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Mini MCAT passage: Blood oxygen levels during exercise


A study compares the “oxygen saturation” of blood coming from muscles in different states of activity. These states of activity include lying down, walking on a treadmill at 1 mile/hour, and jogging on a treadmill at 5 miles/hour.
In order to measure “oxygen saturation,” catheters are inserted into the left femoral artery and left femoral vein, which transport the bulk of arterial and venous blood to and from the left leg, respectively. These catheters continuously sample blood and measure the “oxygen saturation” of that blood.
“Oxygen saturation” is equal to how much oxygen the hemoglobin in the blood is carrying, as a percentage of how much it could theoretically carry. A higher “oxygen saturation” implies a higher concentration of oxygen in blood. The relationship between the two is not exactly linear, but it is a close approximation.
The results of the study are shown below:
Table 1: Oxygen saturations in femoral blood vessels during various physiologic states
Blood sampledLying downWalkingRunning
Femoral artery97%96%97%
Femoral vein81%68%65%
Which of the following are most important in explaining how the body changes the resistance of arterioles to blood flow?
Choose 1 answer: