Spirometric values in obese individuals. Effects of body position.

Obesity is increasingly prevalent. Earlier studies indicated that there was a significant but small difference in spirometric values between sitting and standing position in the normal population. It is not known if this is true for obese individuals. The recommendations of the American Thoracic Society (ATS) are to document if a spirometry is done in a sitting or standing position. We performed a study in which we compared sitting and standing spirometric values in obese individuals. Patients with a body mass index (BMI) > or = 30 kg/m2 who were referred for spirometry were invited to participate. All tests were done according to American Thoracic Society recommendations. We studied 50 subjects (32 females and 18 males; mean age 45 yr [SD +/- 14.4]). Age range was 20-71 years. Average BMI was 39 (SD +/- 7, range 30 to 65). Twenty-two did the first testing in the sitting position and 28 standing. There was a small but statistically significant difference between forced vital capacity (FVC) in the standing versus sitting position (Wilcoxen test, p < or = 0.05). There was no significant difference in FEV1 between sitting and standing. Our conclusion is that body position is not important when performing spirometry in persons with BMI > or = 30 kg/m2.