Respiratory control system and apparatus

• US 5,582,163 A
• Filed: 12/14/1993
• Issued: 12/10/1996
• Est. Priority Date: 12/06/1993
• Status: Expired due to Term

• Current Assignee: Intermed Equipamento Médico Hospitalar Ltda. (Becton Dickinson & Co)
• Original Assignee: Intermed Equipamento Médico Hospitalar Ltda. (Becton Dickinson & Co)
• Inventors: Bonassa, Jorge
• Primary Examiner(s): Lewis, Aaron J.
• Application Number:
  US08/166,409
• Time in Patent Office: 1,092 Days
• Field of Search: 128/204.18, 128/204.21, 128/204.23, 128/204.26
• US Class Current: 128/204.26
• CPC Class Codes: A61M 16/0051 with alarm devices
• 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
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit

Abstract

A respiratory control system and apparatus for delivering controlled and or assisted respiratory cycles to the patient includes a flow and pressure control valve, exhalation valve, flow transducer, pressure transducer, and a central control unit that servo controls the flow and pressure valve and the exhalation valve based upon the flow and pressure signals from transducers and control panel. The cycles are initiated by detection of inspiratory effort or in accordance to other criteria, maintaining simultaneously the inspired flow and pressure in the airway at or above a predetermined controlled flow and controlled pressure until the delivery of a predetermined controlled volume, and also extending the maintenance of the controlled pressure by a predetermined period of time after the instant in which the volume was completed, and beyond this period until the delivered flow has decreased until a minimum flow threshold level.

Claims

1. A method for delivering a controlled volume of breathable gas to a patient to improve synchronism between patient effort and system flow demand while assuring desired minimum requirements for airway pressure, flowrate and volume, the method comprising:

providing a respiratory circuit including an inspiratory tube, expiratory tube, exhalation valve and flow/pressure valve;

monitoring airway pressure at airway entry of a patient;

initiating breathable gas volume delivery to a patient'"'"'s airway at the trigger instant upon detection of an inhalation attempt by a patient which is sufficient to lower airway pressure to a reference trigger pressure;

at trigger instant, opening the flow pressure valve to deliver desired controlled flowrate through said inspiratory tube of said respiratory circuit, at the same time closing the end of the expiratory tube of the respiratory circuit using the exhalation valve and maintaining the respiratory circuit closed during inhalation up to a maximum acceptable airway pressure;

beginning to monitor at trigger instant, the flowrate and delivered volume of breathable gas during inhalation by a patient, said step of monitoring continuing throughout a respiratory cycle;

continuing to deliver breathable gas to patient by the flow/pressure valve, comparing actual airway pressure monitored at airway entry of the patient with the desired controlled pressure;

if patient monitored airway is below desired controlled pressure, continuing to deliver breathable gas to patient, increasing flowrate at airways above desired controlled flowrate, based upon the difference of monitored air pressure and desired controlled pressure, to null existing pressure differences, said step of delivering continuing throughout inspiratory portion of the respiratory cycle, until delivered volume reaches desired controlled volume;

if patient monitored airway pressure is above desired controlled pressure, continuing to deliver breathable gas to the patient, maintaining desired controlled flowrate at airways, said step of delivering continuing throughout inspiratory portion of the respiratory cycle, until delivered volume reaches desired controlled volume; and

at the volume completion instant in which the delivered volume reaches desired controlled volume, terminating the delivery of the controlled volume of breathable gas to patient by closing flow/pressure valve thus decreasing the flowrate through said inspiratory tube of said respiratory circuit to zero, opening the exhalation valve so as to permit such a patient to exhale the delivered volume and thus decreasing airway pressure to a predetermined positive and expiratory pressure.

2. A method as claimed in claim 1 further comprising:

extending inhalation beyond volume completion instant by a desired inspiratory hold time, maintaining inspiratory phase of respiratory cycle until desired inspiratory hold time elapses;

during said inspiratory hold time period, if patient monitored airway pressure is below desired controlled pressure, continuing to deliver breathable gas to the patient, controlling flowrate at airways based solely upon the difference of monitored air pressure and desired controlled pressure, to null existing pressure difference, said step of delivering continuing throughout inspiratory hold time portion of the respiratory cycle, until inspiratory hold time has elapsed;

during said inspiratory hold time period, if patient monitored airway pressure is above desired controlled pressure, opening in a controlled manner the exhalation valve based upon the difference between the desired controlled pressure and monitored airway pressure, to null existing pressure differences, said step of delivering continuing throughout inspiratory hold time portion of the respiratory cycle, until inspiratory hold time elapses; and

at the instant in which inspiratory hold time elapses, terminating the delivery of the controlled volume of breathable gas to patient by closing flow/pressure valve thus decreasing the flowrate through said inspiratory tube of said respiratory circuit to zero, opening the exhalation valve so as to permit such a patient to exhale the delivered volume and thus decreasing airway pressure to a predetermined positive and expiratory pressure.

3. A method as claimed in claim 1 further comprising:

extending inhalation beyond the volume completion instant by an additional flow supplementation period, maintaining inspiratory phase of respiratory cycle until the flowrate through said inspiratory tube of said respiratory circuit decreases to a predetermined minimum flowrate threshold;

during said additional flow supplementation period, if patient monitored airway pressure is below desired controlled pressure, continuing to deliver breathable gas to the patient, controlling flowrate at airways based solely upon the difference of monitored air pressure and desired controlled pressure, to null existing pressure difference, said step of delivering continuing throughout additional period, until the flowrate decreases to a predetermined minimum flowrate threshold; and

at the instant in which flowrate decreases to predetermined minimum flowrate threshold, terminating the delivery of the controlled volume of breathable gas to patient by closing flow/pressure valve thus decreasing the flowrate through said inspiratory tube of said respiratory circuit to zero, opening the exhalation valve so as to permit such a patient to exhale the delivered volume and thus decreasing airway pressure to a predetermined positive and expiratory pressure.

4. A method as claimed in claim 3 in which the value of minimum flowrate threshold that terminates the breathable gas volume delivery to a patient is determined as a percentage of the maximum flowrate monitored during the initiation of inhalation.

5. A method as claimed in claim 1, in which the desired controlled flowrate is a predetermined constant value.

6. A method as claimed in claim 1 in which the desired controlled pressure is a predetermined constant value.

7. A method as claimed in claim 1 in which the desired controlled flowrate is the ratio of desired controlled volume and a desired inspiratory time.

8. A method as claimed in claim 1 in which the desired controlled flowrate is determined during first steps of inhalation based upon a predetermined equation until the difference between monitored airway pressure and desired controlled pressure diminishes to a predetermined value.

9. A method as claimed in claim 1 in which the desired controlled flowrate is a time dependent mathematical function, representing predetermined waveform.

10. A method as claimed in claim 1 in which the desired control flowrate is determined based upon the difference between monitored airway pressure and desired controlled pressure and the rate of change of monitored airway pressure between predetermined time period steps.

11. A method as claimed in claim 1 in which the desired controlled flowrate is determined and continuously updated at predetermined time steps since the initiation of inhalation, computing at every instant the remainder of the volume to complete desired controlled volume (desired controlled volume subtracted from delivered volume at given instant) and the remainder of the inspiratory time (desired controlled inspiratory time subtracted from period of time since initiation of inhalation), and obtaining the instantaneous desired controlled flowrate by the ratio of the remainder of the volume and the remainder of the inspiratory time.

12. A method as claimed in claim 1 in which the desired controlled pressure is determined and continuously updated after a predetermined number of respiratory cycles, as a direct proportion of the average mean delivered flowrate.

13. A method as claimed in claim 1 in which the desired controlled pressure is determined and continuously updated after a predetermined number of respiratory cycles, based upon the patient'"'"'s respiratory system impedance, determined by any means.

14. A method as claimed in claim 1 in which the predetermined positive end expiratory pressure reached during exhalation is zero.

15. A method as claimed in claim 1 in which the breathable gas volume delivery is automatically initiated based upon a desired respiratory rate.

16. A method as claimed in claim 1 in which the breathable gas volume delivery is automatically initiated upon the detection of the occurrence of a patient'"'"'s apnea period which is longer than a desired maximum allowable apnea interval.

17. A method as claimed in claim 1 in which the breathable gas volume delivery is automatically initiated upon the detection of the occurrence of a decrease on monitored minute volume, comprising the summation of the volume delivered in every inhalation during the last minute, which is lower than a desire minimum allowable minute volume.