A PST, or pulmonary stress test, is an exercise-based test that measures how well your lungs and heart work together when your body is under physical demand. Unlike a standard pulmonary function test (PFT), which checks your breathing while you sit still, a pulmonary stress test pushes your body to work harder so doctors can see how your respiratory and cardiovascular systems respond. The clinical name is cardiopulmonary exercise testing, or CPET.
How It Differs From a Standard Lung Function Test
A standard pulmonary function test is a non-invasive breathing test you do while seated. You blow into a mouthpiece, and the device measures things like how much air your lungs can hold and how quickly you can exhale. It’s useful for diagnosing asthma, COPD, pulmonary fibrosis, and narrowing of the airway.
A pulmonary stress test goes further. It evaluates your lungs and heart under conditions of increased metabolic demand, meaning while you’re actively exercising. This matters because some problems only show up when the body needs more oxygen than usual. Your lungs might look fine at rest but struggle to keep up during exertion. If you’re experiencing unexplained shortness of breath during physical activity and your resting lung tests came back normal, a pulmonary stress test is often the next step.
Why Doctors Order This Test
The most common reason is unexplained shortness of breath or fatigue during physical activity. If basic tests haven’t pinpointed the cause, a pulmonary stress test can reveal whether the limitation is coming from your lungs, your heart, or both. Beyond diagnosis, doctors use this test to:
- Diagnose or monitor conditions like heart failure, COPD, pulmonary hypertension, and congenital heart disease
- Assess surgical risk before major operations such as lung resection or lung transplant
- Guide treatment plans and track how a condition is progressing over time
- Develop safe exercise programs tailored to your actual capacity
- Evaluate fitness for demanding jobs that require sustained physical effort
Specific measurements from the test, particularly your anaerobic threshold, peak oxygen consumption, and how efficiently you breathe out carbon dioxide, are linked to surgical outcomes. Deficiencies in these areas are associated with higher rates of complications, longer hospital stays, and greater risk after major abdominal surgery. This makes the test especially valuable for pre-surgical planning.
What Happens During the Test
You’ll either ride a stationary bike or walk on a treadmill. A technician places sensors on your body and fits you with a mouthpiece or mask that captures the air you breathe in and out. Throughout the exercise, the intensity gradually increases, starting easy and getting progressively harder until you reach your limit or the technician stops the test.
While you exercise, the equipment continuously records thousands of data points. The key measurements include how much oxygen your body consumes, how much carbon dioxide you produce, your heart rate and rhythm (via a continuous heart monitor), your blood pressure, your blood oxygen levels, and your breathing rate. One particularly useful metric is called the oxygen pulse, which reflects how much oxygen your body uses per heartbeat. It gives an indirect picture of how effectively your heart pumps blood with each beat.
The test is considered maximal when your heart rate reaches roughly 95% or more of your age-predicted maximum, or when your oxygen consumption plateaus despite increasing effort. A typical session, including setup and recovery, usually takes about 45 minutes to an hour, though the actual exercise portion is shorter.
How to Prepare
You’ll typically be asked to avoid eating, drinking, and smoking for a period before the test. Caffeine should be avoided the day before and the day of the test, since it can affect heart rate and blood pressure readings. Ask about your medications beforehand, as some may need to be paused. If you use an inhaler for asthma or another breathing condition, bring it with you. Wear comfortable clothing and shoes suitable for exercise.
Understanding Your Results
Results are compared to predicted values based on your age, sex, height, and weight. A value below roughly 80% of your predicted result is generally considered abnormal. What the abnormality looks like points to different types of problems.
If the test reveals that your lungs hold too much air and take too long to empty, that pattern suggests an obstructive lung disorder. Conditions like emphysema, chronic bronchitis, asthma, and certain lung infections fall into this category. On the other hand, if your lungs appear smaller than expected and don’t transfer oxygen into your blood efficiently, the pattern suggests a restrictive problem. Pulmonary fibrosis (scarring of lung tissue), sarcoidosis, scleroderma, and even extreme overweight can cause this. Muscular weakness can also produce results that look similar to restrictive lung disease, even when the lungs themselves are healthy.
Your blood oxygen saturation should normally stay above 95% throughout the test. A drop below that threshold during exercise can indicate problems with gas exchange in the lungs or, in rare cases, abnormal blood flow patterns in the heart. The ratio of oxygen consumed to carbon dioxide produced also shifts during the test, and sudden changes in this ratio can flag specific cardiovascular issues.
Risks and Safety
A pulmonary stress test is generally safe. Complications are rare but can include a temporary drop in blood pressure during or right after exercise, which may cause brief dizziness or lightheadedness. Irregular heart rhythms can occur during the test but typically resolve once the exercise stops. Heart attack is a possible but very rare complication. A medical team monitors you continuously throughout the test and can stop it at any point if something looks concerning.