DENSITY DEPENDENCE OF MAXIMAL EXPIRATORY AIR-FLOW IN ASTHMATICS WITH EXACERBATION OF THEIR DISEASE

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Abstract
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 { [.ovrhdot.Vmax50 (He-O2)-.ovrhdot.Vmax50(air)]/predicted .ovrhdot.Vmax50} .times. 100, was associated with: (1) less cigarette consumption (p < 0.02), (2) lesser frequency of chronic productive cough (p < 0.02), (3) more symptom-free intervals (p < 0.02), and (4) greater frequency of allergic rhinitis (p < 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 < 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 < 0.0001) was found between mean baseline percent predicted .ovrhdot.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. The mean He-O2 response of the 13 patients who achieved a ''best FEV1'' of 80% predicted or greater was 19.4% of predicted .ovrhdot.Vmax50, whereas it was 1.1% for the 7 who did not reach this degree of improvement (p < 0.03). These data suggest that asthmatics with predominantly large airways obstruction as determined by increased He-O2 response improved faster and more completely than did those with predominantly small airways obstruction.