A device for determining a level of ventilatory assist to be delivered to a patient by a mechanical ventilator in response to a measure of a patient's neural respiratory drive multiplied by an amplification factor, comprising: means for measuring an electrical activity of a respiratory related muscle of the patient as a representation of the patient's neural respiratory drive EAdi old; a first calculator for multiplying the patient's neural respiratory drive EAdi old by an existing amplification factor AF old to obtain an existing predicted ventilatory assist pressure P target old; a first sensor for sensing an existing resulting pressure P result old delivered to the patient by the mechanical ventilator; a computerized modifier of the amplification factor from the existing amplification factor AF old to a new amplification factor AF new; a second calculator for multiplying the patient's neural respiratory drive EAdi old by the new amplification factor AF new to obtain a new predicted ventilatory assist pressure P target new; a second sensor for sensing a new resulting pressure P result new delivered to the patient by the mechanical ventilator after the amplification factor has been changed from the existing amplification factor AF old to the new amplification factor AF new; a first comparator of the new predicted ventilatory assist pressure P target new and the existing predicted ventilatory assist pressure P target old to determine an anticipated change in pressure ΔP target new-old that will be delivered to the patient by the mechanical ventilator; a second comparator of the new resulting pressure P result new and the existing resulting pressure P result old to determine an actual change in pressure ΔP result new-old delivered to the patient by the mechanical ventilator; a third comparator of the anticipated change in pressure and the actual change in pressure calculating a ratio ΔP resut new-old / ΔP target new-old; and a third calculator including a decision algorithm to take a decision as to increase, maintain or decrease the amplification factor depending on the value of the ratio ΔP result new-old / ΔP target new-old as calculated by the third comparator; wherein the modifier is adapted to automatically change the amplification factor as indicated by the decision from the decision algorithm of the third calculator; and wherein the first calculator, second calculator, first comparator, second comparator, third comparator and third calculator are implemented in a computer or computers. means for measuring an electrical activity of a respiratory related muscle of the patient as a representation of the patient's neural respiratory drive EAdi old; a first calculator for multiplying the patient's neural respiratory drive EAdi old by an existing amplification factor AF old to obtain an existing predicted ventilatory assist pressure P target old; a first sensor for sensing an existing resulting pressure P result old delivered to the patient by the mechanical ventilator; a computerized modifier of the amplification factor from the existing amplification factor AF old to a new amplification factor AF new; a second calculator for multiplying the patient's neural respiratory drive EAdi old by the new amplification factor AF new to obtain a new predicted ventilatory assist pressure P target new; a second sensor for sensing a new resulting pressure P result new delivered to the patient by the mechanical ventilator after the amplification factor has been changed from the existing amplification factor AF old to the new amplification factor AF new; a first comparator of the new predicted ventilatory assist pressure P target new and the existing predicted ventilatory assist pressure P target old to determine an anticipated change in pressure ΔP target new-old that will be delivered to the patient by the mechanical ventilator; a second comparator of the new resulting pressure P result new and the existing resulting pressure P result old to determine an actual change in pressure ΔP result new-old delivered to the patient by the mechanical ventilator; a third comparator of the anticipated change in pressure and the actual change in pressure calculating a ratio ΔP resut new-old / ΔP target new-old; and a third calculator including a decision algorithm to take a decision as to increase, maintain or decrease the amplification factor depending on the value of the ratio ΔP result new-old / ΔP target new-old as calculated by the third comparator; wherein the modifier is adapted to automatically change the amplification factor as indicated by the decision from the decision algorithm of the third calculator; and wherein the first calculator, second calculator, first comparator, second comparator, third comparator and third calculator are implemented in a computer or computers.