Patent GB-1352710-A (GB)
Title: Cardiac pacemaker
IPC: H03K3/53
Filed: 1971-12-15
Abstract: 1352710 Heart pacemakers CHRISTIAN ROVSING AS 15 Dec 1971 [22 Dec 1970] 58317/71 Heading A5R  A heart pacemaker which can be used to determine a patient's threshold value comprises a pulse generator for producing pacing pulses, of substantially fixed frequency, reduction means for the gradual reduction in predetermined steps of the amplitude of selected pacing pulses and means operable during operation of the pacemaker for connecting and disconnecting the reduction means. The pacemaker (see Fig. 3) has input leads 1, a blocking circuit B, an amplifier F, and a detector D which detects heart pulses. The detector triggers a 250 m.sec. monostable multivibrator. MV1 which emits a square pulse along the lead 3 to the reset entrance 4 of a resettable astable multivibrator in the form of a saw tooth oscillator O having an adjustable frequency of 50-90 cycles/min. If the oscillator does not receive a starting pulse from MV1 it activates a monostable multivibrator MV2 which produces square pulses of m.sec.This pulse triggers a monostable multivibrator MV3 which has a pulse time of 1.8 m.sec. and activates an output circuit U to emit pacing pulses via output leads 2. These control pulses from MV3 also pass via lead 7 to the blocking circuit B. The trigger pulses from MV2 are transmitted via lead 8 to a dosage circuit C which activates the output circuit via lead 9 to reduce successive pacing pulses according to a predetermined arithmetic or geumetric progression. The trigger pulses also pass via lead 10 to a restoration circuit R, which also receives the starting pulses for MV1 via lead 11. The restoration circuit generates restoring pulses along lead 12 only when it receives the trailing edge of a trigger pulse in the absence of a starting pulse. When this happens the dosage circuit C adjusts the output circuit U to emit a pacing pulse of full amplitude, due. to its receiving a slightly delayed restoring pulse via lead 13 and MV3. A lead 14 feeds trigger pulses from MV2 back to ocsiliator O to prevent it starting a new working cycle before the end of the trigger pulse. In the output circuit (see Fig. 4) a condenser C4 is connected in series with a transistor T4, the transistor T5 determining the potential to which C4 is charged after each pacing pulse. This depends on the voltage over condenser C3 in the dosage circuit which is controlled by the trigger pulses from MV2 which make transistor T3 conductive. C3 is also controlled by transistor T2 which is made conductive when transistor T1 is blocked, when no starting pulse is received from MV1, and C3 is then discharged to recharge C4 to its starting valve. The amplitude reduction may be activated externally, by a circuit DPM (see Fig. 5) which may be the detector and pulse generator of a demand pacemaker, and which emits pulses to MV3. A patient's threshold value may be determined by holding a permanent magnet M close to the pacemaker, to open a Reed contact RE1 in parallel with dosage condenser C3. The amplitude of successive pacing pulses drops by predetermined steps and by counting the number of pulses before the patient's pulse stops the threshold value is determined. In Fig. 6 (not shown) an electromaget is used. RE1 may be activated automatically by pulses detected by electrodes and a further multivibrator (MV4), Fig. 7 (not shown). RE1 may be controlled by a high frequency circuit in which oscillations are induced by a high frequency generator and coil, Fig. 8 (not shown). Ultrasonic waves and a piezo-electric crystal may be used, Fig. 9 (not shown).