Passage
In hemodynamics, blood flow through the cardiovascular system can be modeled as an electric circuit in which the blood serves as electricity, the blood vessels as resistive wires, and the heart as a battery (see Figure 1) .
Figure 1 Cardiovascular circuit modelOhm's law states that the voltage drop ΔV across each element, the current I flowing through it, and its electrical resistance R are related by ΔV = IR. In a blood vessel, pressure difference between one vessel and the next ΔP replaces ΔV, volumetric blood flow Q replaces I, and vascular resistance R replaces electrical resistance. Therefore, Ohm's law for blood flow in a vessel isΔP = QREquation 1Vascular resistance is due to the blood's viscosity η and the dimensions of the vessel through which it flows. Assuming blood vessels are cylinders, R can be approximated as
Equation 2where L is the length of the vessel, and r is its inner radius. If Equation 2 is combined with Equation 1, the resulting equation is Poiseuille law.In a study of the circulatory system in rats, researchers measured the intravascular blood pressure of the mesenteric blood vessels. The mesentery is the set of tissues that holds the intestines in place. Blood flows in the following order: aorta, superior mesenteric artery (SMA) , arterial arcade, venous arcade, superior mesenteric vein (SMV) .For the procedure, catheters with pressure transducers were inserted into each vessel via laparotomy. Laparotomy is an invasive procedure that involves a surgical incision into the abdominal cavity. Blood pressure measurements were taken simultaneously at the proximal end (beginning) of each blood vessel.
Figure 2 Mesenteric blood pressure profile of rats (Note: SMA = superior mesenteric artery; SMV = superior mesenteric vein.)
-Which change would result in the greatest decrease in the volumetric blood flow rate within a mesenteric vessel?

Question

Passage
In hemodynamics, blood flow through the cardiovascular system can be modeled as an electric circuit in which the blood serves as electricity, the blood vessels as resistive wires, and the heart as a battery (see Figure 1) .

Figure 1 Cardiovascular circuit modelOhm's law states that the voltage drop ΔV across each element, the current I flowing through it, and its electrical resistance R are related by ΔV = IR. In a blood vessel, pressure difference between one vessel and the next ΔP replaces ΔV, volumetric blood flow Q replaces I, and vascular resistance R replaces electrical resistance. Therefore, Ohm's law for blood flow in a vessel isΔP = QREquation 1Vascular resistance is due to the blood's viscosity η and the dimensions of the vessel through which it flows. Assuming blood vessels are cylinders, R can be approximated as

Equation 2where L is the length of the vessel, and r is its inner radius. If Equation 2 is combined with Equation 1, the resulting equation is Poiseuille law.In a study of the circulatory system in rats, researchers measured the intravascular blood pressure of the mesenteric blood vessels. The mesentery is the set of tissues that holds the intestines in place. Blood flows in the following order: aorta, superior mesenteric artery (SMA) , arterial arcade, venous arcade, superior mesenteric vein (SMV) .For the procedure, catheters with pressure transducers were inserted into each vessel via laparotomy. Laparotomy is an invasive procedure that involves a surgical incision into the abdominal cavity. Blood pressure measurements were taken simultaneously at the proximal end (beginning) of each blood vessel.

Figure 2 Mesenteric blood pressure profile of rats (Note: SMA = superior mesenteric artery; SMV = superior mesenteric vein.)
-Which change would result in the greatest decrease in the volumetric blood flow rate within a mesenteric vessel?

Quizplus · Accepted Answer

11ecba2d_12c1_fbf5_a3bf_874238deea2a_MD0008_00 Poiseuille law describes the laminar flow (no turbulence) of a viscous, incompressible fluid through a pipe. The viscosity of a fluid measures the internal frictional force that resists the flow. A fluid is incompressible if its density and volume do not change appreciably due to changes in pressure. As stated in the passage, the combination of Equation 1 and Equation 2 is Poiseuille law, which can be used to determine blood flow rate: 11ecba2d_12c2_2306_a3bf_0b5dc89c1923_MD0008_00 The greatest decrease in blood flow rate is achieved when the radius is reduced by a factor of 2 because Poiseuille law has a fourth-power dependence on r and a linear (first-power) dependence on all the other variables. The change in radius yields 11ecba2d_12c2_2307_a3bf_831315dca707_MD0008_00 Therefore, blood flow rate Q decreases by a factor of 16 when the vessel's radius r is halved. (Choice A and D) A decrease in viscosity increases blood flow rate because the flow rate is inversely proportional to viscosity. Similarly, an increase in the blood pressure difference increases blood flow rate because they are directly proportional to each other. (Choices B) An increase in vessel length reduces blood flow rate by a factor of 9, but this reduction is less than the one produced by a decrease in the vessel radius. Educational objective: Poiseuille law is used to model fluid flow in pipes, assuming laminar flow of viscous and incompressible fluids. According to Poiseuille law, the flow rate is directly proportional to vessel radius and pressure difference, and inversely proportional to viscosity and vessel length.

Passage In Hemodynamics, Blood Flow Through the Cardiovascular System Can Be