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Pflügers Archiv

, Volume 407, Issue 2, pp 211–215 | Cite as

Excretion-retention data of steady state gas exchange in tidal breathing

II. Dependency on the diffusion coefficient
  • Aart Zwart
  • Sybrand C. M. Luijendijk
  • Wouter R. de Vries
Heart, Circulation, Respiration and Blood; Environmental and Exercise Physiology

Abstract

The steady state gas transfer properties of the lung can be derived from excretion-retention (E-R) data of inert tracer gases that are infused intravenously.E =PĒ/PV andR =Pa/PV, wherePĒ,Pa andPV represent the partial pressures of the tracer gases in mixed expired gas, arterial blood and mixed venous blood, respectively. In this paper, we investigate the influence of diffusive gas mixing in the lung onE andR. To that end,E-R data sets were simulated with a lung model that takes into account tidal breathing, the morphometric geometry of the airways, diffusion limited gas mixing in the alveolar space and gas dissolved in superficial lung tissue. The results show a linear relationship betweenR/E andD−0.5, whereD represents the diffusion coefficient of the tracer gases in the alveolar gas mixture. This is in contrast to the results of simulations with a lung model that describes the different gas transport mechanisms, including diffusion, as a constant rate process, where a linear relationship betweenR/E andD−1 is predicted. It is further shown thatE-R data of helium and sulphur hexafluoride cannot be used to demonstrate diffusion limited gas mixing in the lung, in particular, in the presence of a real shunt fraction. For that purpose, excretion data of pairs of tracer gases with differentD but equal, medium blood-gas partition coefficients (1<λ<30) should be used. For such pairs of tracer gases, theE values may differ by more than 10% when theD values for the two gases are 0.22 and 0.1 cm2s−1, respectively. Further, a good agreement was found between the measured and computed effects ofD on transpulmonary gas exchange.

Key words

Excretion-retention Constant rate process Tidal breathing Diffusion limitation 

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Copyright information

© Springer-Verlag 1986

Authors and Affiliations

  • Aart Zwart
    • 1
  • Sybrand C. M. Luijendijk
    • 2
  • Wouter R. de Vries
    • 2
  1. 1.Toxicology and Nutrition InstituteTNO-CIVOZeistThe Netherlands
  2. 2.Department of Medical PhysiologyState University UtrechtUtrechtThe Netherlands

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