Implantable infusion apparatus and method

Claim 1

Implantable infusion apparatus comprising A. a housing, B. a variable volume main infusate reservoir positioned in the housing, C. a variable volume auxiliary infusate reservoir positioned in the housing, said auxiliary reservoir having a smaller volume than said main reservoir, D. a first fluid passage communicating between the main reservoir and the auxiliary reservoir, E. a second fluid passage communicating from the auxiliary reservoir exteriorly of said housing, F. valve means mounted inside the housing, said valve means being movable between a first position that opens said first passage while closing the second passage and a second position that closes the first passage while opening the second passage, G. a confined fluid under pressure acting on the main reservoir tending to reduce its volume and thereby pressurize the infusate therein to a first pressure, H. a confined fluid under pressure acting on the auxiliary reservoir tending to reduce its volume and thereby pressurize the infusate therein to a second pressure less than the first pressure so that (1) when the valve means is in its said first position, infusate flows from the main reservoir to the auxiliary reservoir whereupon, due solely to the higher pressure of the infusate in the main reservoir, the auxiliary reservoir volume is enlarged thereby raising the pressure of the confined fluid acting on that reservoir, and (2) when the valve is in its second position, infusate flows from the auxiliary reservoir through the second fluid passage whereupon, due solely to the raised pressure of the confined fluid acting on the auxiliary reservoir, the volume of the auxiliary reservoir is reduced thereby forcing infusate from the auxiliary reservoir through the second fluid passage, and I. means for moving the valve means between its two positions.