Can you tell me how spirometry aid in their diagnosis?

Spirometry: Spirometry is a test performed used to evaluate for lung disease. It measures flow of air over time. It helps in diagnosis and management of diseases such as asthma, emphysema and chronic bronchitis. Sometimes further testing with lung volumes and diffusion capacity are ordered (called complete PFT). This complements the evaluation, helps with other diseases ie.fibrosis! Hope this helps.