Respiration system with patient assist capability

• US 4,050,458 A
• Filed: 01/26/1976
• Issued: 09/27/1977
• Est. Priority Date: 01/26/1976
• Status: Expired due to Term

• Current Assignee: Puritan Bennett Corp. (Medtronic Plc)
• Original Assignee: Puritan Bennett Corp. (Medtronic Plc)
• Inventors: Friend, Jack M.
• Primary Examiner(s): Michell, Robert W.
• Assistant Examiner(s): Recla, Henry J.
• Application Number:
  US05/652,073
• Time in Patent Office: 610 Days
• Field of Search: 128/145.8, 128/145.6, 128/145.5, 128/142 R, 128/142.2, 128/188, 128/DIG. 17, 128/DIG. 29, 128/2.08, 128/2.06 R, 128/2 C, 128/2.05 V, 340/240, 340/241, 340/239, 340/248 A
• US Class Current: 128/204.23
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor

Abstract

A method and apparatus for initiating a positive-pressure-assisted inspiration phase in response to a patient'"'"'s inspiratory effort, and independently of the absolute pressure at the time of the inspiratory effort, since the absolute pressure may vary from patient to patient or depend upon a particular mode of operation of the respiration system. The invention apparatus includes a differentiator circuit for obtaining a time-differentiated pressure signal, and a circuit for detecting a change in the sign of the slope of the differentiated signal. The patient'"'"'s inspiratory effort is manifested as an increased rate of pressure drop, and this shows up as a change in the sign of the slope of the differentiated pressure, which is detected independently of absolute pressure, and is utilized to initiate an assisted inspiration phase. The apparatus also includes circuitry for detecting a predetermined drop in pressure, from the time of detection of the inspiratory effort, to ensure that minor variations in the pressure signal will not trigger a spurious inspiration phase.

Claims

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

pressure sensing means, for sensing system pressure near the point of delivery of gas to the patient, including means for generating a pressure signal therefrom;

first electrical means for generating from said pressure signal a first output signal indicative of a first time differential signal;

second electrical means for generating a second output signal indicative of the sign of the second time differential of said pressure signal, whereby said second output signal is indicative of an increase in the rate of pressure drop during an expiration phase of the patient breathing cycle;

third electrical means responsive to said second output signal, for generating a third output signal indicative of the change in the system pressure; and

comparator means for comparing said third output signal with a reference value indicative of a predetermined pressure drop, and developing a control signal to initiate an assisted inspiration phase of the breathing cycle when said third output signal reaches said reference value.

2. Apparatus as set forth in claim 1, wherein said second electrical means includes timing means for actuating said second electrical means only at a time during the expiration phase when an inspiratory effort is expected.

3. Apparatus as set forth in claim 1, and further including means for varying said reference value of pressure drop and thereby varying the sensitivity of said apparatus.

4. 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.

5. A method as set forth in claim 4, and further including the step of adjusting the sensitivity of said method by varying the predetermined pressure drop.

6. A method as set forth in claim 4, and further including the step of supressing said step of detecting a change in sign of the slope of the first differential pressure signal until an appropriate time in the expiration phase when an inspiratory effort is expected.

7. 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.

8. Apparatus as set forth in claim 7, and further including means for adjusting the sensitivity of said apparatus by varying the predetermined drop in absolute pressure detected by said means for detecting the predetermined drop in absolute pressure.