Bipedes is bipedestación, I think, and means standing:

Utilidad de la manometría de alta resolución en el ... - Semantic Scholar
https://pdfs.semanticscholar.org/722b/2b1bc49f9e7ae8b930a5be...
de CC de los Ríos - ‎2014 - ‎Citado por 3 - ‎Artículos relacionados
6 may. 2013 - pH-metría de 24 horas sin inhibidores de la bomba de protones. Se evaluaron ... en el periodo total (p = 0,015), en bipedestación (p = 0,022) y supino (p ... 0.015), standing (p = 0.022) and supine (p = 0.001) in patients with GEJ type II .... tiempo pH < 4 en supino en el canal distal y proximal, la puntuación ...

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Note added at 1 hr (2017-10-23 17:21:44 GMT)
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More information to fit in with the other part (episodios de reflujo) which has been answered:

Trastornos motores del aparato digestivo
https://books.google.es/books?isbn=849835112X
Manuel Díaz-Rubio, ‎Enrique Rey Díaz-Rubio - 2007 - ‎Medical
Se caracterizan por presentar un elevado número de episodios en bipedestación
RGE con predominio en bipedestación en un paciente con esofagitis de grado A. Episodios de reflujo en bipedestación y decúbito. postprandial.




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Note added at 1 hr (2017-10-23 17:37:28 GMT)
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Standing position is another way of saying it:

The Role of Esophageal pH-metri Test on Gastro-Esophageal ... - Neliti
https://media.neliti.com/.../66330-EN-the-role-of-esophageal...
de K Setyawati - ‎Artículos relacionados
The Role of Esophageal pH-metri Test on ... pH monitoring test is the gold standard diagnostic test to assess gastric acid .... (2) pH percentage < 4 during standing position

https://books.google.es/books?isbn=274200145X
Robert Giuli - 1998 - ‎Esophagogastric junction
The main examination is pH monitoring performed with a single electrode or, preferably with two [ 1 ], one ... subsequent to reflux (33/78 patients had increased reflux in standing position). Treatment also constitutes a therapeutic test. ... A clinical investigation of 225 patients using ambulatory 24-hour pH monitoring