A self-regulating gastric band apparatus for adjusting stoma size. The apparatus includes an adjustable gastric band with an expandable inner ring. A band adjustment assembly includes a sensor for sensing fluid pressure in the inner ring and a pump assembly connected to the inner ring and to a controller for adjusting the volume of the fluid in the band based on the sensed fluid pressure. A memory stores an operating range of a target fluid pressure, and the pump assembly maintains the sensed band pressure within the operating range. An elongated fluid reservoir extends along part of a fill tube. An expandable fluid reservoir stores a volume of the fluid for adjusting the volume of fluid in the lumen. A protective outer sheath is provided around the exterior of an expandable fluid reservoir in both a first, deflated state, and a second, inflated state of the reservoir.
