A Pulmonary Function Test (PFT) is a non-invasive diagnostic tool used to see how well your lungs are working. It measures how much air your lungs can hold, how quickly you can move air in and out, and how well your lungs put oxygen into your blood.
Why is this test performed?
Your doctor may order a PFT for several reasons:
- Diagnosis: To identify the cause of shortness of breath, wheezing, or a chronic cough.
- Monitoring: To track the progression of conditions like Asthma, COPD, or Pulmonary Fibrosis.
- Surgical Clearance: To ensure your lungs are strong enough for an upcoming surgery.
- Effectiveness: To see if a new medication (like an inhaler) is actually helping.
Understanding Your Lung Function Tests
Think of these tests as a “performance review” for your lungs. While one test looks at how fast you can move air, others look at how much space you have and how well you’re getting oxygen into your blood.
1. Spirometry: The “Speed & Power” Test
This is the most common part of the test. It measures how much air you can pack into your lungs and, more importantly, how quickly you can blow it out.
- The Goal: To see if your airways are narrowed or “obstructed” (common in asthma or COPD).
- What you’ll do: You’ll take the deepest breath possible and then blast the air out as hard and fast as you can into a mouthpiece until your lungs feel empty.
- Key Number: Your FEV1—the amount of air you exhaled in the very first second of that “blast.”
2. Helium Dilution: Measuring “Hidden” Air
Even when you feel like you’ve exhaled every last drop of air, your lungs still contain a “reserve” to keep them from collapsing. Spirometry can’t measure this, so we use a harmless gas called Helium.
- The Goal: To find your Total Lung Capacity (TLC). This helps determine if your lungs are “restricted” (smaller than they should be).
- What you’ll do: You will breathe normally through a mouthpiece connected to a closed circuit containing a tiny, safe amount of Helium.
- How it works: By measuring how much the Helium is “watered down” by the air already in your lungs, the computer calculates the exact space inside your chest.
3. DLCO: The “Gas Exchange” Test
This checks the actual health of the tiny air sacs (alveoli) where oxygen enters your blood.
- The Goal: To see if the “walls” between your lungs and blood vessels are working efficiently.
- What you’ll do: You will take a deep breath of a special mixture, hold your breath for about 10 seconds, and then blow it out.
- Why Carbon Monoxide? We use a tiny amount because it is easily tracked. By measuring how much is absorbed during that 10-second hold, we know how well oxygen is moving into your blood.
Quick Comparison of PFT Components
| Test Component | What it Measures | What it tells the Doctor | Common Target Condition |
|---|---|---|---|
| Spirometry | Airflow speed and “blast” power. | Are your airways open or “clogged”? | Asthma, COPD |
| Lung Volumes | Total “tank” size (including hidden air). | Are your lungs the right size? | Pulmonary Fibrosis, Emphysema |
| DLCO | Gas exchange efficiency. | Is oxygen moving easily into your blood? | Hypertension, Sarcoidosis, Anemia |
Preparation Checklist
To get the most accurate results, please follow these guidelines:
| Action | Instruction |
|---|---|
| Smoking | Do not smoke for at least 6–12 hours before the test. |
| Inhalers | Ask your doctor if you should “hold” your inhalers on the morning of the test. |
| Meals | Eat a light meal. A very full stomach can make it hard to take deep breaths. |
| Clothing | Wear loose, comfortable clothing that doesn’t restrict your chest or abdomen. |
| Activity | Avoid strenuous exercise for several hours prior to your appointment. |
Important Safety Note
PFTs require significant physical effort. If you have recently had a heart attack, stroke, eye surgery, or abdominal surgery, please notify the staff immediately, as the pressure from blowing hard could be risky.
Understanding the Results
The results are calculated by comparing your “score” to a predicted value based on your age, height, gender, and ethnicity.
Note: A PFT doesn’t usually provide a “pass” or “fail” grade. Instead, it helps create a “map” of your lung health so your healthcare provider can tailor your treatment plan.