Rapid maturation of gastric relaxation in newborn infants

We studied gastric volume, wall compliance, sensory perception, and receptive relaxation during the first postnatal 80 h in 17 healthy term infants, using a computer-driven air pump and simultaneously measuring pressure and volume within a latex balloon placed through the oropharynx into the stomach. To evaluate gastric compliance, we measured pressures while we infused air into the intragastric balloon at different rates (10, 20, and 60 mL/min) in random sequence. In all infants, there was a linear relationship between intragastric pressure and volume to the maximum pressure tested, 30 mm Hg. Gastric compliance ranged from 0.2 mL/mm Hg to 3.8 mL/mm Hg. Different infusion rates had no effect on compliance. We calculated gastric receptive relaxation by measuring the volume needed to maintain a constant pressure of 10 mm Hg within the balloon for 5 min. Gastric receptive relaxation ranged from 0.5 mL/min to 54 mL/min. Gastric compliance and receptive relaxation increased with postnatal age (r = 0.70, p < 0.005; r = 0.79, p < 0.001, respectively) and with number of feedings (r = 0.80, r = 0.88, respectively, both p < 0.001). There was no correlation between weight or type of feeding (breast versus formula) and either gastric compliance or relaxation. In conclusion, these results may explain the small feedings that neonates ingest in the first days of life. During the first 3 postnatal d, the newborn stomach becomes more compliant and develops more receptive relaxation, associated with a larger volume capacity.