The test for the boys and girls was simple: to cover as much ground as they could in 6 minutes. But these children, ages 5 to 18, had pulmonary hypertension—high blood pressure in their lungs from constricted blood vessels. Such kids "don't have a lot of energy," explains pediatric cardiologist Tilman Humpl. "They can't exercise at all. They may not be able to walk up from the basement to the first floor."
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