Simple Investigation process involved in bronchial asthma
The diagnosis of
asthma is established by demonstrating reversible airway obstruction, which is
traditionally defined as a 15 percent or greater increase in FEV following two
puffs of a beta-adrenergic agonist.
Once the diagnosis is confirmed, the course of the illness and the effectiveness of therapy can be followed by measuring peak expiratory flow rates at home and the FEV in the laboratory.
Positive wheal and flare reactions to skin tests can be demonstrated to various allergens but such findings do not necessarily correlate with the intrapulmonary events.
Sputum and blood eosinophilia and measurement of srum IgE levels are also helpful but are not specific for asthma. Chest roentgenograms showing hyperinflation are also non-diagnostic.
A diagnosis of asthma is made on the basis of a compatible clinical history plus a demonstration of variable airflow obstruction, which may classically be seen as morning dipping of the peak expiratory flow.
In more difficult situations where the above tests are negative, an exercise test, a histamine or methacholine bronchial provocation test, an occupational exposure test or a trial of oral corticosteroids may be required.
An elevated sputum or peripheral blood eosinophilia count, or an increased serum level of total or allergen specific IgE may also be helpful. It is particularly important, however, to be aware that wheeze is audible in many conditions other than asthma.
Measurement of FEV / VC ratio or PEF provides a fairly reliable indication of the degree of airflow obstruction, and can also be used to determine whether and to what extent it can be relieved by bronchodilator drugs.
These parameters are also used to examine whether asthma is provoked by exercise, hyperventilation or occupational exposure. Serial recording of PEF are useful in distinguishing patients with chronic asthma from those with fixed or irreversible airflow obstruction associated with COPD.
In asthma there is usually a marked diurnal variation in PEF, the lowest values being recorded in the morning, (morning dipping). Serial PEF recording are also invaluable in the assessment of a patients response to corticosteroids therapy and in the long term monitoring of patients with poorly controlled disease.
They are also essential in monitoring response to treatment in acute severe asthma.Measurement of bronchial reactivity can be of value in diagnosing asthma and in assessing the effects of treatment.
This can be achieved by administering increasing concentrations of substances such as histamine and methacholine by inhalation until there is a 20 percent fall in FEV or PEF.
This concentration is called the PC. Patients with asthma show evidence of Bronchoconstriction at much lower concentrations than normal subjects.
In an acute attack of asthma the lungs appear abnormal. Between episodes the chest radiograph is usually not long standing chronic cases.
The appearances may be indistinguishable from hyperinflation caused by emphysema and a lteral view may demonstrate a pigeon chest deformity. Occasionally, when a large bronchus is obstructed by tenacious mucus, there is an opacity caused by lobar or segmental collapse.
A chest radiograph should be performed in all patients with acute severe asthma. This is especially important if there is poor response to treatment and assisted ventilation is being contemplated, since pneumothorax is a rare but potentially fatal complication.
The chest radiograph may rarely show mediatinal, pericardial or subcutaneous emphysema in patients with acute severe asthma. Allergic bronchopulmonary aspergillosis may complicate chronic.
asthma and produce areas of segmental / subsegmental collapse and proximal bronchiectasis.
Measurements of arterial blood gas pressures are indispensable in the management
of patients with acute severe asthma.
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