title: Effect on ventilation of change to the upright posture in newborn infants.
abstract: 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.
mesh_terms: D002245:Carbon Dioxide; D006801:Humans; D007231:Infant, Newborn; D010313:Partial Pressure; D011187:Posture; D012119:Respiration; D013990:Tidal Volume; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide