A high school track athlete approaches her coach to report that training sessions feel much more difficult than before. Also, her times for the 800-meter sprint are getting worse, and she seems to get out of breath easily. The coach suggests a visit to a doctor.
During the doctor’s visit, the nurse finds that the girl has very low blood oxygen saturation levels, despite having a slightly rapid breathing rate. A quick test shows that the girl has severe anemia (low blood iron levels).
How does this diagnosis explain the girl's low blood oxygen levels?