Introduction:High resolution manometry (HRM) has been widely accepted as an easier and more reproducible method to assess the esophageal body. Its usefulness in evaluating the lower esophageal sphincter (LES) has not been well studied. The goal of this study was to compare HRM to the standard pull-through technique in assessment of the resting characteristics of the LES.Methods:Conventional manometry (CM) using the station pull-through technique and HRM with a solid state catheter were performed in 66 patients with foregut symptoms. HRM was performed in the supine position 30 minutes after CM. All patients had a videoesophagogram to identify the presence of a hiatal hernia. The LES was assessed in the spatiotemporal mode of HRM, with the boundaries of the LES defined as 1) distinct color change (blue to green) on the image based analysis, 2) using an isobaric contour of 2 mmHg and 3) a rise from gastric baseline in the diagram mode. In the tracing mode of HRM, the lower border of the LES was defined as in conventional manometry as a 2 mmHg rise above gastric baseline and the upper border as a drop below gastric baseline. The resting characteristics of the LES by HRM and CM were compared. Results:HRM consistently overestimated both overall and abdominal lengths of the LES and had poor correlation with the lengths measured by CM (table). The variability in LES length by HRM was greatest in patients with a hiatal hernia (1.8 vs. 0.9 cm, p=0.027). Bland-Altman analysis showed weak agreement between LES length determined by HRM and CM (95% limits of agreement -1.4 to 4.4 cm). CM identified 22 patients (33%) with a defective LES. Using the image based analysis of HRM, 7/22 patients (32%) with a defective valve on CM would be considered normal. The upper border of the LES varied up to 6 cm compared to CM. There was no significant difference in the resting pressure of the LES between CM and HRM (13.5 vs. 11.5 mmHg, p=0.15).Conclusion: HRM is less accurate in determining LES length with nearly one third of patients with a defective valve on CM considered normal. Discrepancies of more than 4 cm may occur, and are greatest in the presence of a hiatal hernia. There was significant variability in the location of the upper border of the LES which compromises accurate placement of a pH probe.

	Conventional Manometry (CM)	Image-based analysis	SpatioTemporal( isobaric contour =2mmHg)	Diagram	Line Tracing(2 mmHg)
OverallLength	3(2.3,3.5)	3.4*(2.7,4.1)	4.4*(3.5,5.1)	4.7*(3.3,5.4)	3**(2,4)
Spearman R coefficient (95% CI)		0.08(-0.18,0.32)	0.21(-0.23,0.27)	0.06(-0.19,0.3)	0.18(-0.07,0.41)
Abdominal length	1.8(1.1,2.2)	3†(2.2,3.5)	3.7†(2.8,4.5)	3.7†(2.6,4.6)	3†(2,4)
Spearman R coefficient (95% CI)		0.44(0.21,0.62)	0.23(-0.03,0.45)	0.37(0.13,0.56)	0.26(0.1,0.48)

* p<0.005 for comparison to CM, ** p=0.74 for comparison to CM † p<0.0001 for comparison to CM