PFT’s in asthma

The pathophysiology of asthma is characterized by a pattern of lung dysfunction that includes:

• Airflow limitation that reverses with bronchodilator administration.

• Variable airflow limitation, which can be either circadian or episodic in nature.

• Airways hyperresponsiveness, which is an excessive decrease in airflow in response to specific stimuli or "triggers" (See "Risk factors for asthma").

The diagnosis of asthma is based upon an appropriate clinical history and characteristic findings from a series of pulmonary function tests. These tests most often include different measures of airflow, bronchodilator responses, lung volumes, and the diffusing capacity.

The detection of airflow limitation in the patient with asthma:

• peak expiratory flow rate (PEFR)
  • measured during a maximally forceful and rapid exhalation that immediately follows a maximal inhalation. he utility of PEFR to detect the presence of airflow limitation is not particularly good, since the variability of PEFR among individuals is very large (+30 percent). However, PEFR is a useful method of monitoring changes or trends in the patient's lung function.
• forced expiratory volume in one second (FEV1)
• flow-volume relationship.
  

from UpToDate, last updated Spring 2009.