Although asthma is a common disease, it is not always diagnosed early. This is because the symptoms are often relatively non-specific and can thus indicate other diseases. Asthma is also an episodic disease, and the lungs can function normally in the intervals between attacks. It is therefore particularly important the asthma be carefully diagnosed.
In the case of suspected asthma, the physician should ask about medical history e.g.: When, how often, and in what situations do the symptoms occur? Does the patient suffer from allergies? Has the patient suffered from other diseases? Is there a family history of respiratory disease?
The patient then undergoes a physical examination, which includes tapping the chest and listening to the lungs. Wheezing during exhalation can be an initial indication of asthma. The physician will then monitor lung function. Here, a special device (spirometer) measures the airflow and calculates the amount of air that can be exhaled in the first second (forced expiratory volume in one second, FEV1) and the total amount of air the patient can exhale after a deep breath (vital capacity, VC). The ratio of these values indicates the extent to which the respiratory tract is narrowed.
Lung volume and airway resistance can be precisely determined via whole body plethysmography. In this case, the patient is placed in a closed chamber and he or she inhales through a mouthpiece.
The patient can also measure the constriction of the respiratory tract at home using a peak-flow meter. The peak-flow meter measures the maximum speed reached during a vigorous exhalation (peak expiratory flow, PEF). If the respiratory tract is narrowed, the flow rate of the exhaled air is reduced; the PEF value decreases.
If allergic asthma is suspected, the physician will also try to determine the triggering allergens. For this, a skin prick test can be performed; the skin is lightly scratched, and minute amounts of various allergens are applied. The skin reaction provides information about the presence of allergies.
If the results are ambiguous, an inhalation provocation test can be performed, whereby the patient inhales allergens at increasing doses. The physician will measure lung function several times. A deterioration in lung function or the presence of asthma symptoms may indicate that the patient reacts to the inhaled allergen.
If values measured during pulmonary testing indicate a constriction of the respiratory tract, the patient can inhale a short-acting beta 2-agonist (short-acting beta-agonist, SABA), a medication that expands the respiratory tract, in order to further clarify the diagnosis. If pulmonary function improves (i.e. the constriction decreases) after 15–20 mins, the diagnosis of asthma is confirmed.
If necessary, further examinations can be performed (e.g. X-ray, ECG, and ultrasound). These serve to exclude other possible causes or consequential damages.
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