Gas Exchange Tests Make an Appointment Ask a Question Refer Patient When inhaling, the lungs take oxygen from the air and deliver it to the blood stream. When exhaling, the lungs remove carbon dioxide from the blood back into the air. To determine the levels of oxygen and carbon dioxide in the blood, your doctor may perform a gas exchange test. Learn more about the gas exchange tests we offer: Arterial Blood Gas High Altitude Simulation Testing (HAST) Pulse Oximetry (with and without walking) Shunt Study