These lungs appear essentially normal, but are normal-appearing because they are the hyperinflated lungs of a patient who died with status asthmaticus.

Spirometry aids in diagnosing asthma and assessing asthma control in response to treatment.

Asthma causes variable airflow obstruction. A simple handheld spirometer can document FEV1 and FVC. The variable reduction of FEV1 documents findings consistent with asthma, demonstrates presence and reversibility of airflow obstruction to the patient as objective evidence to encourage adherence to a treatment plan, and aids in monitoring and adjusting medication dosages.

In addition, it is useful in asthma to measure peak expiratory fkow (PEF), the maximum expiratory flow occurring just after the start of a forced expiration from the point of maximum inspiration (total lung capacity). A morning PEF measurement before administration of a bronchodilator is a guide to drug dosage.