Peak flow meter is a technique for measuring the maximum (peak) velocity of forced exhalation. Peak flow meter allows you to assess the degree of obstruction of the airways in COPD, bronchial asthma; determine the reversibility of bronchospasm; monitor the effectiveness of drug treatment. During the diagnosis, the patient makes the maximum possible inhalation and exhalation into the mouthpiece of the device-a peak flowmeter. Determination of PEF – peak expiratory flow – can be performed against the background of drug tests and without them. The final cost of peak flow meter consists of the study itself and the pharmacy preparation used.
The importance of peak flow mete in bronchial asthma and various COPD is comparable to the importance of blood pressure control in hypertension or glucose measurement in diabetes mellitus. The procedure is performed using a peak flow meter device, which can be used for self-monitoring. The peak expiratory flow (PEF) depends on a number of factors, including the presence of bronchial obstruction. Diagnostic peak flow meter makes it possible to objectively identify and assess the degree of bronchial obstruction. A dynamic study allows you to record changes in the patency of the bronchi even before the development of critical bronchospasm and take preventive measures in time. Peak flow meter, unlike spirometry, is a more affordable and fast method, which can be carried out both in the clinic and at home after the patient’s instruction.
The scope of diagnostic application of the technique is any lung diseases occurring with bronchial obstruction (COPD, bronchial asthma) and planning their treatment. Peak flow meter can be a screening method that allows to detect the presence of pre-asthma and asthma, as well as be used to determine the provoking factors leading to bronchial obstruction. Peak flow meter is used to diagnose bronchial asthma, determine the severity of the disease, control the course of asthma and the effectiveness of treatment, and prevent an impending exacerbation. Daily monitoring of PEF is indicated for all patients with diagnosed bronchial asthma.
Monitoring of peak flow meter gives the doctor the opportunity to determine the reversibility of bronchial obstruction, detect bronchial hyperreactivity, anticipate an asthmatic attack, diagnose occupational asthma, and select an effective dosage of drugs (bronchodilators and inhaled glucocorticosteroids). Significant is the change in the PEF index over 20% (with an average value for women – between 400 and 550 l/min., and for men – 500-600 l/min.).
Methodology of conducting
Peak flow meter is performed in the morning 5-10 minutes after waking up and before going to bed at night, preferably at the same time. During the selection of therapy, the study is additionally performed during the day (three times a day). This test should be performed before using inhaled medications and 3-4 hours after taking bronchodilators. The obtained PEF indicators are recorded in a special diary of self-observation and are arranged in the form of a graph.
The PEF measurement is performed sitting or standing, after previously taking several normal breaths and exhalations. Then you should take a deep breath, tightly cover the mouthpiece of the picflowmeter with your lips and, holding it horizontally, exhale into the device as quickly and strongly as possible through your mouth. When exhaling, as a result of air pressure on the valve, the arrow of the peak flow meter moves along the scale. The resulting indicator corresponds to the peak expiratory flow, measured in liters per minute. After a few minutes of rest, the test is repeated 2 more times; of the three indicators, the maximum PEF is selected and noted.
To evaluate the indicators, it is necessary to know the best value of the PEF of a particular patient corresponding to the remission phase. This value is determined during the daily 2-3-week peak flow meter. Then, when determining the current PEF indicator, it is compared with the best own result.
Interpretation of results
According to the form of the peak flow meter graph, the doctor can analyze the stability of the course of the disease. With satisfactory control of the disease and the effectiveness of therapy, the graph is close to a straight line; with unsatisfactory, the curve looks zigzagged and broken. In the case of a morning decrease in PEF, they talk about a “morning failure”, which always indicates inadequate asthma control. With low values of PEF or a large gap between morning and evening values (daily variability of PEF > 30%), control of the disease is also considered to be unattainable. Critical is the reduction of PEF by 20% from the best indicator.
Based on the data of peak flow meter, the doctor makes individual recommendations for the patient. Based on the indicators of peak flow meter, according to the “traffic light” principle, several zones and their corresponding activities are allocated. The green zone is indicators exceeding 80% of the individual norm; when these values are obtained, it is sufficient to continue planned therapy. The yellow zone corresponds to the values of PEF in the range of 80-60%, requiring strengthening of the treatment regimen and an early visit to the doctor. Values below 60% belong to the red zone – in this case, urgent relief of exacerbation and specialist consultation are required. Sometimes an additional purple zone is allocated, at the values of which it is necessary to call an ambulance.
Research with bronchodilator
Peak flow meter with bronchodilator – determination of the peak volumetric exhalation rate (PVER) before and after the test with a bronchodilator. It is carried out as part of the diagnosis and treatment planning of bronchial asthma, performed in several stages. First, the initial value of the forced output indicator is measured according to the accepted method – the patient makes the strongest and fastest exhalation into the mouthpiece of the peak flowmeter. Then the bronchodilator is inhaled.
Repeated determination of the peak expiratory flow is performed 15 minutes after the use of beta-2-agonist or 30 minutes after the inhalation application of M-cholinolytic. The coefficient of improvement of bronchial patency is calculated by the formula: (PVER after the sample – PVER before the sample) X 100% : PVER before inhalation. With an increase in the PVER by 15% or more, the sample is evaluated as positive, indicating the reversibility of obstruction and the presence of bronchial asthma.