Journal of Applied Physiology, Vol 56, Issue 1 64-71, Copyright © 1984 by American Physiological Society
Effect on ventilation of change to the upright posture in newborn infants
A. R. Stark, T. B. Waggener, I. D. Frantz 3rd, B. A. Cohlan, H. A. Feldman and P. C. Kosch
We have investigated the effect of postural change on tidal volume (VT),
inspiratory (TI) and expiratory (TE) duration, minute ventilation (VI), and
end-tidal PCO2 in a group of 11 healthy full-term sleeping infants, 2-4
days of age. During tilts from the supine to upright posture, the average
volume increase was 4.3 +/- 4.4 (SD) ml or 1.2 ml/kg in the maneuvers
unassociated with sighs. In the 20% of tilts in which sighs occurred, the
average volume change was slightly higher. Transition from supine to
upright posture resulted in statistically significant increases in VT (6.45
+/- 0.06 to 6.72 +/- 0.06 ml/kg), TI (554 +/- 7 to 604 +/- 7 ms), and TE
(629 +/- 12 to 777 +/- 14 ms), and decrease in VI (328 +/- 5 to 288 +/- 4
ml X kg-1 X min-1) (all means +/- SE, P less than 0.0005). Return to supine
position resulted in statistically significant changes in the opposite
direction. Tilting to the upright posture brought about a small (0.4 +/-
0.1 Torr, means +/- SE) but consistent statistically significant increase
in end-tidal PCO2, which persisted through the first minute when the infant
was returned to the supine position. The expiratory prolongation observed
with tilting appears to minimize changes in end-expiratory lung volume,
obviating the need for an effective compensatory muscle response to defend
ventilation. Thus it appears that infants, in contrast to adults, adopt a
breathing strategy to limit the extent of change in absolute lung volume,
rather than to defend ventilation at increased lung volume.
