Why a bronchodilator test is needed
Performing a baseline pulmonary function test (PFT) is a mandatory step in diagnosing lung diseases. However, simply documenting impaired bronchial patency is not enough. It is necessary to prove that this impairment is reversible, which is typical for bronchial asthma.
The main goals of the pharmacological test:
- Establishing the very fact of reversibility of airway narrowing.
- Assessing the patient's potential response to bronchodilator therapy.
- Monitoring the dynamics of lung function in patients with an established diagnosis.
Important nuance: the bronchodilator test is indicated for all patients over 5 years of age in whom asthma is suspected or confirmed. The test is performed even if baseline standard spirometry results are completely normal, as the method helps detect hidden obstruction.
Key spirometry parameters
When analyzing the results, the physician relies on several basic values reflecting the volume and speed of exhaled air:
- FEV1 (forced expiratory volume in 1 second) is the most significant parameter.
- FVC (forced vital capacity) reflects the total volume of air that the patient can forcefully exhale.
- Tiffeneau index is the ratio of FEV1 to FVC.
- PEF (peak expiratory flow) is the maximum airflow rate during exhalation.
When bronchial obstruction develops, a typical pattern forms: FEV1 drops, while the Tiffeneau index and PEF also decrease. Meanwhile, FVC may remain within the normal range or decrease slightly.
How test results are evaluated
After performing standard spirometry, the patient is given a bronchodilator to inhale. Then a pause is taken for the medication to take effect.
Re-measurement of lung volumes is performed after 15–20 minutes. The test is considered positive if the increase in FEV1 is more than 12% from the baseline value. A positive response confirms the diagnosis, as it proves that bronchial smooth muscle spasm can be relieved medically.
Diagnostic features in young children
In children under 5 years of age, performing classical spirometry and a bronchodilator test is technically impossible because the child cannot correctly and consciously perform the required forced maneuvers.
In this age group, assessing the probability of asthma is based on the clinical picture:
- Presence of typical symptoms: wheezing (wheezing), cough, shortness of breath.
- Occurrence of obstruction outside of viral infection episodes.
- Burdened allergic history (presence of atopy, specific IgE antibodies, or asthma in relatives).
Presence of virus-induced obstruction in early childhood is a major trigger, but it does not guarantee a 100% probability of developing true asthma in the future.
Differential diagnosis of obstruction
Detection of bronchial obstruction syndrome or wheezing is not strictly pathognomonic. Other pathologies can mimic asthma:
- Mechanical causes: foreign body aspiration or meconium aspiration syndrome.
- Congenital anomalies: tracheomalacia, bronchomalacia, bronchogenic cysts, and vascular rings compressing the airways.
- Hereditary conditions: cystic fibrosis, primary ciliary dyskinesia.
- Acquired conditions: acute bronchiolitis, interstitial lung diseases, obliterative bronchiolitis, and heart failure.
Cross-screening rule: all patients with allergic rhinitis must undergo spirometry to rule out hidden persistent bronchial obstruction.
Remember the test numbers: a bronchodilator should IMPROVE FEV1 by more than 12%, while a provocation test (such as exercise) should WORSEN it by more than 20%.
Class and exam questions
Does it make sense to do a bronchodilator test if the first spirometry was normal?
Yes, the pharmacological challenge is prescribed to confirm a diagnosis of bronchial asthma even with normal baseline values—this helps assess hidden variability in lung function.
What to do if the patient cannot perform spirometry at home?
Peak flowmetry is used for self-monitoring of respiratory function. The patient measures peak expiratory flow (PEF) twice daily for 2–3 weeks to assess diurnal variations.
Can normal allergen blood tests rule out asthma?
No. Although sensitization to aeroallergens is a reliable predictor of asthma, normal levels of specific immunoglobulins (IgE) to common allergens do not rule out this diagnosis.
What else to study on this topic
- Bronchial hyperresponsiveness tests: features of methacholine challenge and exercise testing.
- Peak flowmetry: technique for self-monitoring of lung function and assessment of diurnal variability.
- Specific sputum changes in allergic inflammation: Curschmann spirals, Creola bodies, and Charcot-Leyden crystals.
- Features of asthma control assessment in children under 5 years: criteria, questionnaires, and the TRACK test.
- Allergological diagnostics: determination of specific IgE and skin prick tests.
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