Interpretation of Pulmonary Function Tests

There are times when you will want to know if hypoxemia is due to a pulmonary shunt. This is done non-invasively by having the patient inspire 100% oxygen for 20 minutes. Unlike the patient with hypoxemia from, say, emphysema, the patient with a pulmonary shunt will have an abnormal A-a gradient while breathing 100% oxygen. ................
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