Apparatus for measuring impedance of body tissue

Claim 3

An apparatus as claimed in claim 1, wherein said means for filtering is a low-pass filter having an upper limit frequency which permits said lower-frequency signal components of said impedance signal to pass.

Claim 4

An apparatus as claimed in claim 2, wherein said low-pass filter has an upper limit frequency in the range of from about 0.1 through about 0.4 Hz.

Claim 5

An apparatus as claimed in claim 2, further comprising means for varying said limit frequency of said low-pass filter.

Claim 6

An apparatus as claimed in claim 1, further comprising: means for supplying stimulation pulses at a controllable frequency to a patient in whom said body tissue is disposed; and means for controlling the pulse frequency of said means for supplying stimulation pulses, said means for controlling having an input connected to said means for filtering, and including means for modifying said stimulation frequency corresponding to changes in said body tissue metabolism based on said signal components passed by said means for filtering.

Claim 7

An apparatus as claimed in claim 5, wherein said means for filtering is a low-pass filter having a limit frequency and further comprising means for varying said limit frequency dependent on said stimulation frequency for shifting said limit frequency toward higher frequency values given increasing stimulation frequency and shifting said limit frequency toward lower frequency values given decreasing stimulation frequency.

Claim 8

An apparatus as claimed in claim 5, further comprising: means for compensating for the influence of temperature on said lower frequency signal components; and a subtraction means connected between said means for compensating and said means for controlling the stimulation frequency, said subtraction means subtracting a programmable fixed value from an output of said means for compensating.

Claim 9

An apparatus as claimed in claim 7, wherein said subtraction means includes means for calculating mean value of said lower frequency signal components, and means for subtracting a programmable value in the region of from about 80 through about 90% of said mean value.

Claim 10

An apparatus as claimed in claim 1, further comprising means for compensating for the influence of temperature on said lower-frequency signal components.

Claim 13

A method as claimed in claim 10 further comprising the steps of: stimulating the heart of a patient, in whom said body tissue is disposed, with stimulation pulses at a controllable frequency; and controlling the frequency of said stimulation pulses based on said lower-frequency signal components corresponding to said metabolism of said body tissue.

Claim 14

A method as claimed in claim 11, wherein the step of filtering is undertaken in a low-pass filter having a limit frequency, and comprising the additional step of: varying said limit frequency of said low pass filter dependent on said stimulation frequency.

Claim 15

A method as claimed in claim 12, wherein the step of varying is further defined by the steps of: shifting said limit frequency toward higher frequency values given increasing stimulation frequency; and shifting said limit frequency toward lower frequency values given decreasing stimulation frequency.

Claim 16

A method as claimed in claim 10, comprising the additional step of: compensating for the influence of temperature on said lower-frequency signal components.

Claim 17

A method as claimed in claim 14, comprising the additional step of: subtracting a programmable fixed value from said lower-frequency signal components after compensating for the influence of temperature.

Claim 18

A heart pacemaker for stimulating the heart of a patient in whom said pacemaker is implanted, said pacemaker comprising: a signal source means adapted to be connected to body tissue having a conductance in said patient for impressing an electrical measurement signal into said body tissue; means adapted to be connected to said body tissue for acquiring an impedance signal therefrom dependent on the impressed electrical measurement signal and said conductance, said impedance signal including higher-frequency signal components corresponding to periodic body cycles and lower-frequency signal components corresponding to said metabolism of said body tissue; an evaluation means connected to said means for acquiring said impedance signal for evaluating said impedance signal, said evaluation means including means for filtering said lower-frequency signal components out of said impedance signal, said means for filtering having a signal output to which only the filtered-out signal components are supplied; means for generating and supplying stimulation pulses to said heart of said patient at a variable frequency; and control means for said means for generating and supplying for varying said stimulation frequency at least partially in dependence on said filtered-out signal components at said signal output of said evaluation means.

Claim 19

A heart pacemaker for stimulating the heart of a patient in whom said pacemaker is implanted, said pacemaker comprising: a signal source means adapted to be connected to body tissue having a conductance in said patient for impressing an electrical measurement signal into said body tissue; means adapted to be connected to said body tissue for acquiring an impedance signal therefrom dependent on the impressed electrical measurement signal and said conductance, said impedance signal including higher-frequency signal components corresponding to periodic body cycles and lower-frequency signal components corresponding to said metabolism of said body tissue; an evaluation means connected to said means for acquiring said impedance signal for evaluating said impedance signal, said evaluation means including means for filtering said lower-frequency signal components out of said impedance signal, said means for filtering having a signal output to which only the filtered-out signal components are supplied; means for generating and supplying stimulation pulses to said heart of said patient at a variable frequency; and control means for said means for generating and supplying for varying said stimulation frequency at least partially in dependence on said filtered-out signal components at said signal output of said evaluation means.