Relationship Between Airway Obstruction and Respiratory Symptoms in Adult Asthmatics: Results
Figure 3 depicts the significant, though overall poor, relationship between the degree of airway obstruction, as determined by the percent predicted PEF and the total asthma symptom score (r=0.384; p=0.0029; n=58). Plots of individual symptoms and PEF are presented in Figure 4. The only individual relationship of statistical significance was that between PEF and wheeze (r=0.533; p=0.0008; n=56).
In Figure 5, the agreement between the two measures of airway obstruction utilized in this study (percent predicted values of FEVX and PEF) as concurrently measured at the initial clinic evaluation is assessed using the method of Bland and Altman. Using this method, the degree of airway obstruction, as determined by the average of the measured FEVX and PEF percent predicted values, is plotted on the X axis against the difference of the FEVX and PEF percent predicted values on the Y axis. Figure 5 demonstrates that the average (±SD) difference between the two measures of airway obstruction was —9.2±20% predicted. Moreover, within 2 SDs of the average difference, PEF values varied from 31% predicted above to 49% predicted below the concurrently measured FEV1. Indeed, FEVX and PEF varied by <10% only 36% of the time. Figure 5 also demonstrates that the scatter around the mean difference of —9.2 was consistent over the entire range of X axis values. There was a significant relationship between FEV1 and PEF when the two were compared using simple linear regression (r=0.544; p<0.0001; n=58; data not shown). Norepinephrine
Patients were reevaluated an average of 7.9 weeks after their initial clinic visit. Table 2 demonstrates that there was significant improvement in total symptoms, dyspnea, wheeze, chest tightness, and a trend toward improvement in nocturnal awakening (two-tailed t test). This occurred without a significant improvement in PEF values, however. Cough and sputum production did not change significantly between visits.
A significant correlation remained between total asthma symptoms and PEF at the second clinic visit (percent predicted PEF vs total asthma symptoms; r=0.425; p>0.0062; n=40; data not shown). However, in distinction to the initial visit, the PEF did not significantly correlate with any individual asthma symptoms at follow-up (data not shown).
Table 2—Symptoms and PEF Values at Initial and Follow-up Clinic Evaluations
|Symptom||Initial*||Follow-up*||Mean Difference||No.||p Value|
Figure 3. Relationship between total asthma symptoms and PEF (r=0.384; p=0.0029; n=58).
Figure 4. Relationship between individual asthma symptoms and PEF.
Figure 5. Agreement between percent predicted values for FEVj and PEF as concurrently measured in 58 patients (see text).