is infused to the vascular or other system of a medical patient for example this novel fluid metering system 170 accordingly enables detection of subtle pressure differentials changes and rates of change such detection may be at the point of access of the body or alternatively simultaneously at multiple selected sites within the body whereas fluid metering may be grossly accomplished by varying the speed of the motor 75 alone with the enhanced dynamics introduced by the interplay between the pressure sensor 175 and the fluid restrictor 185 particularly when combined with refined flow rates accomplished with the selective variation in number of peristaltic channels utilized in the peristaltic mechanism 70 micro liter volumetric infusion of therapeutic liquids is enabled in the present embodiment with greater specificity continuity reliability and commensurate efficacy and safety than has heretofore been achievable more particularly set forth in fig7 is a signal processing feedback loop a strain gauge amplifier provides feedback signal so that the roller pump controller may establish the targeted fluid pressure at the roller pump exit chamber pressure developed upstream from the flow resistance or restriction stage is sensed with a pressure sensor which may be a strain gauge piezoelectric or similar micro circuit structure such as a four resistive element strain gauge bridge minute differential changes of resistance within the bridge result from changes in the mechanical force applied onto the strain gauge u201c beam u201d these resistance changes are detected and converted to a resultant output voltage by integrated circuit u 1 u 1 also provides a reference voltage used to maintain constant voltage across the strain gauge elements.