January 15, 2024
Written by

The VitalFlo Team

Why Spirometry?


Spirometry stands as a cornerstone in the diagnostic and monitoring arsenal against respiratory diseases. This simple yet powerful tool provides critical insights into lung function, aiding healthcare professionals in diagnosing, managing, and monitoring a range of respiratory conditions.

A common physiological test, spirometry is a pulmonary function test that measures the volumes and rates an individual inhales or exhales. Its primary purpose is to assess lung function, particularly in the diagnosis and management of conditions like asthma, chronic obstructive pulmonary disease (COPD), and other disorders that affect breathing.

The roots of spirometry can be traced back to the 19th century. John Hutchinson is credited with inventing the spirometer in 1846, which he used to measure vital capacity. Since then, the technology and methodology have evolved significantly, making spirometry a fundamental tool in modern respiratory medicine. The evolution of spirometry is well documented in historical reviews of pulmonary function testing.

Spirometry is an important tool in modern clinical practice due to the prevalence of chronic respiratory diseases, such as COPD and asthma, which are major health concerns globally. According to the World Health Organization (WHO), COPD is the third leading cause of death worldwide. Asthma affects an estimated 262 million people and caused 455,000 deaths in 2019.

In addition to the high prevalence of these diseases, in the United States the medical costs associated with respiratory diseases like COPD are forecasted to double over the next five years. This makes early detection and management of respiratory diseases like asthma and COPD more urgent than ever.

Early detection and management of respiratory diseases can significantly improve patient outcomes. Spirometry plays a crucial role in this regard: it can help in the early detection of obstructive airway diseases, sometimes even before symptoms become apparent. Regular spirometric monitoring is also essential in managing patients with chronic respiratory diseases, allowing for timely interventions and adjustments in treatment.

As we delve deeper into the nuances of spirometry in the following sections, it becomes evident that proficiency in this technique is essential for all healthcare professionals involved in respiratory care.

Spirometry Fundamentals

Understanding the basics of spirometry is crucial for healthcare professionals to effectively utilize this tool in clinical practice.

Spirometry measures two key aspects of lung function: the volume and speed of air forcefully exhaled. The primary measurements include Forced Vital Capacity (FVC), which is the total volume of air that can be forcefully exhaled after full inhalation, and Forced Expiratory Volume in one second (FEV1), which is the volume of air exhaled in the first second of the FVC maneuver. The FEV1/FVC ratio is a critical parameter for diagnosing obstructive lung diseases. When spirometry includes a Flow Volume Loop (FVL), inhalation volume and speed is also measured. 

Key Spirometric Indices:

  • FEV1: Indicates the air volume expelled in the first second and is a primary measure in assessing obstruction
  • FVC: Total volume of air that can be forcefully exhaled after inhalation. Reductions can indicate restrictive lung disease
  • FEV1/FVC Ratio: A decreased ratio suggests obstructive disease, while a normal or increased ratio with reduced FEV1 and FVC indicates restrictive patterns
  • FVL: a characteristic patterns of restrictive, obstructive or other pulmonary disease may be revealed by the shape of the graph

The American Thoracic Society and European Respiratory Society routinely collaborate to produce standards for spirometry. Their recommendations include guidelines for the maneuver and interpretation, as well as standards for the use and maintenance of the devices themselves.


Performing Spirometry

Effective spirometry testing is a skill that requires attention to detail, patient cooperation, and adherence to standardized procedures. By following simple guidelines and preparation, it should be straightforward to perform high quality, reproducible spirometry maneuvers. To assist with proper technique, there are spirometry software platforms available that can help patients and providers correctly prepare and perform the tests.

Before conducting a spirometry test, it is essential to prepare the patient adequately. This includes Pretest Instructions and activities to avoid as described in the following table:

Table 1: Pre-test instructions for spirometry. Link: Ruppel's Manual of Pulmonary Function Testing by Carl Mottram


After ensuring pretest instructions were followed, using proper technique during the spirometry maneuver is important. Providing clear instructions to the patient is helpful for ensuring patient cooperation and successful test performance. Finding a spirometry software platform that helps guide patients and providers through the maneuver can make spirometry more accessible in many care settings.

To conduct the spirometry test, the patients should inspire as deeply as they can, and expire as forcefully and rapidly as possible into the spirometer. This should be followed by a deep and complete inspiration through the spirometer. The full maneuver is described in the following table:

Table 2: Performing spirometry with flow volume loop. Link: Ruppel's Manual of Pulmonary Function Testing. Link: Standardization of Spirometry 2019 Update


It can be helpful to remember that there are basically three key components to ensure a high quality spirometry maneuver:

1. The patient needs to take a deep breath to their maximal lung volume. If this step is not achieved, the next two are not relevant to the outcome

2. The blast exhale should be as forceful and rapid as possible

3. The end of forced exhalation (EOFE) should meet one of the following criteria:

  • Expiratory plateau (<0.025 L in the last 1 second of expiration)
  • Expiratory time of greater than 15 seconds, and/or
  • The FVC is within the repeatability tolerance of, or is greater than the largest prior observed FVC

A modern spirometry software platform can help ensure high quality, repeatable, spirometry by providing coaching, feedback and grading (acceptability and repeatability criteria) in real-time throughout the spirometry session.

Interpretation of Spirometry Results

Interpreting spirometry results is a critical skill for healthcare professionals, enabling the diagnosis and management of various respiratory conditions. Modern spirometry software platforms can help provide clinical decision support tools to provide guidelines and tools to aid in the interpretation of the results.

Spirometry results are typically presented as both numerical values and graphical curves. As discussed above, some of the key spirometric indices include:

  • Forced Expiratory Volume in one second (FEV1): the amount expelled during the first second of this maneuver
  • Full Vital Capacity (FVC): the total amount of air that can be expelled from full lungs
  • FEV1/FVC ratio: the ratio between the previous two values, which is used to define the presence of obstruction
  • Flow Volume Loop (FVL): the graph of the full maneuver showing the relationship between the flow rates and total volumes expelled (positive values) or inhaled (negative values).

Once it is determined that the spirometry test has produced valid, repeatable results, interpretation begins. Interpretation of spirometry results is based on comparison with predicted normal values such as the Global Lung Function 2012 (GLI 2012) reference values. These values are derived from population studies and are adjusted for age, sex, height, and ethnicity. Modern spirometry platforms may provide these values as an integrated part of their reporting and interpretation support.

From these reference values, predicted values are determined. These predicted values are determined by dividing the observed value by the reference value (given as a percentage) and are helpful for interpreting spirometry results.

A flow chart of a basic interpretation algorithm is shown in Figure 1 (reproduced from: Office Spirometry: Indications and Interpretation, American Family Physician).

Figure 1: Spirometry interpretation algorithm. Link: Office Spirometry: Indications and Interpretation

The FVLs can reveal normal and abnormal patterns (see Figure 2) that can also be used to determine the subject's condition. A normal spirometry curve shows a rapid rise in flow rate followed by a gradual decline. Abnormal patterns may indicate obstructive or restrictive lung diseases. In obstructive patterns, there is a scooped-out appearance due to a slower maximal flow rate. In restrictive patterns, the curve may appear normal but with reduced lung volumes.

Figure 2: Flow volume loop characteristic patterns. Link: medschool.co

When developing a diagnosis, there are a few interpretive strategies that can help.

Obstructive disorders, such as chronic obstructive pulmonary disease (COPD) and asthma are characterized by airflow limitation. In these cases, spirometry typically shows a reduced FEV1/FVC ratio (<0.70). In asthma, this obstruction is often reversible, whereas in COPD, it is usually not fully reversible.

Diseases such as pulmonary fibrosis are restrictive disorders and lead to a reduction in lung volumes. Spirometry in these cases shows a normal or increased FEV1/FVC ratio with a reduction in FVC.

Spirometry interpretation is a skill that can be developed further with some basic training. The National Institute for Occupational Safety and Health (NIOSH) routinely provides hands-on training workshops.

Spirometry in Clinical Management

Spirometry is not only pivotal in diagnosing respiratory conditions but also plays a significant role in the ongoing management of these diseases. This section explores the use of spirometry in monitoring disease progression and evaluating treatment efficacy.

To monitor disease progression, the frequency of spirometry testing can vary depending on the condition and its severity. For chronic conditions like COPD, annual spirometry is recommended to monitor disease progression and adjust treatment plans accordingly.

Longitudinal spirometry data can provide insights into the rate of disease progression. Modern spirometry platforms can show the trends in FEV1, FVC, the FEV1/FVC ratio throughout the entire monitoring period. In conditions like COPD, a decline in FEV1 over time is expected, but an accelerated decline may indicate a need for treatment reassessment. In asthma, variability in FEV1 can be a sign of poor disease control.

To monitor patients longitudinally, implementing a home monitoring program can provide more granular and timely data about disease progression. Modern spirometry platforms may include the ability to monitor patients with full spirometry, peak flow spirometry, and/or pulse oximetry depending on the technology provider. Automated alerting, reporting and patient status change notifications are an important consideration when implementing a home monitoring program.


Spirometry can also be used to assess the responsiveness to bronchodilators, especially in conditions like asthma. Performing a bronchodilator responsiveness test (BRT) entails performing spirometry twice, once before (pre-bronchodilator) and once after (post-bronchodilator) administration of the medication. A significant improvement in FEV1 following bronchodilator administration indicates reversible airway obstruction, a hallmark of asthma. In COPD, less reversibility is often observed, but any improvement can still guide therapy.

Further Learning and Helpful Resources

Written by

The VitalFlo Team