range of body-mass indexes (BMIs) found that obesity may worsen the impact
of asthma and also mask its severity in standard tests.
"We have demonstrated significant differences in the changes in
respiratory function that occur with asthmatic bronchoconstriction in
relation to obesity," principal investigator Dr. D. Robin Taylor, of the
University of Otago in New Zealand, said in a prepared statement.
The study also found that simple spirometry couldn't determine the
level of pulmonary dysfunction in obese people with asthma.
The findings were published in the first issue for May of the
American Journal of Respiratory and Critical Care Medicine. It's
the first prospective study to find a significant comparative difference
between obese and non-obese people in how the lungs and airways respond to
a simulated asthma attack.
The researchers said it establishes a direct link between obesity and
the development of dynamic hyperinflation -- air breathed into the lungs
can't be expelled. This often occurs with acute asthma, but is more
frequent in obese people.
The study included 30 asthmatic women who were divided into three
groups based on their BMI: normal weight, overweight and obese. All the
women breathed nebulized methacholine to induce an asthma-like attack and
were then assessed for changes in lung function, including functional
residual capacity (FRC -- how much air remained in the lungs after
exhalation) and inspiratory capacity (IC -- how much air could be inhaled
on the next breath).
"After the methacholine challenge, 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," Taylor
said.
The greater a woman's BMI, the higher her FRC and the lower her IC.
"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. The greater dynamic hyperinflation means that obese
individuals lose the ability to inhale as deeply or exhale as fully as
normal weight individuals," Taylor said.
The findings suggest fundamental differences in the way that obese
people with asthma may experience shortness of breath.
"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.
More research is needed 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. Our study was
not large enough to do this," Taylor said.
source:news.yahoo.com
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