The effects of body mass index on spirometry tests among adults in Xi'an, China.

Obese people have higher risk of respiratory symptoms. The relationship between obesity and lung function varies with age, race, and geographical region. The objective of this study is to examine the effects of body mass index on spirometric tests among adults in Xi'an city.This is a cross-sectional study. Pulmonary function testing was conducted on participants recruited from Xi'an, China between July and August 2012. Force expiratory volume in first second (FEV1), force vital capacity (FVC), FEV1/FVC, peak expiratory flow (PEF), and forced expiratory flow at 25-75% (FEF25-75) were measured by portable Spirometer. Lung function was analyzed according to Chinese standard of general obesity.A total of 770 subjects were analyzed in this study, of whom 299 were males and 471 were females. FVC% (P = .037) decreased significantly in obese subjects than in nonobese subjects. FVC% (P = .02) declined significantly in overweight subjects than in normal subjects. For smoker, FEV1% (P = .03) and FVC% (P = .02) were lower notably in overweight subjects than in normal subjects. FEV1% (P = .0008), FVC% (P = .0004), and PEF% (P < .0001) were higher significantly in normal subjects than in underweight subjects.FVC notably decreased in obese people, not FEV1, FEV1/FVC, PEF, and FEF25-75. FEV1, FVC, and PEF were higher significantly in normal subjects than in underweight subjects. FVC is affected by BMI in diphasic change.