Autovent field ventilator
United States Patent 3916890

An automatic ventilator includes a gas input line, a compliant volume means communicating with the input line, a constraint limiting the expansion of the volume means, and a gas output line. A pressure responsive valve is provided which interconnects the lines, the pressure responsive valve being responsive to the pressure in the input line to open to pass gas to the output line, and being responsive to the gas pressure in the input and output lines to close to permit exhalation by a patient. A one way valve is further provided between an inspiration port and the output line so as to allow gas to flow from the output line to the inspiration port in order to periodically deliver a predetermined volume of gas at a predetermined pressure to the inspiration port.

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International Classes:
A61M16/00; (IPC1-7): A61M16/00
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Primary Examiner:
Gaudet, Richard A.
Assistant Examiner:
Recla, Henry J.
Attorney, Agent or Firm:
Flynn & Frishauf
I claim

1. An automatic ventilator for automatically supplying inspiration gas to a patient and for automatically permitting exhalation by a patient without any breathing effort by the patient, including:

2. An automatic ventilator as claimed in claim 1, in which said first compliant volume means comprises a first expandable bag.

3. An automatic ventilator as claimed in claim 2, comprising a second compliant volume means which includes a second expandable bag and a second constraint associated therewith for limiting the expansion thereof and a flow control valve communicating the second compliant volume means with the input line.

4. An automatic ventilator as claimed in claim 1, in which said one way valve and said inspiration port form part of a valve device which further includes an expiration port, an exhaust port and a diaphragm valve controlling the passage of gas between the expiration and exhaust ports, the diaphragm valve being connected to the output line such that the diaphragm valve is closed when the pressure responsive valve is open.

This invention relates to an automatic ventilator for inducing respiration in a patient.

Automatic ventilators generally fall into two classes, namely those that are pressure limited, i.e., will deliver gas to a patient until a pre-set back pressure is attained, and those that are volume limited, i.e., will deliver to the patient a pre-set volume of gas. Both classes of ventilators have uses in dealing with particular respiratory disorders but can be dangerous if used in an unsuitable case.

It is an object of the present invention to provide a simple ventilator incorporating volume control and capable also of providing pressure control.

The present invention is an automatic ventilator including a gas input line, compliant volume means communicating with said input line, a constraint limiting the expansion of said volume means, a gas output line, and a pressure responsive valve interconnecting said lines and responsive to the gas pressures therein to open to pass gas to the output line and to close to permit exhalation by a patient.

The compliant volume means may comprise an expandable bag. Two such expandable bags may be provided the second also having a constraint associated therewith and communicating with the input line through a flow control valve.

A valve device may be provided at the other end of the gas output line to pass gas to an inspiration port and to pass gas from an expiration port to the atmosphere.

An embodiment of the present invention will now be described, by way of example, with reference to the drawing, the single FIGURE of which diagrammatically illustrates an automatic ventilator according to the present invention.

Referring now to the drawing, a gas inlet line 10, intended to be supplied from a constant flow gas source, is connected through a filter 11 and a pressure responsive valve 12 to an output line 13.

In communication with the gas inlet line are compliant volume means, in this embodiment two expandable bags 15 and 16, each of which is located in a container 17 which acts as a restraint to limit the expanded volume of the bags. The bag 15 has a capacity of half a litre and the bag 16 has a capacity of 1 litre and communicates with the line 10 through an adjustable flow control valve 20.

The pressure responsive valve 12 which is preferably of the type disclosed in our British Patent Specification No. 1,208,775 operates to remain closed during which time the line 13 vents to the atmosphere until the pressure in the input line 10 reaches a specified value and remains open until the pressures in the input and output lines 10 and 13, respectively are substantially equal. The specified pressure at which the valve opens is adjustable by means of a collar 25 on the valve body.

Connected with the free end of the output line 13 is a valve device 26 having an inspiration port 27, an expiration port 28 and a vent port 29. The inspiration and expiration ports are coupled to a face mask (not illustrated) (or other patient connection) for a patient while the vent port 29 is open to the atmosphere. The inspiration port 27 is coupled to the output line 13 through a one way valve 30 which permits flow from the line 13 to the port 27. A diaphragm valve 31 uses the pressure in the output line 13 to control communication between the expiration port 28 and the vent port 29.

The cycle of operation of the automatic ventilator commences with the valve 12 closed, the patient then breathing out. The constant flow of gas 10 into the ventilator expands the bag 15 and, at a rate determined by the setting of the flow control valve 20, the bag 16. The pressure in the line 10 rises sharply when the bag 15 has expanded against its restraint, and the valve 12 opens when its preset pressure is reached. Gas then flows from the bags 15 and 16 and the line 10 through the valve 12, the output line 13 and the one way valve 30 through the inspiration port 27 to the patient. The diaphragm valve 31 closes across the expiration port when the pressure in the line 13 increases upon opening of the pressure responsive valve.

When the pressures in the input and output lines 10 and 13 respectively, are equal or substantially so, depending upon the precise characteristics of the valve 12, the valve 12 closes, venting the ouput line 13 to atmosphere and thus closing the valve 30 and opening the diaphragm valve 31 to permit the patient to breathe out through the expiration port and the vent port. The cycle of operation of the automatic ventilator then recommences.

It should be noted that the automatic ventilator described is both pressure and volume limited. The pressure limit is set by adjustment of the pressure responsive valve 12. The volume limit is set by the volume of the bag 15, which is the minimum volume that the ventilator can deliver per cycle, plus the volume of the bag 16 at the moment the valve 12 opens. This latter volume depends on the setting of the flow control valve 20, as the less it constricts flow to the bag 16 the greater is the volume of the bag 16 when the bag 15 is full and the valve 12 is triggered.

While the valve device 26 is not strictly necessary as the valve 12 is capable of exhausting the patient to the atmosphere, it is desired to have the device 26 to avoid inspiratory and expiratory flow in a common line to mitigate risk of cross infection between succesive patients, and to prevent the re-breathing of exhaled gases.

Modifications may be made to the embodiments described. Both bags 15 and 16 may be included in a common restraint chamber, or alternatively other volumetric chambers may be used, and other arrangements for the valve device 26 may be readily devised by those familiar with the art.