Interpretation of Spirometry
Gaseous exchange is the basis for existence of life. Lungs are the organs that perform this function. They help in intake of oxygen for metabolic needs, as well as remove metabolic wastes like carbon dioxide from the body. When these organs fail to function as usual, then diagnosing the disease at an accurate time plays a crucial role in further prognosis. The most common and feasible way to diagnose and investigate a lung disease is spirometry. Spirometry measures the amount of air inhaled and exhaled and the time taken for the process to take place. After you have taken the test, your values are compared with the normal values available, which helps in diagnosis of the disease. Interpreting spirometry can be a tedious process, as it requires the patient's cooperation and the interpreter to have the knowledge about the reference values. Now, let’s look at the possible results of spirometry and what that means.
You might have recently undergone a spirometry test and in a dilemma about your test results. Don’t worry, here is what your test readings tell about your lung status. Spirometry test values give you an idea preoperative and postoperative whether you would likely develop any pulmonary complication.
Spirometry is usually interpreted using three values: forced vital capacity(FVC), forced expiratory volume in 1st second (FEV1), and the ratio of FVC/FEV1.
FORCED VITAL CAPACITY- It is the volume of air that can be exhaled after a maximum forced inspiration. FVC normally ranges from 80%-120%. Generally, it takes 6 seconds to empty the lungs.
FORCED EXPIRATORY VOLUME IN 1ST SECOND- it is the amount of air exhaled in the 1st second of expiration. FEV1 normally ranges from 80%-120%.
FEV1/FVC- it is the volume of forced vital capacity exhaled in the 1st second of the expiration.
The diagram below represents the graphical representation of results obtained through spirometry.
In obstructive lung disorders, the graph shifts towards the left.
In restrictive lung disorders, the graph shifts towards the right.
Spirometric results usually vary depending on various physiological and pathological factors. Some of the factors that may produce major contrast with respective to results include:
RESULTS CLASSIFICATION | FEV1/FVC | %FEV1<> | %FVC<> |
Normal | >70% | >80% | >80% |
Obstructive Lung Disease | <70% | <80% | >80% |
Restrictive Lung Disease | >70% | <80% | <80% |
A spirometry is only valid when its following requirements are meet:
Some occupations expose the individual to particulate matter in the air, such as sugarcane, cotton and coal industries. Overtime, exposure to these particles in the air causes progressive lung damage. To prevent these diseases, the government has introduced many national health policies that recommend regular spirometry tests in these individuals. The employers are also asked to perform these tests before employing the individual as a part of pre-placement examination. This ensures the person is safe, sound and healthy.
Spirometry is one of the safest and best techniques to diagnose lung diseases. Interpretation of spirometry depends on you as well as the interpreter. Make sure you exhale fully while the test is being performed. With different values mentioned in various journals, interpreting spirometry becomes a difficult task. The interpreter must choose comparative values with careful insights, this will minimise the error in diagnosis of disease.
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