Exposure at high altitude and exercise altered membrane diffusion capacity of the lung

To the Editors:

In an article published in a recent issue of the European Respiratory Journal, Dehnert et al. 1 report various measurements made after climbing at high altitude. Among them were carbon monoxide (CO) transfer measurements. I was surprised by the finding of an increase in the transfer factor of the lung for CO (T_L,CO) at altitude, as an article presently in press 2, already published in abstract form 3, in which T_L,CO and the transfer factor of the lung for nitric oxide (T_L,NO) decreased slightly but significantly at altitude. At 5,000 m, two thirds of the subjects decreased their T_L,NO by >5% after a short maximal exercise. This discrepancy could be due to the fact that Dehnert et al. 1 divided the measured value at altitude by a factor <1 which, in fact, should only be used to estimate the predicted values at altitude. Altitude hypoxia, due to reduced capillary oxygen pressure, increases the conductance of blood for CO and, therefore, the CO transfer. Thus, if one wants to compare the results obtained at altitude to those at sea level, we should either multiply the measured results by this factor or express the results as % predicted, taking into account the equation cited in Dehnert et al. 1 for the predicted value at altitude. When looking for a detection of interstitial oedema, NO transfer would be more sensitive than CO, as the former is mainly dependent on the membrane conductance and the latter is dependent on both membrane and blood conductances 4.

• ©2010 ERS