How Doctors Test Lung Function: Spirometry in Plain English

Why doctors measure lung function

Symptoms such as breathlessness, cough and wheeze can come from many causes. Listening with a stethoscope helps, but it cannot tell how well air actually moves through your airways. Lung function tests put numbers on that. They help doctors diagnose asthma and COPD, tell them apart, check how severe a condition is, see whether treatment is working, and monitor people exposed to dust or fumes at work.

The NHLBI COPD page notes that spirometry is the main test used to diagnose COPD, and many people with early COPD do not know they have it. If you are a current or former smoker with a daily cough or breathlessness on stairs, asking about spirometry is reasonable. It is one of the simplest, cheapest tests in medicine and gives information no symptom checklist can.

What happens during spirometry

The test takes about 15 to 30 minutes. You sit upright, a soft clip closes your nose, and you seal your lips around a mouthpiece connected to a spirometer. A technician coaches you through three steps: breathe in as deeply as possible, blast the air out as hard and fast as you can, then keep pushing until your lungs feel empty, often six seconds or more.

You will usually repeat this at least three times so the machine can confirm consistent results. It can leave you briefly lightheaded or coughing, which passes quickly. Often the technician then gives you a few puffs of an airway-relaxing inhaler medicine and repeats the test 15 minutes later. A big improvement after the inhaler points toward asthma; little change is more typical of COPD. The whole thing is uncomfortable for a minute, not painful.

Reading the numbers: FEV1, FVC and the ratio

Three numbers do most of the work:

• FVC, forced vital capacity: the total air you can blow out after a full breath.
• FEV1, forced expiratory volume in one second: how much of that air comes out in the first second.
• FEV1/FVC ratio: the share of your total breath that leaves in the first second.

Healthy airways empty quickly, so most air leaves in the first second. If the airways are narrowed, as in asthma or COPD, the ratio drops. COPD guidelines commonly use a ratio below 0.70 after an airway-relaxing inhaler as a sign of obstruction, though many labs now use age-adjusted limits. If the ratio is normal but FVC is low, the problem may be stiff lungs or a restricted chest. Each result is shown as a percentage of the predicted value for someone of your age, height and sex.

A worked example: reading a sample report

Let us walk through a sample report for a 62-year-old former smoker with a morning cough. His FVC is 92 percent of predicted, which is normal. His FEV1 is 68 percent of predicted, which is reduced. His FEV1/FVC ratio is 0.60, below the common 0.70 cutoff. After the inhaler, the numbers improve only slightly.

What would his doctor likely conclude? A normal total volume with slow emptying and little response to the inhaler fits an obstructive pattern consistent with COPD, though the diagnosis also depends on history and other tests. The value of the report is that it turns "I get winded on stairs" into a measurable baseline. Repeating the test in a year shows whether things are stable. These figures are illustrative, not anyone's real results, and only a clinician can interpret your own report.

Other tests you might hear about

Spirometry is often the first step. Depending on the results, a doctor may order:

• Peak flow: a handheld meter many people with asthma use at home to track changes day to day.
• Lung volume tests: measure the total air your lungs hold, useful when restriction is suspected.
• Diffusing capacity (DLCO): shows how well gas passes from the alveoli into the blood.
• Pulse oximetry: a fingertip clip estimating blood oxygen.
• Six-minute walk test: how far you walk in six minutes and how your oxygen holds up.
• FeNO: measures a marker of a type of airway inflammation seen in some asthma.

For plain-language background on the conditions these tests look for, the MedlinePlus lung diseases page is a reliable start. To prepare for any test, ask whether to skip inhalers beforehand, avoid smoking and heavy meals for a few hours, and wear loose clothing.

Where a supplement fits alongside testing

Lung function tests are the honest way to measure breathing, and they are also a useful reality check for any supplement claim. Vapolung, our once-daily oral spray, has not been studied for effects on FEV1, FVC or any lung function measure, and it is not a treatment for asthma, COPD or anything a spirometry report might show. Our Vapolung benefits page explains what the ingredient research does and does not show.

If testing finds a condition, follow your doctor's treatment plan and never stop or reduce an inhaler because of a supplement. If tests are normal and you want a daily supplement alongside not smoking, activity and clean air, read how Vapolung works, see our Vapolung, asthma and COPD review, and buy only through the Vapolung official website. For symptom background, see shortness of breath warning signs.

Frequently asked questions

Sources

• NHLBI: COPD
• MedlinePlus: Lung Diseases