Breathing pattern in newborns.

Newborn mammals have a high O2 consumption (per unit body weight), which implies a high ventilation. The choice between an increase in volume, frequency, or both is probably dictated by energetic factors, including the likelihood of chest distortion with large inspirations. Data on ventilatory pattern of unanesthetized newborns of eight mammalian species, ranging in size from mice to infants, have been collected. Minute ventilation was linked to the O2 consumption and increased progressively less with the body weight of the species (BW0.86) due to a drop in frequency with size (BW-0.15), whereas tidal volume varied in proportion with body weight (BW1.01). Mean inspiratory flow per unit body weight was more than twice as large in newborn mice and rats than in piglets or infants, whereas the inspiratory time-to-total breath duration ratio was approximately constant among species, averaging 37%. During expiration occasional interruptions of the flow were observed in most newborns; measurements of esophageal pressure and diaphragmatic electromyogram pointed toward upper airways closure and not active breath holding as the explanation of this phenomenon.