Conclusions  In normal individuals, the GEV exhibits a temporary weakening when moved from LLD to upright position. However, the normal GEV is able to maintain LESP in upright position. In contrast, in patients with early GERD, a greater degree of valve incompetence at the GEJ is seen. This is correlated manometrically with a trend toward shorter LES length and lower LESP when moved from LLD to upright position. This upright incompetence of the GEV may be one of the earliest manifestations in GERD. Proper evaluation of the GEV should include endoscopic evaluation in both recumbent and upright positions. Further studies are needed to evaluate the corresponding changes of the GEV in varying degrees of symptomatic GERD. Content Type Journal ArticleDOI 10.1007/s00464-01...