GB1394171A - Blood glucose level monitoring-alarm system and method therefor - Google Patents

Abstract

1394171 Surgical implants WHITTAKER CORP 16 May 1973 23456/73 Heading A5R [Also in Divisions H1 G1 and G3] The blood glucose level of a human body is monitored by an implanted glucose diffusion-limited cell 10. A membrane 14 (materials are exemplified) which permits free transmission of oxygen and glucose &c but impedes the diffusion of large macro-molecules defines a chamber 16 within which are positioned metal catalyst coated anode 18 and cathode 20, body fluid within the chamber acting as an electrolyte. Cathode 20 has a larger surface area than the anode 18 and is covered with a thin layer of membrane 22 which allows free passage of water, oxygen &c but strongly resists the diffusion of glucose molecules so that it serves as an oxygen electrode. The anode 18 is covered with a relatively thick layer 24 of porous plastics material which impedes the diffusion of glucose. Thus the rate of oxygen molecules arriving at the cathode is always larger than the rate of glucose impingement on the anode surface and the current that can be drawn from the cell 10 is proportional to the diffusion of glucose molecules and hence to the concentration of glucose in the body fluid which is in turn proportional to the concentration of glucose in the blood. The anode and cathode catalyst materials are different, suitable materials for the anode being platinum black or group VIII transition metals and for the cathode Group Ib metals such as gold, silver Anion and/or cation exchange membrane may be interposed directly between the two electrodes to serve as a solid electrolyte as well as a partition for two half cells. Circuitry. The output current from cell 10 is after amplification 30 applied to a current to frequency converter 32 connected to a pulse code modulation transmitter 34, Fig. 3 (not shown) so that the blood glucose level signal may be transmitted to an appropriate receiver, Fig. 4 (not shown) outside the body. The receiver circuit includes a voltage comparator which compares the blood glucose level with a voltage or a range of voltages which represent a natural or desired level. If the level goes outside the range an alarm may be operated to signify the requirement of addition of glucose or insulin in a diabetic and appropriate values are actuated to add the glucose or insulin. Degradation of the platinum anode surface is counteracted by using a third biased electrode and cycling the anode from anodic to cathiodic using pulses. Instead of monitoring the output current of the fuel cell other characteristics which may be measured include the rate of potential rise in a cell on charging the temperature rise due to glucose oxidation, the change in pH value as a result of the formation of gluconic acid and the reduction of oxygen tension as a result of O 2 consumption.