The maximum expiratory flow-volume curve (MEFV) is a rapid inspiration to the residual volume after a deep inspiration to the lung volume. A correlation curve between lung volume and corresponding airflow velocity is depicted by an XY recorder. Commonly used indicators are 1. Maximum expiratory flow (PEF) refers to the expiratory flow indicated by the highest point of the MEFV curve. 2.50% of vital capacity Maximum expiratory flow (V↓50) refers to the expiratory flow when the vital capacity is 50%. 3.25% of vital capacity Maximum expiratory flow (V↓25) refers to the expiratory flow when the vital capacity is 25%. A decrease in the V↓50 and V↓25 values ​​indicates a small airway obstruction. Obstructive ventilatory dysfunction, the flow of MEFV is reduced at each stage, and the descending branch is concave. Restrictive ventilation disorder has high MEFV flow, low lung capacity, high curve and high inclination.

Basic Information

Specialist classification: Respiratory examination classification: pulmonary function test

Applicable gender: whether men and women apply fasting: not fasting

Tips: Maintain a normal diet and schedule. Normal value

(1) The ratio of the measured value of Vmax50% and Vmax25% to the predicted value should be ≥80%.

(2) MEFV curve declining slope:

1Vmax50%, Vmax25%;

2 △ MEF / △ V, that is, FEF60-EF40 / ΔV, also known as the mid-section flow curve slope.

Clinical significance

Clinical use:

1 is used to detect small airway lesions and determine the airway obstruction.

2 Identification of restrictive ventilation dysfunction and obstructive ventilatory dysfunction

(1) In small airway obstruction and obstructive pulmonary disease, the curve changes to MEF less than MIF, the descending concave to the lung volume axis, Vpeak decreases and appears earlier, Vmax50%, Vmax25% and Vmax50%/Vmax25% significantly decrease, FVC gradually decreases.

(2) In the case of restrictive lung disease, the curve lung volume axis (FVC) is reduced, the curve shape is narrowed or may not change, the peak flow rate is significantly reduced, and the curve descending branch is straight, even protruding outward, and the slope is increased.

(3) When the upper airway is blocked:

1 such as tracheal stenosis, bilateral vocal cord paralysis and other external fixation, the top and bottom of the ring are flat, close to the rectangle, so MEF = MIF.

2 If unilateral vocal cord paralysis and other variability external chest obstruction, then MIF50% VC ≤ MEF 50% VC.

3 If the maximum inspiratory flow is significantly limited for sleep apnea syndrome, VE50%>>VI50%, sawtooth wave appears in the inspiratory phase and/or expiratory phase.

4 If the unilateral main bronchus is fixed, the alveolar emptying of the obstructed lung is earlier, the curved half (expiratory flow rate) is accelerated, and the latter half reflects the second batch of slowing alveolar.

Scope of application:

1 Study on the effects of smoking and environmental factors on the airway.

2 small airway dysfunction detection.

3 chronic obstructive pulmonary disease and other airflow obstructive diseases.

4 restrictive lung disease.

5 upper airway obstruction examination and coarse screening of sleep apnea syndrome.

Precautions

(1) The technician should master the operation technique skillfully to ensure that the subject has sufficient inhalation, smooth exhalation, uniform force, and synchronous recording, so that the curve rises sharply.

(2) The gender, height, and age of the subjects have an effect on the results.

Inspection process

The maximum expiratory flow-volume curve (MEFV, -V curve, referred to as flow-volume curve) refers to the volume of gas exhaled by the subject during the maximum forced exhalation after deep inhalation. The curve depicted by the corresponding expiratory flow.

1. Method: During the test, the subject takes the standing position (the plethysmograph takes the sitting position), clips the nose, and installs the mouth containing the tube (or mouthpiece), first calmly breathing several times, after the adaptation, the subject deeply inhales to the lungs. The total amount, then immediately exhale with maximum strength and the fastest speed until the residual position, in the process of automatic tracing with XY recorder, draw the MEFV curve related to the expiratory flow and the corresponding lung volume, X-axis Represents the lung volume and the Y axis represents the maximum expiratory flow. Repeat once every 5 to 10 minutes, at least 3 times. The curve with the largest amount of vital capacity and the maximum initial force was used.

2. Measured by MEFV curve

(1) Reflecting small airway function indicators (50% of vital capacity maximal expiratory flow) and 25 (25% of vital capacity maximal expiratory flow).

(2) Indicators reflecting atmospheric function: PEF (maximum expiratory flow, also known as peak expiratory flow, peak flow), 75 (75% of vital capacity maximal expiratory flow).

(3) FVC (forced vital capacity): The normal reference value and the normal predicted value formula refer to the local normal value.

When PEF, 75, 50, 25 measured value / predicted value <70% is abnormal, 69% ~ 55% is mildly reduced, 54% ~ 40% is moderately reduced, <40% is severely reduced.

When FVC measured value/expected value <80% is abnormal, 79%~60% is mildly reduced, 59%~40% is moderately decreased, and <40% is severely reduced. The MEFV curve is simple to operate and has good repeatability. The first half of the curve is related to the force, reflecting the function of the airway and the strength of the respiratory muscles. The latter part has nothing to do with the force, reflecting the small airway function and the elastic retractive force of the alveoli.

Not suitable for the crowd

Generally there are no special taboos.

Adverse reactions and risks

Generally no special complications.