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parameters lung function test

Thank you for telling me what the following parameters mean:

Thank you for your interesting question. I will try to explain this in a simple and not too technical way.
FVC, FEV1 and FEF75 are values obtained after performing a lung function test, also called ‘a spirometry’. Lung function a parameter to assess the degree of normality/abnormality of the lungs. For doctors, it is therefore a valuable test in the follow-up CF.
The reference values or ‘predicted’ normal values for a lung function parameter depend on age, sex and height. Normal values are indeed based on values measured in people without CF. Thus, when spirometry is measured in a person with disease the values indicate how severely CF has affected the lung but above all spirometry is useful to follow a patient over time.
When performing a lung function, the patient is asked to breathe in as deep as possible and then blow out as hard and as long as possible. The three values you mention in your question can then be determined:

- FVC stands for "Forced vital capacity". It is the total volume of air displaced from maximum inhalation to maximum exhalation.

- FEV1 represents "Forced expiratory volume in 1 second". This is the amount of air that is exhaled during the first second fo a maximum blow-out after maximum inhalation. In people with CF this is an important value as FEV1 relates to survival. People with a high FEV1 have a better life expectancy and vice versa.

- FEF75 stands for "Forced expiratory flow at 75% of FVC".
This value corresponds to the maximal expiratory flow at the point when you have already blown out 75% of the vital capacity (FVC). Whilest FEV1 mainly gives information about the large airways, FEF75 gives information about the smaller airways. In addition, FEF75 is less dependent on the effort performed during the lung function, while FEV1 is really underestimated when the patient has not blown out powerfully.

We hope you now understand a bit more about a lung function test.
Best regards,
Prof. K. de Boeck