Patients with asthma who are obese had significantly worse small airway dysfunction (SAD) as defined by oscillometry compared with patients who were not obese, according to a study published in Annals of Allergy, Asthma & Immunology.
Previous studies have linked airway reactivity and obesity, but more research is needed on the effects of obesity on airway oscillometry patterns in persistent asthma.
Dr. Brian Lipworth and Dr. Rory Chan conducted a study to determine how obesity affects lung function using oscillometry, a test that measures the resistance and compliance of the airways.
The researchers collected and analyzed data from 188 patients diagnosed with moderate-to-severe asthma. The researchers then divided the participants into 4 subgroups according to BMI, which are as follows:(1) normal weight—18.5 to 24.9 kg/m2; (2) overweight—25 to 29.9 kg/m2; (3) obese—30 to 39.9 kg/m2 and (4) morbidly obese—≥40 kg/m2.
The researchers observed that compared to patients with normal weight, patients who are obese or morbidly obese had significantly worse resistance between 5 Hz and 20 Hz (R5-R20). However, across all groups, the researchers did not find any significant difference between the forced expiratory volume (FEV), forced vital capacity (FVC), FEV1/FVC ratio, Asthma Control Questionnaire scores, or severe exacerbation frequency. This finding suggests that obesity is associated with increased airway resistance and decreased airway compliance, even in the absence of other measures of airway obstruction.
Furthermore, the researchers identified 4 distinct asthma phenotypes using cluster analysis incorporating oscillometry.
- Cluster 1: (n = 72) Younger patients with obesity and preserved spirometry and oscillometry.
- Cluster 2: (n = 42) Older patients with obesity, normal spirometry, and SAD on oscillometry.
- Cluster 3:(n = 38) Older patients who are overweight, impaired spirometry, and airflow obstruction based on FEV1/FVC but relatively well-preserved oscillometry.
- Cluster 4: (n = 31) Older women with obesity, combined spirometry and oscillometry impairment.
The researchers observed that participants in the fourth cluster also had a significantly worse airway function based on FVC, R5-R20 ratio, R5-R20, and severe exacerbation frequency than the other three clusters.
According to the researchers, “the presence of obesity alone confers worse peripheral airway resistance and reactance measurements; therefore, there may be an additive effect on lung mechanics by having both obesity and severe asthma.”