An implantable medication infusion unit wherein a generally cylindrical manifold (20) is employed having a shallow recess (28) on one face thereof. A flexible diaphragm (26) is positioned to form with the face of said manifold a medication reservoir (30). A circular cover member (24) is positioned over the diaphragm to form with said diaphragm a pressure stabilizing chamber (32) within which is positioned a two-phase fluid for maintaining a constant pressure on said diaphragm. A permanent magnet (42) is positioned at the center of said diaphragm and is movable therewith. A Hall effect transducer (34) positioned on said manifold opposite said permanent magnet is employed continuously to measure the position of said diaphragm and provide an indication of the amount of medication in said reservoir (30).
A method of filling and sealing the pressure stabilizing chamber (32) which ensures that a small bubble of two-phase fluid is present in said chamber at all times.
An inlet filter (100) may be positioned between the medication reservoir (30) and an inlet check valve (102) to act as a bubble trap during the intake stroke of a pulsatile pumping unit also mounted in the manifold.