A cardiac pacer for pacing a human heart

Claim 2

A cardiac pacer for pacing a human heart comprising a) means (4) for generating pacing pulses (9) at a predetermined pacing rate; b) means (2, 3) for transmitting the pacing pulses (9) to the human heart (1) for pacing; c) means (7) for processing the pacing pulses (9) for obtaining a respiratory signal according to an impedance measurement; and d) means (5) for varying the predetermined pacing rate dependent on the respiratory signal.

Claim 3

The cardiac pacer according to claim 1, further comprising a) means (21) for non-linearly amplifying the respira­tory signal in a manner that signal portions having higher amplitudes are more amplified than signal portions having lower amplitudes; b) means (22) for integrating the non-lineary amplified respiratory signal over a period of time, e.g. 5 to 30 s; and c) means (5) for varying the predetermined pacing rate dependent on the integrated signal.

Claim 4

The cardiac pacer according to claim 1 or 2, further comprising means (18) for measuring the amplitude (V1) of a pacing pulse (9) at the beginning and the amplitude (V1) of the same pacing pulse (9) at the end of the pacing pulse and means (9) for obtaining a measure for the decay (10) between the two amplitudes (V1, V2) which is a measure for the respiration.

Claim 5

The cardiac pacer according to claim 3, wherein said means (18) for measuring the amplitudes (V1, V2) com­prises a sample and hold circuitry.

Claim 6

The cardiac pacer according to claim 3 or 4, wherein said means (19) for obtaining a measure for the decay (10) comprise a difference former for the amplitudes (V1, V2).

Claim 7

The cardiac pacer according to one of the preceding claims 2 to 8, wherein said means (7) for processing the pacing pulses further comprising a voltage to pulse rate converter (23) for the integrated signal.

Claim 8

The cardiac pacer according to claim 6, wherein said means (5) for varying the predetermined pacing rate comprises an analog signal to digital control word converter (27) for the output signal of the voltage to pulse rate converter (23), a time register (26) for the output signal of the analog signal to digital control word converter (27), a down counter (25) which is set to higher zero counting speed when the respira­tion rate increases and a zero decoder (24) at the output of the down counter (25), said zero decoder (24) being connected with and controlling the pacing pulse generator (4) in a manner that a pacing pulse is generated at each zero count.