Medical ventilator

• US 5,494,028 A
• Filed: 11/04/1987
• Issued: 02/27/1996
• Est. Priority Date: 11/04/1986
• Status: Expired due to Term

• Current Assignee: Bird Products Corporation (Becton, Dickinson & Co)
• Original Assignee: Bird Products Corporation (Becton, Dickinson & Co)
• Inventors: Baker, Lindon A., DeVries, Douglas F.
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): LACYK, JOHN P
• Application Number:
  US07/116,701
• Time in Patent Office: 3,037 Days
• Field of Search: 435/6, 435/68.1, 435/70.1, 435/820, 435/41, 435/69.3, 436/501, 530/358, 530/350, 530/387.1, 536/27, 536/22.1, 536/25.3, 935/9, 935/19, 935/34, 935/78
• US Class Current: 128/205.24
• CPC Class Codes: A61M 16/00 Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes stimulating the respiratory movement by mechanical, pneumatic or electrical means, iron lungs combined with gas breathing means A61H31/00
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 16/12 by mixing different gases
• CPC Class Codes: A61M 16/204 used for inhalation control
• CPC Class Codes: A61M 16/205 used for exhalation control
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A62B 9/02 Valves non-return valves mounted in breathing masks or helmets A62B18/10

Abstract

A medical ventilator having a valve which controls the flow of gas from a pressurized gas source to a patient for inhalation. Flow through the valve is choked and pressure upstream of the valve is held stable so that a known relationship exists between the position of the valve and the flow rate through the valve. An open loop control system causes the valve to open or close as needed to deliver a preselected tidal volume of gas to the patient on each breath. Since the flow rate is known, no feedback to the controller regarding actual flow conditions is required. The exact positioning of the valve and length of time that the valve is to be held open is predetermined by the controller before the breath is delivered, and is repeated for subsequent breaths. Preferably, the valve is driven by a stepping motor, and the controller comprises a microcomputer. The controller compensates for ramping of the stepping motor as the valve opens and closes in determining the positions of the valve required to deliver the preselected tidal volume. To ensure precise engagement between a valve member and a valve seat, the valve member is mounted on a flexible, linear wire. Additionally, a spirally-wound spring surrounds a stepping motor shaft and biases the shaft so as to close the valve in the event of a power loss.

Claims

1. A ventilator for delivering a breath of a predetermined volume to a patient, said ventilator comprising:

means for determining a breath delivery period based upon a selected tidal volume, the undelivered volume that would be lost during the increase of the flow rate during the initial portion of a breath, the extra volume that would be delivered during the decrease of the flow rate during the final portion of a breath and a peak flow rate, the contribution of the undelivered volume that would be lost increasing the breath delivery period and the contribution of the extra volume that would be delivered decreasing the breath delivery period whereby the actual tidal volume delivered to the patient substantially equals the selected tidal volume; and

means for delivering a breath at a variable flow rate to a patient, said breath delivering means being coupled to said means for determining a breath delivery period, said breath being delivered in accordance with said breath delivery period.

2. A ventilator as defined in claim 1, wherein said means for determining a breath delivery period determines an actual peak flow rate based upon a preselected peak flow rate and uses said actual peak flow rate in the determination of said breath delivery period.

3. A ventilator as defined in claim 1, wherein said means for determining a breath delivery period adjusts said breath delivery period based upon the profile of the breath to be delivered.

4. A ventilator as defined in claim 3, wherein said profile is a tapered profile.

5. A ventilator for delivering a breath of a predetermined volume to a patient, said ventilator comprising:

means for determining a breath delivery period in accordance with the following equation;

space="preserve" listing-type="equation">BDP=(V.sub.X +VOLUME-V.sub.Y)/FLOW,

where V_X is the undelivered volume that would be lost during the increase of the flow rate during the initial portion of a breath, V_Y is the extra volume that would be delivered during the decrease of the flow rate during the final portion of a breath, VOLUME is a preselected tidal volume, FLOW is a peak flow rate and BDP is the breath delivery period; and

means for delivering a breath at a variable flow rate to a patient, said breath delivering means being coupled to said means for determining a breath delivery period, said breath being delivered in accordance with said breath delivery period.

6. A ventilator as defined in claim 5, wherein said means for determining a breath delivery period adjusts said breath delivery period based upon the profile of the breath to be delivered.

7. A ventilator for delivering a plurality of substantially identical breaths to a patient whose breathing ability is impaired by determining what the flow profile of a plurality of breaths will be prior to the delivery of the breaths, said ventilator comprising:

means for electronically determining what the flow profile of a plurality of breaths will be prior to the delivery of the breaths, said flow profile being predetermined based upon the settings of a plurality of switches which specify a desired peak flow rate and a desired tidal volume, said flow profile being variable, depending upon the settings of said switches;

a flow control valve including a valve member and a valve seat capable of delivering a breath at an incrementally variable flow rate by varying the displacement of the valve member relative the valve seat; and

means coupled to said flow control valve for causing said flow control valve to deliver a plurality of breaths to a patient, each of said breaths having a substantially identical flow profile.

8. A ventilator for delivering a plurality of substantially identical breaths to a patient whose breathing ability is impaired by determining a breath delivery period prior to the delivery of a plurality of breaths, said ventilator comprising:

means for electronically determining a breath delivery period prior to the delivery of a plurality of breaths, said breath delivery period being prepared based on the settings of a plurality of switches which specify a desired peak flow rate and a desired tidal volume;

a flow control valve including a valve member and a valve seat for delivering a breath to a patient at an incrementally variable flow rate by varying the displacement of the valve member relative the valve seat; and

means coupled to said flow control valve for using said breath delivery period to cause said flow control valve to deliver a plurality of breaths to a patient, said breaths being delivered in accordance with said breath delivery period, each of said breaths being substantially identical.

9. A ventilator comprising:

means for electronically determining what the flow profile of a breath will be based upon the settings of a plurality of switches which specify a desired peak flow rate and a desired tidal volume prior to the delivery of a breath;

a flow control valve including a valve member and a valve seat capable of delivering a breath to a patient at an incrementally variable flow rate by varying the displacement of the valve member relative to the valve seat; and

means for causing said control valve to deliver a breath to a patient, said breath being delivered in accordance with said flow profile.

10. A ventilator comprising:

means for electronically determining what the flow profile of a breath will be based upon the settings of a plurality of switches prior to the delivery of a breath;

means for delivering a breath to a patient at a variable flow rate; and

means for causing said breath delivering means to deliver a breath to a patient, said breath being delivered in accordance with said flow profile, wherein said breath delivering means comprises a valve coupled to a stepping motor.

11. A ventilator which provides artificial respiration to a patient from a pressurized source of gas, said ventilator comprising:

a ventilator flow control valve including a valve member and a valve seat for delivering a breath to a patient, said flow control valve controlling the flow of gas to the patient from the source of gas, said valve member being movable to a plurality of positions relative said valve seat so as to permit various flow rates of gas to the patient;

means for storing data relating to a flow profile;

control means for controlling the position of said flow control valve, said control means generating command signals which cause opening or closing of said flow control valve without requiring feedback regarding the position of said flow control valve or the actual flow rate of gas through said flow control valve, said command signals being generated based upon the data stored in said storing means; and

an exhalation valve coupled to said control means for allowing the patient to exhale after said flow control valve has delivered a breath to the patient.

12. The ventilator of claim 11, wherein said control means causes said flow control valve to deliver breaths to the patient according to a predetermined rate of breaths per minute.

13. The ventilator of claim 12, wherein said control means causes said flow control valve to deliver breaths to the patient according to a predetermined flow rate versus time waveform.

14. The ventilator of claim 11, wherein a known relationship exists between the position of said flow control valve and the flow rate of gas through said flow control valve.

16. The ventilator of claim 14, wherein said control means causes said flow control valve to deliver a predetermined tidal volume of gas to the patient during each breath.

17. The ventilator of claim 16, wherein said control means determines the position of said flow control valve required to deliver said predetermined tidal volume prior to the delivery of a breath to the patient.

18. The ventilator of claim 11, wherein said flow control valve comprises:

a stepping motor having a rotatable shaft, said stepping motor causing rotation of said shaft in response to said command signal;

a valve seat having an orifice therein, said respiratory gas flowing through said orifice;

a ball which mates with said seat, movement of said ball relative to said seat causing the area of said orifice to vary, thus causing the flow rate of gas through said orifice to vary; and

means for translating rotation of said shaft into

movement of said ball relative to said seat.

19. The ventilator of claim 18, wherein said translating means comprises:

a cam mounted on said shaft, said cam having a cam surface;

a cam follower which engages said cam surface, said cam follower being displaced in a direction parallel to said shaft upon rotation of said shaft; and

an elongated, linear wire which is joined at one end to said ball and at another end to said cam follower, said wire being flexible to enable radial displacement of said ball and permit sealing engagement between said ball and said seat despite misalignment or wear.

20. The ventilator of claim 18, wherein said flow control valve further comprises a spring for biasing said flow control valve into a closed position in the event of an emergency, said spring causing rotation of said shaft, said stepping motor overcoming the biasing force of said spring during normal operation.

21. The ventilator of claim 20, wherein said spring is formed of a thin strip of spirally-wound material, said spring surrounding said shaft.

15. A ventilator which provides artificial respiration to a patient from a pressurized source of gas, said ventilator comprising:

a ventilator flow control valve for delivering a breath to a patient, said flow control valve controlling the flow of gas to the patient from the source of gas, said flow control valve being movable to a plurality of positions so as to permit various flow rates of gas to the patient;

means for storing data relating to a flow profile;

control means for controlling the position of said flow control valve, said control means generating command signals which cause opening or closing of said flow control valve without requiring feedback regarding the position of said flow control valve or the actual flow rate of gas through said flow control valve, said command signals being generated based upon the data stored in said storing means; and

an exhalation valve coupled to said control means for allowing the patient to exhale after said flow control valve has delivered a breath to the patient, wherein a known relationship exists between the position of said flow control valve and the flow rate of gas through said flow control valve, and flow through said flow control valve is choked.

22. A valve, comprising:

a valve seat which surrounds an orifice through which fluid passes;

a valve member which engages said valve seat to prevent flow through said orifice;

means for displacing said valve member relative to said valve seat so as to vary the flow rate of fluid through said valve; and

an elongated, linear wire joined at one end to said valve member and at another end to said displacing means, said wire having a longitudinal axis, said displacing means causing said wire to move substantially parallel to said longitudinal axis, wherein said wire is sufficiently flexible to permit said valve member to move far enough radially relative to said seat to effect a tight sealing engagement with said seat despite misalignment of said valve member and said seat.

23. The valve of claim 22, wherein said displacing means comprises:

a stepping motor having a rotatable shaft;

a cam mounted on said shaft; and

a cam follower which engages said cam, rotation of said cam causing displacement of said cam follower, said wire being operatively coupled to said cam follower, whereby the displacement of said cam follower causes said wire to be displaced.

24. The valve of claim 22, wherein said wire has a diameter of approximately thirty-five thousandths of an inch.

25. The valve of claim 22, wherein said valve member comprises a ball.

26. A valve for a ventilator which provides artificial respiration to a patient from a pressurized source of gas, said valve comprising:

a valve seat having an orifice through which fluid passes in order to be delivered to a patient to whom artificial respiration is being provided;

a valve member which is movable relative to said valve seat to vary flow through said orifice;

a motor having a shaft, motion of said shaft causing movement of said valve member relative to said valve seat; and

a spring which engages said shaft so that, in the event of a power loss to said motor, said shaft is biased by said spring to cause said valve to assume a closed position so that pressurized gas is not forced into the patient'"'"'s lungs, said motor overcoming the force of said spring during normal operation, said spring surrounding said shaft of said motor in a substantially planar fashion so that the said spring provides torsional force without providing any substantial linear force in a direction parallel to said motor shaft.

27. The valve of claim 26, wherein rotation of said shaft causes movement of said valve member, and wherein said spring is spirally-wound around said shaft.

28. The valve of claim 26, wherein said motor comprises an electrically powered stepping motor.

29. A ventilator for delivering a plurality of substantially identical breaths to a patient whose breathing ability is impaired by determining what the flow profile of a plurality of breaths will be prior to the delivery of the breaths, said ventilator comprising:

means for electronically determining what the flow profile of a plurality of breaths will be prior to the delivery of the breaths, said flow profile being predetermined based upon the settings of a plurality of switches which specify a desired peak flow rate and a desired tidal volume, said flow profile being variable, depending upon the settings of said switches;

a flow control valve coupled to a stepping motor capable of delivering a breath at a variable flow rate; and

means coupled to said flow control valve for causing said flow control valve to deliver a plurality of breaths to a patient, each of said breaths having a substantially identical flow profile.

30. A ventilator for delivering a plurality of substantially identical breaths to a patient whose breathing ability is impaired by determining a breath delivery period prior to the delivery of a plurality of breaths, said ventilator comprising:

means for electronically determining a breath delivery period prior to the delivery of a plurality of breaths, said breath delivery period being prepared based on the settings of a plurality of switches which specify a desired peak flow rate and a desired tidal volume;

a flow control valve coupled to a stepping motor capable of delivering a breath at a variable flow rate; and

means coupled to said flow control valve for using said breath delivery period to cause said flow control valve to deliver a plurality of breaths to a patient, said breaths being delivered in accordance with said breath delivery period, each of said breaths being substantially identical.