Spirometry is a standard test that doctors use to determine how well your lungs are functioning. The test works by measuring airflow into and out of your lungs.
To take a spirometry testyou sit and breathe into a small machine called a spirometer. This medical device records the amount of air you breathe in and out as well as the speed of your breath.
Doctors use spirometry tests to diagnose these conditions:
chronic obstructive pulmonary disease (COPD)
asthma
other disorders affecting lung function
Results from spirometry tests can also suggest the presence of other conditionssuch as restrictive lung disease.
But spirometry is a simple test. Aloneit is not enough to diagnose many underlying conditions. In these instancesdoctors may order broader pulmonary function tests to definitely assess any underlying conditions affecting lung output.
A spirometry test typically happens in a doctor’s office. In some caseswhen more in-depth tests are necessaryit may take place at a respiratory laboratory.
Here’s what happens during a spirometry procedure:
You’ll sit in a chair in an exam room at your doctor’s office. The doctor or a nurse will place a clip on your nose to keep both nostrils closed. They’ll also place a cup-like breathing mask around your mouth.
Your doctor or nurse will next instruct you to take a deep breath inhold your breath for a few secondsand then exhale as hard as you can into the breathing mask.
You’ll repeat this test at least three times to ensure consistent results.
If you have evidence of a breathing disorderyour doctor might give you an inhaled medication called a bronchodilator to open up your lungs after the first round of tests.
They’ll often ask you to wait 15 minutes before taking another set of measurements. Afterwardyour doctor will compare the results of the measurements to see whether the bronchodilator helped increase your airflow.
Few complications typically occur during or after a spirometry test. Yet you may want to be aware of some possible effects.
You may feel dizzy or have some shortness of breath just after performing the test. In this casetell your doctor immediately. In very rare casesthe test may trigger severe breathing problems.
When you do this testit will increase the pressure in your headcheststomachand eyes as you breathe out. Soit is unsafe if you have heart problems or hypertension or if you’ve had surgery on your chestabdomenheador eyes.
A spirometry test itself has few risksbut there is a minor risk of infection. This may occur due to contamination of the spirometer tubing and mouthpieces if they are not disinfected properly.
The American Thoracic Society and the European Respiratory Society have official technical standards for conducting spirometry. These include disinfection guidelines and recommend disposable mouthpieces with filters to avoid spreading infections.
“Normal” results for a spirometry test vary from person to person. They’re based on your:
age
height
race
sex
Your doctor calculates your predicted “normal” value before you do the test. Once you’ve done the testthey look at your test score and compare it with the predicted score. It is typically reported that a score of 80% or more of this predicated value indicates typical lung function. Yet some research from 2018 claims that this figure is inaccurate.
Spirometry measures two key factors: expiratory forced vital capacity (FVC) and forced expiratory volume in one second (FEV1). Your doctor also looks at these as a combined number known as the FEV1/FVC ratio.
If you have obstructed airwaysthe amount of air you can blow out of your lungs quickly will be reduced. This translates to a lower FEV1 and FEV1/FVC ratio.
FVC measurement
One of the primary spirometry measurements is FVCthe greatest total amount of air you can forcefully breathe out after breathing in as deeply as possible. If your FVC is lower than expectedsomething is restricting your breathing.
An “abnormal” FVC could be due to restrictive or obstructive lung disease. You could have an obstructive or restrictive lung disease by itselfbut it’s also possible to have a mixture of these two types at the same time.
Different spirometry measurements are required to determine which type of lung disease is present.
FEV1 measurement
The second key spirometry measurement is FEV1. This is the maximum air you can force out of your lungs in 1 second.
This measurement can help your doctor evaluate how severe your breathing issues are. An FEV1 reading that’s lower than expected shows you might have a significant breathing obstruction.
Your doctor will use your FEV1 measurement to grade how severe any breathing concerns are.
FEV1/FVC ratio
Doctors often analyze the FVC and FEV1 separatelythen calculate your FEV1/FVC ratio. The FEV1/FVC ratio is a number that represents the percentage of your lung capacity you’re able to exhale in 1 second.
In the absence of restrictive lung disease that affects FEV1/FVC ratiothe higher the percentage a doctor calculates from your FEV1/FVC ratiothe healthier your lungs are.
A low ratio suggests that something is blocking your airways
Spirometry produces a graph that shows your flow of air over time. If your lungs are healthyyour FVC and FEV1 scores are plotted on a graph that could look something like this:
If your doctor finds that your results fall into the “abnormal” categorythey’ll likely perform other tests to determine whether a breathing disorder causes impaired breathing. These could include chest X-rayssinus X-raysand blood tests.
The primary lung conditions that will cause unexpected spirometry results include obstructive diseasessuch as asthma and COPDand restrictive diseasessuch as interstitial pulmonary fibrosis.
Your doctor may also screen for commonly occurring conditions with breathing disorders that can worsen your symptoms. These include heartburnhay feverand sinusitis.
Spirometry tests are standard procedures doctors use to assess lung function. These tests measure how much air a person can force out of their lungs within 1 second and in total.
The results of a spirometry test can help diagnose obstructive lung disease and other respiratory conditions.
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