EP0089014A2 — Physiological implantable cardiac pacemaker in wh…

Claim 1

Independent Claim 314 words

1) An implantable heart pacemaker in which the rate of stimulation is regulated by the patient's ventila= tion rate, detected by measuring the impedance variations of a suitable distance within the body of said patient, usually a distance inside the thoracic area, characterized by the fact of comprising: - an impedance/current conversion unit that detects the impedance variations of the human body depending upon the respiration act and transforms them into a corresponding analogical signal; - a signal extration unit that can change a disturbed signal coming from the unit afore mentioned, into a clear and perfectly repetitive signal, for example, a clipped signal, that presents a transition each time the input signal exceeds a prefixed value which is preferred for programming, all of this so as to eliminate improper signals to make sure that the ventilation rate will be easily and correctly detected from the new signal extracted; - a programmable unit, that correlates in a linear way the heart stimulation rate of the pacemaker to the respiratory rate (RR) which is detected from the output signal of the unit mentioned in the preceding point, since the said unit has a converter that transforms the number or quantity of impulses that reach it periodi= cally at the corresponding intensity of current (1CH); - a traditional pacemaker unit, for example a demand type circuit, to which the output current is supplied by the ' unit mentioned in the preceding point, and is used for artificial stimulation of the heart at a rate included between the minimum and maximum programmable values if the spontaneous EKG signal is absent; - a means to program the variabilities of the units mentioned in the preceding point from a distance, in order to adapt the entire device to the patient's needs; - a means that supplies the voltage and necessary timing so that the said device will work properly.

Claim 2

Dependent Claim 314 words

1) An implantable heart pacemaker in which the rate of stimulation is regulated by the patient's ventila= tion rate, detected by measuring the impedance variations of a suitable distance within the body of said patient, usually a distance inside the thoracic area, characterized by the fact of comprising: - an impedance/current conversion unit that detects the impedance variations of the human body depending upon the respiration act and transforms them into a corresponding analogical signal; - a signal extration unit that can change a disturbed signal coming from the unit afore mentioned, into a clear and perfectly repetitive signal, for example, a clipped signal, that presents a transition each time the input signal exceeds a prefixed value which is preferred for programming, all of this so as to eliminate improper signals to make sure that the ventilation rate will be easily and correctly detected from the new signal extracted; - a programmable unit, that correlates in a linear way the heart stimulation rate of the pacemaker to the respiratory rate (RR) which is detected from the output signal of the unit mentioned in the preceding point, since the said unit has a converter that transforms the number or quantity of impulses that reach it periodi= cally at the corresponding intensity of current (1CH); - a traditional pacemaker unit, for example a demand type circuit, to which the output current is supplied by the ' unit mentioned in the preceding point, and is used for artificial stimulation of the heart at a rate included between the minimum and maximum programmable values if the spontaneous EKG signal is absent; - a means to program the variabilities of the units mentioned in the preceding point from a distance, in order to adapt the entire device to the patient's needs; - a means that supplies the voltage and necessary timing so that the said device will work properly.

Claim 3

Dependent Claim 61 words

2) A pacemaker according to claim 1, characte= rized by the fact that the circuit that measures the thoracic impedance consists of two leads; one that coincides preferably with the external case and is in common with one of the leads that stimulate the heart, while the other is inserted subcutaneously at a correct but not critical distance from the latter.

Claim 4

Dependent Claim 94 words

3) A pacemaker according to claim l, characte= rized by the fact that it comprises a means that applies at the tip of the leads that measure the thoracic impedance, a very short impulse of the needed intensity with a very high ratio between the period of repetition and width, i.e. 1 to 1000, so that the system for measuring the impedance will have a reduced current drain and can therefore be supplied by the same cell that supplies energy to the implanted pacemaker without compromising the normal independent life of the said cell.

Claim 5

Dependent Claim 76 words

4) A pacemaker according to claim 3, characte= rized by the fact that the circuit that generates the current at the suitable intensity needed measuring the thoracic impedance is activated by a short signal, for instance around 100 psec and repeats at much wider intervals, for instance around 100 msec, so that the generator mentioned will turn off and not drain current when the said signal is low thus giving the pacemaker a longer independent life.

Claim 6

Dependent Claim 70 words

5) A pacemaker according to claim 3, characte= rized by the fact that it comprises a means by which the same signal that pilots the current generator for thoracic impedance measuring, when it lowers and de-activates the said generator, will activate a static switch in opposition that short circuits the leads of said measuring circuit because the impedance between them is not a pure resistance and could therefore cause inconveniences.

Claim 7

Dependent Claim 275 words

6) A pacemaker according to claim 1, characte= rized by the fact that: - the output of the thoracic impedance measuring circuit, varying accordingly to the amplitude of the respiratory act in the patient, opportunely shifted, is sent to the first input of an amplifier; - the said amplifier is preferably part of a modified delta modulator; - the output of the said amplifier is sent to one of the input of a first comparator whose second input is wired to a reference voltage (V A ) equal to the half at the supply voltage; - the output of the comparator is sent to the reset of a flip-flop; - a signal (D) with the same characteristics (except for the phase) of the signal (A) which activates the constant current generator in the thoracic impedance meter, is sent to the set of the said flip-flop; - the output of the said flip-flop is wired to the second input of the first amplifier, above mentioned, by means of a RC network whose time constant is of suitable value; - all of the above realized so that, if V is the first input of the first amplifier, V C the second input of the same amplifier, V H the output, the peaks envelope average value of V H equals V A , that is the second amplifier input, that is V H = A O |I C - V X where A O is the amplifier gain; - the above mentioned time constant has a high enough value so that the whole circuit will be able to adopt itself to the slow variation of the thoracic impedance.

Claim 8

Dependent Claim 139 words

7) A pacemaker according to claim 6, character rized by the fact that the output (V H ) of the first amplifier in the modified delta modulator as mentioned above, is also sent to the input of a second comparator Whose second input is wired to a reference voltage (V ) having a higher value than the reference threshold (VA) of the first comparator mentioned in the preceding claim, in order to create a sensitivity control circuit capable of discriminating between consistent and inconsistent variations of the thoracic impedance since at the first comparator's output there will be a signal indicated as V J that will go high only when V H exceeds V A , while at the second comparator's output there will be a V K signal that will go high only when V exceeds V .

Claim 9

Dependent Claim 82 words

8) A pacemaker according to claim 7, characteri= zed by the fact that the amplifiers used in the amplifying and comparing circuit are programmable amplifiers that are over-supplied in phase with the impulse that measures the thoracic impedance, so as to have the adequate slew-rate at the time in which such amplifiers must intervene, all of this has been studied in order to contain energy consumption by the device here described and so as to make it fit for an implantable pacemaker.

Claim 10

Dependent Claim 82 words

9) A pacemaker according to claim 7, characte= rized by the fact that the signals V J and V K at the output from two comparators are sent to a further comparator created in any suitable way so as to have a VOUT signal at its output that goes high at the first positive impulse of V K and remains high as long as positive impulses of V J exist and goes down when, after the sampling interval, V J returns down.

Claim 11

Dependent Claim 59 words

10) A pacemaker according to claim 9, characte= rized by the fact that deriving from the time constant resistor of the modified delta modulator, as already stated, another resistor with lower values is provided that is temporarily and automatically inserted when the pacemaker is activated so that the elaboration circuit of the thoracic impedance variations reaches functioning conditions rapidly.

Claim 12

Dependent Claim 83 words

11) A pacemaker according to claim 1, characte= rized by the fact that the (V DUT ) signal, that goes high as many times as the respiration acts considered consistent, is sent to a means of any suitable kind and nature in order to create a relation, which is linear and can be chosen within a limited field with pre-established values, between the number of respiration acts and the inhibition rate and/or the atrial and/or ventricular stimulation rate of any suitable pacemaker circuit.

Claim 13

Dependent Claim 79 words

12) A pacemaker according to claim 1, characte= rized by the fact of comprising suitable means for the dialogue of its significant parameters with the outside; that is, it includes devices that transmit information on the respiration acts to the outside and systems that receive from the outside the programming impulses necessary to modify the device's sensitivity to the intensity of the respiration act and to choose the co-relation function between ventilation and inhibition rate and/or pacemaker stimulation rate.

Claim 14

Dependent Claim 43 words

13) A pacemaker according to claim 12, characte= rized by the fact that the programming impulses of suitable rate coming from the outside act upon a recognition device, with a safety code, that when activated starts the function as described at claim 10.

Claim 15

Dependent Claim 90 words

14) A pacemaker according to claim 13, in which, when passing the safety code device, the programming impulses are sent to a circuit that can supply the thresholds (V A and V B ) to the recognition and detection system of the ventilation rate and can supply the variables that permit the selections among the possible working curves, of the curve that expresses the relation between the ventilation rate and the inhibition rate and/or the stimulation that from time to time is most suitable for the patient with this pacemaker.

Claim 16

Dependent Claim 48 words

15) A pacemaker according to claim 14, characte= rized by the fact that when safety code device is passed the programming can, preferably as a last choice, disable the pacemaker from detecting the thoracic impedance variations and make it work with a fixed or a programmed reference rate.

Claim 17

Dependent Claim 43 words

16) A pacemaker according to claim l, characte= rized by the fact that for obvious safety reasons it includes means, which will not allow the stimulation and/or inhibition rate from going beyond the maximum and minimum limit independently of the respiration rate variations.

Physiological implantable cardiac pacemaker in which the stimulation rate is regulated by the respiration rate of the patient

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