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Methods of investigation - How to detect Asthma ?
Physical examination of the chest remains important, as it may reveal the presence of an area of inflammation, a pleural effusion, or an airway obstruction; the first two of these conditions will be visible on chest radiographs, but the third is usually audible only. Examination of the sputum for bacteria allows the identification of many infectious organisms and the institution of specific treatment; sputum examination for malignant cells is occasionally helpful. The conventional radiological examination of the chest has been greatly enhanced by the technique of computerized tomography, which shows small lesions and permits their precise location to be defined. The introduction of the flexible bronchoscope (in place of a rigid instrument) has greatly lessened the discomfort and danger associated with visual inspection of the bronchi and allows small tissue samples to be taken for histological study at the same time.
A number of tests are available to determine the functional status of the lung and the effects of disease on pulmonary function. A simple ventilatory test, the measurement of the velocity of a forced maximal expiration after a full inspiration, allows the degree of airway obstruction to be quantified. Airflow obstruction occurs in asthma and emphysema. A related test, of ventilatory capability, measures the volume that can be forcibly expired in one second after a full inspiration. Ventilatory capability can be simply measured with a spirometer or flow meter, and these devices are widely used in field studies. More complex laboratory equipment is necessary to measure the volumes of gas in the lung; the distribution of ventilation within the lung; airflow resistance; the stiffness of the lung, or the pressure required to inflate it; and the rate of gas transfer across the lung, which is commonly measured by recording the rate of absorption of carbon monoxide—used for this purpose because of the high affinity of hemoglobin for it. Gas transfer is impaired in diseases that destroy the lung or cause severe generalized thickening. Arterial blood gases and pH values indicate the adequacy of oxygenation and ventilation and are routinely measured in intensive care unit patients. Tests of exercise capability, in which work load, total ventilation, and gas exchange are compared before and in response to exercise, are useful in assessing disability.
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