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What does MEF25% represent in pulmonary function tests?

Mar 18, 2025 Source: Cainiu Health
Dr. Ren Yi
Introduction
In pulmonary function tests, MEF25% represents the maximum expiratory flow when 75% of the forced vital capacity has been exhaled, leaving 25% remaining. This parameter is commonly used to assess a patient's respiratory muscle strength and airway patency. A reduced MEF25% may indicate the presence of respiratory diseases such as chronic obstructive pulmonary disease (COPD), asthma, or bronchitis.

MEF25% in pulmonary function testing represents the maximum expiratory flow when 75% of the forced vital capacity has been exhaled, leaving 25% remaining. This parameter is commonly used to evaluate respiratory muscle strength and airway patency. Detailed analysis is as follows:

MEF25% does not have a specific normal value, as it varies among individuals with different heights and weights. Clinically, the percentage of the measured value relative to the predicted value is usually used to determine whether MEF25% is within the normal range. Generally, if the measured value/predicted value ratio is below 65%, it suggests the presence of small airway disease or abnormal pulmonary function.

A decreased MEF25% may indicate the presence of respiratory diseases such as chronic obstructive pulmonary disease (COPD), asthma, or bronchitis. These diseases can cause airway narrowing, inflammation, or increased mucus secretion, thereby affecting expiratory flow. For patients with diagnosed respiratory diseases, changes in MEF25% can serve as a reference indicator for assessing disease status. As the disease progresses, MEF25% may gradually decrease.

Due to individual variations, the normal reference range for MEF25% may differ. Moreover, MEF25% is only one parameter in pulmonary function testing and cannot be used alone for disease diagnosis. A comprehensive evaluation combining other pulmonary function parameters, clinical symptoms, and imaging findings is necessary for accurate diagnosis.

References:

[1] Feng Haijun, He Hangyong, Lian Yueyang, et al. Predictive value of high-resolution chest CT combined with the ratio of maximum mid-expiratory flow/forced vital capacity and fractional exhaled nitric oxide levels in patients at risk for chronic obstructive pulmonary disease. Chinese Journal of Medicines, 2024, 59(03): 265-270.

[2] Mao Zhengdao, Shi Caiwen, Liu Zhiguang, et al. Assessment of small airway dysfunction in asthma patients using fractional exhaled nitric oxide levels and maximum mid-expiratory flow. Guide to Chinese Medicine, 2020, 18(20): 1-3.

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