Obesity-related Changes in Diffusing Capacity and Transfer Coefficient of the Lung for Carbon Monoxide and Resulting Patterns of Abnormality across Reference Equations

In 2017, an American Thoracic Society/European Respiratory Society Task Force report recommended further research on the effects that body mass index (BMI) has on diffusing capacity of the lung for carbon monoxide (Dl ), the transfer coefficient (Kco), and the alveolar volume (VA). Our goals were to ) quantify the magnitude and direction of change to measured and predicted Dl values as BMI increases in patients free of cardiopulmonary disease and ) identify how BMI and obesity-related changes differ by reference set. Using data from a prospective cohort study of service members free of cardiopulmonary disease, we modeled the effect that BMI has on measured values of Dl , Kco, and VA, after adjusting for age, sex, hemoglobin (Hgb), and height. We then referenced Dl , Kco, and VA to normal values using four different reference equations. There were 380 patients with data available for analysis, and 130 had a BMI ⩾ 30 kg/m (87.7% class I obesity). After controlling for age, sex, Hgb, and height, increased BMI was significantly associated with Kco (β = 0.09,