Spirometry test options
There are two main spirometry tests to help measure and diagnose lung conditions. Forced Vital Capacity (FVC) and Slow Vital Capacity (SVC or VC). The most important spirometry test is the FVC, as this is used to provide more detailed results.
| Forced Vital Capacity (FVC) |
Slow Vital Capacity (SVC or VC) |
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On average, a healthy individual should be able to exhale at least 80% of their predicted FVC.
A lower-than-predicted FVC value in a spirometry test can indicate restricted lung function, which can be caused by conditions like pulmonary fibrosis, scoliosis, or obesity.
Higher-than-predicted FVC could suggest hyperinflation of the lungs, often seen in conditions like emphysema.
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The FVC and SVC or VC both record similar information as they are measuring the amount of air that can be exhaled after a full intake of breath.
The difference between the two measurements is the FVC is a forced breath, and the VC is a slow exhalation.
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The results of these two tests can then be compared in a spirometer graph. If a big difference is found between the VC and FVC it can indicate airway collapse or air trapping which is useful in assessing neuromuscular disorders that affect the respiratory muscles.
Other types of spirometry test
| Inspiratory Capacity (IC) |
FEV1/FVC Ratio |
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IC is the maximum volume of air a person can inhale after a normal exhalation.
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The FEV1/FVC Ratio (FEV1%) is the ratio of the FEV1 (the amount of air you exhale in the first second) to the FVC (the total amount of air exhaled). This helps to identify whether there's an obstruction in your airways, which is characteristic of conditions like COPD.
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| Peak Expiratory Flow (PEF) |
Forced Inspiratory Flow (FIF) |
| This measures the maximum speed at which you can exhale forcefully. It's often used in spirometry tests to monitor the severity of lung conditions like asthma. |
FIF measures the maximum flow rate of air during a forceful inhalation. |
| Forced Expiratory Flow at 25-75% (FEF25-75%) |
Maximum Voluntary Ventilation (MVV) |
| This test measures the average flow rate during the middle part of the forced exhalation and provides additional information about small airway function. |
Some medications can influence lung function, so it's important to check whether the patient is using bronchodilators or other respiratory medications that might affect the results. |
| Forced Expiration Volume in 1 second (FEV1) |
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FEV1 should be around 80-120% of the predicted value. FEV1/FVC ratio should be greater than 70-75% (this means that at least 70-75% of the air should be exhaled in the first second).
A lower-than-expected FEV1 could indicate obstruction in the airways, which can be seen in conditions like asthma, chronic bronchitis, or COPD. The FEV1/FVC ratio is crucial as if it’s less than 70-75%, this suggests airway obstruction.
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Factors that can affect spirometry test results
When interpreting spirometry results, healthcare professionals often compare test results against predicted values, such as:
| Age |
Sex |
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Lung function changes with age, so expected values can vary accordingly. Children and adolescents might have lower absolute values, but their lung function should increase as they grow.
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Men generally have slightly higher lung function values compared to women of the same age, height, and ethnicity.
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| Height |
Ethnicity |
| Taller individuals usually have larger lung volumes, so spirometry values should be adjusted to account for height. |
Some studies, although subtle, have shown that lung function norms can differ according to ethnic groups. |
| Clinical history |
Medications |
| A patient's medical history can provide vital context. Whether it's smoking habits, exposure to pollutants, family history of lung diseases, or symptoms like coughing and shortness of breath, this can all have an impact on expected spirometry results. |
Some medications can influence lung function, so it's important to check whether the patient is using bronchodilators or other respiratory medications that might affect the results. |
| Reproducibility |
Flow-Volume curve shape |
| Spirometry test results need to be consistent across multiple attempts. If results show a significant variation, it might be necessary to repeat the test. |
The shape of the curve in a spirometer graph can provide further insights into the nature of an obstruction or restriction. A flattened curve can suggest an obstructive pattern, while a reduced curve might indicate a restrictive pattern.
Abnormal spirometry test results may indicate respiratory diseases, such as asthma, COPD, restrictive lung diseases, and more.
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Interpreting spirometry test results
Interpreting spirometry results goes beyond looking at individual values. The shape of the flow-volume curve and the patient's medical history must also be considered.
Some variation can occur based on factors like lung size, age and height, so the key is to look for consistency and patterns that could suggest an underlying lung condition.
To correctly diagnose any spirometry results, they should always be assessed by a trained healthcare professional.
Industry-leading spirometers
Spirometry is essential for diagnosing and monitoring lung conditions, aiding in treatment decisions, and assessing the effectiveness of interventions over time.
Amplivox is proud to offer a suite of industry-leading EMR-compatible spirometers to meet the requirements of occupational and respiratory health professionals.
With the inclusion of class-leading spirometry PC database applications, users can benefit from comprehensive data analysis, trending, and transfer capabilities.
For more information on our spirometry devices please visit our spirometers webpage, contact our customer support team on +44 (0)1865 880 846 or email.
References
1National Library of Medicine, Increased difference between slow and forced vital capacity is associated with reduced exercise tolerance in COPD patients. (2024). Accessed at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3938036/
2MediTech, Vital capacity and the difference Between FVC & VC. Accessed at: https://www.meditech.com.cn/Education/Measurement-of-the-vital-capacity-of-lung.html
3European Respiratory Society, Spirometry: step by step. Accessed at: https://breathe.ersjournals.com/content/8/3/232
4American Family Physician, An Approach to Interpreting Spirometry. (Mar 2024). Accessed at: https://www.aafp.org/pubs/afp/issues/2004/0301/p1107.html