Shunt flow

When portosystemic shunting is present total hepatic blood flow (Q) equals the sum of perfusion flow (Q ) and shunt flow (Qs). Portocaval shunting will impair the efficiency of hepatic extraction and reduce the extraction ratio as indicated by the following modification of Equation 7.5 (23). 

Fig. 19.9. Imaging of complications after renal biopsy. Color Doppler sonography depicted an area with atypical colour signals and color aliasing suspicious for an arteriovenous fistula. Duplex Doppler sonography trace confirms the shunt flow of a post biopsy arteriovenous fistula...

In making measurements of current flowing within a structure, it is extremely important that additional resistance, as for example a shunt, is not introduced into the circuit, as otherwise erroneous results will be obtained. One method is to use a tong test meter. Such instruments are, however, not particularly accurate, especially at low currents, and are obviously jmpracticablein thecaseof, say, a 750 mm diameter pipeline. A far moreaccurate method and onethat can beapplied to ail structures, isthe zero-resistance ammeter or, as it is sometimes called, the zero-current ammeter method. The basic circuit of such an instrument is shown in Fig. 10.47. 

In many cases it will suffice to include in the circuit a shunt of appropriately low resistance over which 7/ -drop potential measurements can be made for ready calculation of the magnitude of the current flow. This technique permits measurements to be made as required without opening the circuit even momentarily for the introduction of current-measuring devices. It is also possible to arrange instruments in a circuit so that no measuring resistance is introduced in the galvanic current circuit . 

Ductus arteriosus The structure that shunts fetal blood flow away from the undeveloped fetal lungs. 

A special type of cross-flow reactor was developed in the laboratories of Vogt [16] to handle continuous gas / liquid reactions. The challenge in the reactor design was to combine efficient gas-liquid mixing, liquid level control in the reactor, turbulent flow across the membrane, and efficient gas-liquid separation to avoid gas contacting the membrane, which would lead to a shunt of gas. The total internal volume should not... 

The goal of sympathomimetic therapy is to augment both coronary and cerebral perfusion pressures during the low-flow state associated with CPR. These agents increase systemic arteriolar vasoconstriction, thereby improving coronary and cerebral perfusion pressure. They also maintain vascular tone, decrease arteriolar collapse, and shunt blood to the heart and brain. 

The resulting resistance to blood flow results in portal hypertension and the development of varices and ascites. Hepatocyte loss and intrahepatic shunting of blood results in diminished metabolic and synthetic function, which leads to hepatic encephalopathy (HE) and coagulopathy. 

The purpose of the shunt equation is to give a ratio of shunt blood flow to total blood flow. The normal ratio is 0.3. Under abnormal conditions, the ratio will tend to increase and so markedly reduce the Pao2. 

Now consider the blood flow generated in a single beat. The 02 delivered in this volume of blood is equal to (Qr.Cao2). This must be made up of shunted blood (Qs.Cvo2) and capillary blood ([Qt - Qs].Cc o2). 

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