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Effect on ventilation of change to the upright posture in newborn infants
Insights
Infant breathing patterns change with posture. Upright positions increase tidal volume (VT) and expiratory time (TE), while decreasing minute ventilation (VI), suggesting infants prioritize lung volume stability over ventilation.
Area of Science:
- Neonatal physiology
- Respiratory mechanics
- Infant development
Background:
- Postural changes significantly impact respiratory function in adults.
- Limited research exists on how postural shifts affect breathing mechanics in neonates.
Purpose of the Study:
- To investigate the effects of postural changes (supine to upright) on respiratory parameters in sleeping neonates.
- To understand the infant's breathing strategy in response to gravitational stress.
Main Methods:
- Studied 11 healthy, full-term infants (2-4 days old) during sleep.
- Measured tidal volume (VT), inspiratory (TI) and expiratory (TE) durations, minute ventilation (VI), and end-tidal PCO2 during supine and upright positions.
- Analyzed data for statistically significant changes.
Main Results:
- Transitioning to upright posture significantly increased VT, TI, and TE.
- Minute ventilation (VI) significantly decreased in the upright position.
- A small but consistent increase in end-tidal PCO2 was observed in the upright posture.
- Expiratory prolongation appeared to stabilize end-expiratory lung volume.
Conclusions:
- Newborn infants alter their breathing strategy with postural changes, prioritizing lung volume maintenance over ventilation.
- Unlike adults, infants seem to adapt by prolonging exhalation to minimize changes in absolute lung volume.
- This suggests a distinct developmental adaptation in respiratory control during the neonatal period.
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.