WO1996009847A1

WO1996009847A1 - Breathing apparatus

Info

Publication number: WO1996009847A1
Application number: PCT/FR1995/001257
Authority: WO
Inventors: Nicolas Bloch; Michel Jounenc; Stéphane Ruton
Original assignee: Taema
Priority date: 1994-09-29
Filing date: 1995-09-28
Publication date: 1996-04-04
Also published as: EP0754070A1; FR2725137B1; FR2725137A1; AU3610595A

Abstract

When a treatment involves delivering a non-pressurised gas, particularly oxygen, to the respiratory tract, it is important to know the exact times when the prescribed treatment has been carried out. For this purpose, the parameter taken into account is the flow rate through the feed line (T) to the patient (P). Given that the signals are weak compared with the noise, a discrimination procedure is executed by a computer (17, 18) connected to the flow rate sensor (15). The procedure comprises generating a standard signal by calculating the difference between the average flow rates over two periods, and carrying out a statistical calculation on the basis of the changes in said signal.

Description

RESPIRATORY ASSISTANCE APPARATUS

The present invention relates to a respiratory assistance device provided with a device for detecting respiratory cycles, in particular for controlling the execution of a treatment during which a patient is made to breathe a treatment gas, or a mixture of such a gas with air, which is sent to the inlet of the patient's respiratory tract.

In the remainder of this text, we will essentially speak of oxygen therapy, that is to say of the case where the treatment gas is oxygen, but it should be understood that the device may possibly be used in cases where the treatment gas is different.

The medical prescription usually provides that the sending of treatment gases must be carried out, under the responsibility of the patient, for a determined time, which is generally greater than one hour. It is important, not only from a purely medical point of view, but also to satisfy the wishes of the Medical Insurance Bodies, to be able to check whether the treatment has been carried out for the correct time and correctly.

For this purpose, it has been imagined to control either the pressure or the flow rate in the conduits connecting the source of treatment gas to the patient. In fact, inspiration results in a drop in pressure or an increase in flow rate at the outlet of these conduits at the inlet of the patient's respiratory tract. Expiration results in an increase in pressure or a drop in flow in the same place. It is understood that such variations of a pressure or flow signal can be processed in appropriate electronics to obtain signals indicating that the treatment is in progress and therefore to count the times of use in order to deduce the diagnosis of treatment.

A device making it possible to obtain this result is described in international patent application WO 94/13349.

SUBSTITUTE SHEET (RULE 26) This device comprises a unit for supplying the gas or the mixture of treatment gases, essentially formed by a reserve of bottled gas for example, which flows into a pipe leading to a mask intended to be placed against the face of a patient . This mask establishes a more or less perfect seal on the facial skin so that the patient who is equipped with it almost breathes only the gas which reaches him from the supply unit of this gas.

The device also includes a pressure or flow measurement means which makes it possible to determine the time during which the patient actually breathes the gas delivered.

As in this previous proposal, the connection between the supply unit and the patient's respiratory tract is relatively isolated from the external environment, the variations due to the respiratory cycles of the pressure and flow signals are clear and therefore easily measurable by a sensor placed somewhere in this link. It is therefore easy to deduce from these signals the time of use of the device.

However, since conceived, new respiratory assistance techniques have been developed intended above all to ensure treatment in a non-hospital environment, while allowing the patient to have an almost normal activity at home, without the nursing staff being present.

These techniques essentially consist in sending, at the inlet of the respiratory system of the patient, in particular in his nostrils, a permanent and constant flow, fixed in advance, of treatment gas, for example a mixture of 90 ° ό of oxygen and 10% nitrogen, for periodic treatment times set by the practitioner.

For this purpose, not waterproof masks are used, but devices commonly called "breathing glasses", composed of a frame to which are attached small tubes opening into the patient's nostrils, a short distance from their entrance. These small tubes are connected to the breathing gas supply unit by a flexible and light conduit whose length can reach several meters, typically 10 to 15 m.

These devices therefore have the important characteristic of not being watertight vis-à-vis the exterior whereby, during inspiration, the patient sucks in his respiratory tract, a mixture formed of atmospheric air and treatment gas. . During exhalation, oxygen mixes with the exhaled air.

In addition, for these recent respiratory assistance devices, small delivery units are used, also called "concentrators" in which oxygen is not supplied from a reserve such as a bottle, but continuously produced in production columns which contain molecular sieves capable of separating oxygen from the other components of the air and in particular from nitrogen. These production devices generally comprise two columns placed alternately in production and in regeneration, this last phase making it possible each time to regenerate the molecular sieves of the column which was previously in production. To fix the ideas, a production / regeneration phase can last between 7 and 15 seconds for example.

In these recent respiratory assistance devices, the pressure and flow variations are relatively clear at the inlet of the patient's respiratory tract, that is to say at the outlet of the treatment gas ducts. Due to the pressure drops in the flexible conduit which connects the source of treatment gas to the patient, the signals become weaker, and more difficult to separate from the noise, if one moves away from the end of the conduit towards the '' processing gas production unit. The signal to be detected, whether a flow signal or a pressure signal, then has an extremely unfavorable signal / noise ratio.

The noise on this signal comes firstly from the fact that, as already indicated, the concentrator operates with a switching cycle between production and regeneration which is about the same frequency as the patient's respiratory cycles. This phenomenon therefore introduces an oscillation on the signal which is very difficult to distinguish from the variations introduced by the respiratory cycles.

In addition, the breathing gas must pass through a bubbling humidifier which, by producing bubbles, also contributes significantly to increasing the background noise of the signal.

To reduce the influence of noise on the signal, we would therefore be tempted to place the pressure or flow sensor in the supply gas supply duct near the user, where the respiratory signal is most marked. . However, this solution requires heavy glasses of special design and therefore expensive.

In addition, as already indicated above, the concentrator respiratory assistance devices have above all been designed to increase patient mobility, in particular by providing the device with a supply duct of considerable length. Therefore, it is understood that placing the sensor close to the user would cause considerable discomfort, not only by the increase in weight of the glasses, but also by the inevitable presence of several connecting elements to the supply unit. such as electrical conductors and a measurement pipe parallel to the supply pipe for the process gas. This solution is far from satisfactory, then that a priori in terms of signal / noise ratio, this arrangement would be the most favorable.

If, on the contrary, the sensor is placed close to the supply unit, this favorable signal-to-noise ratio can only be obtained by also providing an additional conduit connecting the "breathing glasses" to the sensor (which would be, in this case placed immediately downstream of the humidifier). This solution would therefore lighten the respiratory glasses thanks to the absence of the sensor, but would not prevent an increase in the rigidity and the weight of the supply duct.

In the first analysis, a measurement of the flow rate or pressure of the respiratory gas therefore seems unsuitable for accounting for the time of use of a breathing apparatus with concentrator endowed with convenient and undemanding possibilities of use for the patient.

It should also be noted that patent EP 0 602 734 describes a respiratory device in which, from a measurement of the flow rate of the treatment gas, the supply of predetermined doses of treatment gas is synchronized with the respiratory cycle of the patient . In this document, we are not concerned with the accuracy of the flow measurement, neither this problem nor the location of the sensor in the process gas circulation duct being addressed there.

The object of the present invention is to provide a respiratory assistance device equipped with a concentrator which allows effective control of the application of medical prescriptions, without causing discomfort for the patient, while being of a reduced complication and low cost.

The subject of the invention is therefore a respiratory assistance device comprising a source of treatment gas in the form of a concentrator intended to provide a flow with little near constant treatment gas, a conduit for carrying this treatment gas to the patient and breathing glasses connected to said conduit and intended to allow the patient to breathe a mixture of ambient air and said treatment gas, this apparatus also comprising a sensor flow intended to detect the flow of process gas and electronic calculation means to, from the flow signal supplied by said sensor, determine the actual duration of respiratory assistance provided by the device, the latter being characterized in that said electronic calculation means comprise means for sampling the flow signal supplied by said sensor, means for calculating the current average of said samples, means for, periodically and over a first duration, extract from said current average of the first successions of values; means for periodically and over a second duration longer than said first duration, extracting from a plurality of said first successions of values, second successions of values; comparison means capable, by comparison with a beam of data recorded empirically while said glasses are supplied with treatment gas, but not worn, to determine which of said second predetermined durations during which said second successions of values correspond to the actual wearing said glasses, when they are supplied with treatment gas, and calculation means for cumulating the durations thus determined in order to obtain said effective duration of respiratory assistance. It follows from these characteristics that only the irregularities in the flow signal due to the patient's respiratory cycles are taken into account to establish the duration of use of the device. According to a first embodiment of the apparatus according to the invention, the values of said first successions of values are amplitudes of the flow rate measured during the flow of each of said first predetermined time periods. Preferably, these amplitudes are the maximum amplitudes recorded respectively during said first predetermined time periods.

According to a second embodiment, the values of said first successions of values are formed by the number of times that the measured flow signal crosses a predetermined threshold.

The invention will now be explained in more detail with the aid of practical examples illustrated with the drawings among which: FIG. 1 is a simplified diagram of the respiratory assistance device according to the invention; FIG. 2 is a flowchart illustrating a first mode of operation of the computer of the apparatus according to the invention; and FIG. 3 is a flow diagram illustrating a second mode of operation of the computer and the way in which the signals on which this computer works are prepared.

FIG. 1 shows a respiratory assistance unit A capable of producing treatment gas, in this case oxygen, possibly mixed in defined proportions with air. This unit is advantageously made in the form of equipment placed in a small cabinet mounted on casters for example, so as to be easily movable at home by the patient during the treatment. The cabinet is connected by a single tube T of suitable diameter, to respiratory glasses L intended to be worn by the patient symbolized in P. As an indication, the tube T can have a length of several meters, preferably between 10 and 15 m to give the patient the desired mobility. It will be noted that the treatment gas supplied by the unit A is breathed in by the patient P by mixing at the level of the entry orifices of his respiratory tracts with ambient air, the respiratory glasses therefore being essentially leaktight with respect to to the facial skin of patient P.

Unit A comprises a concentrator 1 essentially comprising the following members: a primary filter 2 receiving ambient air; - a compressor 3 delivering pressurized air at 4 to a buffer capacity 5; a cooling system 6 equipped with a fan 7 and an exchanger 8; two columns 9 and 10 with molecular sieves capable of isolating the oxygen in the air which is supplied to them through: a rotary switching valve 11 intended to connect alternately columns 9 and 10 in production mode and in regeneration regime ; - a bacteriological filter 12 connected to the outlet of columns 9 and 10; a flow selector 13 placed downstream of the filter 12 and a humidifier 14 placed downstream of the selector 13.

The humidifier 14 is connected to the connection pipe T by means of a flow sensor 15 which is incorporated in the cabinet A, that is to say in the case illustrated, located at a significant distance from the respiratory glasses L.

As shown, the humidifier 14 can also be connected to a pressure sensor 16 which is used in particular in the second embodiment of the invention described below.

The flow sensor 15 can be of the "AWM 5101" type from the company Honey ell, and it is electrically connected, like the pressure sensor 16, to an electronic card 17, itself in communication with a calculator 18.

The function of the electronics 17 is to transform the signals from the sensors 15 and 16 into data usable by the computer 18. The latter is connected to a display device 19 allowing, according to the present invention, the reading of the duration of effective use of the respiratory assistance device and possibly other useful data relating to its operation.

We will now describe a first embodiment of the invention and more precisely the operation of the computer 18, with reference to FIG. 2.

The flow signal supplied by the sensor 15 is sampled in the electronics 17 with a short period, typically 10 milliseconds. Two averages are calculated on different and sufficiently large numbers of points, for example one on 25 points and one on 30 points. The difference between these two means produces a normalized signal around zero, regardless of the value of the flow rate. Breathing signals, especially expiration, are generally rapid and therefore poorly damped.

An interval around zero is fixed: when the signal remains confined within this interval, it is considered that there is no respiration; otherwise, it is possible to detect a cycle. A respiratory cycle can cause several threshold crossings, a relationship is necessary between the number of exceedances and the presence or absence of a patient. The threshold defining the interval is empirically chosen so as to limit the number of false detections (no overshoot if the glasses are not worn), and to guarantee good sensitivity whatever the flow rates.

The influence of many parameters (artefacts, height of water in the humidifier, breathing amplitude, etc.) on exceeding thresholds means that additional identification criteria must be considered.

According to the mode of implementation of FIG. 2, four criteria (C1, C2, C3, C4) have been retained in order to make a decision as to the connection of the patient P (wearing of glasses L). They correspond to the conversion of qualitative findings into digital data.

Each of the criteria can evolve between 0 and 1 continuously. The closer it is to 1 the more certain the connection will be.

The first three provide information on the possibility of a connection during the last elapsed period of time, for example one minute, the fourth provides information on a longer elapsed time, for example the last five minutes.

A period is broken down into two half-periods here of 30 seconds, during which the number of threshold crossings is counted (blocks 20 and 21, FIG. 2).

Cl and C2 (calculated in 22 and 23) are the ratio between the number of exceedances and 7 (in the example described). Seven exceedances are interpreted as a certain connection during the last half-period (Cl or C2 equal to 1). The third criterion C3 (calculated in 24) is the average of the first two. We set 75% (C3 = 0.75) the threshold to conclude to a connection during the last period of time. Likewise, if C3 is less than 25%, a disconnection is concluded (see blocks 25 to 28 respectively).

Between these two thresholds, no conclusion is drawn, we remain in the previous state. Thus, it is possible to conclude a connection during the last period with a confidence equal to C3.

The fourth criterion is calculated (in 29) every half period (30 seconds). It assesses the confidence in a connection during the corresponding elapsed time (5 minutes for example).

C4 = Σ (C3 / 10) * branch branch = 1 if branching during the last minute, 0 otherwise. C4 is the average of the confidence over the last elapsed time (5 minutes for example). A threshold on C4 has been set at 50%. This last criterion (C4) is the one which allows to conclude or not a connection (see respectively blocks 30 to 33). Using the data indicated above by way of example, the patient's connection time is evaluated with a maximum error of ± 5 minutes. This data, which represents the effective duration of use of the respiratory system, is displayed on the display device 19. Whereas the durations of treatment prescribed medically are usually at least one hour, this precision is considered sufficient by the practitioners.

FIG. 3 schematically represents a second embodiment of the invention.

The output signal from the flow sensor 15 is sampled at 34 with a period which in this case can be 25 milliseconds, for example. The samples are subjected to the establishment of a current average called "short" over the last 10 seconds (block 35) and a current average called "long" over the last minute, for example (block 36). The two means are then used to obtain at 37 a sampled signal normalized around zero. This signal is updated at the sampling frequency.

In the embodiment of FIG. 3, the samples are subjected to a calculation at 38, respectively 39 to determine, over the last 10 seconds for example (that is to say with 40 samples), the amplitude maximum and minimum amplitude occurred during this period. From these data, the computer 18 calculates, over the same duration of 10 seconds, the maximum difference by making the difference between them (block 40). Over a second period longer than the period described above which may be the last minute for example, the deviation signals are in turn subjected to a calculation (in the present case therefore on a set of six values), to determine the 'maximum amplitude (block 41) and the minimum amplitude (block 42) occurred during this second duration and from this data, the maximum difference is established (block 43).

Consequently, at the output of block 43, a value is available every minute representing, over the last minute elapsed, the irregularities or variations in the measured flow signal due to the patient's breathing.

Furthermore, the only "short" average signal (block 35) is subject to the calculations symbolized in blocks 46 to 51, these calculations being analogous to those carried out in blocks 38 to 43. Consequently, these calculations on the average " short "flow allow to obtain at the output of block 51, each time over the last minute elapsed another value representing the variation in flow. In the present embodiment, in order to improve the accuracy of the determination of the connection of the patient, the pressure signal supplied by the sensor 16 is sampled at 44, preferably at the same sampling frequency as the signal flow in 34.

In 45, these samples are subjected to the establishment of a "short" average over the last 10 seconds for example. This average is subject to the calculations symbolized in blocks 46A to 51A, these calculations being analogous to those carried out with regard to the flow rate in blocks 38 to 43 and in blocks 46 to 51. Consequently, one obtains at the outlet of the block 51A, each time over the last minute elapsed, a value which represents the variation of the pressure measured at the level of the pressure sensor 17. The calculated amplitude of flow deviations (block 43 and

51) and the calculated pressure amplitude deviations (block 51A) are then treated by statistical comparison (block

52) to a flow and pressure data bundle (block

53) recorded in the memory of the computer 18 and recorded, under reference measurement conditions, while the breathing glasses are not worn by a patient. These measurements can therefore be carried out for example during the factory calibration of the respiratory assistance device. A statistical comparison can thus be carried out every minute in the example described, and if the comparison determines that the calculated data do not match the data stored in the computer, we conclude that the patient is connected for the minute elapsed. These times are accumulated in block 54 to provide the total connection time of the patient.

Claims

1. Respiratory support apparatus comprising a source of process gas in the form of a concentrator

(1) intended to provide an almost constant flow of treatment gas, a conduit (T) for carrying this treatment gas to the patient and breathing glasses (L) connected to said conduit (T) and intended to allow the patient to breathe a mixture of ambient air and said treatment gas, this apparatus also comprising a flow sensor (15) intended to detect the flow of the treatment gas and electronic calculation means (17, 18) for, from the signal of flow supplied by said sensor (15), determining the actual duration of respiratory assistance provided by the device, the latter being characterized in that said electronic calculation means (17, 18) comprise means for sampling the flow signal supplied by said sensor (15), - means (20, 21; 35, 36, 37) for calculating the current average of said samples, means (22, 23, 24; 38, 39, 40, 46, 47, 48 ) to, periodically and for a first period, extract from said current average of the first successions of values; means (29; 41, 42, 43, 49, 50, 51) for, periodically and over a second duration longer than said first duration, extracting from a plurality of said first successions of values, second successions of values; comparison means (30, 32; 52, 53) capable, by statistical comparison with a beam of empirically recorded data while said glasses (L) are supplied with treatment gas, but not ranges, to determine those from said second predetermined durations during which said second successions of values correspond to the effective wearing of said glasses (L), when they are supplied with treatment gas, and calculation means (31, 33; 54) for cumulate the durations thus determined in order to obtain said effective duration of respiratory assistance.

2. Respiratory assistance device according to claim 1, characterized in that the values of said first successions of values are amplitudes of the flow rate measured during the flow of each of said first predetermined time periods.

3. Respiratory assistance device according to claim 2, characterized in that said amplitudes are the maximum amplitudes recorded respectively during said first predetermined periods of time.

4. Respiratory assistance device according to any one of claims 1 to 3, characterized in that the values of said second successions of values are amplitudes of the values of said first successions of values calculated during the flow of each of said second periods of predetermined times.

5. Respiratory assistance device according to claim 4, characterized in that the amplitudes calculated to obtain said second successions of values are maximum amplitudes.

6. Respiratory assistance device according to claim 5, characterized in that said comparison means (52) make a comparison on the maximum amplitude values calculated to obtain said second successions of values and on the averages established by said means d 'average establishment (35).

7. Respiratory assistance device according to any one of the preceding claims, characterized in that it also comprises a pressure sensor (16) and in that said calculation means (17, 18) are arranged to subject the output signal of said pressure sensor of the calculation operations (45A to 51A) analogous to those to which the output signal of said flow sensor (15) is subjected and in that the result of said calculations are taken into account for said statistical comparison ( 52).

8. Respiratory assistance device according to claim 1, characterized in that the values of said first successions of values are formed by the number of times that the measured flow signal crosses a predetermined threshold (20, 21).

9. Respiratory assistance device according to claim 8, characterized in that said calculation means (17, 18) are programmed to operate in the following manner: a) determination of the average flow over two periods of time, b) subtraction of these two bit rates, to create a normalized signal around zero, c) study of the variations of this signal during two consecutive time periods, and calculation of a confidence coefficient during this period, d) calculation of a confidence coefficient during a longer period and conclusion, e) repetition of operations a) to d).

10. Respiratory assistance device according to any one of the preceding claims, characterized in that the flow sensor (3) is incorporated into said concentrator (1).