Asthma in obese more severe

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Obesity can worsen the impact of asthma and may also increase its severity, according to new University of Otago research.

The study, which tested lung function in asthmatic women with a range of body mass indexes (BMIs), is the first to reveal a significant difference in how the airways and lungs respond to a simulated asthma episode in obese versus non-obese individuals.

The findings appear in the latest edition of the American Journal of Respiratory and Critical Care Medicine.

Lead author Professor D. Robin Taylor says the research establishes a direct link between obesity and the development of a phenomenon known as “dynamic hyperinflation” ? this occurs in asthmatics when they get acutely wheezy, and air is taken into the lungs but cannot be adequately exhaled. This effect is greatest in patients with asthma who are also obese.

“We have shown significant differences in the changes in respiratory function that occur with asthmatic bronchoconstriction in relation to obesity,” says Professor D. Robin Taylor who leads the Otago Respiratory Research Unit in the Dunedin School of Medicine.

The researchers recruited 30 asthmatic women and divided them into three groups by BMI: normal weight, overweight and obese.

After asthma-like episodes were artificially induced, the women were assessed for changes in several measures of lung function. This included how much air remained in their lungs after exhalation (functional residual capacity, or FRC) and how much air they could breathe in on her next breath (inspiratory capacity, or IC).

“After the induced attacks, the amount of bronchoconstriction was identical for each of the three groups, but the changes in FRC and IC were greatest in the obese group. This indicated to us that greater dynamic hyperinflation was occurring among obese individuals,” says Professor Taylor.

With increasing BMI, FRC was higher, whereas IC was significantly decreased. “This means that among women with high BMI, an asthma-like episode has the potential to cause greater breathing difficulties than in non-obese women,” he says.

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 inhaler treatment in order 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.”

The study also showed that simple spirometry testing was inadequate to determine the level of pulmonary dysfunction which was occurring in obese individuals.

“Our findings need to be explored further. We need to confirm that the differences in dynamic hyperinflation between obese and non-obese asthmatics are sufficient to explain the differences in symptoms between the two groups. A larger study is required to do this,” says Professor Taylor.

Source: University of Otago, New Zealand

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