FR2725137A1 - DEVICE FOR DETECTING RESPIRATORY CYCLES, PARTICULARLY FOR MONITORING THE EXECUTION OF A TREATMENT - Google Patents

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

 The present invention relates to 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 patient's airway entrance.

 According to a common technique for respiratory assistance, a constant flow rate, fixed in advance, of treatment gas, for example a mixture of, is sent to the patient's respiratory system, in particular in his nostrils. 90% oxygen and 10% nitrogen. For this purpose, devices are commonly used, commonly called "breathing glasses", composed of a spectacle frame to which are fixed small tubes opening into the nostrils of the patient, a short distance from the entry thereof. During inspiration, the patient sucks a mixture of atmospheric air and treatment gas into his respiratory tract. During exhalation, oxygen mixes with the exhaled air.

 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 to be able to check whether the treatment has been carried out correctly and for the expected time.

 For this purpose, it has been imagined to control the pressure in the conduits connecting the source of treatment gas to the patient. In fact, inspiration results in a drop in pressure at the outlet of these conduits at the inlet of the patient's respiratory tract. Expiration results in increased pressure in the same place. It is understood that variations in a pressure signal can be processed in appropriate electronics to obtain signals indicating that the processing is in progress.

 The pressure variations are clear at the inlet of the patient's respiratory tract, that is to say at the outlet of the treatment gas conduits. 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 source of process gas. If a humidifier, consisting of a container containing water in which the process gas is bubbled, is placed in the process gas circuit, the pressure sensing point must be placed downstream of this device by relative to the direction of flow of treatment gas. We therefore have to either place the sensor close to the user, which is inconvenient for the user, or to provide an additional tube connecting the "breathing glasses" to the sensor , which increases the rigidity and the weight of the conduit, and which requires the use of special "breathing glasses", and therefore expensive.

It has also been proposed to place a temperature sensor of the thermistor type on the respiratory glasses, in the immediate vicinity of the end of the treatment gas duct. We are then forced to connect the sensor to a signal processing unit by electrical wires which are added to the processing gas conduit. This solution is also expensive and complicated, and likely to annoy the patient.

 Another disadvantage of devices with a pressure variation sensor is that they do not, by themselves, control the proper functioning of the means for supplying treatment gas or air enriched with treatment gas: in the event of the source of treatment gas, or obstruction or rupture of duct upstream of the sensor, it will only be possible to verify that the patient has used the device correctly, even if he has not received the prescribed dose of treatment gas . If the obstruction or rupture is downstream of the sensor, a dispute may arise between the patient and the doctor, the former having carried out what was asked of him, and the latter seeing no recorded trace. Control and alarm means can be provided, but they constitute an additional complication for the device.

 The present invention aims to provide a device which allows effective control of the application of medical prescriptions, without causing discomfort for the patient, while being of a reduced complication and a low cost.

To obtain this result, the invention provides a device of the type indicated at the start, this device being usable for determining the periods of time when the treatment has been effective and having the particularity that it comprises
a flow sensor placed on said duct serving to send the flow of treatment gas or air enriched with treatment gas to the patient,
- electronics and a computer capable of determining, from the sensor output signals, the average flow rate of process gas or air enriched in process gas, as well as the number and direction of flow rate variations during a predetermined period of time, and to issue signals of existence or absence of respiratory cycles accordingly.

 Thanks to the fact that a flow rate is detected, the sensor can be placed at a distance from the end of the conduit much greater than in the conventional technique.

Advantageously, it will be incorporated into a device for producing treatment gas or air enriched with this gas.

 Preferably, the computer is able to record the average flow rate of process gas or air enriched in process gas, for at least a period of time chosen in advance.

 In this way, a single sensor can control both the proper functioning of the means of production of treatment gas, or air enriched with treatment gas, and the proper observation of medical prescriptions: in the event of the device being stopped or obstruction of the duct, the flow is zero.

A rupture of the duct results in a constant flow, even if the user has correctly fitted the "breathing glasses
An important problem to be solved in order to detect the correct use of the equipment lies in the existence of very unfavorable signal / noise ratios.

However, to obtain acceptable results in an acceptable manner, the computer must extract the "respiratory cycle" information from the flow signal. For this, it advantageously proceeds as follows
a) determination of the average flow over two time periods,
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 for a longer period and conclusion,
e) repetition of operations a) to d).

The invention will now be explained in more detail with the aid of a practical example illustrated with the drawings among which
Figure 1 is a simplified diagram of the apparatus.

 Figure 2 is a flowchart of operation of the computer.

FIG. 1 shows a device for producing treating gas, here oxygen, which sends, via a line 2, oxygen to a patient symbolized by P. A flow sensor 3 is inserted on line 2. I1 can be of the "AWM 5101" type from the Company
Honeywell, and it is electrically connected to an electronic card 4, itself in communication with a computer 5.

 The function of the electronics 4 is to transform the signals from the sensor 3 into data usable by the computer 5.

 The operation of the computer will be described. I1 is illustrated in FIG. 2.

 The flow signal is sampled 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 in this interval, we consider that there is no breathing, 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 fitted), 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.

 Following an interesting practical realization, four criteria (C1, C2, C3, C4) were retained in order to make a decision as to whether or not to connect the patient. 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.

 C1 and C2 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 (C1 or C2 equal to 1). The third criterion C3 is the average of the first two. The threshold was set at 75% (C3 = 0.75) to conclude that there was a connection during the last period of time. Likewise, if C3 is less than 25%, it concludes with a disconnection.

 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 every half period (30 seconds). It assesses the confidence in a connection during the corresponding elapsed time (5 minutes for example).

C4 = s (C3 / lO) * branch
branch = 1 if connection during the last minute,
O 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 50t. This last criterion (C4) is the one which allows to conclude or not a connection.

 Using the data indicated above by way of example, with a maximum error of + 5 minutes, the evaluation of the time of presence of the patient is obtained. Whereas the medically prescribed treatment times are usually at least one hour, this precision is considered sufficient by practitioners.

Claims (5)

 1. 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 at the entrance to the patient's respiratory tract, said device being usable for determining the periods of time during which the treatment has been effective,  characterized in that it includes  - a flow sensor (3) placed on said duct used to send the flow of treatment gas or air enriched in treatment gas to the patient,  - an electronics (4) and a computer (5) capable of determining, from the sensor output signals, the average flow rate of treatment gas or air enriched in treatment gas, as well as the number and the direction of the variations of flow during a predetermined period of time, and to issue signals of existence or absence of respiratory aid treatment accordingly.  2. Device according to claim 1, characterized in that the flow sensor (3) is incorporated in a device (1) intended to supply the treatment gas or the air enriched with treatment gas.  3. Device according to claim 1 or 2, characterized in that the electronics is capable of recording the average flow rate of treatment gas or of air enriched in treatment gas, for at least a period of time chosen in advance. .  4. Device according to one of claims 1 to 3, characterized in that the computer is programmed to operate in the following manner  a) determination of the average flow over two time periods,  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 for a longer period and conclusion,  e) repetition of operations a) to d).  5. Device according to one of claims 1 to 4, characterized in that it is intended for the case where the treatment gas is essentially formed of oxygen.