Journal of Applied Physiology, Vol 54, Issue 6 1745-1753, Copyright © 1983 by American Physiological Society
Expiratory and arterial partial pressure relations under different ventilation-perfusion conditions
A. Zwart, S. C. Luijendijk and W. R. de Vries
Inert tracer gas exchange across the human respiratory system is simulated
in an asymmetric lung model for different oscillatory breathing patterns.
The momentary volume-averaged alveolar partial pressure (PA), the
expiratory partial pressure (PE), the mixed expiratory partial pressure
(PE), the end-tidal partial pressure (PET), and the mean arterial partial
pressure (Pa), are calculated as functions of the blood-gas partition
coefficient (lambda) and the diffusion coefficient (D) of the tracer gas.
The lambda values vary from 0.01 to 330.0 inclusive, and four values of D
are used (0.5, 0.22, 0.1, and 0.01). Three ventilation-perfusion conditions
corresponding to rest and mild and moderate exercise are simulated. Under
simulated exercise conditions, we compute a reversed difference between PET
and Pa compared with the rest condition. This reversal is directly
reflected in the relation between the physiological dead space fraction
(1--PE/Pa) and the Bohr dead space fraction (1--PE/PET). It is argued that
the difference (PET--Pa) depends on the lambda of the tracer gas, the
buffering capacity of lung tissue, and the stratification caused by
diffusion-limited gas transport in the gas phase. Finally some determinants
for the reversed difference (PET--Pa) and the significance for conventional
gas analysis are discussed.
