Asthma is a chronic nonspecific inflammatory response of the respiratory tract, manifested mainly by reversible airway obstruction, episodic wheezing, expiratory dyspnea, chest tightness and cough, especially aggravated at night and in the early morning. Asthma is often diagnosed on the basis of these complaints and clinical symptoms of the child. However, these common symptoms do not have a specific diagnostic value. Therefore, in addition to the diagnosis of asthma based on the history of recurrent wheezing episodes related to certain factors (such as allergens, exercise and infections) and symptoms that can be relieved on their own or with bronchodilators, lung function measurements of the child are important objective indicators for the diagnosis of asthma and are also very important for grading the condition and guiding the use of medication. As asthma attacks manifest as bronchial smooth muscle spasm caused by the release of allergic inflammatory mediators, combined with increased mucus secretion, resulting in airway narrowing and airflow restriction; lung function manifests as obstructive ventilation dysfunction and decreased expiratory flow rate. Although there are many ways to estimate the degree of airflow limitation, the most commonly used and widely accepted parameters of expiratory effort are expiratory volume in one second (FEV1) and peak expiratory flow rate (PEF). These parameters can be measured during expiration and are closely related to the size of the airway internal diameter and the elasticity of the surrounding lung tissue. However, the measurement of pulmonary function in children can only be done regularly in the hospital, and it is not possible to keep track of changes in the condition, while spirometers in the laboratory are too bulky and expensive for children to use at home. So although FEV1 is the best indicator of the severity of airway obstruction, it can only be obtained when lung function is measured with a spirometer because it is much easier to determine with the simple PEF. The peak flow rate value (PEF) measured by the inexpensive, simple to use and easy to grasp peak flow rate meter is more beneficial for monitoring changes in the child’s condition at any time, and it has a good correlation with FEV1 and can be repeatedly measured, so peak flow rate meters are important and easy to use for outpatient, emergency and home monitoring of asthma. Peak flow velocity values as a measurement for diagnosing and monitoring pulmonary function in asthma are similar to related measurements made in other chronic diseases, just as blood pressure is measured with a sphygmomanometer to diagnose and monitor hypertension, and blood glucose is measured with test paper or a digital display meter to diagnose and monitor diabetes, so the significance of PEF measurement in asthma can be seen. I. Significance of PEF measurement 1. Significance to the physician PEF provides the physician with an objective indicator of the severity of the disease and the child’s response to treatment. Because it is very unreliable to judge the degree of airflow limitation only by the child’s complaints, and it is difficult for the doctor to make a correct evaluation of the severity of asthma based on the observation of the child’s wheezing and dyspnea, asthma treatment may be delayed or even cause severe asthma attacks and increase the mortality rate; moreover, the degree of mastery of lung auscultation varies from doctor to doctor, and the condition of asthma changes at any time. Some children may have a 25% or lower PEF by the time the physician hears the croup with a stethoscope; others may have airway obstruction before they feel symptoms. All of these conditions can be detected at any time when the PEF is measured. At the same time, the PEF measurement provides a basis for the physician to adjust the medication according to the child’s PEF and to add or remove bronchodilator drugs such as beta2-agonists. PEF can also monitor the child’s response to medication and prevent the development of persistent asthma. Therefore, for children over 5 years of age, in addition to measuring PEF at each visit, daily home monitoring of PEF with a simple peak flow rate monitor is recommended for moderate to severe cases. The use of peak flow tachograph provides an ideal tool for daily asthma monitoring at home, which can help children to understand the changes of asthma objectively, detect the signs of worsening asthma as early as possible, increase medication or seek medical attention before asthma symptoms appear, and avoid serious asthma attacks; at the same time, the continuous recording of daily PEF changes can understand the fluctuation of the disease and provide objective information for doctors to use medication and analyze the disease. It also provides an objective basis for doctors to use medication and analyze the condition to improve the therapeutic effect of medication. Peak flow velocity meter is an important tool to assist in the diagnosis of asthma and to monitor the changes in the condition of the child and the effect of treatment. It should be recommended for children with asthma where available, especially for those who have had severe asthma attacks or have been hospitalized before and those who are unresponsive to the severity of their condition, and the importance of long-term adherence to peak flow rate monitoring should be emphasized. For those children who cannot be monitored with a peak flow velocity monitor for various reasons (e.g., children who cannot buy or cannot afford a peak flow velocity monitor, children who cannot use it consistently over time, etc.), short-term peak flow velocity monitoring should also be performed at certain stages of asthma, such as in the context of establishing an asthma diagnosis, evaluating treatment regimens, or changing treatment regimens (escalating or downgrading therapy) (recent studies have shown that using the ” Childhood Asthma Control Test (C-ACT)” questionnaire can be used as a partial substitute for peak flowmetry to test the control of asthma in children). The types of peak flowmeters can be divided into mechanical and electronic peak flowmeters. Mechanical peak flowmeters are increasingly accepted by families with children with asthma because they are convenient, practical and inexpensive. Recently, a new generation of electronic peak flowmeters (“asthma companion”) has also started to enter the lives of children with asthma. Compared with the traditional mechanical type, it can measure not only the maximum peak expiratory flow rate (PEF), but also the important index of pulmonary ventilation function parameters: the first second forceful expiratory volume (FEV1). The electronic peak flow rate meter uses pressure difference electronic sensing element, digital display results, more accurate and repeatable; small size, light weight, can store 96 times the test value, generally more than 5 years old children can use. Third, the determination of PEF to carry out PEF measurement, the only need for the child to do is to blow a brief maximum burst of airflow. We can figuratively inspire the child to blow like a candle on a birthday cake, but with a faster and stronger exhalation. This is usually done well in children over the age of 5. However, no matter how old the child is, it is important to train at the beginning because only with the correct technique can we get a true and objective picture of the changes in lung function. The following is still the traditional mechanical peak flowmeters as an example to illustrate. 1, the correct action when blowing peak flow tachometer ①, the pointer to the scale “0” position, take the peak flow tachometer fingers do not interfere with the pointer activity; ②, stand up, deep inhalation; ③, the peak flow tachometer mouthpiece into the mouth, with the mouth lips wrapped tightly around the mouthpiece, exhale forcefully and quickly; ④, write down the value of the pointer, and the pointer to “0” position; ⑤, three consecutive repetitions of the above actions, take the best value recorded. Among the things that should be noted are: exhale with maximum force and fastest speed; mouth and lips wrapped tightly around the mouthpiece, no air leakage; do not block part of the mouthpiece hole with the tongue. 2, the expected value of PEF The expected value of PEF is obtained from the population survey, which is related to gender, height and age, and has racial characteristics, among which height has the greatest influence on children’s PEF, and the expected value obtained from different races may be different. We are now using the predicted values of PEF in children in China obtained from the Guangzhou Institute of Respiratory Diseases during the population survey in the early 1990s. Although these estimates are subject to revision, they are still relevant as a criterion for determining whether the PEF measured in a child is normal. In practice, many children’s PEF values are often higher or lower than the average expected value of normal, so in order to use PEF values more effectively for asthma monitoring, it is important to find the best value for each individual child as a criterion for determining whether the child has an attack. The personal best value is obtained when the child has well-controlled asthma for more than two weeks without any asthma symptoms and feels good about himself, and the highest PEF value is blown by two weeks of careful PEF measurement. 3, the best time to measure PEF The measurement of PEF should be done twice a day, after waking up in the morning and before going to bed at night, i.e. the first thing you do after waking up in the morning and the last thing you do before going to bed at night. Each measurement is taken three times and its optimal value is recorded, preferably plotted as a curve, which is more visual. For children with inhaled β2-agonists, it is best to measure before and 10-15 minutes after the drug and record both values; the significance of the data measured after the drug is that it can confirm whether it is effective for inhaled drugs and can also be used to calculate the variability of PEF. In the case that PEF can only be measured once a day, it is best to fix it every morning after waking up, and fix it before or after inhalation, so that the measured results can be comparable and can be detected once changes occur. 4.PEF variability The regular application of peak flow rate meter to determine PEF can monitor the severity of asthma attacks and the development process of the disease. The severity of the disease is reflected in the basal level of PEF, that is, the PEF value measured each time; on the other hand, it is also reflected in the variability of PEF, especially the 24-hour variability, for example, in some children, although the measured value of PEF is within the normal range, the day-to-day variability of PEF is >20%, which still indicates that the child is in an asthma attack, the disease is not very effectively This still indicates that this child is in the exacerbation phase of asthma and that the disease is not very effectively controlled and requires further modification of the treatment plan. Therefore, to a large extent, the magnitude of the variability is related to the severity of the disease. Calculation of inter-day variability: The difference between the PEF measured before the inhalation of bronchodilator in the morning and after the inhalation of bronchodilator in the evening of the previous day (if the child is not using inhalation of bronchodilator, the difference between the second measurement in the morning and the evening), which is the maximum variation of PEF in a day, can be used to describe the inter-day variability of PEF directly and sensitively. When the optimal PEF value and the minimum inter-day variability are obtained, the child can be warned that the daily measured PEF value should not be lower than 80% of the individual optimal value or the inter-day variability should not be greater than 20%, otherwise further treatment is needed or the child can be seen in the hospital. You can also use the analogy of a traffic light to explain to the child what to do in detail. The green signal zone indicator is 80-100% of the individual PEF optimum and the day-to-day variability.