Oxygen Saturation in Exhaled Breath During Exercise (Fraction of Respiratory Exchange)

What This Test Measures

This test analyzes the concentration of oxygen in your exhaled breath during a controlled exercise session. It measures how well your lungs transfer oxygen into your bloodstream while you’re active. The test often uses a specialized device to capture and analyze your breath samples after you perform a set of exercises, such as walking or cycling.

Why It’s Done

Your healthcare provider may order this test if you have symptoms like shortness of breath, fatigue, or if you’re being evaluated for conditions like chronic obstructive pulmonary disease (COPD), asthma, or other lung-related issues. It can also help monitor how well your lungs respond to treatments or exercise regimens.

Preparation for the Test

You’ll likely be asked to fast for a few hours before the test, but hydration is usually encouraged. Wear comfortable clothing and shoes suitable for light exercise. Follow any specific instructions your doctor provides, such as avoiding caffeine or smoking before testing.

What to Expect During the Test

You’ll start by completing a short physical activity, like walking on a treadmill or riding a stationary bike. As you exercise, you’ll breathe into a special mask or device that collects your exhaled breath. The test may last about 10–15 minutes, and you’ll be monitored closely for your oxygen levels and breathing patterns.