Question

1. Why did the percent saturation of hemoglobin in Sue’s blood decrease (from 97% to 90%) when she exercised? How did the decrease in percent saturation affect Sue’s exercise tolerance?

Answer 1

Why did the percent saturation of hemoglobin in Sue’s blood decrease (from 97% to 90%) when she exercised?

The concentration of hemoglobin with oxygen is about 100% when it leaves the pulmonary alveolus of lungs. As it moves along towards the heart in pulmonary vein it mixes with some deoxygenated blood from bronchial veins bringing the hemoglobin concentration to around 97%. As Sue exercises, the requirement of oxygen intake for the muscles increases. With this, during the process of energy release in the muscles, carbon dioxide is released and this reduces the concentration of hemoglobin carrying oxygen in blood to decrease from 97% to around 90%.

How did the decrease in percent saturation affect Sue’s exercise tolerance?

The decrease in percent saturation of hemoglobin in blood affects Sue’s exercise tolerance because with the increase in exercise the uptake of oxygen which is directly proportional to level of exercise increases. But there is a ceiling to the uptake of oxygen through cardiac output. With a certain level of exercise the consumption of oxygen reaches the plateau which is VO2max or maximal oxygen uptake. At this level the concentration of oxygen starts decreasing and goes from 97% to around 90%. At 100% the oxygen carrying capacity of hemoglobin is 4 molecule of O2 but as the concentration decreases to 90% the oxygen carrying capacity of hemoglobin is decreases to around 1-2 molecule of O2. So the muscle intake is at its peak but the supply of oxygen decrease thereby decreasing the exercise tolerance of Sue.

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