I. Overview Respiration refers to the exchange of gases between the body and the outside world, i.e., the process of taking in oxygen from the outside world, using oxygen and expelling carbon dioxide, including the following four interrelated links: (1) lung ventilation, i.e., the process of gas entering and leaving the lungs; (2) lung ventilation, i.e., the exchange of gases between the alveoli and the blood; (3) the transport of gases by the blood circulation; (4) tissue cell ventilation, i.e., tissue cells use oxygen and produce (4) tissue cell gas exchange, which is the process by which tissue cells use oxygen and produce carbon dioxide. Impairment of any of the above can lead to tissue hypoxia and carbon dioxide retention, affecting the normal metabolism, which can be life-threatening in serious cases. Xu Jianqiang, Department of Respiratory Medicine, Shenzhen Children’s Hospital The role of the lungs in the respiratory process is to perform pulmonary ventilation and pulmonary ventilation, so the pulmonary function test (PFT) includes ventilation and ventilation. Ventilation includes lung volume, ventilation (resting ventilation, maximal ventilation), gas distribution, respiratory mechanics (resistance, compliance, respiratory work), and respiratory regulation (respiratory center, respiratory muscles). Ventilation function includes diffusion, ventilation/blood flow ratio, and blood gas analysis. Pulmonary function tests are one of the important tools for diagnosis, differential diagnosis and evaluation of the condition of respiratory diseases and have been routinely used in adults for: (1) diagnosis of pulmonary diseases and assessment of the severity of the condition. (2) Evaluating the effect of treatment, such as observing the efficacy of applying bronchodilators. (3) To determine prognosis. (4) Objective information on the patient’s response to the treatment plan. (5) Determination of the limits of self endurance. (6) Adjustment of mechanical ventilation parameters and monitoring. (7) To provide a reference opinion on whether the surgical child needs and can tolerate surgery, and to evaluate the effect of surgery. Ventilation function test Ventilation function test is the main and most commonly used part of pulmonary function test, including lung volume, flow rate of airflow in the airway and its influencing factors. Third, children’s pulmonary function examination methods Most children over 5 years old can actively cooperate with breathing and can complete a more comprehensive pulmonary function examination, such as lung volume (VC, VT, IRVpERV, etc.), forceful lung volume (FVC, FEVl.0% or FEV1.0/FVC, MMEF or FEF25-75%, PEFR or PEF, etc.), maximum ventilation volume (MVV), and The maximum expiratory flow-volume curve (ring) and respiratory kinetics (compliance and airway resistance) are examined using the same pulmonary function testing instruments as in adults. However, when testing, we should pay attention to the different normal values for each age of children. In addition, we should also combine the characteristics of children, ask them to practice repeatedly and demonstrate patiently, and it is very important to teach their parents first, so that they can guide the children to test together. Pulmonary function changes in asthma are obstructive ventilatory dysfunction, with the following abnormalities during an attack: 1. PEFR can also be monitored with a simple peak flow rate meter. PEFR can also be monitored with a simple peak flow velocity meter. These indicators can be recovered during asthma remission. The most important indicators of small airway resistance, such as FEF25-75% in FVC or Vmax50 and Vmax25 in the maximum expiratory flow-volume (MEFV) curve, generally persist in asthma remission. 2. Lung volume: During an asthma attack, FRC increases, RV/TLC increases, and spirometry (VC) decreases. 3.Maximum expiratory flow-volume (MEFV) curve or tidal flow velocity-volume loop (TBFV, TFV): the slope of the descending branch increases, or even shows an inward depression. 4. Airway resistance and compliance: Airway resistance measured by simple methods (e.g., blocking) or IOS is increased during an attack and may recover during remission. The dynamic compliance of the lung is reduced. 5.Bronchodilator test: In an asthma attack, airway obstruction is reversible and the bronchodilator test is positive. Bronchial excitation test: Bronchial hyperresponsiveness (BHR) is one of the main features of asthma and may be positive in remission. 7.Peak expiratory flow rate (PEF) variability: PEF variability can be monitored using a peak flow rate monitor to understand the stability of airway function. If the PEF variability is greater than 20%, it indicates unstable airway function and poor asthma control. 5. Precautions for pulmonary function tests in children 1. Pulmonary function tests only reflect the ventilation or ventilation function of the lungs and cannot determine the cause of the disease. 2, normal people have a strong reserve of lung function, and minor changes may not show abnormalities. 3.The normal value of lung function varies greatly among individuals and is affected by age, gender, height and weight. Generally 80%-120% of the normal expected value for the same age, sex and height is the normal range, and if it exceeds this range, it is considered abnormal. Some lung function instrument manufacturers provide reference values, it is best to take the local normal value as the standard. 4, children’s pulmonary function tests should be based on the age of the child and the degree of cooperation to choose a variety of methods. For school-age children who can actively cooperate with breathing, the same pulmonary function instrument as for adults can be used to detect forceful spirometry and maximum expiratory flow-volume curve (ring), etc. For infants and children who cannot cooperate with the examination, an infant and child spirometer should be used to test tidal respiratory lung function, including tidal flow-volume loops (TBFV), compliance, etc. Measurement of airway resistance or compliance by blocking method or pulse oscillation alone is suitable for children over 2 years of age who can breathe calmly. Volumetric tracer testing can be used if available. 5.When interpreting the results of bronchodilator test and bronchial excitation test, attention should be paid to false negatives caused by the use of bronchodilator drugs or airway secretions and other influencing factors.