Electronic circuit detecting respiratory parameters in implantable devices, such as implantable and physiologic pacemakers

Claim 2

An electronic circuit to detect respiratory parameters in devices implantable in a patient's body, such as for example implantable cardiac pacemakers of the type described in European application EP-A2-0 089 014 and in Italian patent application 12421 A/84, and comprising: a measurement and impedance/voltage conversion unit (10) which detects the impedance variations (ZL) of a part of the patient's body depending on respiration and turns them into a corresponding analog signal with sampling signals lasting about 122 )1s and repeated at intervals of about 125 ms; a unit (20) which extracts from the noisy output signal from the previous unit a clean and regular signal, for example a squared one, from which it is easier to obtain the right variable proportional to the respiratory parameter chosen, said variable is then used to physio= logically control the electrostimulation circuit, characterized in that it is designed to make up said signal extracting unit (20) and to include the means that at the sample rate of the body impedance detect the time variations (Δ) of the voltage corresponding to the impedance measurement (ZL) taken from time to time being said variation either positive or negative with regard to the line corresponding to the so called base impedance.

Claim 3

The electronic circuit according to claim 1, characterized in that the adequate translated voltage (V H ) in output from the chest impedance variation measuring circuit and with respiration depending variations is sent to a differential amplifier (Ul) which compares that signal with the charge voltage of a capacitor (Cx), the output of the amplifier being connected, with an in--between electronic switch (SW1) driven by a signal (Q) in phase with that (A) of the body impedance variation sample, to the plate of a second capacitor (Cy) and is also connected by shunt to the comparator (U2) output, with a constant reference voltage (-V/2) being supplied to the second input, being also designed for the non grounded plates of said capacitors to be connected one to the right contact and to the left one and the other to the left contact and to the right one of a couple of electronic deviators (SW5-SW6) to the common poles of which two equal and opposite constant current sources (Io+, Io-) controlled by the same very fast clock (CKo) signal, one charging and the other discharging, are connected, with in between the relevant electronic switches (SW2-SW3), being the deviators and their relevant switches controlled by the connection to zeroing logic group (LU) outputs (CH, DIS and EN) the main input of which is connected to the comparator (U2) output and the start input (GO) is supplied with a signal (B) which is adequately out of phase with the body impedance sample signal but with the same recurrence period; the whole in such a manner that at the time of each body impedance sample, switch (SW1) upstream from the differential amplifier is closed so that the second capacitor (Cy) changes its charge due to the properly amplified difference that will be between the body impedance sample voltage and the voltage of the first capacitor (Cx), after that said switch (SW1) is opened and a start pulse (B) is supplied to said zeroing logic group which closes switches (SW2-SW3) of the charge and discharge sources (Io-, Io+) the deviators of which (SW6-SW5) are positioned according to comparator (U2) operation so that the second capacitor (Cy) is charged or discharged in order to reach the reference voltage (-V/2) taking into consideration that the first capacitor (Cx) undergoes an equal but opposite charge or discharge operation by the other source so that the voltage by which the second capacitor (Cy) is cyclically charged during one of the body impedance sample instants is proportional to the difference between the voltage present sample coming out of the body impedance variation detecting unit and the previous sample.

Claim 4

The electronic circuit according to claim 2, characterized in that if it supplies a variable pro= portional to the patient's respiratory rate, when the switches (SW2-SW3) of the charge and discharge (Io+ and Io-) sources are closed, another switch (SW4) is closed, this switch, by means of a deviator (SW7) the position of which automatically changes according to the negative or positive increase of the voltage of the second capacitor (Cy), sends the pulse number of the activation clock of said charge and discharge sources to one or the other input of a saturating and programmable counter (U3) of finite length, wherein said pulses are added algebraically starting from a saturation state to the next being the output of this counter connected to a flip-flop (U4) which transforms the higher or lower saturation signal of the counter (U3) into a squared signal (V OUT ) ) which shows a transition each time thet the difference between minimum and maximum value or between maximum and minimum value of the input signal exceeds a fixed a programmable value (V TH ).

Claim 5

The electronic circuit according to claim 2, characterized in that between the differential amplifier (Ul) of the extraction unit of the signal corresponding to the respiratory rate and unit (10) detecting the impedance variations of the patient's body and turning them into voltage, there is a fast and low energy consumption "peak and hold" (P/H) so that said differential amplifier can be slow enough to allow to save considerable electric energy during operation.

Claim 6

The electronic circuit according to claim 2, characterized in that the operational amplifiers used in the amplifying and comparing circuits are programmable and are fully supplied only in phase with the chest impedance measurement pulse so as to guarantee gain and slew rate adequate for the time in which these operational amplifiers are actually operating, the whole designed to reduce the energy consumption of the whole circuit.

Claim 7

The electronic circuit according to claim 3, characterized in that the programming number supplied to the counter or register (U3), as a maximum saturation limit is, for example, 32.

Claim 8

The electronic circuit according to claim 2, characterized in that the duration of the charge or discharge (Io-, Io+) sources operating pulses lasts approximately 30 micro-seconds and said pulses are timed by the clock (CKo) signal controlling the same sources.

Claim 9

The electronic circuit according to claim 2, characterized in that if it supplies a variable pro= portional to the patient's pulmonary minute ventilation (1/min), when the charge and discharge (Io+ and Io-) sources are closed, another switch (SW4) is closed, this switch supplies the activation clock pulse number of said charge or discharge sources to a microprocessor-based or other type of electronic unit (100) that knowing the repetition time (125 ms) of these pulse trains [v' (Δ ZL] and the time interval (122 ps) between a pulse and the following one in a train, supplies a signal Vm ( Δ ZL) that is the average of the input signal variations, that is proportional to the variation speed of the body impedance and that is, therefore, proportional to the patient's pulmonary ventilation.