Closed Volume (CV)

The closed volume (CV) refers to the amount of air that can be exhaled when the small airway in the lower part of the lung begins to close during a calm exhalation. The closed volume + residual gas volume is the closed capacity (CC). The closed volume/% of vital capacity (CV/CC%) or the closed volume/% of total lung (CC/TLC%) is usually used as an evaluation index. Small airway lesions cause early closure of the small airway during exhalation and increased closure volume. Basic Information Specialist classification: Respiratory examination classification: pulmonary function test Applicable gender: whether men and women apply fasting: not fasting Tips: Closed volume is negatively correlated with age and lung tissue elasticity. Normal value (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 volume (TLC) male 0.4988 × age +14.7662; female 0.2913 × age + 27.3905. Clinical significance Clinical use for small airway function tests. CV/VC and CC/TLC higher than normal predicted values ​​can be found in smokers, subjects in air pollution, asthma remission, early emphysema, early pneumoconiosis and chronic obstructive pulmonary disease. Scope of application: 1 Diagnosis of early obstructive pulmonary disease. 2 Study on the harm of respiratory tract by environmental factors such as smoking or air pollution. High results may be diseases: obstructive emphysema, emphysema, coal workers' pneumoconiosis (1) When the metered nitrogen analyzer is used to monitor the inhalation or exhalation of indoor air, the change in nitrogen concentration should not exceed 5%. (2) After the initial exhalation of 500ml, the expiratory flow must be continuously controlled at 0.3~0.5L/s, otherwise the curve cannot be selected. (3) The nitrogen concentration at the beginning of phase III of the closed volume curve cannot exceed 30%. (4) The difference in capacity between inspiratory vital capacity and expiratory lung capacity is less than 5%. Inspection process One breath nitrogen assay (singlebreathnitrogentest, SBN2) 1. The subject is seated, the mouthpiece is connected to the three-way valve, clip the nose clip, and after breathing the indoor air several times, slowly exhale deeply to the residual volume. 2. Turn the three-way valve to store the oxygen sac and slowly inhale pure oxygen to the lung level. 3. Immediately turn the three-way valve through the lung meter, and the examinee will slowly and evenly (flow 0.3-0.5L/min) exhale to the residual position. Turn the three-way valve through the indoor air when the residual air position is reached. 4. At the same time as exhalation, the exhaled air volume and the exhaled air nitrogen concentration were continuously measured, and the exhaled volume-nitrogen concentration curve was traced by an XY recorder. 5. Calculation Closed volume: According to the exhaled-nitrogen concentration curve, the volume between the starting point and the RV position of the IV phase is measured, which is CV. Rating indicators are often expressed in CV/VC%. Helium determination method (bomb method, bolustechnique) The test method and calculation method are basically the same as the previous method. The difference is that 200 ml of helium gas is injected at the beginning of inhalation, and then the air is sucked to the lung total amount. Simultaneously trace exhaled volume and radon concentration. The starting point of the IV phase of this method is clear, the measurement is accurate and reliable, and is not affected by the local RV distribution in each lung area. It can truly reflect the small airway closure in the lower lung area, but the operation is complicated, the equipment is expensive, and the indicator gas is needed. Not suitable for the crowd If you have a serious cardiopulmonary disease, you should consult your doctor before doing this check. Adverse reactions and risks Generally no complications and harm.