Journal of Applied Physiology, Vol 65, Issue 3 1055-1061, Copyright © 1988 by American Physiological Society
Mechanism of improvement in pulmonary gas exchange during growth in awake piglets
P. J. Escourrou, B. P. Teisseire, R. A. Herigault, M. O. Vallez, A. J. Dupeyrat and C. Gaultier
Service d'Explorations Fonctionnelles, Hopital Henri-Mondor, Creteil, France.
Previous studies have shown a lower arterial PO2 (PaO2) in infants and
young animals than in adults. To investigate the mechanism of this
impairment of gas exchange we studied 13 piglets from 12 to 65 days of age.
Two days after instrumentation we measured the distribution of
ventilation-perfusion ratios (VA/Q) by use of the multiple inert gas
technique on awake animals. We showed that PaO2 is lower in young animals,
increasing from 72 +/- 11.5 Torr before 2 wk to 102 Torr at 2 mo. This
hypoxemia is due to an enlarged alveolar-arterial O2 pressure difference
that significantly decreases with age. This impairment in gas exchange is
not due to shunting (0.6 +/- 1.3%). Mean dead space (36 +/- 11%) was not
related to age. Mean modes of perfusion and ventilation did not differ
significantly between age groups. However, the dispersion of perfusion as
expressed by its logSD decreased significantly with age, whereas dispersion
of ventilation remained constant. Furthermore, in the young animals only, a
significant difference was evidenced between measured alveolar-arterial PO2
gradient and the value predicted by the inert gas model. We therefore
conclude that the impairment of gas exchange in piglets is due to two
mechanisms: VA/Q mismatch and diffusion limitation for O2.
