AIM: To determine the possible existence of a hepato-cardiovascular response and its regulatory mechanism in normal rats. METHODS: Systemic hemodynamic changes following intraportal injection of latex microspheres wer...AIM: To determine the possible existence of a hepato-cardiovascular response and its regulatory mechanism in normal rats. METHODS: Systemic hemodynamic changes following intraportal injection of latex microspheres were studied in two modified rat models of hepatic circulation, in which the extrahepatic splanchnic circulation was excluded by evisceration and the liver was perfused by systemic blood via either the portal vein (model 1) or hepatic artery (model 2) in vivo. RESULTS: In model 1, intraportal injection of two sized microspheres (15-μm and 80-μm) induced a similar decrease in mean arterial pressure, while extrahepatic portal venous occlusion induced an immediate increase in mean arterial pressure. In model 2, microsphere injection again induced a significant reduction in mean arterial pressure, aortic blood flow and aortic resistance. There were no significant differences in these parameters between liver-innervated rats and liver-denervated rats. The degrees of microsphere-induced reduction in mean arterial pressure (-38.1±1.9% in liver-innervated rats and -35.4±2.1% in liver-denervated rats, respectively) were similar to those obtained by withdrawal of 2.0 mL of blood via the jugular vein (-33.3±2.1%) (P>0.05). Injection of 2.0 mL Haemaccel in microsphere-treated rats, to compensate for the reduced effective circulating blood volume, led to a hyperdynamic state which, as compared with basal values and unlike control rats, was characterised by increased aortic blood flow (+21.6±3.3%), decreased aortic resistance (-38.1±3.5%) and reduced mean arterial pressure (-9.7±2.8%). CONCLUSION: A hepato-cardiovascular response exists in normal rats. It acts through a humoral mechanism leading to systemic vasodilatation, and may be involved in the hemodynamic disturbances associated with acute and chronic liver diseases.展开更多
The torsional vibration of power transmission shaft is a phenomenon whose analytical modeling can be represented by a differential equation of motion proposed by technical literature. The solutions of these equations ...The torsional vibration of power transmission shaft is a phenomenon whose analytical modeling can be represented by a differential equation of motion proposed by technical literature. The solutions of these equations need coefficients and parameters that, usually, must be experimentally estimated. This work uses a resistive electric SG （strain gage） to dynamically determine strains produced in the shaft due to harmonic oscillatory motion under multiaxial loading. This movement is simulated on a prototype specially developed for this purpose. It comprises a pulley attached to the end of a stepped cantilevered shaft, which is clamped at the opposite end. In this configuration, a cam generates a torque to the system, springs regulate the stiffness and the damping coefficient of the assembly, as well as they can be suitably adjusted to produce an underdamped condition. The main advantage, highlighted in this study, refers to a major simplification. Although the system under study shows multiple degrees of freedom （torsion and bending）, the shape and the positioning of linking SGs with the resistor bridge （Wheatstone Bridge）, allow ＂to evaluate the loading effects independently, as if only one degree of freedom of the system exists at a time domain. Strains graphs for two forms of cyclic torsional oscillation, analytical and experimental, were successfully generated.展开更多
基金Supported by the Medical Science and Technology Development Foundation of Health Department of Jiangsu Province, China. No.H200204
文摘AIM: To determine the possible existence of a hepato-cardiovascular response and its regulatory mechanism in normal rats. METHODS: Systemic hemodynamic changes following intraportal injection of latex microspheres were studied in two modified rat models of hepatic circulation, in which the extrahepatic splanchnic circulation was excluded by evisceration and the liver was perfused by systemic blood via either the portal vein (model 1) or hepatic artery (model 2) in vivo. RESULTS: In model 1, intraportal injection of two sized microspheres (15-μm and 80-μm) induced a similar decrease in mean arterial pressure, while extrahepatic portal venous occlusion induced an immediate increase in mean arterial pressure. In model 2, microsphere injection again induced a significant reduction in mean arterial pressure, aortic blood flow and aortic resistance. There were no significant differences in these parameters between liver-innervated rats and liver-denervated rats. The degrees of microsphere-induced reduction in mean arterial pressure (-38.1±1.9% in liver-innervated rats and -35.4±2.1% in liver-denervated rats, respectively) were similar to those obtained by withdrawal of 2.0 mL of blood via the jugular vein (-33.3±2.1%) (P>0.05). Injection of 2.0 mL Haemaccel in microsphere-treated rats, to compensate for the reduced effective circulating blood volume, led to a hyperdynamic state which, as compared with basal values and unlike control rats, was characterised by increased aortic blood flow (+21.6±3.3%), decreased aortic resistance (-38.1±3.5%) and reduced mean arterial pressure (-9.7±2.8%). CONCLUSION: A hepato-cardiovascular response exists in normal rats. It acts through a humoral mechanism leading to systemic vasodilatation, and may be involved in the hemodynamic disturbances associated with acute and chronic liver diseases.
文摘The torsional vibration of power transmission shaft is a phenomenon whose analytical modeling can be represented by a differential equation of motion proposed by technical literature. The solutions of these equations need coefficients and parameters that, usually, must be experimentally estimated. This work uses a resistive electric SG （strain gage） to dynamically determine strains produced in the shaft due to harmonic oscillatory motion under multiaxial loading. This movement is simulated on a prototype specially developed for this purpose. It comprises a pulley attached to the end of a stepped cantilevered shaft, which is clamped at the opposite end. In this configuration, a cam generates a torque to the system, springs regulate the stiffness and the damping coefficient of the assembly, as well as they can be suitably adjusted to produce an underdamped condition. The main advantage, highlighted in this study, refers to a major simplification. Although the system under study shows multiple degrees of freedom （torsion and bending）, the shape and the positioning of linking SGs with the resistor bridge （Wheatstone Bridge）, allow ＂to evaluate the loading effects independently, as if only one degree of freedom of the system exists at a time domain. Strains graphs for two forms of cyclic torsional oscillation, analytical and experimental, were successfully generated.
