Woolcock et al studied 876 adults (mean age, 49). Subjects were considered to be responsive if their FEV, decreased by 20% with ^3.9 mol of histamine. Females (13.7%) were more likely to respond than males (8.9%). Finally, Rijcken et al studied 1,905 adult subjects (mean age, 35) in The Netherlands. A nonsignificantly greater percentage of males (26%) than females (22%) had a PC,0 FEV, below 16 mg/ml. The reasons for these inconsistent results are not clear. Lack of standard definitions of responsiveness, different definitions of a responder, different challenge techniques, different distribution of covariates influencing responsiveness, especially age and smoking, and lack of adjustment of baseline level of lung function could all potentially explain the discrepant results.
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A number of studies have documented that allergy as measured by skin test positivity is associated with increased airways responsiveness. However, the odds ratios for skin test score and bronchial responsiveness vary from 0.6 to 3.5 in epidemiologic studies in adults (Table 5).
Inouye and co-workers studied 144 adult asthmatics to determine the effect of skin test reactivity on asthma severity (Table 6). The skin tests were negative in 71 subjects; 73 subjects had a strongly positive response to z or more antigens.
Table 5—Relationship of Atopy to Airway Responsiveness in Population-Based Studies: Adults
|United States||Erythema ^ 5 mm||FEV./FVC > 9%||0.6|
|(ages 20-59)||to 4 antigens||cold air|
|Australia||Wheal > 2 mm||Single-dose 0.3 mg||1|
|(ages 23-45)||to 8 antigens||methacholine|
|Australia||Wheal > 2 mm||PDa„ FEV, < 3.9 mol||2.3|
|(ages 20-69)||to 14 antigens||histamine|
|Australia||Wheal > 3 mm||PDa, FEV, <; 15 mol||3.5|
|(ages 15-30)||to 12 antigens||methacholine|
Table 6—Comparison of Skin Test-Negative and Skin Test-Positive Adult Asthma
|Asthma frequency||5.5± 1.2||4.9± 1.5|
|Doctor visits/year||12 ±14||10 ±15|
|Hospital (days/year)||0.7 ±1.6||0.5±0.9|
|Oral bronchodilator (days/year)||188 ±157||148 ±162|
|Oral steroid (days/year)||123 ±151||107 ±163|
|FEV, (% pred.)||73 ±31||77 ±28|
Tags: Airway responsiveness, Asthma, bronchial responsiveness, lung function, smoking