Question

What is the purpose of pulmonary function tests when diagnosing asthma?

1) To evaluate the degree of airway obstruction
2) To evaluate oxygenation, carbon dioxide elimination, and acid-base status
3) To identify specific allergens if an allergic trigger is suspected
4) To confirm an asthma diagnosis

Answer 1

Spirometry is used to measure lung volumes and evaluate airway obstruction. The FEV1/FVC ratio is used to diagnose lung diseases, including asthma. A low FEV1/FVC ratio indicates resistance in the lung, characteristic of asthma.

Step-by-step explanation:

Lung volumes are measured by a technique called spirometry. An important measurement taken during spirometry is the forced expiratory volume (FEV), which measures how much air can be forced out of the lung over a specific period, usually one second (FEV1). In addition, the forced vital capacity (FVC), which is the total amount of air that can be forcibly exhaled, is measured. The ratio of these values (FEV1/FVC ratio) is used to diagnose lung diseases including asthma, emphysema, and fibrosis.

If the FEV1/FVC ratio is high, the lungs are not compliant (meaning they are stiff and unable to bend properly), and the patient most likely has lung fibrosis. Patients exhale most of the lung volume very quickly. Conversely, when the FEV1/FVC ratio is low, there is resistance in the lung that is characteristic of asthma. In this instance, it is hard for the patient to get the air out of his or her lungs, and it takes a long time to reach the maximal exhalation volume. In either case, breathing is difficult and complications arise.