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Background and Aim: The effects of body position on the antireflux barrier are poorly understood. The purpose of this study was to assess the effect of body position on lower esophageal sphincter structure and clinical presentation in two different patterns of reflux: isolated upright and combined/supine.Methods: Patients with typical and/or atypical symptoms were referred for the evaluation of GERD and underwent high-resolution manometry (HRM), in which 10 swallows with 5ml water were delivered in the supine position; this was followed by 5 swallows in the upright position. Subsequently, a 48-hour wireless pH test or 24-hour multichannel intraluminal impedance-pH (MII-pH) was performed. The pH probe was placed 5cm proximal to the upper border of the lower esophageal sphincter in both testing modalities. Isolated upright reflux was considered present when the supine fraction of time pH< 4 was 0; combined/supine reflux was present when the supine fraction of time pH< 4 was equal or greater than upright fraction time. Patients in who both the supine and upright fraction time pH<4 were 0, were excluded. Clinical presentation of patients was reviewed. Results: Between 12/2009 and 11/2010, 128 symptomatic patients (male 42, female 86, mean age 54.4 years) underwent bi-positional HRM. Of 128, 58 underwent 48-hour pH testing and 70 underwent 24-hour MII-pH. 36 patients (male 10, female 26, mean age 54.2 years, mean BMI 29.1) were identified as upright refluxers and 27 (male 10, female 17, mean age 53.9 years, mean BMI 26.2) exhibited combined/supine reflux. Nineteen of 36 (52.8%) of patients with upright reflux and 17 of 27 (63%) with combined/supine reflux had predominantly atypical symptoms such as cough or hoarseness. Although lower esophageal sphincter pressure (LESP) was significantly lower in upright than in supine in both groups, upright refluxers had significantly shorter LES length in upright than in supine. In 7 of 36 of upright (19.4%) and 4/27 of combined/supine refluxer (14.8%), a hiatal hernia was not present in supine, but appeared in upright position manometrically. DeMeester scores of upright refluxers were significantly lower than those of combined/supine refluxers (5.03±5.3 vs 26.2±5.2, p<0.0001). However, 22 of 36 (61.1%) upright refluxers were found to have either esophagitis, hiatal hernia or PPI-responsive symptoms. In addition, antireflux surgery (Nissen 6, esophagojejunostomy 1) was performed on 7 upright refluxers with objective evidence of GERD and a negative DeMeester score, all of whom showed complete symptomatic relief postoperatively. Conclusion: Isolated upright refluxers have lower LESP and shorter LES length in upright than in supine position. Symptomatic isolated upright refluxers are highly associated with a pathological GERD and would benefit from antireflux surgery even if pH testing is negative.

	isolated upright refluxers (n=36)			combined/supine refluxers (n=27)
	supine	upright	p-value	supine	upright	p-value
LESP	19.3 (10.6)	13.6 (12.7)	0.003	14.7 (6.9)	11.6 (8.8)	0.03
LES length	2.4 (0.6)	2.2 (0.6)	0.018	2.0 (0.4)	2.0 (0.6)	0.94

The valuables were reported as the mean and SD.