Background: GERD is common in preterm infants and may worsen CLD. In healthy preterm infants, the lower esophageal sphincter (LES) is an anti-reflux barrier and transient LES relaxation (TLESR) is the major mechanism of GER. Method: 45 preterm infants (23 controls, 10 GERD, 12 CLD) (mean postconceptual age 36, 34, 36 wks respectively) were studied with esophageal manometry and pH monitoring. Esophageal pressures were recorded using a miniature sleeve-side hole manometer (2 mm o.d.) perfused @ 0.01-0.04 ml/min. An antimony pH electrode (1.5 mm o.d.) was positioned 5 cm. above the manometrically defined LES. Manometry with pH monitoring was performed for 2-3 hrs post prandially. GER episodes were defined as a drop in esophageal pH to ≤ 4 for 15 sec or ≥ 1 pH unit (if basal pH was < 4).Results: 131 GER episodes occurred, more commonly in infants with GERD compared to controls and CLD(see table-*p<0.05 compared with control using ANOVA). GER episodes occurred most frequently with TLESR (66%, 57%, 71% for controls, GER and CLD infants). Abdominal straining was associated with GER, usually concurrently with LES relaxation (control 31%, GER 62%, CLD 41%). Clearance time did not differ significantly. In all groups, the predominant response to swallowing was normal peristalsis. In infants with CLD, the proportion of non-peristaltic pressure waves was increased (47% vs 31% for both controls and GERD, p<0.05).Conclusion: The frequency of GER episodes is increased in preterm infants identified clinically as having GERD, but not in infants with CLD. TLESR's are a major mechanism of GER in premature infants with GERD.

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