RELATIONSHIP BETWEEN ATOPY AND BRONCHIAL RESPONSIVENESS TO HISTAMINE IN A RANDOM-POPULATION

Abstract

There are theoretical reasons to suggest that atopy might predispose to nonallergic bronchial hyperresponsiveness; studies have yielded conflicting results. This was assessed by determining the atopic status and bronchial responsiveness to inhaled histamine in 400 randomly selected college students. An atopy score was determined as the number of + from a standard battery of 7 allergy prick skin tests each graded from + to ++++; the atopic status was graded as nonatopic (no +), mildly atopic (1 to 4 +), moderately atopic (5 to 8+) or markedly atopic (> 8 +). Nonallergic bronchial responsiveness to inhaled histamine was measured with a standardized histamine inhalation test from which the histamine provocation concentration producing a 20% FEV1 (1 s forced expiratory volume) fall (PC20) was calculated. The prevalence of bronchial hyperresponsiveness to histamine (PC20 .ltoreq. 8 mg/ml) was 10.3% in the entire population. There was a progressive increase from 6.1% in the nonatopic group to 33% in the markedly atopic group (P < 0.001). In 43 subjects with both measurable atopy score (.gtoreq. 1) and PC20 (.ltoreq. 16 mg/ml), a regression of atopy score vs. log PC20 produced a small (r = -0.36) but significant (P < 0.02) correlation. Evidently a significant relationship exists between atopic status and increased nonallergic bronchial responsiveness to histamine. Although cause and effect cannot be inferred from this study, atopy may be one factor which predisposes to nonallergic bronchial hyperresponsiveness.