Relationship Between Airway Obstruction and Respiratory Symptoms in Adult Asthmatics: Materials and Methods
FEV1 and PEF values are expressed as a percentage of predicted according to the predicted values of Nunn and Gregg (PEF) and Morris et al (FEV1). Linear regression analysis was used to examine the relationship between the measures of airway obstruction and asthma symptom scores. The percent predicted values for FEV1 and PEF were compared using the method of Bland and Altman. Individual symptom scores reported at the initial and follow-up visits were compared using Student’s paired t test. All statistical analyses were computed with an analysis program (StatView, Version 4.01; Abacus Concepts Inc; Berkeley, Calif). A p value <0.05 was considered significant.
The records of 94 individual patients were reviewed. Of these, 27 were excluded from analysis due to an excessive smoking history (n=21) or incomplete pulmonary function data (n=6). The characteristics of the remaining 67 patients included in this analysis are presented in Table 1. Most patients included in this study were young African-American women. The frequent need for hospital-based asthma care and oral steroid therapy as well as the degree of baseline airway obstruction are indicative of a moderate to advanced degree of asthma severity in this patient cohort. Most patients (73.2%) required at least one tapering course of prednisone therapy over the year prior to their initial evaluation, yet only 39.4% were using an inhaled corticosteroid at the time they were enrolled in the clinic. Although almost half of the patients in this study were current or past smokers, no patient had smoked for >10 pack-years.
As demonstrated in Figure 1, there was no significant relationship between the degree of airway obstruction, as determined by the FEV1, and the total asthma symptom score reported by patients at the initial clinic evaluation (r=0.143; p=0.237; n = 70). Lines are drawn at an FEVi of 60% predicted and a total symptom score of 12 to represent the cutoff between high and low levels of airway obstruction and symptoms, respectively. When viewed in this way, 31% and 17% of patients overestimated and underestimated their level of airway obstruction, respectively. Plots of individual asthma symptoms and FEVl are presented in Figure 2. There was no significant relationship between any individual symptom and FEV1 although there was a trend toward significance between the FEVX and subjective wheeze (r=0.237; p=0.089; n>O). There was no significant relationship between the degree of reversible airways obstruction and total symptoms scores (percent increase in FEVl postbronchodilator vs total symptoms; r=0.17; p=0.897; n=64; data not shown).
Table 1—Patient Characteristics
|Age, yr||32.7± 12.9|
|Duration of asthma, yr||18.4+13.6|
|Gender, % female||65|
|Hospital/ED (prior 12 mo), %||81.7|
|Prednisone therapy (prior 12 mo), %||73.2|
|Current inhaled steroids, %||39.4|
|FEVjpre, L (% predicted)||2.2+0.95 (65.5)|
Figure 1. Relationship between total asthma symptoms and FEV1 (r=0.143; p=0.237; n = 70). Lines are drawn at a total asthma symptom score of 12 and FEV2 of 60% predicted (see text).
Figure 2. Relationship between individual asthma symptoms and FEV1