Respiration system with patient assist capability

For use in a respiration system, a method for detecting a patient's inspiratory effort independently of absolute pressure, comprising the steps of:

• monitoring system pressure during an expiration phase of the patient breathing cycle and generating a pressure signal indicative of the system pressure;
• differentiating the pressure signal with respect to time, to obtain a first differential pressure signal;
• detecting a change in sign of the slope of the first differential pressure signal;
• detecting a predetermined drop in absolute pressure following the detection of a change in sign of the slope of the first differential pressure signal;
• and, in response to the detection of the predetermined drop in absolute pressure,
• generating a control signal to be used to initiate an assisted inspiration phase of the breathing cycle, whereby an inspiratory effort by the patient causes an increase in the rate of pressure drop during the expiration phase, the increase being detectable as a change in sign of the slope of the first differential pressure signal, and whereby the detection of the subsequent predetermined pressure drop prevents the initiation of an assisted inspiration phase by spurious fluctuations of the pressure signal.

For use in a respiration system, apparatus for detecting a patient's inspiratory effort independently of absolute pressure, said apparatus comprising:

• means for monitoring pressure in the system and generating an electrical pressure signal therefrom;
• means for differentiating said pressure signal;
• means for detecting a change in sign of the slope of the differentiated pressure signal, and thereby detecting an increased rate of pressure drop due to an inspiratory effort by the patient, said means for detecting a change in sign also generating a first control signal indicative thereof;
• means coupled with said means for detecting a change in sign and responsive to said first control signal, for detecting a predetermined drop in absolute pressure after detection of the change in sign of the slope of the differentiated signal and also generating a second control signal indicative thereof;
• and
• means for comparing said second control signal with a reference value indicative of a predetermined pressure drop, whereby the inspiratory effort is unambiquously indicated by a change in sign of the slope of the differentiated pressure signal coupled with a subsequent drop in pressure by the predetermined amount.