Spirometry is a simple, non-invasive test that has become a cornerstone for assessing lung function in real-life situations. It measures how much air enters and exits the lungs, as well as the speed at which it is exhaled , thus helping to detect respiratory problems early and monitor the progression of diagnosed conditions such as asthma or COPD.
If you smoke, have a history of smoking, experience a persistent cough , wheezing, or shortness of breath when climbing stairs, this test can provide clear answers. Many specialists consider it the basic pulmonary function test because it demonstrates, with data and graphs, lung capacity and the speed at which air moves through the bronchi.
What is spirometry?
Spirometry is a pulmonary function test performed in a doctor's office or laboratory that quantifies respiratory volumes and flows. It helps detect obstructions (difficulty in exhaling air) or restrictions (lungs that do not expand properly) , two patterns that lead to different diagnoses and treatments.
In addition to numerical data, current equipment generates a highly illustrative flow-volume curve. This graph helps visualize in real time how air enters and exits the lungs , providing clues about bronchial collapse, incomplete maneuvers, or insufficient effort, and refining clinical interpretation.
What does it measure and what parameters will you see in the report?
Spirometry assesses the amount of air the lungs move and the speed of exhalation. This data is compared to "predicted" values based on age, sex, height, and sometimes weight , to determine if you are within the normal range or if there is an abnormality.
- FVC or Forced Vital Capacity: The total volume you can exhale after a maximal inspiration. A low FVC suggests a restrictive pattern or an incomplete maneuver.
- FEV1 or Forced Expiratory Volume in the first second: liters that you forcefully expel in the first second; it is key to detecting airway obstruction.
- FEV1/FVC ratio: percentage that distinguishes between obstruction (reduced ratio) and restriction (both parameters low, with a relatively preserved ratio).
Modern reports also review the quality of the test (repeatability and acceptability) and the shape of the curve. A low FEV1/FVC ratio with a decreased FEV1 usually points to obstruction, as in COPD or asthma ; if FEV1 and FVC decrease proportionally, restriction is suspected.
The flow-volume curve adds context to the numbers: low flow peaks, "bites" during expiration, or abrupt drops can indicate bronchospasm, insufficient effort, or dynamic collapse. Therefore, not only the numbers matter, but also the shape of the graph and the technique.
How to do it step by step
The test is outpatient and lasts between 15 and 30 minutes. It does not require fasting or complicated preparation , although it is advisable to follow some recommendations to ensure reliable results.
You will sit down, place your lips around a disposable mouthpiece, and a nose clip will be placed to prevent air from escaping. Following the professional's instructions, you will inhale deeply and then exhale with all your might until your lungs are completely empty.
The maneuver must be repeated at least three times to ensure consistency. If the three measurements differ significantly, you will be asked to make more attempts until valid curves are obtained (generally no more than six). It is normal for the staff to encourage you with vigorous instructions to make the exhalation as forceful as possible.
In many centers, a second series of tests is performed after administering an inhaled bronchodilator. After 15 to 30 minutes, spirometry is repeated to check if airflow improves with the medication.
When is it advisable to have a spirometry test?
This test is useful both for studying symptoms and for preventing complications. If there is a chronic cough, wheezing, shortness of breath, or difficulty exercising, it is one of the first tests to request because it helps guide the diagnosis and treatment.
- Diagnosis of respiratory diseases: essential in asthma, COPD (chronic bronchitis and emphysema) and in restrictive disorders such as some fibrosis.
- Smokers and ex-smokers: It detects obstruction even before symptoms slow you down in your daily life; in ex-smokers it helps to assess aftereffects and recovery.
- Monitoring of chronic pathologies: It allows you to adjust medication and check if the therapies are working.
- Preoperative assessment: useful for estimating whether lung function is sufficient for general anesthesia.
- Workplace surveillance: It helps to rule out or confirm respiratory disorders linked to workplace exposures.
- Apparently healthy people at risk: Smoking, family history, or exposure to environmental toxins may justify it early on.
Public health campaigns emphasize offering spirometry to current and former smokers. The sooner an abnormality is detected, the sooner intervention can take place to slow the decline and improve quality of life.
Preparation: what to do and what to avoid
Following a few simple guidelines helps to obtain reliable results. If you use inhalers or bronchodilators, always check if you should stop using them sooner ; sometimes you are advised to avoid using them for 6 to 24 hours, and with very long-acting medications, up to 48 hours, depending on medical advice.
- Clothing: Come in comfortable clothes, without belts or ties, to facilitate deep breathing.
- Foods: Avoid heavy meals in the 2 hours prior; fasting is not necessary.
- Caffeine: It is best not to drink coffee, tea or caffeinated soft drinks in the 6 to 8 hours beforehand.
- Alcohol and sedatives: Try to avoid them at least 4 hours beforehand.
- Exercise: Avoid strenuous activity before the test and rest for 5 to 15 minutes sitting down upon arrival.
- Tobacco: Ideally, you should not smoke for at least several hours beforehand; some protocols require 1 to 4 hours, and others recommend 24 hours without smoking to avoid altering the results.
- Dental prosthesis: Inform the staff; depending on the case, they will tell you if it is advisable to remove it during the test for greater safety and watertightness.
Pay attention to the instructions given by the healthcare staff and ask any questions you may have. Proper technique is key to ensuring the report is interpretable and useful for your doctor.
Risks, discomforts and contraindications
This is a very safe and well-tolerated test. It may momentarily cause dizziness, coughing, or a transient feeling of shortness of breath due to the effort of forced exhalation; these symptoms pass in seconds with a brief rest.
Serious complications are rare, but the procedure should not be performed in certain situations. Your team will assess whether there are any temporary or permanent contraindications before scheduling it.
- Important contraindications: recent pneumothorax; unstable cardiovascular disease (active angina, recent heart attack or pulmonary thromboembolism); recent hemoptysis; retinal detachment or recent eye surgery; recent thoracic or abdominal surgery; aneurysm (cerebral, thoracic or abdominal); recent vertigo.
- Following acute cardiac events: If you have had a heart attack or other recent serious problem, it is postponed for safety.
If you experience intense dizziness or a coughing fit during the test, please ask to be stopped for a few seconds. The staff will give you time to recover and safely resume the procedure.
The bronchodilator trial: measuring reversibility
In many cases, spirometry is performed before and after bronchodilator administration. First, measurements are taken under baseline conditions; then, you inhale a medication that dilates the bronchi , wait between 15 and 30 minutes, and repeat the measurements.
Comparing both results reveals whether the obstruction clearly improves with the medication. A significant response suggests a reversible component typical of asthma ; if there is no change or only slight change, it points to a more fixed obstruction, as in COPD.
How to interpret the results (with the help of a doctor)
The report will include FEV1, FVC, the FEV1/FVC ratio, and the appearance of the curve. Only a healthcare professional can integrate this data with your symptoms and examination to make a diagnosis and determine treatment.
A common way to estimate the severity of the obstruction is based on FEV1 expressed as a percentage of the predicted value. These bands are for guidance only and should be individualized.
- FEV1 ≥ 80%: function within expectations in many cases (according to age, sex and size).
- FEV1 70%–79%: mild obstruction.
- FEV1 50%–69%: moderate obstruction.
- FEV1 < 49%: severe obstruction.
Besides the percentage, the pattern is also important: if the FEV1/FVC ratio is reduced, we're talking about obstruction; if both decrease with a relatively normal ratio, we're thinking about restriction . The shape of the curve and the quality of the maneuvers complete the interpretation.
In people with a prior diagnosis (e.g., asthma or COPD), serial measurements allow for monitoring. Seeing whether FEV1 improves, worsens, or remains stable helps adjust inhalers, dosages, and management strategies such as action plans or respiratory rehabilitation.
Where is it done and what to expect on the day of the test?
It is usually performed in pulmonology clinics or pulmonary function laboratories in hospitals and health centers. The setting is outpatient, with trained staff guiding each step to ensure the effort is appropriate and the data is reliable.
Upon arrival, the procedure will be explained to you, and your condition and medication will be checked. You will be seated, a nose clip and disposable mouthpiece will be placed on your nose, and you will perform several maneuvers until consistent results are obtained. The team will choose the best value from acceptable and repeatable curves.
Some institutions will give you very specific logistical instructions (floor, testing area, access points). Follow these instructions to arrive on time and take a short break before starting , which improves the stability of the measurement.
Practical tips for a good blow
A powerful and sustained technique is half the test. Fill your lungs to the maximum with diaphragmatic breathing and start blowing suddenly, strongly, and continuously until there is no air left (ideally, 6 seconds or more for adults if your team indicates it).
During exertion, do not let air escape from the corners of your mouth or separate your lips from the mouthpiece. Seal your mouth tightly and hold your breath until you are told to "stop ," even if you feel like you're empty: pushing through the last few seconds improves your FVC.
If you feel like coughing or dizzy, rest and try again. The quality of the maneuver is just as important as the number of attempts , and sometimes a short break makes a big difference.
Who should consider it a priority?
In addition to people with symptoms, there are groups for whom spirometry is very valuable. Those who smoke or have smoked, those with occupational exposure to dust or fumes, or those with a family history of lung disease should consult their healthcare professional.
In routine checkups for asthma or COPD, scheduling the test at intervals allows for timely intervention. If your FEV1 falls below your personal bests , it's a sign to adjust your treatment or reinforce environmental control measures and lifestyle changes.
For surgeries, especially those requiring general anesthesia, spirometry is part of the preoperative assessment. Knowing your respiratory reserve helps plan anesthesia and postoperative care , reducing respiratory risks.
Quick FAQ
Does it hurt? No. It's demanding because it requires blowing hard, but it's not painful. You might feel momentarily tired.
How long does it take? Between 15 and 30 minutes, depending on the number of maneuvers and whether a bronchodilator test is performed.
Do I need to fast beforehand? No. Just avoid heavy meals beforehand and follow the preparation guidelines.
What if I wear dentures? Let us know. In some cases, we ask you to remove them to ensure a proper seal and safety during the blowing process.
Can I do sports that day? Avoid intense exercise beforehand; after the test, if you feel well, you can continue with your usual routine.
Spirometry objectively summarizes how you breathe and how your bronchi respond to exertion and, if necessary, to a bronchodilator. It is a primary tool for diagnosing, classifying, and monitoring major respiratory diseases , and performing it with proper technique and preparation makes the difference between doubt and certainty.
Anyone considering this test should take into account the guidelines mentioned, prepare for the appointment following the recommendations, and resolve any doubts with their healthcare professional. Breathing better starts with accurate measurements and making informed decisions based on reliable data and expert clinical interpretation.
