What is Spirometry?
Spirometry is a common pulmonary function test that measures how much air a person can inhale and exhale, and how quickly they can exhale it. It is used to assess lung function and diagnose or monitor a variety of respiratory conditions.
Table of Contents
Definition of Spirometry
Spirometry is a pulmonary function test (PFT) that measures the volume and speed of air a person can inhale and exhale. It is a key diagnostic and monitoring tool used to assess the function of the lungs and detect respiratory conditions that affect airflow.
What Spirometry Measures?
Spirometry measures several key lung function parameters:
1. Forced Vital Capacity (FVC): This is the total amount of air you can forcefully exhale after taking the deepest possible breath. It indicates the overall volume of air your lungs can hold.
2. Forced Expiratory Volume in 1 Second (FEV1): This measures how much air you can force out of your lungs in the first second of the forceful exhalation. This is a crucial indicator of how quickly air can move out of your airways.
3. FEV1/FVC Ratio: This is the ratio of FEV1 to FVC, expressed as a percentage. It's a very important value for distinguishing between different types of lung problems.
4. Peak Expiratory Flow (PEF): This measures the maximum speed at which you can exhale air.
Why is the Spirometry Test Performed?
Spirometry is a commonly used test to evaluate lung function in individuals and is performed for several reasons.
The most common reasons for spirometry include:
Diagnosis of Respiratory Conditions
One of the primary reasons spirometry is performed is to help diagnose various respiratory conditions that affect airflow in and out of the lungs. It is especially useful in identifying obstructive lung diseases like asthma and chronic obstructive pulmonary disease (COPD), where the airways become narrowed or blocked. Spirometry can also detect restrictive lung diseases, such as pulmonary fibrosis, where the lungs lose their ability to expand fully. By measuring lung function and airflow patterns, doctors can accurately determine the presence and type of respiratory disorder.
Assessment of Disease Severity
Beyond diagnosing respiratory conditions, spirometry is essential for assessing the severity and stage of lung disease. For instance, in patients with COPD, spirometry can indicate how advanced the disease is by analyzing the forced expiratory volume (FEV₁) and forced vital capacity (FVC). This information is vital for deciding the most appropriate treatment and for monitoring whether the condition is progressing or remaining stable over time.
Monitoring the Effectiveness of Treatment
Doctors often use spirometry to monitor how well a patient is responding to treatment. If a person with asthma or COPD is using inhalers or other medications, periodic spirometry tests can show whether the treatment is helping to open up the airways and improve breathing. It can also guide the need to adjust dosages or switch medications based on changes in lung function.
Pre-operative Evaluation
Spirometry may be performed before a patient undergoes surgery, especially if the procedure involves the chest or lungs, or if the patient has a history of lung problems. Evaluating lung function before surgery helps assess the risk of postoperative complications, such as breathing difficulties or infections, and may influence the choice of anesthesia or surgical approach.
Detection of Early Lung Problems in At-risk Individuals
In individuals who are at increased risk of lung disease, such as smokers, occupational exposure workers, or those with a family history of respiratory conditions, spirometry can help detect problems before symptoms appear. Early detection allows for timely intervention, which can prevent further lung damage and improve long-term outcomes.
Evaluation of Unexplained Symptoms
Spirometry is also valuable in investigating unexplained respiratory symptoms like chronic cough, shortness of breath, wheezing, or tightness in the chest. These symptoms could be caused by a range of conditions, and spirometry provides objective data to help determine whether the lungs are functioning properly or if further testing is needed.
Occupational and Environmental Health Monitoring
Workers in industries involving dust, chemicals, fumes, or other airborne irritants may be required to undergo regular spirometry tests to ensure their lungs are not being adversely affected. This kind of monitoring is important for occupational health and safety compliance and early detection of work-related respiratory issues.
Types of Spirometry
Spirometry is a foundational test in respiratory medicine, but it can be performed using different methods and devices, depending on the clinical purpose, setting, and level of detail required. While the basic principle remains the same—measuring airflow in and out of the lungs—several types or approaches to spirometry vary in technique and equipment.
Basic or Diagnostic Spirometry
This is the most commonly used form of spirometry, typically performed in clinics, hospitals, or pulmonary function labs. Diagnostic spirometry measures two key values: Forced Vital Capacity (FVC) and Forced Expiratory Volume in one second (FEV₁). The FEV₁/FVC ratio helps in diagnosing conditions like asthma and COPD. It is usually done using a handheld spirometer or desktop unit and requires the patient to breathe into a mouthpiece connected to the device while following specific breathing instructions.
Pre and Post-Bronchodilator Spirometry
In this form of spirometry, the test is conducted before and after administering a bronchodilator medication. The goal is to assess the reversibility of airway obstruction, which is especially useful in distinguishing between asthma (reversible obstruction) and COPD (typically non-reversible). If there is a significant improvement in lung function after taking the bronchodilator, the result suggests that the airway narrowing is reversible and treatable with inhalers.
Screening Spirometry
Screening spirometry is often used in primary care settings or during occupational health evaluations. Its purpose is not necessarily to diagnose a specific disease but to identify early signs of lung function abnormalities, especially in asymptomatic individuals at risk—such as smokers, people exposed to environmental irritants, or those with a family history of lung disease. This type is typically quicker and less detailed than full diagnostic spirometry.
Incentive Spirometry
Incentive spirometry differs from diagnostic spirometry in purpose and design. It is commonly used in postoperative care or for patients with limited lung expansion, such as those recovering from surgery, pneumonia, or prolonged immobility. The device encourages the patient to take slow, deep breaths by providing visual feedback (usually a rising ball or piston) when air is inhaled. While it does not provide diagnostic data, incentive spirometry helps prevent complications like atelectasis (lung collapse) and improves lung expansion.
Portable or Handheld Spirometry
Portable spirometers are compact devices used outside traditional clinical settings, such as in home monitoring or field assessments. These are particularly useful for patients managing chronic conditions like asthma or COPD at home. While they may not be as comprehensive as lab-based spirometers, they offer key measurements like FEV₁ and peak expiratory flow (PEF), and are useful for tracking changes over time or identifying flare-ups.
Peak Flow Meter Testing
Although not technically spirometry, peak flow measurement is often considered a simplified form. It measures the maximum speed of expiration (Peak Expiratory Flow – PEF) and is primarily used in the self-monitoring of asthma. It helps patients recognize early signs of worsening airway obstruction and adjust treatment accordingly. While not as detailed as spirometry, it is highly useful for day-to-day asthma management.
Computerized or Digital Spirometry
Digital spirometry systems integrate advanced software that can automatically interpret results, graph flow-volume loops, and store patient data electronically. These systems often allow for more detailed assessments and are frequently used in hospitals and pulmonary function testing labs. They provide more reliable and reproducible results, especially when used by trained technicians.
Different types of spirometry are used depending on the clinical need—whether for diagnosis, monitoring, screening, or rehabilitation. From basic diagnostic tests in clinics to incentive breathing tools in recovery wards, spirometry plays a versatile and essential role in respiratory care.(alert-passed)
How is the Spirometry Test Performed?
The spirometry test is a straightforward and non-invasive procedure that measures how well your lungs are working. It helps detect and monitor respiratory conditions such as asthma, chronic obstructive pulmonary disease (COPD), and other disorders that affect breathing. Though the test is simple, it must be performed with precision and patient cooperation to ensure accurate results.
A. Preparation Before the Test
Before undergoing a spirometry test, patients may receive specific instructions from their healthcare provider, including:
➧ Avoid smoking for several hours before the test.
➧ Refrain from heavy meals, as a full stomach can restrict lung expansion.
➧ Avoid vigorous exercise at least 30 minutes before the test.
➧ Wear loose clothing to allow unrestricted breathing.
➧ Patients may also be advised to withhold certain medications, such as bronchodilators, to get an accurate baseline reading.
The healthcare provider may ask about the patient’s medical history, current symptoms, and any medications being taken. In some cases, a pre-test questionnaire or baseline check (such as blood pressure or pulse oximetry) may be done.
B. Initial Instructions and Demonstration
A trained technician or respiratory therapist will explain the procedure in detail. They will:
➧ Show the patient how to use the mouthpiece and nose clip.
➧ Demonstrate the correct way to inhale deeply and exhale forcefully and completely.
➧ Emphasize that the exhalation should be fast and continued until all air is expelled, usually lasting 6 seconds or more in adults.
➧ Encourage the patient to make a tight seal around the mouthpiece to prevent air leakage.
The accuracy of the test depends heavily on the patient's effort, so clear instructions and encouragement are vital.
C. Performing the Test
Step-by-Step Procedure
1. Seating and Setup: The patient is usually seated upright in a chair. A nose clip is placed to prevent air from escaping through the nose, ensuring all airflow passes through the mouthpiece.
2. Inhale Deeply: The patient takes a deep breath to fill their lungs completely.
3. Exhale Forcefully: The patient then places their mouth tightly around the mouthpiece and blows out as hard and as fast as possible. The exhalation should be sustained until the technician says to stop.
4. Repeat Trials: The test is typically repeated at least three times to ensure consistency. The best of the three acceptable efforts is recorded. If results vary significantly, more attempts may be required.
5. Post-Bronchodilator Testing (if needed): If your doctor suspects asthma or reversible airway obstruction, you may be given a bronchodilator medication through an inhaler or nebulizer. After 10–15 minutes, the test is repeated to assess improvement in lung function.
D. Monitoring During the Test
Throughout the procedure, the technician monitors:
➧ The patient’s technique to ensure accuracy.
➧ Signs of dizziness, shortness of breath, or discomfort.
➧ The spirometry graph or curves for each blow to determine acceptability and reproducibility.
If the patient becomes lightheaded or cannot continue, the test may be paused or stopped.
E. After the Test
Once the spirometry test is completed:
➧ The nose clip is removed, and the patient can relax.
➧ The results are reviewed for quality control, ensuring that all blows were acceptable and reproducible.
➧ The values obtained (like FEV₁, FVC, and FEV₁/FVC ratio) are compared to normal predicted values based on the patient's age, sex, height, and ethnicity.
In some cases, the doctor may discuss the preliminary results immediately, or they may be reviewed during a follow-up appointment.
The spirometry test is a quick, safe, and reliable method to assess lung function. While the process only takes a few minutes, accurate results require proper preparation, good technique, and full patient cooperation.
Understanding Spirometry Test Results
Spirometry test results provide crucial information about lung function and help diagnose and monitor respiratory conditions. The results are typically presented in both numerical values and graphical form (flow-volume or volume-time curves). They are interpreted by comparing the patient’s values to predicted normal values based on age, gender, height, and ethnicity.
A. Key Measurements in Spirometry
Several important parameters are measured during a spirometry test. The most common and clinically significant ones include:
1. FVC (Forced Vital Capacity)
Definition: The total amount of air a person can forcibly exhale after taking the deepest breath possible.
Importance: A reduced FVC may indicate a restrictive lung disease (e.g., pulmonary fibrosis), where the lungs are unable to fully expand.
2. FEV₁ (Forced Expiratory Volume in 1 Second)
Definition: The amount of air exhaled in the first second of the FVC maneuver.
Importance: A key measure of airway obstruction. Low FEV₁ values are commonly seen in asthma and COPD.
3. FEV₁/FVC Ratio
Definition: The percentage of the total air (FVC) expelled in the first second (FEV₁).
Interpretation:
➧ Normal: ≥ 70% (in adults; the threshold may vary with age)
➧ Obstructive Pattern: FEV₁/FVC < 70%
➧ Restrictive Pattern: FEV₁/FVC is normal or high, but FVC is reduced
This ratio is critical in distinguishing obstructive from restrictive lung disease.
4. PEF (Peak Expiratory Flow)
Definition: The highest flow rate achieved during forced expiration.
Importance: Useful for assessing the severity of airway obstruction.
B. Interpreting the Results: Patterns of Lung Disease
Spirometry results are interpreted by identifying one of the following functional patterns:
1. Obstructive Lung Disease
Examples: Asthma, Chronic Obstructive Pulmonary Disease (COPD), bronchiectasis
Spirometry findings:
➧ Reduced FEV₁
➧ Normal or reduced FVC
➧ Low FEV₁/FVC ratio (<70%)
Mechanism: Obstruction makes it hard to exhale air quickly, causing air trapping.
2. Restrictive Lung Disease
Examples: Pulmonary fibrosis, interstitial lung disease, obesity, neuromuscular diseases
Spirometry findings:
➧ Reduced FVC
➧ Normal or reduced FEV₁
➧ Normal or high FEV₁/FVC ratio
Mechanism: Lungs are unable to fully expand, reducing overall lung volume.
3. Mixed Pattern
Findings: Both FEV₁ and FVC are reduced, and the FEV₁/FVC ratio may be low or normal.
Indicates: A combination of obstructive and restrictive features, which may require further testing such as lung volume measurements or imaging.
C. Bronchodilator Response (Reversibility Testing)
In some cases, the spirometry test is repeated after administering a bronchodilator (like salbutamol) to assess reversibility:
➧ Significant improvement in FEV₁ (increase of ≥12% and ≥200 mL) after bronchodilator use may suggest asthma or a reversible airway condition.
➧ Little or no improvement is more consistent with COPD or fixed obstruction.
D. Graphical Output
Spirometry also produces two types of graphs:
Flow-Volume Loop: Shows flow rate versus volume during forced exhalation and inhalation.
➧ Obstructive patterns: "Scooped" or concave shape during exhalation.
➧ Restrictive patterns: Narrow but peaked curves with reduced volume.
Volume-Time Curve: Shows the volume of air exhaled over time.
➧ In normal lungs, the curve rises sharply and plateaus.
➧ In obstruction, the curve rises slowly and takes longer to plateau.
E. Limitations of Spirometry Results
While spirometry is very informative, its interpretation should always consider:
➧ Patient effort – Poor technique or inadequate effort can distort results.
➧ Age-related changes – Lung function naturally declines with age.
➧ Ethnic and environmental factors – Influence predicted values.
Spirometry is often the first step; if abnormalities are found, further tests such as lung volumes, diffusion capacity (DLCO), imaging, or sleep studies may be recommended.
Risks and Contraindications of the Spirometry Test
Spirometry is generally considered a safe test. However, because it involves forceful breathing, it can temporarily increase pressure in the head, chest, and abdomen. Therefore, it may be avoided or delayed in certain situations, including:
➧ Recent heart attack or stroke (within 3 months)
➧ Unstable angina or uncontrolled high blood pressure
➧ Recent eye, abdominal, or chest surgery
➧ Recent collapsed lung (pneumothorax)
➧ Coughing up blood without a known cause
➧ Active or suspected transmissible respiratory infection (e.g., tuberculosis, severe flu)
➧ Aneurysms (cerebral, thoracic, or abdominal)
You might feel lightheaded, dizzy, or breathless for a moment after the test, but these symptoms usually resolve quickly. It's important to communicate any discomfort or pre-existing conditions to the healthcare professional performing the test.
Spirometry is a valuable tool in the evaluation and management of respiratory conditions. It is a simple, safe, and non-invasive test that provides important information about an individual's lung function. If you have been referred for a spirometry test, it is important to follow your doctor's instructions carefully to ensure the best possible results.(alert-passed)
