For the 25 individuals with not-so-sudden irritant-induced asthma (^24 h), 10 had a history of preexisting asthma. Characteristically, the irritant exposures of the not-so-sudden asthma case were not massive or single (as for RADS) but were moderate and repeated. Data of 25 subjects with not-so-sudden asthma were as follows: in 9 subjects (36%), asthma developed within 1 week of repeated exposures; in 8 persons (32%), asthma appeared within a month of repetitive exposures; and in the remaining 8 individuals (32%), the irritant exposure persisted >1 month before asthma began. Patients were included only if asthma began during the irritant exposure; asthma appearing >24 h after the exposure disqualified the diagnosis of irritant-induced asthma. Figure 1 depicts the distribution of cases in each subcategory of irritant-induced asthma (new onset vs preexisting) and the number of atopic and nonatopic subjects in the subcategories of sudden and not-so-sudden asthma. Apnea-Hypopnea
Table 4 and Figure 2 correlate the relation between time to onset and the presence of atopy/ allergy for subjects with irritant-induced asthma. The prevalence of allergy/atopy was increased as the time to onset increased. Of 29 subjects with sudden-onset (<24 h) asthma, 15 (52%) evidenced allergy/atopy status, not significantly increased (p>0.05). In contrast, of 25 individuals with not-so-sudden asthma (>24 h), there were 22 (88%) found to be atopic (p<0.004). Of 16 individuals with an onset time of >1 week, 15 were atopic (p<0.01).
Sudden-onset, irritant-induced asthma (clinically manifests within 24 h) corresponds to the previously described RADS. Affected individuals are immediately ill and require prompt medical care. RADS was a sudden response to a brief but massive exposure to an irritant gas, vapor, or fume. Because of the enormity of the exposure, extensive airway damage ensues that induces bronchial mucosal inflammation leading to airways hyperresponsiveness and clinical asthma. An atopic status was not deemed operative in the pathogenesis of RADS, which exemplified the extreme end of the spectrum of an irritant effect on the airways.
Table 4—Time to Onset and Presence of Atopy Among Subjects With Irritant-Induced Asthma
Figure 2. Graphic presentation showing the relationship between the prevalence of allergy/atopy (percent) and the time to onset for asthma initiation. As the irritant exposure time became longer, the prevalence of allergy/atopy was found to be higher. It approached 100% for exposures that were >1 week duration (p<0.01).