US3738371A - Cardiac pacers with source condition-responsive rate - Google Patents

Cardiac pacers with source condition-responsive rate Download PDF

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Publication number
US3738371A
US3738371A US3738371DA US3738371A US 3738371 A US3738371 A US 3738371A US 3738371D A US3738371D A US 3738371DA US 3738371 A US3738371 A US 3738371A
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Prior art keywords
power supply
generating circuit
pulse generating
operatively connected
electrochemical cell
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English (en)
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J Smithmyer
W Raddi
R Johnson
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ESB Inc
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ESB Inc
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00—Electrotherapy; Circuits therefor
    • A61N1/18—Applying electric currents by contact electrodes
    • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
    • A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
    • A61N1/372—Arrangements in connection with the implantation of stimulators
    • A61N1/378—Electrical supply
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00—Electrotherapy; Circuits therefor
    • A61N1/18—Applying electric currents by contact electrodes
    • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
    • A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
    • A61N1/362—Heart stimulators
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K3/00—Circuits for generating electric pulses; Monostable, bistable or multistable circuits
    • H03K3/02—Generators characterised by the type of circuit or by the means used for producing pulses
    • H03K3/26—Generators characterised by the type of circuit or by the means used for producing pulses by the use, as active elements, of bipolar transistors with internal or external positive feedback
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K3/00—Circuits for generating electric pulses; Monostable, bistable or multistable circuits
    • H03K3/02—Generators characterised by the type of circuit or by the means used for producing pulses
    • H03K3/26—Generators characterised by the type of circuit or by the means used for producing pulses by the use, as active elements, of bipolar transistors with internal or external positive feedback
    • H03K3/30—Generators characterised by the type of circuit or by the means used for producing pulses by the use, as active elements, of bipolar transistors with internal or external positive feedback using a transformer for feedback, e.g. blocking oscillator

Definitions

  • ABSTRACT In a pulse generating circuit, such as an implantable cardiac pacer having parallel connected batteries as its power supply, additional resistors are connected be tween the power supply and the pulse generating circuit of the pacer and form a part of the pulse generating circuit to indicate by a change in pulse rate when one or more cells of the batteries of the power supply fail prematurely.
  • heart block is the reduction or complete lack of coordination in the beating of the atria and ventricles of the heart.
  • blood is pumped primarily by the contractions of the ventricles of the heart which are triggered by natural electrical signals originating in the atrium of the heart.
  • Physiological conditions which weaken or eliminate these natural signals result in a lack of coordination between the atria and ventricles and consequently, the natural pumping action of the heart is affected, at times resulting in death.
  • cardiac pacer have been developed to artifically stimulate the contraction of the ventricles with electrical pulses generated by the pacer. These pacers are implanted in the body of a patient along with batteries for pacer and electrical leads attached to the heart.
  • pacers utilize a set of five or six primary mercury cells connected in series as their power source. With such pacers, a change in pace or pulse rate reflects a change in battery volt- 45- age, for example, a rate decrease of several pulses per minute will indicate a drop in battery voltage, suggesting pacer replacement.
  • a pulse rate decrease in pacers that use five or six cells connected in series is an indication of battery exhaustion.
  • a disadvantage of such a configuration is that should an individual cell of the power source fail prematurely, it is possible for the failed cell to be driven by the other cells of the battery into potential reversal and thus generate internal gas pressure from the electrolysis of the electrolyte in the failed cell.
  • performance and reliability of such pacers are also affected as a result of reduced battery voltage. Consequently, when one or two cells fail in a conventional pacer utilizing a power supply of five or six series connected cells, future operation of the pacer be comes doubtful and the unit is preferably replaced.
  • Pacer longevity therefore, is not necessarily determined by the average cell life but instead it can and often times is limited by the performance of the weakest cell in the battery forming the power supply of the pacer.
  • the parallel connection of the cells or batteries is generally made through diodes or transistors such that when a cell or battery in one parallel branch fails prematurely the diode associated with that battery reverse biases thereby automatically disconnecting that battery from the load.
  • the voltage of the power supply supplying the pacer remains relatively unchanged and the operation of the pacer remains virtually unchanged.
  • pacers having parallel connected batteries as a power source will, near the end of life of the batteries of the power source, manifest a change in operation due to lower voltage which is reflected in a change in the pulse rate.
  • the invention provides apparatus that will indicate when one or more of the electro-chemical cells powering a pulse generating devices fails.
  • a pulse generating device having a power supply comprising a plurality of batteries connected in parallel wherein each battery is comprised of at least one electrochemical cell.
  • a pulse generating circuit is provided operatively connected across the power supply to translate the power supplied by the power supply into electrical impulses. Means are provided adapting the pulse generating circuit to generate pulses at a first frequency and, upon failure of at least one of the electrochemical cells of the power supply, to generate pulses at a second frequency different from the first frequency.
  • the apparatus in accordance with the invention,'is essentially free of the defects of the prior art devices having parallel connected batteries in that it provides an outward indication of cell or battery failure in the powersupply when such failure occurs.
  • the apparatus of the invention is an improvement over devices having five or six series connected cells as a power supply in that if a cell or battery of the power supply of the apparatus of the invention fails, there is an ample reserve of energy to permit continued operation of the pacer.
  • FIG. 1 is a schematic diagram of a prior art pacer having a power supply comprising a plurality of cells connected in parallel;
  • FIG. 2 is a schematic diagram of a pacer is accordance with the invention. 7
  • FIG. 3 is a bar graph illustrating the effect of cell failure in the pacer of FIG. 2.
  • FIG. 4 is a perspective view of the encapsulation container in which the circuit of FIG, 2 is housed.
  • the pacer 10 includes a power supply 12 comprising three parallel branches 14, 16 and 18 and the pacer circuitry shown at 19.
  • Each branch of the power supply comprises a battery preferably consisting of two electrochemical primary cells connected in series.
  • Each cell is preferably a l ampere-hour, medically cer- 'tified cell having a terminal voltage of approximately 1.38 volts at 25C.
  • Other suitable batteries may, of
  • the power supply described stores sufficient energy to operate the pacer 10 for a projected 5 year life.
  • Each parallel branch of the power supply includes a diode 20.
  • the diodes 20 are germanium diodes to minimize the forward voltage drop across them.
  • the diodes 20 effect the parallel connection of the bat,-
  • the pacer circuitry 19 includes the pulse generating circuit, shown generally at 22.
  • the pulse generating circuit 22 is connected across the power supply 12 to can be used to predict normal pacer failure or normal battery exhaustion.
  • the transistor 25 is of the NPN type and the transistor 26 is the PNP type. Both transistors have the usual emitter, collector and base 'electrodes. When the power supply charges capacitor 28 via resistors 30 and 32 sufficiently to forward bias the emitter base junction of the transistor 25, this transistor conducts.
  • the resistor 31 is connected between the emitter of transistor 25 and point 35. Since the collector of transistor 25 is connected to the base of transistor 26, it in turn causes transistor 26 to conduct. As transistor 26 conducts, current flows through the primary winding 33 of transformer 34 which induces a voltage in the secondary winding 36 of transformer 34.
  • the secondary winding is so connected that'the induced voltage further increases the base current supplied to transistor 25. This regenerative action causes a rapid pulse rate which continues until both transistors 25 and 26 are in saturation. Transistors 25 and 26 remain saturated for the duration of the pulse during which capacitor 28 is partially discharged. The width of the pulse thus produced is controlled primarily by the inductance of the transformer 34 and the capacitance of capacitor 28 with little dependence upon supply voltage.
  • the pulse appearing across the primary winding 33 of transformer 34 is coupled through resistor 40 to the base of transistor 42.
  • Transistor 42 acts as a switch which connects the voltage of the power supply, less the voltage drop across the diodes 20, via capacitor 43 to a simulated heart load, shown here as resistor 44, which is connected across the output terminals.
  • the resistor 46 discharges capacitor 43 between pulses.
  • the pacer circuit of FIG. 1 is characterized by the fact that the pulse repetition rate of the pulse generating circuit 22 is determined by the rate at which capacitor 28 charges to the base potential at which transistor 25 will conduct current.
  • the current that charges capacitor 28 is determined by the resistors 30 and 32. Accordingly, the values of the resistors 30, 32 and the value of the capacitor 28 may be considered as a RC timing means or circuit which determines the length of time between pulses, i.e., the pulse repetition rate. As described above, as the voltage of the power supply 12 decreases, the pulse rate will also decrease.
  • the pacer of FIG. 1 was modified as shown in FIG. 2.
  • FIG. 2 has included therein three resistors 50, 52, and 54.
  • Each of the resistors is connected at one end to the junction point 56 which in turn is connected to the junction point 58 between resistors 30 and 32.
  • the opposite end of each resistor 50, 52 and 54 is connected to one of the batteries of the power supply 12; the resistor 50 being connected to the point 60 between the battery of and the diode of parallel branch 18; the resistor 52 being connected to the point 62 between the battery and the diode 20 of parallel branch 16; and the resistor 54 being connected to the point 64 between the battery and the diode 20 of parallel branch 14.
  • resistors 50, 52 and 54 portions of the current that charge capacitor 28 in FIG. 2 are provided through the resistors 50, 52 and 54 in addition to the current provided through resistors 30 and 32, the latter resistors being the only ones in the charging path between the power supply 12 and the capacitor 28 in the circuit of FIG. 1.
  • the resistors 50, 52 and 54 therefore, form part of the RC timing circuit of pulse generating circuit 22 of FIG.
  • the portion of capacitor current provided by the specific resistor 50, 52, or 54 associated with the failed battery will be reduced which in turn will reduce the pulse rate of the pacer.
  • the modified pacer shown in FIG. 2 will, therefore, provide an outward indication of battery failure reflected in a reduction in pulse rate. This indication can be used to inform the patient or physician of impending pacer failure.
  • FIG. 3 is a bar graph illustrating the effect of catastrophic or irregular cell failure in the pacer of FIG. 2.
  • the failure mode in each situation was'simulated by replacing a cell of the various batteries of the power supply 12 with a short circuit.
  • the data given for three and four cells failed was obtained with one of the 2-cell batteries in one parallel branch intact.
  • FIG. 4 shows the circuit of FIG. 2 in an encapsulation container designated by the reference numeral 70.
  • the components of the circuit are assembled on a circuit board, not shown, and encapsulated in a suitable epoxy resin or other suitable body implantable material.
  • the container 70 may be surgically implanted in a body with the insulated unipolar transvenous catheter 72 connected to the heart at the desired location, preferably, the endocardium.
  • a large corrosive resistant metal anode plate functions as the catheter antipode and is physically located on the outer surface of the encapsulation container as is shown at 77. Saline body fluids complete the current path between catheter electrode 78 and the anode plate 77 when the pacer is implanted in the body.
  • the components of the described apparatus can have the following values.
  • an artificial cardiac pacer having a. a power supply comprising a plurality of batteries connected in parallel and wherein each battery is comprised of at least one electrochemical cell and,
  • a pulse generating circuit operatively connected across the power supply to translate the power supplied by the power supply into electrical impulses, and being operable to provide said electrical impulses to electrodes operatively connected to a patients heart
  • the improvement comprising, means for causing the pulse generating circuit to generate pulses at a first frequency and, upon failure of any of the batteries of the power supply, to generate pulses at a second frequency different from the first frequency;
  • the power supply being further characterized as having at least two parallel branches, each parallel branch of the power supply having disposed therein at least one electrochemical cell, and at least one semiconductor means operatively connected with the electrochemical cell, the semiconductor means in each parallel branch being arranged to permit current flow therethrough from the electrochemical cell connected therewith to the pulse generating circuit and to prevent current flow therethrough from the electrochemical cells in other parallel branches of the power supply, said means for causing the pulse generating circuit to generate pulses at a first frequency and, upon failure of any of the batteries of the power'supply, to generate pulses at a second frequency different from the
  • each resistor is operatively connected to a parallel branch of the power supply at a point between the electrochemical cell and the semiconductor means disposed in each parallel branch of the power supply.
  • a body implantable artificial cardiac pacer comprising a. a body compatible implantable insulating encapsulation container,
  • a power supply in the encapsulation container comprising at least two parallel branches, each parallel branch of the power supply having disposed therein at least one electrochemical cell and at least one semiconductor means in series circuit with the electrochemical cell,
  • a semiconductor pulse generating circuit in the encapsulation container operatively connected across the power supply to translate the power supplied by the power supply into electrical impulses and being operable to provide said electrical impulses to electrodes operatively connected to a patients heart
  • the semiconductor means in each parallel branch being arranged to permit current flow therethrough from the electrochemical cell in series circuit therewith to the pulse generating circuit and to prevent current flow therethrough from the electrochemical cells in other parallel branches of the power supply, and
  • timing means in the encapsulation container operatively connected to the power supply and forming a part of the pulse generating circuit to govern the pulse repetition rate of the pulses generated by the pulse generating circuit and, upon failure of any of the electrochemical cells of the power supply to vary the pulse repetition rate of the pulse generating circuit; said timing means including at least a pair of resistors, each of the resistors being operatively connected to a different parallel branch of the power supply at a point between the electrochemical cell and the semiconductor means disposed in each parallel branch of the power supply.
  • an artificial cardiac pacer having a. a power supply comprising a plurality of batteries connected in parallel and wherein each battery is comprised of at least one electrochemical cell and,
  • a pulse generating circuit operatively connected across the power supply to translate the power supplied by the power supply into electrical impulses, and being operable to provide said electrical impulses to electrodes operatively connected to a patient's heart
  • the improvement comprising, means including circuit means operatively connected to each of the batteries and to the pulse generating circuit and forming a part of the pulse generating circuit for causing the pulse generating circuit to generate pulses at a first frequency and, upon failure of any of the batteries of the power supply, to generate pulses at a second frequency different from the first frequency.
  • a body implantable artificial cardiac pacer comprising a. a body compatible implantable insulating encapsulation container,
  • a power supply in the encapsulation container comprising at least two parallel branches, each parallel branch of the power supply having disposed therein at least one electrochemical cell and at least one semiconductor means in series circuit with the electrochemical cell,
  • a semiconductor pulse generating circuit in the encapsulation container operatively connected across the power supply to translate the power supplied by the power supply into electrical impulses and being operable to-provide said electrical impulses to electrodes operatively connected to a patient heart
  • the semiconductor means in each parallel branch being arranged to permit current flow therethrough from the electrochemical cell in series circuit therewith to the pulse generating circuit and to prevent current flow therethrough from the electrochemical cells in other parallel branches of the power supply
  • timing means including means operatively connected to each branch of the power supply and to the pulse generating circuit and forming a part of the pulse generating circuit in the encapsulation container for governing the pulse repetition rate of the pulses generated by the pulse generating circuit and, upon failure of any of the electrochemical cells of the power supply to vary the pulse repetition rate of the pulse generating circuit.
  • a power supply comprising a plurality of batteries connected in parallel and wherein each battery has substantially the same terminal voltage andis comprised of at least one electrochemical cell and,
  • a pulse generating circuit operatively connected across the power supply to translate the power supplied by the power supply into electrical impulses
  • the improvement comprising, means for causing the pulse generating circuit to generate pulses at a first frequency and, upon failure of any of the batteries of the power supply, to generate pulses at a second frequency different from the first frequency.
  • a body implantable artificial cardiac pacer comprising a. a body compatible implantable insulating encapsulation container,
  • a power supply in the encapsulation container comprising at least two parallel branches, each parallel branch of the power supply having disposed therein at least one electrochemical cell and at least one semiconductor means in series circuit with the electrochemical cell, each electrochemical cell having substantially the same terminal voltage,
  • a semiconductor pulse generating circuit in the encapsulation container operatively connected across the power supply to translate the power supplied by the power supply into electrical impulses and being operable to provide said electrical impulses to electrodes operatively connected to a patients heart
  • the semiconductor means in each parallel branch being arranged to permit current flow therethrough from the electrochemical cell in series circuit therewith to the pulse generating circuit and to prevent current flow therethrough from the electrochemical 'cells in other parallel branches of the power supply
  • pulse generating circuit and, upon failure of any of the electrochemical cells of the power supply to vary the pulse repetition rate of the pulse generating circuit.

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  • Health & Medical Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Cardiology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Power Engineering (AREA)
  • Electrotherapy Devices (AREA)
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US3738371D 1970-12-11 1970-12-11 Cardiac pacers with source condition-responsive rate Expired - Lifetime US3738371A (en)

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US9725470A 1970-12-11 1970-12-11

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US (1) US3738371A (pt)
BE (1) BE776557A (pt)
BR (1) BR7108014D0 (pt)
CA (1) CA984467A (pt)
CH (1) CH546573A (pt)
DE (1) DE2160727A1 (pt)
DK (1) DK143934C (pt)
FR (1) FR2117641A5 (pt)
GB (1) GB1303016A (pt)
IT (1) IT953203B (pt)
SE (1) SE383259B (pt)
ZA (1) ZA717641B (pt)

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3882322A (en) * 1973-01-26 1975-05-06 Medtronic Inc Pulse generator
US3893462A (en) * 1972-01-28 1975-07-08 Esb Inc Bioelectrochemical regenerator and stimulator devices and methods for applying electrical energy to cells and/or tissue in a living body
US3946375A (en) * 1974-10-07 1976-03-23 The Boeing Company Redundant DC power supply for analog computers and the like
US4120307A (en) * 1976-10-26 1978-10-17 Medtronic, Inc. Cardiac pacemaker
US4276883A (en) * 1978-11-06 1981-07-07 Medtronic, Inc. Battery monitor for digital cardiac pacemaker
US4345603A (en) * 1980-02-19 1982-08-24 Pacesetter Systems, Inc. Implantable battery monitoring means and method
US4390020A (en) * 1983-02-17 1983-06-28 Medtronic, Inc. Implantable medical device and power source depletion control therefor
US4728807A (en) * 1984-08-02 1988-03-01 Nec Corporation Power source system comprising a plurality of power sources having negative resistance characteristics
US4958632A (en) * 1978-07-20 1990-09-25 Medtronic, Inc. Adaptable, digital computer controlled cardiac pacemaker
US5076272A (en) * 1990-06-15 1991-12-31 Telectronics Pacing Systems, Inc. Autocontrollable pacemaker with alarm
US6149683A (en) * 1998-10-05 2000-11-21 Kriton Medical, Inc. Power system for an implantable heart pump
US20040210272A1 (en) * 2002-07-26 2004-10-21 John Erickson Method and system for energy conservation in implantable stimulation devices
US6871090B1 (en) * 2000-10-13 2005-03-22 Advanced Bionics Corporation Switching regulator for implantable spinal cord stimulation

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2913399A1 (de) * 1979-03-31 1980-10-09 Biotronik Mess & Therapieg Schaltung zur kontrolle des batteriezustands bei einem herzschrittmacher
DE69500673T2 (de) 1994-05-19 1998-03-19 Mitsubishi Chem Corp Arzneimittel zur therapeutischen und prophylaktischen Behandlung von Krankheiten, die durch Hyperplasie der glatten Muskelzellen bedingt sind

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3454012A (en) * 1966-11-17 1969-07-08 Esb Inc Rechargeable heart stimulator
US3474353A (en) * 1968-01-04 1969-10-21 Cordis Corp Multivibrator having pulse rate responsive to battery voltage
US3620220A (en) * 1969-10-01 1971-11-16 Cordis Corp Cardiac pacer with redundant power supply

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3454012A (en) * 1966-11-17 1969-07-08 Esb Inc Rechargeable heart stimulator
US3474353A (en) * 1968-01-04 1969-10-21 Cordis Corp Multivibrator having pulse rate responsive to battery voltage
US3620220A (en) * 1969-10-01 1971-11-16 Cordis Corp Cardiac pacer with redundant power supply

Cited By (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3893462A (en) * 1972-01-28 1975-07-08 Esb Inc Bioelectrochemical regenerator and stimulator devices and methods for applying electrical energy to cells and/or tissue in a living body
US3882322A (en) * 1973-01-26 1975-05-06 Medtronic Inc Pulse generator
US3946375A (en) * 1974-10-07 1976-03-23 The Boeing Company Redundant DC power supply for analog computers and the like
US4120307A (en) * 1976-10-26 1978-10-17 Medtronic, Inc. Cardiac pacemaker
US4958632A (en) * 1978-07-20 1990-09-25 Medtronic, Inc. Adaptable, digital computer controlled cardiac pacemaker
US5318593A (en) * 1978-07-20 1994-06-07 Medtronic, Inc. Multi-mode adaptable implantable pacemaker
US4276883A (en) * 1978-11-06 1981-07-07 Medtronic, Inc. Battery monitor for digital cardiac pacemaker
US4345603A (en) * 1980-02-19 1982-08-24 Pacesetter Systems, Inc. Implantable battery monitoring means and method
US4390020A (en) * 1983-02-17 1983-06-28 Medtronic, Inc. Implantable medical device and power source depletion control therefor
US4728807A (en) * 1984-08-02 1988-03-01 Nec Corporation Power source system comprising a plurality of power sources having negative resistance characteristics
US5076272A (en) * 1990-06-15 1991-12-31 Telectronics Pacing Systems, Inc. Autocontrollable pacemaker with alarm
US6149683A (en) * 1998-10-05 2000-11-21 Kriton Medical, Inc. Power system for an implantable heart pump
US6592620B1 (en) 1998-10-05 2003-07-15 Kriton Medical, Inc. Power system for an implantable heart pump
US6871090B1 (en) * 2000-10-13 2005-03-22 Advanced Bionics Corporation Switching regulator for implantable spinal cord stimulation
US20040210272A1 (en) * 2002-07-26 2004-10-21 John Erickson Method and system for energy conservation in implantable stimulation devices
US7047079B2 (en) * 2002-07-26 2006-05-16 Advanced Neuromodulation Systems, Inc. Method and system for energy conservation in implantable stimulation devices
US20060200210A1 (en) * 2002-07-26 2006-09-07 John Erickson Method and system for energy conservation in implantable stimulation devices
US7584000B2 (en) 2002-07-26 2009-09-01 Advanced Neuromodulation Systems, Inc. Method and system for energy conservation in implantable stimulation devices
US20090292339A1 (en) * 2002-07-26 2009-11-26 John Erickson Method and system for energy conservation in implantable stimulation devices
US7979132B2 (en) 2002-07-26 2011-07-12 Advanced Neuromodulation Systems, Inc. Method and system for energy conservation in implantable stimulation devices
US8209020B2 (en) 2002-07-26 2012-06-26 Advanced Neuromodulation Systems, Inc. Method and apparatus for providing complex tissue stimulation patterns
US8433416B2 (en) 2002-07-26 2013-04-30 Advanced Neuromodulation Systems, Inc. Method and apparatus for providing complex tissue stimulation patterns

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SE383259B (sv) 1976-03-08
FR2117641A5 (pt) 1972-07-21
BR7108014D0 (pt) 1973-06-05
ZA717641B (en) 1972-08-30
IT953203B (it) 1973-08-10
CA984467A (en) 1976-02-24
BE776557A (fr) 1972-04-04
DK143934B (da) 1981-11-02
DE2160727A1 (de) 1972-06-15
CH546573A (fr) 1974-03-15
DK143934C (da) 1982-04-19
GB1303016A (pt) 1973-01-17

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