Abstract
Diffusion tests with NO and CO give smaller membrane conductance values (Dm) than morphometry. This discrepancy is likely due to the uncertainty surrounding the estimates for θNO and θCO.
A method was devised to estimate θNO and θCO in healthy subjects by measuring NO and CO transfer with either 21 or 15% FIO2 making the assumption that the latter mixture would not change Dm and Vc. Vc and Dm/Vc were calculated using the usual multi step oxygenation method and the NO/CO method. From the identity of these 2 estimations θNO and θCO values could be derived.
10 subjects aged between 20 and 68 years performed the measures (Hyper’compact Medisoft Dinant, Be). They breathed either air or a mixture with 15% O2 and performed then the single breath maneuver with the usual tracers. FEO2 was measured and PcapO2 was calculated.
The target finite value for θNO of 4.5 (mmHg min)-1 was that recommended by Borland et al.
Seven θCO vs PO2 equations were tested, among them a mix of Holland and Forster equations (HF).
With (1) and (2) corresponding to 21% and 15% FI O2 respectively:
ΘNo = 1.97/[1/Θco1 - (1/Θco1- 1/Θco2)*(1/TLCO(1,2) -1.97/ TLNO(1,2))/(1/TLCO1 - 1/TLCO2)]
None ΘNO value was compatible with an infinite or high θNO value. The best compromise was obtained with the HF equation (1/ θCO =1.19 + 0.0053 PO2), ΘNo=2.1±5.3 (mmHg min)-1. The target value of 4.5 was within the confidence interval (t =2). Dm would be twofold the previous value in the range of the morphometric values.
Adopting these results would change the interpretation of NO and CO transfer, DLNO would depend for a half of the membrane and blood components of the transfer, DLCO would depend for 80% of the blood component.
- © 2013 ERS