Effect of Obesity on Diffusing Capacity of Lung for Carbon Monoxide: Quality Improvement Project

Abstract

SESSION TITLE: Pulmonary Physiology Posters SESSION TYPE: Original Investigation Poster PRESENTED ON: Wednesday, October 28, 2015 at 01:30 PM - 02:30 PM PURPOSE: Various reference equations are available to determine predicted values for the diffusing capacity of the lung for carbon monoxide (DLCO). Most were derived many years ago from reference populations with a lower the prevalence of obesity than is seen in contemporary patients. We conducted this study to evaluate the effect of elevated body mass index (BMI) on the predicted value for DLCO in patients without known lung disease. METHODS: A retrospective analysis of pulmonary function tests (PFTs) of patients with BMI > 30 and age >18 years was performed. We excluded patients with obstructive and restrictive lung disease defined as FEV1/FVC <0.7% and FVC<80% predicted or unacceptable study as per ATS guidelines. DLCO was determined by the single breath method with predicted values derived by Burrows and Roca reference equations. RESULTS: Analyses were carried out on 359 patients, 178 males and 181 females. The mean age, BMI and measured DLCO for males was 56 +15.4 years, 34.7+3.95 kg/m2and 22.2+5.98 ml/mmHg/min, and for females 55+15.3 years, 36.8+5.16 kg/m2 and 16.4+3.65 ml/mmHg/min. The measured DLCO declined with increasing age regardless of sex.. Females had significantly higher BMIs than males whereas the latter had significantly higher DLCO actual than females. We found a decline in DLCO measured with increasing age regardless of sex (ANOVA, p< 0.001) whereas an effect of BMI was not significant. Reference equations for predicted DLCO (Burrows and Roca) were examined; these gave estimates that were larger than DLCO measured regardless of gender. ANCOVA was performed on DLCO predicted: a significant effect of age was noted and the effect of BMI was now found to be highly significant (p < 0.001). CONCLUSIONS: DLCO predicted (Burrows and Roca) appeared to be larger than DLCO measured in patients with BMI> 30. This may lead to unnecessary diagnostic testing; hence, predicted DLCO should be cautiously interpreted in this cohort of patients. CLINICAL IMPLICATIONS: Physicians should cautiously interpret DLCO values predicted by Burrows and Roca equations in patients with BMI ≥ 30. DISCLOSURE: The following authors have nothing to disclose: Alexander Blood, Anup Singh, Annamaria Iakovou, Anthony Sica, Harly Greenberg, Arunabh Talwar No Product/Research Disclosure Information