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Method and apparatus for determining respiratory system resistance during assisted ventilation

  • US 6,837,242 B2
  • Filed: 04/25/2001
  • Issued: 01/04/2005
  • Est. Priority Date: 04/26/2000
  • Status: Expired due to Term
First Claim
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1. A method of determining respiratory system resistance (R) in a patient receiving gas from a ventilatory assist device (ventilator), comprising:

  • estimating the flow rate ({dot over (V)}) and volume (V) of gas received by the patient from the ventilator;

    estimating pressure near the airway of the patient (Paw);

    generating a signal that results in a step decrease (negative pulse) in the pressure and/or flow output of the ventilator during selected inflation cycles;

    measuring Paw, {dot over (V)} and V at a point (TO) near the beginning of the pulse (PawO, {dot over (V)}, VO), at a point (TI) near the trough of the negative pulse (Paw1, {dot over (V)}1, V1), and at a point (T

    1
    ) preceding TO but after the onset of inspiratory effort (Paw

    1
    , {dot over (V)}

    1
    , V

    1
    ); and

    calculating the value of resistance (R) from the differences between Paw, {dot over (V)} and V at TO and at TI and where the change in patient generated pressure (Pmus) in the interval TO

    TI

    Pmus(TO

    TI)) is estimated, by extrapolation, from the differences between Paw, {dot over (V)} and V at TO and at T

    1
    , in accordance with equation (8), as follows;


    R=[(PawO

    Paw
    1+(Δ

    t/Δ

    t


    I
    )(PawO

    Paw


    1
    ))−

    E(VO

    V
    1+(Δ

    t/Δ

    t


    I
    )(VO

    V


    1
    ))]/(VO

    V
    1+(Δ

    t/Δ

    t


    I
    )({dot over (V)}O

    {dot over (V)}


    1
    )) 



    (8).

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