Obesity-related breathing pattern may explain air pollution sensitivity in kids with asthma
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Children with asthma and obesity breathe at higher tidal volumes, which may increase the efficiency of particulate matter deposition in the lung, researchers reported in the European Respiratory Journal.
“In this study of children with asthma, we found positive associations between BMI and tidal volume, respiratory rate and minute ventilation. We identified that obesity was associated with higher tidal volume and higher minute ventilation, which were in turn associated with greater breath-to-breath efficiency and higher rate of PM2.5 deposition in the lung,” Nima Afshar-Mohajer, PhD, postdoctoral researcher in the department of environmental health and engineering at Johns Hopkins Bloomberg School of Public Health, and the division of environmental sciences at the Gradient Corp. in Boston, and colleagues wrote. “These results provide evidence for a unique mechanism which may partially explain why obese children with asthma demonstrate greater susceptibility to air pollution.”
Researchers evaluated baseline data from 174 children with asthma aged 8 to 17 years in the single-center, randomized, parallel, prospective AIRWEIGHS study. The researchers measured tidal breathing using a pitot-tube flow meter and obtained tidal volume, respiratory rate and minute ventilation. In a multivariable model adjusted for age, height, race, sex and asthma severity, researchers estimated the association of BMI z score with breathing patterns, and based on BMI-associated changes in breathing patterns, they used a particle dosimetry model simulating PM2.5 lung deposition.
Overall, 86 children included were categorized as obese (mean age, 10.9 years; 45% girls; 87% Black) and 88 were nonobese (mean age, 11.1 years; 34% girls; 84% Black)
Children with a higher BMI had higher tidal volume (adjusted mean difference, 25 mL) and higher minute ventilation (adjusted mean difference, 453 mL per minute) compared with children with a normal BMI.
Children with higher tidal volumes also had higher fractional PM2.5 deposition in the lung, which was driven by greater alveolar deposition, according to the researchers. This meant that children with obesity had greater per-breath retention of inhaled PM2.5 with an adjusted mean difference of 3.4%, which led to worse PM2.5 deposition rates, the researchers wrote.
According to the researchers, these results highlight a “dual hit” scenario, wherein children with obesity and asthma are cumulatively exposed to greater PM2.5 levels compared with children with normal weight, even when breathing the same ambient air.
“These findings characterize a mechanism for why obese children with asthma are more susceptible to air pollution, and thus rationale for why obesity is a risk factor for more severe and uncontrolled asthma,” the researchers wrote. “Follow-on investigation of particle deposition characteristics in children with asthma is warranted.”