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 of the following experimental groups would aid in determining if the procedure described in the passage has a confounding variable?

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 of the following experimental groups would aid in determining if the procedure described in the passage has a confounding variable?

Quizplus · Accepted Answer

11ecba2d_12c3_81a0_a3bf_a9db5cd0a368_MD0008_00 In an ideal experiment or study, any and all changes in the measured dependent variable are due to changes in the independent variable. However, this model may not be realistic due to confounding variables, uncontrolled variables that have an effect on the dependent variable. Experiments should be designed to minimize the influence of confounding variables if they cannot be eliminated. To determine the magnitude of any effect of a possible confounding variable on the dependent variable, an experimental group that differs in the suspected confounding variable is tested. In the study described in the passage, different blood vessels of rats (independent variable) were accessed through an invasive laparotomy procedure (suspected confounding variable) to measure mesenteric blood pressures (dependent variable). The inclusion of an alternative procedure that is minimally invasive or noninvasive but still measures mesenteric blood pressures would determine if laparotomy is a confounding variable by determining if differences are found in the measured blood pressures. (Choices A and D) The suspected confounding variable (procedural invasiveness of laparotomy) is not changed. In addition, the dependent variable (mesenteric blood pressure) should not change. (Choice C) Although the suspected confounding variable (procedural invasiveness of laparotomy) is changed by using a tail cuff, the dependent variable (mesenteric blood pressures) should not change. Educational objective: A confounding variable is an uncontrolled variable different from the independent variable but that still has an impact on the dependent variable. The effect of a confounding variable can be observed by including a group that differs in the confounding variable.

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