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A gain controller and method for controlling the value of a gain is used in conjunction with an electrode array for detecting a signal representative of respiratory drive output of a patient during inspiration, and a lung ventilator for assisting inspiration of the patient. The gain controller compr

A gain controller and method for controlling the value of a gain is used in conjunction with an electrode array for detecting a signal representative of respiratory drive output of a patient during inspiration, and a lung ventilator for assisting inspiration of the patient. The gain controller comprises an input for receiving the signal representative of respiratory drive output; a comparator for determining whether the signal representative of respiratory drive output is higher or lower than a target drive signal; and a gain adjustment unit for increasing the value of a gain when the amplitude of the signal representative of respiratory drive output is higher than the amplitude of the target drive signal and for decreasing the value of this gain when the amplitude of the signal representative of respiratory drive output is lower than the amplitude of the target drive signal. The gain is applied to the signal representative of respiratory drive output to produce an amplified respiratory drive output representative signal used for controlling the lung ventilator. The advantage of target drive ventilation is that this mode of ventilation does not depend on pressure, flow or volume measurements. A leaky ventilatory line will introduce a change in respiratory drive which will change the ventilatory assist in order to return the respiratory drive to its target level. Also, changes in the patient's metabolic or patho-physiological status which result in altered respiratory drive will be compensated.

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1. A lung ventilator control system for maintaining at a sustainable target level a respiratory drive of a patient assisted by a lung ventilator during inspiration, comprising:a detector of the electrical activity of a muscle of the patient indicative of a respiratory drive of said patient, said det

1. A lung ventilator control system for maintaining at a sustainable target level a respiratory drive of a patient assisted by a lung ventilator during inspiration, comprising:a detector of the electrical activity of a muscle of the patient indicative of a respiratory drive of said patient, said detector producing a respiratory drive signal in response to the detected electrical activity;a target drive signal supply which, in operation, produces a target drive signal of given amplitude, said target drive signal being representative of the sustainable respiratory drive target level;a signal comparator responsive to the respiratory drive signal and the target drive signal to produce a comparison signal indicative of whether the respiratory drive signal has an amplitude lower or higher than the amplitude of the target drive signal;a gain supply responsive to the comparison signal from the signal comparator to supply a gain, said gain supply having a gain-increasing unit which increases the gain when the comparison signal indicates that the amplitude of the respiratory drive signal is higher than the amplitude of the target drive signal, and a gain-decreasing unit which decreases the gain when the comparison signal indicates that the amplitude of the respiratory drive signal is lower than the amplitude of the target drive signal; anda gain multiplier responsive to the gain from the gain supply and the respiratory drive signal to multiply said respiratory drive signal by said gain and therefore produce a ventilator control signal for application to and control of the lung ventilator.2. A lung ventilator control system as recited in claim 1, wherein said target drive signal supply comprises means for producing a target drive signal having an amplitude located within a range of amplitudes.3. A lung ventilator control system as recited in claim 2, wherein said gain-increasing unit comprises means for increasing the gain by a fraction of a given value, and wherein said gain-decreasing unit comprises means for decreasing the gain by said fraction of the given value.4. A lung ventilator control system as recited in claim 3, wherein said given value is the target drive signal.5. A lung ventilator control system as recited in claim 3, wherein said given value is the respiratory drive signal.6. A lung ventilator control system as recited in claim 3, further comprising means for calculating a difference between the amplitude of said signal representative of respiratory drive signal and the amplitude of said target drive signal, wherein said given value is said difference between the amplitude of said respiratory drive signal and the amplitude of said target drive signal.7. A lung ventilator control system as recited in claim 2, wherein said muscle of the patient comprises the patient's diaphragm.8. A lung ventilator control system as recited in claim 1, wherein said detector of the electrical activity of the patient's muscle comprises an array of electrodes.9. A lung ventilator control system as recited in claim 8, wherein said array of electrodes is a linear array electrodes.10. A lung ventilator control system as recited in claim 1, comprising means for expressing said respiratory drive signal and said target drive signal as mean signal amplitudes.11. A lung ventilator control system as recited in claim 1, comprising means for expressing said respiratory drive signal and said target drive signal as median signal amplitudes.12. A lung ventilator control system as recited in claim 1, comprising means for expressing said respiratory drive signal and said target drive signal as peak signal amplitudes.13. A lung ventilator control system as recited in claim 1, comprising means for expressing said respiratory drive signal and said target drive signal as total signal amplitudes.14. A method of controlling a lung ventilator for maintaining at a sustainable target level a respiratory drive of a patient assisted by a lung ventilator during inspiration, comprising:detecting the electrical activity of a muscle of the patient indicative of a respiratory drive of said patient, said detecting comprising producing a respiratory drive signal in response to the detected electrical activity;producing a target drive signal of given amplitude, said target drive signal being representative of the sustainable respiratory drive target level;comparing the respiratory drive signal to the target drive signal to produce a comparison signal indicative of whether the respiratory drive signal has an amplitude lower or higher than the amplitude of the target drive signal;supplying a gain, said gain supplying comprising increasing the gain when the comparison signal indicates that the amplitude of the respiratory drive signal is higher than the amplitude of the target drive signal, and decreasing the gain when the comparison signal indicates that the amplitude of the respiratory drive signal is lower than the amplitude of the target drive signal; andmultiplying the respiratory drive signal by said gain and therefore producing a ventilator control signal for application to and control of the lung ventilator.15. A method of controlling a lung ventilator as recited in claim 14, wherein producing a target drive signal comprises producing a target drive signal having an amplitude located within a range of amplitudes.16. A method of controlling a lung ventilator as recited in claim 14, wherein increasing the gain comprises increasing the gain by a fraction of a given value, and wherein decreasing said gain comprises decreasing the gain by said fraction of the given value.17. A method of controlling a lung ventilator as recited in claim 16, wherein said given value is the target drive signal.18. A method of controlling a lung ventilator as recited in claim 16, wherein said given value is the respiratory drive signal.19. A method of controlling a lung ventilator as recited in claim 16, further comprising calculating a difference between the amplitude of said respiratory drive signal and the amplitude of said target drive signal, wherein said given value is said difference between the amplitude of said respiratory drive signal and the amplitude of said target drive signal.20. A method of controlling a lung ventilator as recited in claim 14, wherein said muscle of the patient comprises the patient's diaphragm.21. A method of controlling a lung ventilator as recited in claim 14, wherein detecting the electrical activity of the patient's muscle comprises detecting said electrical activity through an array of electrodes.22. A method of controlling a lung ventilator as recited in claim 21, wherein said array of electrodes is a linear array electrodes.23. A method of controlling a lung ventilator as recited in claim 14, comprising expressing said respiratory drive signal and said target drive signal as mean signal amplitudes.24. A method of controlling a lung ventilator as recited in claim 14, comprising expressing said respiratory drive signal and said target drive signal as median signal amplitudes.25. A method of controlling a lung ventilator as recited in claim 14, comprising expressing said respiratory drive signal and said target drive signal as peak signal amplitudes.26. A method of controlling a lung ventilator as recited in claim 14, comprising expressing said respiratory drive signal and said target drive signal as total signal amplitudes.