Introduction:
Forced expiratory volume (FEV) is the volume of air that an individual can expire during a forced breath in "t" seconds. Forced expiratory volume in one second (FEV1) is the maximum amount of air an individual can forcibly exhale during the first second following a maximal inhalation. Likewise, forced expiratory volume in six seconds (FEV6) is the maximum amount of air an individual can exhale during the sixth second following a maximal inhalation.
What Is Spirometry?
Spirometry is a simple, non-invasive, and painless test used to measure lung volume and capacities. It is one of the most common pulmonary function tests. It helps diagnose and monitor certain lung conditions by measuring the amount of air a person can breathe in one forced breath.
Conditions that can be monitored using spirometry include
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COPD (chronic obstructive lung disease).
The two key measurements in spirometry are:
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FEV1.
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FVC.
FEV is one of the main results of spirometry.
What Are the Clinical Significance of Forced Expiratory Volume?
Forced expiratory volume can be useful for categorizing the severity of obstructive lung diseases like asthma and chronic lung diseases. The FEV1 is not just a part of the pulmonary function test. Still, also, it is a marker of premature death in assessing the baseline risk of COPD, lung cancer, coronary artery disease, and stroke, which collectively is accountable for most of the premature deaths in smokers.
It is also used to interpret the reversibility test, known as the bronchodilator test. The test analyzes the response to bronchodilators in a patient with obstructive lung disease. An increase in the FEV1 of greater than or equal to 12 %, or greater than or equal to 200 ml, is considered a positive response. A positive response is typically present in reversible airway obstructions such as asthma. In contrast, an irreversible airway obstruction such as COPD will not show a positive response to the administration of Bronchodilators.
What Is the FEV1/FVC Ratio?
FEV1/ FVC is the proportion of a person's vital capacity that can expire in the first second of forced expiration (FEV1) to the forced vital capacity (FVC). The ratio reflects the amount of air one can forcibly exhale. The ratio is usually useful in diagnosing obstructive and restrictive lung diseases and monitoring their treatment. The normal value ranges between 75 to 85 %. Values less than 70 % suggest airflow limitation with an obstructive pattern. Higher than normal values is suggestive of restrictive lung disorder. To determine the severity, FEV1 should be considered and not the ratio. If the ratio is abnormal, grading based on the abnormality to determine the severity is done.
The American thoracic society has set specific guidelines for this purpose:
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Mild - more than 70 %
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Moderate - 60 to 69 %
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Moderately severe- 50 to 59 %
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Severe - 35 to 49 %
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Very severe - less than 34 %
In restrictive lung disease, lung compliance is reduced, such as in pulmonary fibrosis, pneumonia, and pulmonary edema. The FVC is smaller than normal, but the FEV1 is relatively large compared to FEV1/FVC is relatively larger than normal. It is easy for a person with restrictive lung disease to breathe out because of the high elastic recoil of the stiff lungs.
In obstructive lung disease, airway obstruction causes an increase in resistance. The FVC is smaller than normal, but FEV1 is smaller than normal. This is because it is very difficult for a person with obstructive lung disease to exhale quickly because of the increased airway resistance.
What Are the Factors Affecting FEV?
Age and gender can affect the values of FEV in a healthy individual. Other factors are height, weight, and ethnicity, affecting the FEV values. Poor inhalation, reduced patient effort, and inability to follow instructions can also affect the results.
What Is COPD?
It is a chronic inflammatory lung disease that results in irreversible airflow obstruction from the lungs. The leading cause of COPD is prolonged cigarette smoking. Other factors that may cause COPD are genetic disorders such as alpha 1 antitrypsin deficiency and occupational hazards due to long-term exposure to obnoxious chemical fumes, vapors, and dust particles which can inflame the lung parenchyma.
The enzyme alpha 1 antitrypsin is produced by the liver and then passed into the bloodstream to protect the lungs. The enzyme helps inhibit the elastase enzyme; therefore, all the elastin is broken down. COPD mainly consists of two disorders: chronic bronchitis and emphysema. These two conditions can co-occur and can vary in severity. Chronic bronchitis is the inflammation of the bronchial epithelium. Emphysema is a condition in which the alveolar sacs are destroyed due to exposure to irritating gasses and cigarette smoking.
How Is FEV1 Used to Stage COPD?
FEV values of more than 80% are considered to be normal. COPD can be staged according to FEV1 scores. According to the COPD global initiative for chronic obstructive lung disease (GOLD) guidelines, 2016:
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Mild - 80 %
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Moderate - 50 to 79 %
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Severe - 30 to 49 %
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Very severe - less than 30 %
In COPD, lower FEV1 scores are suggestive of severe conditions.
Conclusion:
Forced expiratory volume is integral to the respiratory system's screening, diagnosis, and monitoring. It is the amount of air a person can expire forcefully in one second. FEV1 value plays an important part in evaluating COPD and monitoring the condition's progression. It is useful to categorize the severity of obstructive lung diseases like asthma and COPD. Impaired lung with reduced FEV1 levels is a potential marker of future morbidity and mortality. Specifically, reduced FEV1 establishes the presence and severity of COPD and is a powerful predictor of increased risk of lung cancer, cardiovascular disease, and premature death.
