Comparison of three normal breathing techniques to assess reversibility of airway obstruction.

Measurement of forced expiratory volume in one second (FEV1) is generally used to assess airway obstruction. Function tests during normal breathing are used as complementary tests as well as alternatives. Studies have been done comparing the esophageal pressure method with body plethysmography, and respiratory acoustical impedance with body plethysmography. We have not found any other studies comparing all three methods in the same subject. It is not clear whether those tests contribute to the assessment of reversibility of airways obstruction. We addressed the following questions: (1) How does the response of FEV1 to an inhaled beta agonist (400 micrograms fenoterol) relate to the response of lung function tests during normal breathing? (2) Are values obtained with three normal breathing techniques comparable in assessing severity of obstruction? We collected these data in 17 patients. A significant correlation was found between airway resistance measured with any of the three methods. The scatter was large, both before and after bronchodilation. The reversibility by the three methods expressed as absolute values (before and after inhalation) were comparable. In order of preference it appears that acoustical impedance is to be preferred to esophageal pressure because of less discomfort to the patient, and to body plethysmography because of the lower cost of the apparatus. Acoustical impedance can be used to assess acute changes in bronchomotor tone.