ISSN:
1432-2013
Keywords:
Blood
;
gas partition coefficient
;
Excretion
;
Lung model
;
Tracer gases
;
Buffering of lung- and airway tissue
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The excretion (E) of inert gases by the lung depends on, among other things, their blood-gas partition coefficients (λ). According to conventional gas exchange models, E should increase with increasing λ However, recent models that take into account the tidal character of breathing and the buffering capacity of lung tissue predict that E will show a minimum in the range of large λ values (λ〉10). Further, this local minimum should shift to larger λ values in exercise conditions as compared to rest conditions. The aim of this study is to verify this predicted behaviour of E. The experiments were carried out with seven healthy subjects at rest and at three work loads (50 W, 100 W and 150 W) on a bicycle ergometer. The behaviour of E was determined from the results of a simultaneous washin of four tracer gases: ethyl acetate (λ≈75), acetone (λ≈330), ethanol (λ≈2000) and acetic acid (λ≈20000). The washin lasted 4 min, and E was calculated from E = 1−p Ē/p I, where p I and P Ē are the partial pressures of the tracer gas in inspired and mixed expired gas determined from the recordings obtained during the last minute of washin. p I and P Ē were measured with a mass spectrometer. Comparison of the E values of the four gases shows that at rest a minimum value for E is found for acetone. In exercise conditions, however, the smallest E value is found for the more soluble ethanol or acetic acid. Further, under exercise conditions the E values for ethyl acetate and acetone are larger than their respective values at rest. In general, the experimental findings are consistent with the predicted behaviour of E. This means that gas exchange in the airways between gaseous and dissolved tracer gas in the airway lumen and in the airway tissue, respectively, cannot be ignored for highly soluble tracer gases. In addition, the observed differences between the E values of the four highly soluble tracer gases imply that the dead space ventilation ( $$\dot V_{\text{D}}$$ ) depends on λ, i.e. the value of $$\dot V_{\text{D}}$$ is not unique. Therefore, the result for $$\dot V_{\text{D}}$$ obtained from a highly soluble tracer gas will, in general, not apply to other tracer gases.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00370595
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