Patent GB-1398875-A (GB)
Title: Implantable electromedical apparatus
IPC: A61N1/372
Filed: 1972-07-24
Abstract: 1398875 Implantable electro-medical stimulators MEDTRONIC INC 24 July 1972 [26 July 1971] 34519/72 Heading A5R [Also in Division H3] An implantable electromedical stimulator, such as a device for treating cardiac disorders, particularly a pacemaker, a nerve or muscle stimulator, a brain stimulator, a dorsal column stimulator or a skeletal tissue stimulator, has first 40, Fig 1 and second 70 stores each capable of storing a multiplicity of binary data bits, a r.f. receiver 10 and decoder 20 connected to store 40 for selectively charging data therein and arranged for receiving coded data signals from an r.f. transmitter and encoder, Fig 3, a clock 80, Fig 1, for continually charging data in store 70, means 50 for comparing data in the stores 40, 70 and providing a signal in the presence of a predetermined comparison, and means 90, 100 responsive to receiving said signal for providing a stimulation signal. Stores 40 and 70 are in the form of counters. To prevent noise signals from having unwanted effects, the r.f. transmitted data signals consist of an r.f. pulse train (A) Fig 2 (not shown), which to be effective and enable a gate 36 must last for a period of between a maximum period determined by R-C circuit 31, 27 and a minimum period determined by R-C circuit 22, 26, the gate 36 then being enabled for a period determined by R-C circuit 37, 34 during which period a plurality of r.f. pulse trains (B) are transmitted, each train (B) giving rise to an envelope pulse at the output of circuit 10, this pulse passing through gate 36 to change the count in memory counter 40 by one. Counter 40 is initially reset to zero at the trailing edge of the envelope pulse produced at the output of circuit 10 in response to the r.f. pulse train (A). Every second time outputs 42-45 of counter 40 are the same as outputs 72-75 of the counter 70 a signal from inverter 69 activates a one-shot multivibrator 90 to give an output to circuit 100 so producing a stimulating pulse. The output of one-shot 90 also resets counter 70. The state of outputs 42-45 determine the stimulating pulse rate, the pulse width being determined by R-C circuit 99,98 and being adjustable by varying the data in counter 40 so that one or more of resistors 123, 125, 127 are shunted across resistor 99. The apparatus may also be arranged so that the pulse amplitude can be controlled by the state of counter 40. A modified embodiment employs a logic circuit (450), Fig 4 (not shown) comparing data in a memory counter with data in a clock counter to determine the stimulating pulse rate, and a circuit (490) comparing data in these counters to determine the stimulating pulse width. The clock counter may be reset by an external reset signal so that for example, the apparatus can act as a a demand pacemaker. AN R.F. TRANSMITTER for charging the memory counter 40 comprises an oscillator 230, Figure 3, producing pulse trains in a coil 231 for periods determined by a circuit 220. On closing a switch 203 a one-shot multivibrator 200 is actuated and causes resetting of a counter 270 and the transmission of the pulse train (A) which lasts for a period determined by an R-C circuit 215, 214, thereafter a gated clock 250 is activated to cause transmission of the pulse trains (B), the pulse train repetition rate being determined by the clock. The number of trains (B) transmitted is selected by switches 281, 291, thus selecting the stimulating pulse rate and pulse width. Switches 281, 291 connect selected diodes 282, 292 between a bus 301 and outputs 271-277 of the counter 270, which counts the clock output, so that when the counter reaches a count selected by switches 281, 291 a locking gate 240 stops the clock 250, thus stopping transmission of the pulse trains (B), gate 240 and clock 250 being turned on when one-shot 200 reverts to its normal state at the end of pulse train (A).