Health
May 6, 2024
Treatments Strategies for Rheumatoid Arthritis
Menu
Bronchial hyper-reactivity is a significant aspect of respiratory health, particularly in the field of pneumology. It is a condition that is commonly associated with asthmatic individuals and is characterized by an abnormal broncho-constrictive response to various stimuli. These stimuli can be both internal, such as moods and emotions, and external, like allergens, cold and humid air, physical exertion, and viral infections.
In individuals with bronchial hyper-reactivity, the airways tend to close excessively easily and intensely when exposed to such stimuli. This is why we refer to it as bronchial hyper-activity; the same stimuli, at the same dose, do not cause significant responses in healthy individuals.
While it's typical of asthmatic individuals, excessive bronchial reactivity can also be observed in obese individuals and during the last months of pregnancy. This hyper-reactivity is also a characteristic of various health conditions, including chronic obstructive pulmonary disease, bronchiectasis, atopic dermatitis, allergic and non-allergic rhinitis, cystic fibrosis, heart failure, and viral respiratory tract infections.
The bronchial provocation test with Methacholine is a widely used test in the study of bronchial asthma due to its good reproducibility of results and safety, with a low risk of systemic side effects. The test has excellent sensitivity, and while considering the many possible causes of bronchial hyper-reactivity, the specificity of the methacholine test is moderate.
In essence, the methacholine test is more useful for excluding than for confirming the diagnosis of bronchial asthma. Its negative predictive value is higher than the positive predictive value, making it particularly useful when symptoms, spirometry, and reversibility tests do not allow for a definitive diagnosis. For known asthma cases, the methacholine test helps assess the severity of the asthma attack.
The methacholine test is based on the unique characteristic of methacholine, a synthetic muscarinic acetylcholine agonist. At the doses used in this test, it can trigger a minor post-inhalation asthmatic crisis only in subjects with bronchial hyper-responsiveness. Following its onset, this crisis can be effectively managed and resolved by administering an inhaled bronchodilator drug.
The test involves the aerosol administration of increasing doses of methacholine, followed by spirometry after each single inhalation. The results are compared to those of the basal spirometry, performed before starting the test to evaluate any pre-existing bronchial obstruction. The test is stopped when the dose of methacholine administered causes mild bronchial obstruction or after inhalation of the maximum expected dose.
Since bronchial hyper-reactivity can vary over time, it is advisable to take specific precautions before the methacholine test. Some therapies may need to be suspended, and individuals are generally asked to stop smoking for at least 24 hours. Other factors, like exposure to allergens or sensitizers, viral respiratory infections, air pollutants, cigarette smoke, chemical irritants, and certain medications, can amplify the physiological response to methacholine.
The methacholine bronchial stimulation test is contraindicated in certain cases, including recent heart attack or episodes of angina pectoris, recent cerebral ischemia or hemorrhage, known arterial aneurysm, severe uncontrolled arterial hypertension, epilepsy under pharmacological treatment, pregnancy or breastfeeding, inability to perform spirometry tests correctly, current use of cholinesterase inhibitors, and severe flow limitation.
In conclusion, understanding bronchial hyper-reactivity and its role in the study of asthma is crucial for health professionals and patients alike. The methacholine test, despite its limitations, provides valuable insights into an individual's respiratory health, aiding in both the diagnosis and management of asthma and other respiratory conditions.