Correlation between spirometry results and body mass index in patients with asthma

Background: Studies have suggested that asthma in obese individuals differs from the classic asthma phenotype, presenting as a disease that is more difficult to control and that does not respond as well to inhaled corticosteroids. The objective of the present study was to determine whether obesity, age or a combination of the two are associated with abnormal spirometry results in patients with asthma.

Method: This was an observational, cross-sectional, retrospective study involving patients over 18 years of age who had been diagnosed with asthma. We evaluated the results of spirometric tests conducted between February of 2009 and August of 2009. The patients were classified in accordance with two criteria: body mass index (BMI) and age.

Results: We evaluated 453 patients and 453 corresponding sets of spirometry results. In the present study, the pulmonary function parameters were negatively correlated with BMI. In the obese group, the mean FEV₁ value was 17.4% lower than that observed in the normal-weight group. Within that group, the number of abnormal spirometry results was significantly higher among the patients ≥ 60 years of age than among those 18-59 years of age. The proportion of females was also higher in the obese group.

Conclusion: Our results indicate that FEV₁ and FVC decrease significantly in proportion to increases in BMI and age. Because obesity is yet another factor that makes asthma control difficult, the weight of asthma patients should be closely monitored.