Researchers Identify Factors in Asthma Severity Variance

Researchers used a conceptual model to examine the relationship between risk factor domains and asthma severity and found that the relative impact of the different domains could be quantified and used to select appropriate interventions. The investigation, conducted by Andrew Liu, MD, of National Jewish Health in Denver, CO, and colleagues, used data from the Inner-City Asthma Consortium Asthma Phenotypes in the Inner City (APIC).

The researchers looked at eight specific risk factor domains: allergen sensitization, allergic inflammation, pulmonary physiology, stress, obesity, vitamin D, environmental tobacco smoke (ETS) exposure, and rhinitis severity. Their goal was to “conceptualize which domains have a direct influence on asthma severity and/or an indirect influence on asthma severity by acting through another domain(s).”

They developed a conceptual model and used the data collected from APIC participants, who were 6 to 17 year olds diagnosed with a broad spectrum of asthma. The participants lived in low-income areas of 9 cities in the United States. The researchers used four of the components of the Composite Asthma Severity Index and the Asthma Control Test/Childhood Asthma Control Test categories.

“Altogether, this pathways construct accounted for 53.4% of the observed variance in asthma severity in this study, a remarkable effect considering the complexity of this condition,” report the researchers. Additionally, the researchers found that asthma severity and allergen sensitization were positively associated through multiple domains. Exposure to tobacco smoke was positively associated with asthma severity, however, obesity, vitamin D, and stress were not directly associated with asthma severity.

This model provides support for the idea that multiple risk factors contribute to asthma severity. The researchers note that it is important “that allergen sensitization is perhaps the originating domain in this pathophysiologic chain.” They list four conclusions based on the results of this model.

First, they say, “allergy acts through more than 1 pathway to exert its effect on asthma severity”. This suggests that more interventions at an earlier stage, and designed to stop the allergy pathway at the beginning would improve outcomes.

Second, “ETS exposure exerts significant direct and indirect effects on asthma severity”. The researchers used two different measures for ETS and there was a significant correlation with asthma severity using each measure.

Next, “Rhinitis severity had a remarkably strong effect on asthma severity”. The researchers say that this finding supports a concept known as “one airway”. They further note that rhinitis severity does not appear to directly affect pulmonary physiology.

The fourth and final conclusion that the researchers report was that “Other pathways contributed less to asthma severity.” Vitamin D, obesity, and even the measure of stress (Caretaker Perceived Stress Scale), did not have a significant impact on the severity of asthma. However, the researchers do say these results may have to do with the sample.

The authors concluded that their model explains “more than half of the variability in asthma severity,” noting that “the strong contributors are high priority targets for improving asthma outcomes in addition to standard care.”

The full study, titled “Pathways Through Which Asthma Risk Factors Contribute to Asthma Severity in Inner-City Children” can be found in the Journal of Allergy and Clinical Immunology.

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