To define the effects of obesity on DLCO and DL/VA.
We retrospectively reviewed our pulmonary function testing (PFT) data for overweight individuals, defined as a body mass index (BMI) of >25, who underwent PFTs. We selected for overweight non-smoking individuals who had a total lung capacity (TLC) > 80% of predicted, FEV1/FVC > 70%, and DL/VA >60% of predicted. Miller non-smoking predicted values were used. Hemoglobin corrections were not performed. Nonparametric parameters were compared using Kendall’s tau.
Out of 10,590 PFTs performed between Feb., 1999 and Feb., 2004 PFTs, 477 met criteria. Data are in Table 1.
n = 477MeanSDRangeAge54± 178–93BMI, kg/m233± 6.525–60FVC, % pred.81± 14141–129FEV1, % pred.87± 1640–155TLC, % pred.93± 1280–149RV, % pred.103± 2935–293ERV, % pred.41± 245–157DLCO, % pred.79± 1928–128DL/VA, % pred.101± 1839–163The DLCO % predicted and DL/VA % predicted were significantly different, with a p < .001. DLCO was decreased and was not correlated with BMI. DL/VA, however, was correlated with BMI (r = .15, p < .001).
This is the largest study of diffusion in overweight individuals of which we are aware. Our results contradict some of those from other studies. Our results suggest that, 1) When using predicted values, the DLCO will tend to be low in overweight individuals; 2) In contrast, the DL/VA equation is not as “distorted” by weight; and 3) BMI is positively correlated with DL/VA in this population.
The goal of predicted values in testing is to be able to use variance from the norm to identify the effect of a disease process upon function. In overweight individuals, DL/VA may be more accurate than DLCO in separating normal from abnormal physiology.
H.N. Dagher, None.