Reappraisal of DLCO adjustment to interpret the adaptive response of the air-blood barrier to hypoxia

Abstract DLCO measured in hypoxia must be corrected due to the higher affinity (increase in coefficient θ ) of CO with Hb. We propose an adjustment accounting for individual changes in the equation relating DLCO to subcomponents Dm (membrane diffusive capacity) and Vc (lung capillary volume): 1/ DLCO  = 1/ Dm  + 1/ θVc . We adjusted the individual DLCO measured in hypoxia (HA, 3269m) by interpolating the 1/ DLCO to the sea level (SL) 1/ θ value. Nineteen healthy subjects were studied at SL and HA. Based on the proposed adjustment, DLCO increased in HA in 53% of subjects, reflecting the increase in Dm that largely overruled the decrease in Vc . We hypothesize that a decrease in Vc (buffering microvascular filtration) and the increase in Dm (possibly resulting from a decrease in thickness of the air-blood barrier) represent the anti-edemagenic adaptation of the lung to hypoxia exposure. The efficiency of this adaptation varied among subjects as DLCO did not change in 31% of subjects and decreased in 16%.