Systemic inflammation and higher perception of dyspnea mimicking asthma in obese subjects

There are a variable number of obese subjects with self-reported diagnosis of asthma but without current or previous evidence of airflow limitation, bronchial reversibility, or airway hyperresponsiveness (misdiagnosed asthma). However, the mechanisms of asthma-like symptoms in obesity remain unclear.

We sought to evaluate the perception of dyspnea during bronchial challenge and exercise testing in obese patients with asthma and misdiagnosed asthma compared with obese control subjects to identify the mechanisms of asthma-like symptoms in obesity.

In a cross-sectional study we included obese subjects with asthma (n = 25), misdiagnosed asthma (n = 23), and no asthma or respiratory symptoms (n = 27). Spirometry, lung volumes, exhaled nitric oxide levels, and systemic biomarker levels were measured. Dyspnea scores during adenosine bronchial challenge and incremental exercise testing were obtained.

During bronchial challenge, patients with asthma or misdiagnosed asthma reached a higher Borg-FEV1 slope than control subjects. Moreover, maximum dyspnea and the Borg-oxygen uptake (V'O2) slope were significantly greater during exercise in subjects with asthma or misdiagnosed asthma than in control subjects. The maximum dyspnea achieved during bronchial challenge correlated with IL-1β levels, whereas peak respiratory frequency, ventilatory equivalent for CO2, and IL-6 and IL-1β levels were independent predictors of the Borg-V'O2 slope during exercise (r(2) = 0.853, P < .001).

A false diagnosis of asthma (misdiagnosed asthma) in obese subjects is attributable to an increased perception of dyspnea, which, during exercise, is mainly associated with systemic inflammation and excessive ventilation for metabolic demands.