Transfer factor of the lung for carbon monoxide (TL_CO) in morbid obese subjects

Abstract

Rationale and objectives: The impact of severe obesity on transfer factor of the lung for carbon monoxide (TL_CO) remains uncertain. We hypothesized that, in addition to the potential intrinsic effects of obesity on lung function, morbidly obese subjects may require specific TL_CO reference values. To this end, TL_CO was measured in obese subjects before and after bariatric surgery (BS) and adjustment of the data to reported TL_CO reference values was assessed.

Methods: We explored 220 morbidly obese subjects (BMI ≥40 kg/m²) before BS and 129 of them were studied one year after BS. The Lin's concordance coefficient (LCC) (1) was used to assess adjustment between TL_CO measurements and the corresponding predicted values derived from different sets of reference equations.

Results: TL_CO measurements significantly increased after BS (p<0.001). A poor LCC (between 0.25 to 0.58) was observed for most of the reference equations analyzed. Accordingly, we calculated a set of new reference equations using a cohort of 148 obese non-smokers before BS (123 were females; 43±13 yrs; BMI, 46±6 kg/m²) which markedly increased LCC (0.74, from 0.67-0.79).

Conclusions: The results indicate that obesity has a significant negative impact on TL_CO. Moreover, current reference equations are not adequate for lung function assessment of these subjects. The new TL_CO reference equations herein developed may contribute to enhance evaluation of morbidly obese subjects.

References:

• 1) Lin LI. A note on the concordance correlation coefficient. Biometrics 2000; 56:324-325.