How Does a Pulmonary Function Test Work?

Many people think pulmonary function tests just measure how hard you can blow into a tube. That's only part of the story.

At Northwest Pulmonary and Sleep Medicine in Algonquin, Illinois, our team runs these tests every day to get a complete picture of how your lungs work under different conditions.

We recommend testing when patients come in with symptoms that point to lung problems:

• Persistent shortness of breath
• Chronic cough without a clear cause
• Wheezing or chest tightness
• Reduced exercise tolerance
• Frequent respiratory infections

These symptoms tell us something’s not right, and pulmonary function tests help us figure out what’s going on.

The machine captures thousands of data points

When you breathe into the spirometer, sensors track much more than air volume. The equipment measures pressure changes and airflow speed thousands of times per second. Think of it like a high-speed camera for your breathing.

Normal lungs follow predictable patterns. Airways open fast when you exhale, maintain steady flow through the middle, then slow down as your lungs empty. 

Different diseases upset these patterns in specific ways. That’s how we can tell asthma from emphysema from lung scarring by looking at the data on our screen.

What each test tells us about your breathing

Here’s what we look for with each test.

Spirometry shows airway function

The spirometer calculates resistance as air moves through your airways. High resistance usually means narrowed passages. Low total capacity with normal flow rates suggests stiff lung tissue.

Peak flow catches early inflammation

Peak flow measures how fast air shoots out in the first split second of exhaling. This number drops when larger airways get inflamed, even before you notice symptoms.

Airways create turbulence when swollen, slowing down that initial burst of air. We use this test to catch asthma flares early and monitor how well treatments work.

Stress testing reveals how lungs handle demand

The stress test shows us what happens when your body needs more oxygen. We measure how efficiently your lungs pull oxygen from the air and dump carbon dioxide.

What to expect during testing

Each test works a little differently, but none of them hurts.

Spirometry and peak flow testing

These happen while you sit comfortably. We place a clip on your nose so all breathing goes through your mouth. The mouthpiece needs a tight seal for accurate readings. When we tell you to blow, you take the deepest breath possible and exhale as hard and fast as you can.

Cardiopulmonary stress testing

This test involves pedaling a stationary bike while wearing electrode patches on your chest. The resistance increases gradually while you breathe through a mouthpiece. We watch how your heart and lungs respond to increasing workload.

Six-minute walk test

The walk test uses a treadmill at whatever pace feels comfortable. An oximeter clipped to your finger tracks blood oxygen levels continuously. That mimics real-world activities better than other tests.

Many lung problems only show up when your respiratory system faces extra demands. Walking while monitoring oxygen levels bridges the gap between resting measurements and daily life function.

Multiple tests create the complete picture

One test might look normal while another reveals the problem. Someone with shortness of breath could have perfect spirometry but abnormal stress test results. That combination points to a specific lung issue that needs targeted treatment.

At Northwest Pulmonary and Sleep Medicine, we perform comprehensive pulmonary function testing in our office and at local hospitals. These tests help us diagnose asthma, COPD, emphysema, and pneumonia with the accuracy needed for effective treatment.

Call our office at 815-584-0976 or schedule your consultation online to find the cause of your breathing difficulties.