Obese asthmatics may have dysfunction in distal airways at baseline that worsens with methacholine

The study showed that this subgroup reported increased asthma exacerbations and increased symptoms, suggesting this distal airway dysfunction is clinically significant. Many obese people without asthma also develop distal airway dysfunction in response to moderate doses of methacholine.

Anne E. Dixon from the University of Vermont in Burlington, VT, and colleagues aimed to investigate physiological phenotypes of asthma in obesity.

They addressed the question of physiological responses during bronchoconstriction, differentiated different groups of asthma in patients with obesity, and differentiated responses related to obesity.

For this purpose, they performed a cross-sectional study of obese patients (22 without lung disease and 31 with asthma). Participants underwent methacholine challenge testing with spirometry measurement and respiratory system impedance by oscillometry.

The study revealed the following findings:

· People had class III obesity (BMI, 46.7 ± 6.6 kg/m2 in control and 47.2 ± 8.2 kg/m2 in asthma patients).

· Most participants had remarkable changes in peripheral airway impedance in response to methacholine. In control subjects, there was an increase in resistance at 5 Hz measured by oscillometry by 45% ± 27% and area under the reactance curve (AX) by 268% ± 236% in response to 16 mg/mL methacholine; in asthma patients, there was an increase in resistance at 5 Hz measured by oscillometry by 52% ± 38% and AX by 361% ± 295% in response to provocation concentration producing a 20% fall in FEV1 dose of methacholine. These responses indicate that obesity predisposes to peripheral airway reactivity.

· Two distinct asthma groups emerged based on respiratory system impedance: one with lower reactance and more concordant bronchoconstriction in central and peripheral airways, the other with high reactance and discordant bronchoconstriction responses in central and peripheral airways.

· The high reactance asthma group included only women and reported significantly more gastroesophageal reflux disease, worse chest tightness, more wheezing, and more asthma exacerbations than the low reactance group.

"Oscillometry testing can reveal a physiological phenotype of asthma in obesity that may be linked with more severe disease and worse symptoms, and also reveal subclinical abnormalities in obese people, but without clinically diagnosed lung disease," the researchers conclude.

Reference:

Dixon, A. E., Poynter, M. E., Garrow, O. J., Kaminsky, D. A., Tharp, W., & Bates, J. H. (2023). Peripheral Airway Dysfunction in Obesity and Obese Asthma. Chest, 163(4), 753-762. https://doi.org/10.1016/j.chest.2022.12.030