Abstract
Introduction: Desaturation during maximal exercise can be caused by several problems; decreased diffusing capacity, leading to an increased Alveolar-arterial (A-a) oxygen gradient, or V/Q mismatch or a contact time problem. The present method to establish decreased diffusing capacity is the measurement of diffusing capacity for carbon monoxide (TLCO). We hypothesize that the diffusing capacity for nitric oxide (TLNO) is more accurate than TLCO.
Aim: The aim of this study is to find out whether diffusing capacity for NO, as a marker for the membrane component of diffusion, can be a more accurate predictor of the A-a gradient at maximal exercise, compared to diffusing capacity for CO, as a marker for the membrane and hemodynamic component of diffusion.
Methods: 15 patients with pulmonary complaints (mean age 58 years) performed a combined single breath TLNO/TLCO measurement and a maximal exercise test. We constructed a model to predict the A-a gradient at maximal exercise.
Results: The A-a gradient at maximal exercise can be predicted by TLCO%R, and resulted in an R2 (coefficient of determination) of 0.64. TLNO%R predicted the A-a gradient at maximal exercise with an R2 of 0.81 (see figure).
Conclusion: The diffusing capacity for NO is a more accurate predictor of the A-a gradient at maximal exercise than the diffusing capacity for CO, and thereby a more accurate predictor of desaturation during exercise.
Reference:
1. Lee, I van der Resp Med 2007;101:1579-84.
- © 2011 ERS