Test Parameters

After going through a spirometry test using the necessary test modes and getting to the result page of the test, it is very important to know about the parameters seen on the page.

All of the results for the calculated test parameters are compared to predicted test values, obtained based on age, ethnicity, height, weight, etc. Read on to learn about what these parameters are and what they reflect. 


FVC (forced vital capacity) can be explained as the air amount exhaled forcefully until the lungs are completely empty after taking the deepest breath possible quickly and forcefully. It can decrease in the cases of both obstructive and restrictive lung diseases.


FEV1 (forced expiratory volume in one second) is measured during ex-only and full loop tests. It refers to the air amount a subject can forcefully exhale in one second. It reflects the severity of the problem and lower scores generally refer to more severe stages of lung disease. 

FEV0.75: the same value for the first 0.75 seconds of the test.

FEV3: the same value for the first 3 seconds of the test.

FEV6: the same value for the first 6 seconds of the test.


FEV1/FVC ratio is used to determine whether the subject has an obstructive or restrictive lung disease, and is an important factor when it comes to a COPD diagnosis.

For obstructive lung diseases, it is expected for the FEV1 value to be low because there is something that is hindering the airflow in the lungs, hence the FEV1/FVC ratio is low

But restrictive diseases also may cause these two values to be low, so the ratio either should be normal or the ratio should increase because FVC decreased more than FEV1.

FEV0.75/FVC: the same ratio calculated using FEV0.75.

FEV3/FVC: the same ratio calculated using FEV3.

FEV6/FVC: the same ratio calculated using FEV6.


FEV6 is an easier parameter on the subject, so these ratios are sometimes used in the diagnosis of diseases such as COPD in the events where the trial is too difficult to complete for the subject.


Maximal mid-expiratory flow or MMEF is used to determine small airway dysfunctions. 

FEF25, FEF50, FEF75

Forced expiratory flow or FEF refers to the airflow that comes out of the lung in a forced expiration. FEF25 means 25% of the FVC was exhaled, FEF50 means 50% of it and so on. 


This parameter shows the average flow from the point in which 25% of the FVC is exhaled to the point 75% of it is exhaled. It is the most sensitive measure of airflow in peripheral airways where primary airflow obstruction originates, and is reduced in problems that have to do with small airway disease.

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Mi̇d-expi̇ratory ti̇me is synonymous with FET25-75.


This ratio is used in the diagnosis of obstructive lung diseases and positively correlates with the FEV1/FVC ratio.


This ratio is used in the diagnosis of COPD and according to one study, its accuracy is higher than FEV1 and FEV1/FVC (8). It also can detect the subjects who are in the at-risk group and can diagnose the early stages of COPD.


Forced expiratory time or FET is not sensitive or specific enough to detect airflow limitations and small airway diseases solely on its own but is used to confirm the diagnosis of small airway diseases. 


BEV or back-extrapolated volume determines the onset of the FVC maneuver, and it being excessive usually indicates hesitation or false start.


Peak expiratory flow or PEF is the maximum speed of expiration of a subject. The measurements are higher when subjects are well and they go lower if there is a constriction in the subject's airways.


Forced inspiratory vital capacity or FIVC is the total volume of air that can be inhaled during a rapid forced inhalation after a maximal exhalation. It can be used to evaluate airway obstructions.


Peak inspiratory flow is the reflection of the functioning of the larger airways, meaning the respiratory muscle function. Any amount of stress or an infection or inflammation in these airways causes adverse reactions, so PIF is used to monitor this.


Forced inspiratory volume in one second is used to quantify extra-thoracic airway obstructions.


This ratio can be used to find out information about the state of a subject's airway obstruction.


The vital capacity is the volume of air that can be exhaled or inhaled by a maximal expiration from total lung capacity. VC records the maximum amount of air exhaled (VCEx) or inhaled (VCIn) when breathing normally. VC decreases may result from both inspiratory and expiratory muscle weakness and may be associated with restrictive lung and chest wall diseases.


Inspiratory reserve volume is the maximum volume of air that can be inspired over and above the tidal volume. This value helps to figure out if the subject has an airway obstruction.


Expiratory reserve volume (ERV) is the volume of air that can be expired after the expiration of the tidal volume and helps to figure out if the subject has an airway obstruction.


Respiratory frequency is the number of breaths a subject takes over one minute. Abnormal rates can mean there is an airway obstruction.


Inspiratory capacity is the maximal volume of air that can be inhaled from the resting expiratory level. Abnormally low IC may indicate the onset of static/dynamic hyperinflation and this may be accompanied by dyspnea and an increase in the work of breathing.


Tidal volume is the amount of air that moves in or out of the lungs with each respiratory cycle. It helps keep oxygen and carbon dioxide levels stable in the blood. 

In restrictive lung disease, the subject adapts a breathing pattern of rapid, shallow breaths to minimize the work of breathing. This lowers the tidal volumes. In contrast to this, the problem in obstructive lung disease is expiratory, so breathing with higher tidal volumes helps overcome airway resistance. Subjects acquire a breathing pattern of deep, slow breaths to minimize the work of breathing.


Maximal voluntary ventilation is defined as the maximum minute volume of ventilation that the subject can maintain for 12 to 15 s. It reflects both the strength of lung muscles and the coordination.

A low MVV can point to upper airway obstructions, respiratory muscle weaknesses, or obstructive lung disease.

MVV6, the same value measured for 6 seconds, is also calculated.


These are all the parameters you will see on the result pages for any test administered using the SpiroClinic Pro. Click here to learn more and here to request one for yourself!


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  16. "Vital capacity and the difference Between FVC & VC", Meditech Library.
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