After spirometry is completed, the patient is given an inhaled bronchodilator and the test is repeated. The purpose of this is to assess whether a patient's pulmonary process is bronchodilator responsive by looking for improvement in the expired volumes and flow rates. However, the lack of an acute bronchodilator effect during spirometry does not exclude a response to long term therapy. Similarly, spirometry can be used to detect the bronchial hyperreactivity that characterizes asthma. By inhaling increasing concentrations of histamine or methacholine, patients with asthma will demonstrate symptoms and produce spirometric results consistent with airways obstruction at much lower threshold concentration than normals.
Normal values vary depending on gender, race, age, and height.
It is therefore not possible to interpret PFT's without such information. It is therefore important to ensure that the reference formulas in a PFT lab are applicable to the patient population being tested. At the University of Iowa Hospitals and Clinics, reference values have been obtained from Morris et al. Requirements for Good PFT's Obtaining useful information from pulmonary function tests requires both adequate equipment and reproducible performance. If these requirements are not met, the results must be interpreted with caution.