Determination of viscous pressure loss and resistance upstream from the choke point from breathing gases of different physical properties Ole F. Pedersen, Institute of Public Health, University of Aarhus, Denmark. AIM. To determine viscous pressure losses and resistances upstream to CP. BACKGROUND. If maximum expiratory flow is corrected for density (Fmaxcorr = Fmaxgas * (rair/rgas)0.5 ,and plotted against elastic recoil pressure, these curves would be superimposed, if the viscous loss was negligible (Pfr = 0). If they are not, Pfrgas/Pfrair = (Fmaxgas /Fmaxair) a (rgas/rair) a-1(mgas/mair)2- a (JAP 48:313-319,1980), where r is gas density and m is viscosity. a is an exponent = 1 for laminar flow and 2 for turbulent flow MATERIAL AND METHOD: Nine healthy males , mean age (sd) = 32 (10) years examined in a pressure corrected flow body-plethysmograph, with measurement of maximum flows after breathing air, 20% oxygen in He and 20% oxygen in SF6 . For construction of MFSR-curves. Lung elastic recoil pressures were estimated from ECCS reference values (Bull. europ. Physiopath. resp. 1983, 19 (suppl 5),28-31). The model described in the figure was used. The extrapolated flow FY and a were determined by solving two equations with two unknowns. RESULTS: a was found to be 0.86(0.69) mean (SD), and FY was 1.28(0.8) times FA., Pfrair = 0.18 (0.12) kPa, and Rfrair = 0.029 (0.019) kPa/(L/s). DISCUSSION AND CONCLUSION: a is determined with a considerable uncertainty, but not different from 1, but certainly different from1.5, indicating predominant laminar flow upstream to CP. The upstream resistance is low, and lower than directly measured (JAP 83:1721-32,1997). This is a possibility if CP is more peripheral than assumed in that study.
American Journal of Respiratory and Critical Care Medicine, Abstracts , Ats 2007-international Conference P A260, 2007