For the diagnosis of bronchial asthma, dynamic monitoring of patients and assessing the effectiveness of therapy, expiratory flow rates are recorded. Such studies are especially useful when a patient has no asthma symptoms or signs of difficulty breathing.
Air flow rate and lung volume are recorded by spirometry during forced expiration. Limitation of air flow rate in bronchial asthma causes smaller partial volumes of expiration of the lungs. Spirometric standard values of OOB1 have been developed for children of different height, gender, and ethnicity. A decrease in FEV1, expressed as a percentage of the standard value, is one of four criteria for the severity of bronchial asthma.
Since the patients’ lungs are usually inflated, and often very strongly, the ratio of FEV1 to FVC makes it possible to calculate their total expiratory volume. A ratio of FEV1 / FVC less than 0.8 usually indicates a significant restriction of air flow. However, it is impossible to diagnose bronchial asthma only on the basis of a decrease in air flow rate, as this is also characteristic of many other pathological conditions. In bronchial asthma, inhalation of p-adrenostimulants (for example, salbutamol through a nebulizer) expands the bronchi more strongly than in the absence of asthma; asthma is characterized by an increase in FEV1 by more than 12%.
It is important to remember that the diagnostic value of spirometric data depends on the patient’s ability to repeat full and forced exhalations. Children over 6 years old usually easily perform this procedure. Spirometric data only matter if they are reproducible during the course of the study. If during three consecutive attempts, FEV1 differs by no more than 5%, then they are guided by the best of the three indicators.
To diagnose asthma and optimize its treatment, provocative tests with narrowing of the bronchi are also used. The respiratory tract in patients is hypersensitive and therefore responds more strongly to the inhalation of methacholine, histamine and cold or dry air. The degree of increased sensitivity of the bronchi to these irritants corresponds to the severity of asthma and airway inflammation. Conducting provocative tests requires careful dosing of stimuli and monitoring of patients. Therefore, in practical work such samples are rarely used.
A test with physical activity (for example, running for 6-8 minutes) reveals bronchial asthma of physical effort. If in healthy people, the functional lung volume during exercise increases, and FEV1 increases slightly (by 5-10%), then untreated bronchial asthma is characterized by a decrease in air flow rate: OFB1 during and after exercise, as a rule, decreases by more than 15% . Bronchospasm usually begins in the first 15 minutes after intense physical exertion and after 60 minutes spontaneously disappears. Studies conducted in the USA among school-age children show that a test with physical activity adds another 10% of previously undiagnosed patients with bronchial asthma.
In patients at high risk, this test can cause a severe asthma attack. Therefore, for such a study, it is necessary to carefully select children and be prepared in advance to eliminate the attack.
There are simple and inexpensive instruments for determining peak volume expiratory flow (PEF) at home. The diagnostic value of this indicator is not absolute; in some cases, a decrease in PEF is recorded only with pronounced bronchospasm. Therefore, it is advisable to determine the PEFV in the morning and in the evening (preferably 3 times) for several weeks in order to master the method of its registration, establish the best personal indicator and identify the relationship of the PEFV with clinical symptoms (and ideally with spirometry). For bronchial asthma, differences between morning and evening PELVs exceeding 20% are characteristic.
Radiography for bronchial asthma . An X-ray examination of the chest (in the anterior direct and lateral projections) in children with bronchial asthma often reveals only mild and nonspecific signs of hyperventilation (for example, flattening of the domes of the diaphragm) and increased pulmonary pattern. Radiography helps to identify changes characteristic of conditions that mimic bronchial asthma, such as aspiration pneumonia or increased transparency of pulmonary fields with obliterating bronchiolitis, as well as complications of asthma itself, such as atelectasis or pneumothorax.
Some changes in the lungs are better seen with high-resolution CT . So, bronchiectasis, characteristic of cystic fibrosis, allergic bronchopulmonary mycoses (for example, aspergillosis), ciliary dyskinesia or immunodeficiencies, is sometimes difficult to see on radiographs, but they are clearly detected on scans.
Skin tests help establish sensitization to airborne allergens, which helps to treat and predict the course of bronchial asthma. In an extensive study conducted in the United States among children with asthma in children aged 5-12 years, sensitization to air allergens was detected using puncture skin tests in 88% of cases.