Study shows Obesity worsens impact of asthma

The study has established a direct link between obesity and the development of a phenomenon known as dynamic hyperinflation — when air breathed into the lungs cannot be exhaled. This is more frequent in obese individuals.

According to lead researcher Robin Taylor of Otago University in New Zealand, “We have demonstrated significant differences in the changes in respiratory function that occur with asthmatic bronchoconstriction in relation to obesity.

“The greater dynamic hyperinflation means that obese individuals lose the ability to inhale as deeply or exhale as fully as normal weight individuals.” The researchers recruited 30 asthmatic women and divided them into three groups by body mass index — normal weight, overweight and obese.

Each participant breathed nebulised methacholine to artificially induce an asthma-like attack, and was then assessed for changes in lung function on several measures, including how much air remained in her lungs after exhalation or functional residual capacity (FRC).

“After the methacholine challenge, the amount of bronchoconstriction was identical for each of the three groups, but the changes were greatest in the obese group. This indicated to us that greater dynamic hyperinflation was occurring among obese individuals.

“This means that among women with greater BMI, an asthma-like episode has the potential to cause greater breathing difficulties than in non-obese women,” Taylor said.

However, the group of obese individuals with asthma differed from their non-asthmatic counterparts in having a lower FRC before the methacholine challenge than the non-obese group, yet still recorded a greater increase in FRC after the methacholine challenge.

“This is the surprising finding in our study. It is quite counterintuitive. You would expect individuals with a heavier chest wall not to develop hyperinflation quite so readily as those who are lighter. But that is not what happened,” Taylor said.

Perhaps most importantly, these findings point to fundamental differences in the way that obese individuals might experience shortness of breath if they have asthma.

“We know that asthma in obese subjects is more likely to persist and is more likely to be perceived to be severe.

These individuals often require more treatment to achieve asthma control. Our study provides an insight into why this might be happening — the same asthma “trigger” produces a greater effect in obese individuals,” Taylor said.