AU4012899A - Pressure-controlled breathing aid - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

S.

Name of Applicant/s: Nellcor Puritan Bennett France Developpement Actual Inventor/s: Guy Bourdon Address for Service: BALDWIN SHELSTON WATERS MARGARET STREET SYDNEY NSW 2000 Invention Title: 'PRESSURE-CONTROLLED BREATHING AID' Details of Original Application No. 33904/95 dated 11 SEP 1995 The following statement is a full description of this invention, including the best method of performing it known to me/us:- File: 22492.00 -1- Pressure-controlled breathing aid

DESCRIPTION

The present invention relates to a pressure-controlled breathing aid.

Breathing aid devices or ventilation devices currently used in mechanical ventilation can be divided into two main groups, namely volumetric devices characterised by the supply of a specified volume in each respiratory cycle, and pressure-controlled devices characterised by the provision of a specified pressure in each respiratory cycle.

Volumetric devices have the advantage of guaranteeing a specified breathed volume, but they have major disadvantages. In particular, they expose the patient to risks o 10 of barotrauma as they tend to apply pressure which increases at the end of insufflation.

Furthermore, the patient risks not being matched to the device in the sense that the respiratory reflexes of the patient can appear at different times from those at which the volumes imposed by the device finish being supplied.

On the contrary, pressure-controlled devices allow better synchronisation of the 15 patient with the device and avoid the risk of barotrauma since the maximum pressure supplied is known in advance. On the other hand, the volume supplied to the patient in each cycle and the breathed volume are not guaranteed.

It is an object of the present invention, at least in the preferred embodiment, to overcome or substantially ameliorate one or more of the disadvantages of the prior art.

According to a first aspect of the invention there is provided a breathing aid device, comprising: a patient connection; an inspiratory branch in fluid communication with said patient connection, said inspiratory branch including an inspiration valve; laan expiratory branch in fluid communication with said patient connection and said inspiratory branch; means for controlling expiration in fluid communication with said expiratory branch, said means for controlling expiration including an expiration valve; means for detecting pressure operatively connected to said inspiratory branch; means for ventilating in fluid communication with said inspiratory branch, said means for ventilating including means for supplying a breathable gas through said inspiratory branch at an adjustable pressure, said means for ventilating further including pressure control means for comparing a pressure command to a pressure signal provided by said 10 means for detecting pressure and for adjusting the pressure of the means for supplying; and means for regulating a patient's breathed volume, said means for regulating including means for controlling volume and means for measuring volume, wherein the means for controlling volume provides the pressure command to the pressure control means, and wherein the means for measuring volume provides a signal indicative of a measured volume of breathed gas to the means for controlling volume.

According to a second aspect of the invention there is provided a breathing aid device, comprising: a patient connection; an inspiratory branch in fluid communication with said patient connection, said inspiratory branch including an inspiration valve; an expiratory branch in fluid communication with said patient connection and said inspiratory branch; lb an expiratory device in fluid communication with said expiratory branch, said expiratory branch including an expiration valve; a pressure detector operatively connected to said inspiratory branch; a ventilation unit in fluid communication with said inspiratory branch, said ventilation unit including a source of breathable gas at an adjustable pressure, said ventilation unit further including a valve controller for opening and closing the inspiration valve and the expiration valve, said ventilation unit further including a pressure controller for comparing a pressure detected by said pressure detector to a pressure command and for adjusting the pressure of the source of breathable gas; and 10 a regulator for regulating a patient's breathed volume, said regulator including a control unit and a measuring unit, wherein the control unit provides the pressure command ~to said ventilation unit, and wherein the measuring unit provides a signal indicative of a measured volume of breathed gas to the control unit.

According to another aspect of the invention there is provided a breathing aid device, comprising: Soa patient connection; an inspiratory branch in fluid communication with said patient connection, said inspiratory branch including an inspiration valve; an expiratory branch in fluid communication with said patient connection and said inspiratory branch, said expiratory branch including an expiration valve; a pressure detector operatively connected to said inspiratory branch; a source of breathable gas at an adjustable pressure in fluid communication with said inspiratory branch; Ic a valve controller for opening and closing the inspiration valve and the expiration valve; a pressure controller for comparing a pressure detected by said pressure detector to a pressure command and for adjusting the pressure of the source of breathable gas; a control unit for providing the pressure command to said pressure controller; and a measuring unit for providing a signal to the control unit indicative of a measured volume of breathable gas detected per breathing cycle to the patient connection.

*y oo -2- A preferred embodiment of the invention provides that the pressure can be adjusted to reach the predetermined volume applied as a command. In this way a volume is guaranteed without taking the risk of increasing the pressure in an uncontrolled manner, nor of creating the particular risk of mismatch between the breathing timing of the patient and that of the device. In particular, the invention is perfectly compatible with devices of the type described in FR-A-2,695,830 in which the device detects the respiratory reflexes of the patient in order to change from inspiratory phases to expiratory phases and vice-versa.

In order to prevent any risk of barotrauma, it is advantageous to provide means of setting a maximum predetermined pressure which the pressure applied to the patient will ~not be able to exceed even if the volume supplied is insufficient.

It is also advantageous to provide a signalling device or other alarm detecting the ~simultaneous occurrence of insufficient volume and the setting of the pressure at its •maximum predetermined value, in order to signal this situation of the device's inability to provided the breathed volume set as a command.

*e.e In the framework of the present invention, the expression "breathed volume" is a. aused to denote both the volume of the breathable gas inspired or expired per unit time and the volume or quantity of gas inspired or expired per breathing cycle.

S' Preferably, the adjustment means apply to the inspiratory pressure a pressure variation which is equal in percentage to the difference between the inspiratory volume and the command.

However, in the case where an extreme value of pressure is predetermined and if the application of such a variation would result in exceeding the extreme value, the new inspiratory pressure is made equal to the extreme value of the pressure.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

Other features and advantages of the invention will furthermore emerge from the following description relating to non-limitative examples.

-3- In the accompanying drawings: Figure 1 is a block diagram of a first embodiment of the device according to the invention; Figure 2 is an operational flowchart of the regulating means of the device of Figure 1; and Figures 3 and 4 are two block diagrams similar to Figure 1 but relating to two embodiments of the device according invention.

In the example shown in Figure 1, the breathing aid device comprises a patient circuit 1 which itself comprises a patient connection 2, namely a facial or nasal mask, or an intubation or tracheotomy tube, connected to an inspiratory branch 3 and to an expiratory branch 4 by the intermediary of a bidirectional branch 5. The expiratory .branch 4 comprises an expiration device 6 which, in a way which is not shown, comprises an expiration device 6 which, in a way which is not shown, comprises an expiration valve and means of controlling this valve. The expiration valve is closed during the inspiratory phases of the patient's breathing. During the expiratory phases of the patient's breathing the expiration valve can either be open so that the patient expires at atmospheric pressure, or it can operate like a discharge valve to oblige the patient to expire at a certain predetermined excess pressure.

The inspiratory branch 3 is connected, at .its end furthest from the mask 2, to a unit 8 for ventilation through inspiratory aid which comprises means, such as an adjustable speed motor-turbine set, for supplying breathable gas 'through the inspiratory branch 3 at anadjustable pressure, in the direction of the mask 2, means of detecting the patient's respiratory reflexes, for example from instantaneous flow rate variations, and means of controlling the expiration valve of the expiration means 6 and an inspiration valve placed in the inspiratory branch 3 in order to open the inspiration valve and to close the expiration valve during the inspiratory phase, and to close the inspiration valve and to release the expiration valve during the expiratory phases. Thus, in the inspiratory phase, the patient is connected in a gas-tight manner with the inspiratory branch 3, and the volume flowing in the inspiratory branch 3 corresponds to the volume of gas inspired. And during the expiratory phases, the patient is connected in a gas-tight manner with the expiratory branch 4 and the volume flowing in the expiratory branch 4 corresponds to the volume of gas expired.

Such inspiratory aid devices, or inspiratory aid devices of the same kind are described in the prior art, in particular in FR-A-2 695 830.

The ventilation unit 8 can comprise pressure control means by means of which the pressure P detected in the inspiratory branch 3 by a detector 10 is compared with a pressure command AI in order to adjust, for example, the speed of rotation of the motor-turbine set in the direction tending to make the pressure P equal to the command AI.

According to the invention, the breathing aid device. comprises means 11 of regulating the patient's breathed volume. The regulating means 11 comprise a control unit 9 for controlling the pressure command AI which the ventilation unit 8 must apply to the inspiratory branch 3 during the inspiratory phases.

The regulating means 11 furthermore comprise a unit 12 for measuring the volume VTI inspired by the patient during each breathing cycle. The unit 12 provides the control unit 9 with a signal indicative of the volume VTI. The control unit 9 comprises an input 13 for receiving the signal VTI, and three inputs 14, 16, 17, allowing the user of the device to enter a minimum breathed volume command into the control unit, in the 9.

15 form of a minimum inspired volume per cycle VTImini, a minimum inspiratory pressure command AImini, and a maximum inspiratory pressure command AImaxi.

In general, the control unit 9 compares the measured volume VTI with the command VTImini and adjusts 20 the pressure command AI in the direction tending to bring the measured volume VTI towards the command VTImini, without however causing the command AI to move 9.9.9 outside of the range included between the two extreme values AImini and AImaxi. Within this range, the control unit 9 tends to increase the command AI when the 9measured volume VTI is lower than the command VTImini, and to reduce the pressure command AI in the opposite case.

When starting up the device, the commands VTImini and AImini are chosen such that the breathed volume VTI is established at a value higher than VTImini when the pressure command AI is equal to AImini. Thus, if the patient breathes as expected, the pressure command AI stabilises at AImini with a breathed volume above the minimum command VTImini. It is only in the event of a breathing anomaly or incident, for example a partial obstruction of the breathing channels, that the measured breathed volume VTI is likely to become lower than VTImini, thus causing an increase in the command AI generated by the control unit 9. When the breathing becomes normal again, the breathed volume again becomes higher than the.command VTImini, such that the control unit 9 returns the pressure command Al more or less rapidly to the value AImini.

The flowchart used by the control unit 9 will now be described in greater detail with reference to Figure 2. At the start, Al is made to equal to AImini (step 18).

U Then, at the end of each breathing cycle, or during 15 each expiratory phase; the measurement VTI of the volume inspired during the preceding inspiratory phase is acquired (step 19) and is then compared with the command VTImini by the test 21. If the measured volume VTI is greater than or equal to VTImini, in other words if the 20 volume inspired by the patient is satisfactory, a test 22 determines if the pressure command AI is or is not greater than the minimum AImini. If the pressure command is equal to the minimum, the conditions are therefore ideal (volume at least equal to the minimum, minimum pressure) and the sequence therefore returns directly to step 19 for acquiring the next inspired volume measurement. In the opposite case, advantage will be taken of the fact that the inspired volume is satisfactory in order to attempt to reduce the pressure command by a step 23 in which there is applied to the pressure command Al, expressed in relative value, a variation equal in percentage and opposite in sign to the difference between the measured inspired volume VTI and the command VTImini. The formula is such that, in the particular case in which the measured volume VTI is equal to VTImini, no modification is applied to the pressure command AI variation).

M--

-7- Returning now to the test 21 on the measured volume VTI, if the latter is lower than the command VTlminj, an attempt will be made to increase the pressure command Al in order to assist the patient more. But prior to this, by a test 24, it will be checked that the pressure command AI has not already reached the maximum Almaxi.

If the answer is yes, an alarm is triggered (step 26) to indicate the necessity of an urgent intervention.

On the other hand, if the pressure command AI is not yet equal to Almaxi, the sequence returns as before to step 23 in which there will be applied to the command AI a variation equal in percentage and opposite in sign to the difference between the measured volume VTI and the command VMmini.

Before actually applying the command AI, reduced or increased such as it has been computed in step 23, to the input of the ventilation unit 8, it will firstly be checked, by a test 27, that' the new computed AI value does not exceed the maximum Almaxi and, by a test 28, that it is not less than the minimum Almini.

If the new Al value has gone beyond one or other of these extreme values, the command AI which will be applied to the ventilation unit 8 will be equal to the extreme value in question (steps 29 and 31).

The example shown in Figure 3 will only be described where it differs with respect to the example shown in Figure 1.

In the example of Figur 'e 3, the breathed volume is no longer measured by means of the volume inspired in each cycle but by means of the volume VTE expired in each cycle. For this purpose, the VTI measuring unit 12 in the inspiratory branch 3 has been eliminated and it has been replaced by a VTE measuring unit 32 in the expiratory branch 4.

The minimum breathed volume command applied to the control unit 9 is therefore the command VTEmini for the volume expired per cycle, in order to be able to be 8 compared directly with the measurement provided by the unit 32.

It can be advantageous to select, case by case, measurement of the inspired volume or measurement of the expired volume. This is the solution proposed by the embodiment shown in Figure 4, which will be described only where it differs with respect to the example shown ii Figure 1.

The measuring unit 42 is this time installed in the bidirectional branch 5 of the patient circuit 1 and it comprises means 43 of selecting the direction of flow in which the volume is to be measured. In accordance with this selection, the unit 42 provides, by choice, a measurement of VTI or of VTE. In accordance with the operating mode of the measuring unit 42, the control i unit 9 interprets the input applied at 14 as an inspired volume command or as an expired volume command. There is no longer any measuring unit in the inspiratory branch 3 2. nor in the expiratory branch 4.

20 In all of the described embodiments, the speed of execution of the flowchart in Figure 2 is sufficient for the measurement carried out in each breathing cycle to .*00 make it possible to correct the pressure applied during the following inspiratory phase. When the measurement is 25, based on the expired volume, it is however possible that the pressure correction will occur only during, and not from the start, of the following inspiratory phase.

The invention is applicable to all ventilators capable of measuring the volumes delivered and of automatically controlling the value of the insufflation pressure.

The invention is applicable to all methods of ventilation using pressure control, and in particular to "inspiratory aid" and "controlled pressure" methods.

Inspiratory aid is a method consisting in maintaining a substantially constant pressure in the patient circuit 9 during the insufflation, the patient initiating the start and end of the insufflation by his respiratory reflexes. The controlled pressure method is identical to the inspiratory aid method except that the patient does not initiate the end of the insufflation, the latter being determined by a fixed time.

It would also be conceivable for the control unit, instead of adjusting the pressure command AI applied to the ventilation unit, to adjust, for example, the speed of rotation of the motor turbine set, or the electrical power supplied to it. It would then be possible to avoid abnormal pressures in the inspiratory branch 3 by comparing the pressure in the inspiratory branch 3 with limits such as AImini and AImaxi, and by initiating a corrective modification of the speed or of the power of the motor turbine set in the case of exceeding, or of risk of exceeding such limits.

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Claims (11)

1. A breathing aid device, comprising: a patient connection; an inspiratory branch in fluid communication with said patient connection, said inspiratory branch including an inspiration valve; an expiratory branch in fluid communication with said patient connection and said inspiratory branch; means for controlling expiration in fluid communication with said expiratory ooo.oi branch, said means for controlling expiration including an expiration valve; means for detecting pressure operatively connected to said inspiratory branch; means for ventilating in fluid communication with said inspiratory branch, said means for ventilating including means for supplying a breathable gas through said inspiratory branch at an adjustable pressure, said means for ventilating further incuding pressure control means for comparing a pressure command to a pressure signal provided by said means for detecting pressure and for adjusting the pressure of the means for supplying; and means for regulating a patient's breathed volume, said means for regulating including means for controlling volume and means for measuring volume, wherein the means for controlling volume provides the pressure command to the pressure control means, and wherein the means for measuring volume provides a signal indicative of a measured volume of breathed gas to the means for controlling volume.

2. The device of claim 1, wherein said patient connection includes a facial mask.

3. The device of claim 1, wherein said patient connection includes a nasal mask. -11-

4. The device of claim 1, wherein the means for supplying breathable gas includes an adjustable speed motor-turbine set.

The device of claim 1, wherein the means for controlling volume includes an input for a minimum inspired volume per cycle, an input for a minimum inspiratory pressure command, and an input for a maximum inspiratory pressure command, wherein the means for controlling volume compares the measured volume from the means for •"measuring volume with the minimum inspired volume per cycle and adjusts the pressure o. command in the direction tending to bring the signal from the means for measuring oo volume toward the minimum inspired volume per cycle, and wherein the means for controlling volume maintains the pressure command within the range of the minimum inspiratory pressure command and the maximum inspiratory pressure command.

6. A breathing aid device, comprising: o S a patient connection; an inspiratory branch in fluid communication with said patient connection, said °15 inspiratory branch including an inspiration valve; an expiratory branch in fluid communication with said patient connection and said inspiratory branch; an expiratory device in fluid communication with said expiratory branch, said expiratory branch including an expiration valve; a pressure detector operatively connected to said inspiratory branch; a ventilation unit in fluid communication with said inspiratory branch, said ventilation unit including a source of breathable gas at an adjustable pressure, said ventilation unit further including a valve controller for opening and closing the inspiration valve and the expiration valve, said ventilation unit further including a 12 pressure controller for comparing a pressure detected by said pressure detector to a pressure command and for adjusting the pressure of the source of breathable gas; and a regulator for regulating a patient's breathed volume, said regulator including a control unit and a measuring unit, wherein the control unit provides the pressure command to said ventilation unit, and wherein the measuring unit provides a signal indicative of a measured volume of breathed gas to the control unit.

7. The device of claim 6, wherein the source of breathable gas at an adjustable 4 pressure includes an adjustable speed motor-turbine set.

The device of claim 6, wherein the control unit includes an input for a minimum inspired volume per cycle, an input for a minimum inspiratory pressure command, and an input for a maximum inspiratory pressure command, wherein the control unit compares the measured volume from the measuring unit with the minimum inspired .volume per cycle and adjusts the pressure command in the direction tending to bring the signal from the measuring unit toward the minimum inspired volume per cycle, and wherein the control unit maintains the pressure command within the range of the minimum inspiratory pressure command and the maximum inspiratory pressure command.

9. A breathing aid device, comprising: a patient connection; an inspiratory branch in fluid communication with said patient connection, said inspiratory branch including an inspiration valve; an expiratory branch in fluid communication with said patient connection and said inspiratory branch, said expiratory branch including an expiration valve; a pressure detector operatively connected to said inspiratory branch; 13 a source of breathable gas at an adjustable pressure in fluid communication with said inspiratory branch; a valve controller for opening and closing the inspiration valve and the expiration valve; a pressure controller for comparing a pressure detected by said pressure detector to a pressure command and for adjusting the pressure of the source of breathable gas; a control unit for providing the pressure command to said pressure controller; and a measuring unit for providing a signal to the control unit indicative of a measured volume of breathable gas detected per breathing cycle to the patient connection.

10. The device of claim 9, wherein said control unit includes an input for a minimum ao a. oo. inspired volume per cycle, an input for a minimum inspiratory pressure command, and an input for a maximum inspiratory pressure command, wherein said control unit a compares the measured volume from said measuring unit with the minimum inspired volume per cycle and adjusts the pressure command in the direction tending to bring the 6:6* 15 signal from said measuring unit toward the minimum inspired volume per cycle, and wherein the control unit maintains the pressure command within the range of the minimum inspiratory pressure command and the maximum inspiratory pressure command.

11. A breathing aid device substantially as herein described with reference to any one embodiment and its accompanying drawings. DATED this 15th day of July 1999. NELLCOR PURITAN BENNETT FRANCE DEVELOPPEMENT Attorney: PETER R. HEATHCOTE Fellow Institute of Patent Attorneys of Australia of BALDWIN SHELSTON WATERS