Ventilating system for supplying a patient with respiratory gas and method for triggering the respiratory phases in said system

• US 5,647,351 A
• Filed: 09/07/1995
• Issued: 07/15/1997
• Est. Priority Date: 09/10/1994
• Status: Expired due to Term

• Current Assignee: Draeger Medical Systems Incorporated (Dragerwerk AG)
• Original Assignee: Dragerwerk AG
• Inventors: Fiebelkron, Dirk, Colla, Gregory-Alan, Weismann, Dieter
• Primary Examiner(s): Lewis, Aaron J.
• Application Number:
  US08/524,535
• Time in Patent Office: 677 Days
• Field of Search: 128/204.18, 128/204.21, 128/204.23, 128/204.26
• US Class Current: 128/204.21
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 16/204 used for inhalation control
• CPC Class Codes: A61M 16/205 used for exhalation control
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase

Abstract

A ventilating system for supplying a patient with respiratory gas has an apparatus for measuring a respiratory gas flow curve 27 and a respiratory gas pressure curve 28 and has an evaluation circuit 8 for processing at least the respiratory gas flow curve and switching over the respiratory phases. As switchover values from one respiratory phase to the other, the evaluation circuit 8 utilizes predetermined trigger thresholds T_IL, T_EL of the respiratory gas flow curve 27. The ventilating system is improved in such a manner that a good adaptation thereof to the breathing effort of the patient 2 is provided even when leakage is present. This task is solved in that, in the evaluation circuit, the respiratory gas flow curve 27 and the respiratory gas pressure curve 28 are logically coupled during both the inspiratory phase and the expiratory phase. This logic operation takes place in accordance with a predetermined function. From the foregoing, an inspiratory trigger ancillary threshold Z_I and an expiratory trigger ancillary threshold Z_E are computed as an additional switchover criterion. These trigger ancillary thresholds Z_I and Z_E are added to the trigger thresholds T_IL and T_EL, respectively. A method for triggering the respiratory phase in the system is also disclosed.

Claims

1. A ventilating system for supplying a patient with respiratory gas during inspiratory and expiratory phases of breathing, the ventilating system comprising:

a source of compressed respiratory gas;

valve means connected to said source of compressed respiratory gas and being provided for metering a flow of said respiratory gas to the patient thereby adjusting predetermined pressures of said respiratory gas during said inspiratory phases and expiratory phases of the patient;

a pressure measuring device for measuring the pressure of the respiratory gas supplied to the patient during inspiration and expiration and for providing measured pressure values defining a first curve representing respiratory gas pressure;

a flow measuring device for measuring respiratory gas flow during inspiration and expiration and for providing measured flow values defining a second curve representing respiratory gas flow and said second curve having an amplitude;

an evaluation circuit for processing said curves and for controlling said valve means to switch over between said inspiratory and expiratory phases of the patient upon predetermined values of the amplitude of said second curve, said predetermined values being trigger thresholds T_IL and T_EL of said second curve; and

,

said evaluation circuit including means for executing a logic operation pursuant to a predetermined function between said first and second curves during said inspiratory phases and expiratory phases of the patient to form an inspiratory ancillary trigger threshold Z_I and an expiratory ancillary trigger threshold Z_E and to add said ancillary trigger thresholds (Z_I and Z_E) to said inspiratory and expiratory thresholds (T_IL and T_EL), respectively, to form composite trigger thresholds (T_IL Z_I) and (T_EL Z_E) for controlling the switchover between said phases.

2. The ventilating system of claim 1, wherein said means for executing said logic operation is configured to compute said ancillary trigger thresholds (Z_I and Z_E) as follows:

##EQU3## wherein;

V_MI =the value of the respiratory gas flow v averaged over the inspiratory phase;

V_ME =the value of the respiratory gas flow averaged over the expiratory phase;

P_I =the mean respiratory gas pressure during the inspiratory phase;

P_E =the mean respiratory gas pressure during the expiratory phase;

T_EL Z_E =a first new trigger threshold; and

,

T_IL Z_I =a second new trigger threshold.

3. A method of triggering breathing phases in a ventilating system for supplying a patient with respiratory gas from a source of compressed respiratory gas during inspiratory and expiratory phases of breathing, the method comprising the steps of:

adjusting an inspiratory pressure P_I during an inspiratory phase and adjusting an expiratory pressure P_E during an expiratory phase;

measuring the pressure of the respiratory gas supplied to the patient during inspiration and expiration and providing measured pressure values defining a first curve representing respiratory gas pressure;

measuring respiratory gas flow during inspiration and expiration and providing measured flow values defining a second curve representing respiratory gas flow and said second curve having an amplitude;

utilizing an evaluation circuit to process said curves and controlling a valve to switch over between said inspiratory and expiratory phases of the patient upon predetermined values of the amplitude of said second curve, said predetermined values being trigger thresholds T_IL and T_EL of said second curve;

determining a volume V_MI of respiratory gas averaged over the inspiratory phase and a volume V_ME of respiratory gas averaged over the expiratory phase;

determining the mean values of said inspiratory pressure P_I and said expiratory pressure P_E ;

forming an inspiratory ancillary trigger threshold Z_I from at least the product of said mean expiratory pressure P_E and the difference (V_MI -V_ME);

forming an expiratory ancillary trigger threshold Z_E from at least the product of said mean inspiratory pressure P_I and the difference (V_MI -V_ME);

switching from the inspiratory phase to the expiratory phase in response to a drop of said second curve to a composite trigger threshold (T_EL Z_E); and

,

switching from the expiratory phase to the inspiratory phase in response to an increase of said second curve to a composite trigger threshold (T_IL Z_I).

4. The method of claim 3, wherein said ancillary trigger thresholds Z_I and Z_E are computed from the equations:

##EQU4##