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Biomedical subjects

A H Moreno

Publications and source records attributed to A H Moreno.

25 records · Page 2Linked to original sources
PubMed1969

Flow through a collapsible tube. Experimental analysis and mathematical model.

Flow through thin-wall axisymmetric tubes has long been of interest to physiologists. Analysis is complicated by the fact that such tubes will collapse when the transmural pressure (internal minus external pressure) is near zero. Because of the absence of any body of related knowledge in other sciences or engineering, previous workers have directed their efforts towards experimental studies of flow in collapsible tubes. More recently, some attention has been given towards analytical studies. Results of an extensive series of experiments show that the significant system parameter is transmural pressure. The cross-sectional area of the tube depends upon the transmural pressure, and changes in cross-section in turn affect the flow geometry. Based on experimental studies, a lumped parameter system model is proposed for the collapsible tube. The mathematical model is simulated on a hybrid computer. Experimental data were used to define the functional relationship between cross-sectional area and transmural pressure as well as the relation between the energy loss coefficient and cross-sectional area. Computer results confirm the validity of the model for both steady and transient flow conditions.

Computers, Hybrid↗
PubMed1967

Portal blood flow in cirrhosis of the liver.

Direct measurements of portal flow and pressure in a relatively large number of patients with cirrhosis show a marked reduction in flow associated with a nearly constant plateau of portal pressure. This lack of correlation indicates the complex relationships of resistances in the splanchnic, collateral, and hepatic circuits determining the division of the available splanchnic flow between the portal vein and the collateral pathways. Subtracting the measured portal flow from well-established estimates of total hepatic blood flow in cirrhosis suggests that the hepatic artery contributes more than one-half of the blood perfusing the cirrhotic liver. There was no instance of retrograde portal flow during the preshunt measurements, although such reversal was frequent after side-to-side portacaval anastomosis. Attempting to explain the plateau of portal pressure in the face of an increasing outflow resistance presumably associated with progress of the disease, we postulate that an augmented inflow resistance to the splanchnic chamber reduces splanchnic flow in cirrhosis. End-to-side portacaval anastomosis did not return normal portal flow, although it decreased pressure to accepted control levels. The assumption is that most of the splanchnic blood was flowing through the shunt, leading to a high splanchnic resistance in the immediate postshunt status. If this resistance was previously elevated, as suggested by the plateau of portal pressure, the mechanism responsible for the elevation was not immediately deactivated after the shunt, and the true effect of the operation upon splanchnic flow may not be measurable at such time. Respiratory oscillations were a significant component of portal flow in cirrhosis before and after portacaval anastomosis, indicating the limitations of any steady state analysis of the circulatory derangement in cirrhosis.

Blood Pressure↗