INTERPRETATION OF SPIROMETRIC TESTS IN ASTHMATIC-PATIENTS WITH REDUCED FORCED VITAL CAPACITY

We have studied 175 consecutive asthmatic patients presenting with: 1) a reversible airflow obstruction, demonstrated by an increase in the forced expiratory volume in 1 second (FEV(1) or in the forced vital ca pacity (FVC) by at least 12% along with an absolute increase of 200 mi versus prebronchodilator values after inhalation of salbutamol; 2) FV C below the lower normal limit before administration of the bronchodil ator; and 3) normal FVC or slow vital capacity after bronchodilator. T wo different criteria for the lower normal limit of the FEV(1)/FVC rat io were used to determine whether prebronchodilator spirometric patter ns could be considered obstructive or not. The use of the predicted FE V(1)/FVC ratio as the lower normal limit allowed correct identificatio n of obstruction in 94.9% of the patients, whereas taking the estimate d fifth percentile as the lower normal limit of the FEV(1)/FVC correct ly identified obstruction in only 78.9% of the asthmatics. Our results suggest that the predicted FEV(1)/FVC ratio is an adequate estimate o f the lower normal limit in asthmatic patients with reduced FVC in ord er to distinguish obstructive from nonobstructive patterns.