Density dependence of maximal expiratory air flow in asthmatics with exacerbation of their disease

In an effort to evaluate the relationship between the site of air-flow obstruction and rate of improvement with therapy, we studied 20 asthmatics with spirometry, before and after bronchodilator, using air and 80% helium-20% oxygen (He-O2). Studies were obtained on 3 consecutive days after hospital admission and approximately 18 days after discharge. Greater He-O2 response ([Vmax50(He-O2)--Vmax50(air)]/predicted Vmax50) X 100, was associated with: less cigarette consumption (p less than 0.02), lesser frequency of chronic productive cough (p less than 0.02), more symptom-free intervals (p less than 0.02), and greater frequency of allergic rhinitis (p less than 0.03). Patients with greater He-O2 response (Group 1) reached maximal improvement in air flow by Hospital Day 2, whereas those with a lesser He-O2 response (Group 2) continued to improve throughout the observation period. The Group 1 mean peak expiratory flow rate (PEFR) improved by 24% of predicted per day to maximum, which was significantly greater (p less than 0.025) than the 11% per day rate of improvement of Group 2. The He-O2 response remained relatively stable throughout the course of the study except for 3 patients who dramatically improved their response with therapy. A highly significant correlation, adjusted for regression to the mean, (r = 0.95, p less than 0.0001) was found between mean baseline percent predicted Vmax50 and the mean He-O2 response. After adjustment for regression to the mean, there was no significant relationship between the degree of prebronchodilator He-O2 response and increase in He-O2 response with bronchodilator.(ABSTRACT TRUNCATED AT 250 WORDS)