Measurement of upper esophageal sphincter tone and relaxation during swallowing in premature infants

Upper esophageal sphincter (UES) motor function has not been previously eva luated in premature infants. The motor patterns associated with tonic activ ity and swallow-related relaxation of the UES were recorded for 1 h after c ompletion of gavage feeding in 11 healthy preterm neonates (postmenstrual a ge 33-37 wk) with a micromanometric assembly, which included a sleeve senso r specifically adapted for UES recordings. A clearly defined UES high-press ure zone was observed in all premature infants studied. Resting UES pressur e ranged from 2.3 to 26.2 mmHg and was higher during periods of irritabilit y and apparent discomfort. During dry swallows, UES pressure relaxed from a resting pressure of 28.2 +/- 4.0 mmHg to a nadir of 1.1 +/- 3.3 mmHg. The mean UES relaxation interval (the time from relaxation onset to relaxation offset) was 0.31 +/- 0.11 s. We conclude that in premature infants greater than or equal to 33 wk postmenstrual age the motor mechanisms regulating UE S resting pressure and the onset of UES relaxation are well developed.