small airway function

Small airways refer to airways with a diameter of 2 mm or less. Before the patient has no clinical discomfort and normal lung function tests, small airway function tests may find early changes, which have positive significance for early detection and early treatment of the disease. Commonly used indicators are maximum expiratory flow (flow rate) - volume curve (ring), equal flow volume and closed volume measurement. Basic Information Specialist classification: Respiratory examination classification: pulmonary function test Applicable gender: whether men and women apply fasting: not fasting Tips: Before the inspection, the operator should give the patient a patient stone measurement process in advance to achieve a good match. Normal value 1. Maximum expiratory flow rate (speed) - volume curve (ring) (MEFV) (1) The ratio of the measured value of Vmax50% and Vmax25% to the predicted value should be 80%. (2) The slope of the MEFV curve is Vmax50%/Vmax25%, ΔMEF/△V, ie FEF60-FEF40/△V, also called the mid-flow curve slope. 2. Equal flow volume (1) Breathing He-O2 mixture is higher than breathing air, and Vmax increases at higher lung capacity. (2) VisoV/VC 25%, that is, the equal flow volume is small. 3. Closed volume (CV) (1) Closed volume (CV) / vital capacity (VC) Male 0.3856×age-2.3081; Female 0.3569 × age - 0.688. (2) Closed volume (CV) / total lung (TLC) Male 0.4988× age +14.7662; Female 0.2913 × age + 27.3905. Clinical significance 1. Maximum expiratory flow rate (speed) - volume curve (ring) (MEFV) (1) In small airway obstruction and obstructive pulmonary disease, the MEFV curve changes to MEF less than MIF, and the descending convexity is toward the lung volume axis. Vpeak decreases and appears earlier, and Vmax50%, Vmax25%, and Vmax50%/Vmax25% decrease significantly. The FVC is gradually decreasing. (2) In the case of restrictive lung disease, the curve lung volume axis (FVC) is reduced, the MEFV 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 obstructed, such as tracheal stenosis, bilateral vocal cord paralysis and other external fixation, the top and bottom of the MEFV curve are flat and close to rectangular. 2. Equal flow volume (1) When a small airway lesion occurs, an equal flow volume point advances and an equal flow volume increases. (2) When the airway obstructs in the airway, ΔVmax50>20% of the higher lung volume level often occurs after breathing He-O2 mixture gas; otherwise, when the obstruction site is in the small airway, △Vmax50<20% Even no change. 3. CV/VC, CC/TLC higher than normal expected values ​​can be found in smokers, subjects in air pollution environment, asthma remission, early emphysema, early pneumoconiosis, chronic obstructive pulmonary disease and other patients. Precautions 1. Before the examination, the operator should patiently evaluate the patient's stone measurement process in advance to achieve a good fit. 2. Check for no absolute or relative contraindications. Inspection process During the measurement, the subject takes a sitting position, clips the nose clip, and contains a mouthpiece, which is connected with the pulmonary function meter. The patient first calmly breathes several times, then inhales deeply into the lungs, and then exhales to the residual position at the fastest speed. The spirometer automatically measures the volume of exhaled gas and the corresponding expiratory flow and traces it to a curve. Not suitable for the crowd Severe cardiopulmonary patients need to consult a doctor before doing this test. Adverse reactions and risks Generally no complications and harm.