/+1.192 microg/g respectively, suggesting homogeneous propofol distribution in these cerebral tissues (P>0.05). CONCLUSION: At T50, the cerebral uptake of propofol reached equilibrium when propofol is distributed homogeneously in the cerebral tissues in dogs.