Ventilation device and method for determining a fresh gas flow

Abstract

Ventilation device (1) with a fresh gas connection (23, 25, 27), a gas outlet (3), an absolute pressure sensor (21) and a data processing device (37), wherein the gas outlet (3) is designed to connect a supply line for a patient and is fluidically connected to the fresh gas connection (23, 25, 27) via an inspiration branch (17), wherein the absolute pressure sensor (21) is arranged and configured to measure an absolute pressure in the inspiration branch (17), and wherein the fresh gas connection (23, 25, 27) is configured for connecting a fresh gas supply and comprises a control valve (31) and a differential pressure sensor (33), wherein a gas flow from the fresh gas supply to the inspiration branch (17) can be adjusted via the control valve (31) and the differential pressure sensor (33) is arranged and configured to measure a differential pressure in the fresh gas connection (23, 25, 27) between the inspiration branch (17) and the control valve (31), wherein the data processing device (37) is connected to the absolute pressure sensor (21) and the differential pressure sensor (33) to receive and record the absolute pressure measured by the absolute pressure sensor (21) at a plurality of times and the differential pressure measured by the differential pressure sensor (33) at a plurality of times, wherein the data processing device (37) is designed to determine a fresh gas flow through the fresh gas connection (23, 25, 27) at a specific time from the differential pressure measured at the specific time, the absolute pressure measured at the specific time and one or more absolute pressures measured at times prior to the specific time, wherein the data processing device (37) is configured to determine the fresh gas flow or the fresh gas flows from a corrected differential pressure or corrected differential pressures, wherein the corrected differential pressure or the corrected differential pressures are determined by means of a transfer function from the measured differential pressure or the measured differential pressures and the absolute pressures used in determining the respective fresh gas flow.

Description

[0001] The present invention relates to a ventilation device with a fresh gas connection, a gas outlet, an absolute pressure sensor and a data processing device, wherein the gas outlet is configured to connect a supply line for a patient and is fluidically connected to the fresh gas connection via an inspiration branch, wherein the absolute pressure sensor is arranged and configured to measure an absolute pressure in the inspiration branch, and wherein the fresh gas connection is configured to connect a fresh gas supply and comprises a control valve and a differential pressure sensor, wherein a gas flow from the fresh gas supply to the inspiration branch can be adjusted via the control valve and the differential pressure sensor is arranged and configured to measure a differential pressure in the fresh gas connection between the inspiration branch and the control valve, as well as a method for determining a fresh gas flow.

[0002] To ventilate a patient with a ventilator or an anesthesia machine, the patient is connected to a gas outlet of the ventilator via a supply line. The air exhaled by the patient is collected by an expiratory branch of the device and conditioned by the ventilator. Among other things, the air is cleaned of carbon dioxide and used components of the breathing gas, such as oxygen and anesthetic gases, are reintroduced from a fresh gas supply via a fresh gas connection. The conditioned breathing air is made available to the patient at the gas outlet via an inspiratory branch. The fresh gases are supplied via one or more fresh gas connections, which are connected to the gas outlet via the inspiratory branch.The fresh gas connections are designed to connect fresh gas supplies, for example in the form of gas cylinders, a central gas supply or a redundant gas supply, which can be used to automatically switch between a central gas supply and a gas cylinder.

[0003] Each fresh gas connection comprises a control valve and a differential pressure sensor. The control valve, which can be electronically or manually controlled, is used to adjust the flow of fresh gas. The differential pressure sensor is designed to measure or determine the differential pressure between the control valve and the inspiratory branch. The measured or determined differential pressure can in turn be used to determine the flow of fresh gas – the fresh gas flow – into the ventilator, which is used as the basis for adjusting the control valve. If the control valve is electronically controlled or regulated, the determined fresh gas flow can be used directly to regulate or control the control valve so that a predetermined fresh gas flow or target flow is achieved. However, the control valves often have to be regulated manually, for example for regulatory reasons. For this purpose, the determined fresh gas flow is shown on a display orshown on a display and an operator adjusts the control valve so that the determined fresh gas flow corresponds to the target flow.

[0004] However, adjusting the control valves has proven difficult in practice. Since the differential pressure measured by the differential pressure sensors is not constant or at least changes only slowly, a constant fresh gas flow cannot be displayed for adjustment. When pressure changes, for example when a valve in the expiratory branch closes and / or the patient's breathing phase changes, brief compensatory processes occur that become noticeable as pressure waves in the ventilator. These pressure waves lead to a short-term fluctuation in the differential pressure determined by the differential pressure sensor. These fluctuations are imprinted as narrow-band disturbances on the specific fresh gas flows and make correct adjustment of the control valves more difficult. A simple temporal averaging of the specific fresh gas flows or the specific differential pressures would, in principle, be suitable for filtering out the narrow-band disturbances.In this case, averaging would make the adjustment of the fresh gas flow even more difficult, since changes in the set fresh gas flow only lead to changes in the specific fresh gas flow with a significant time delay.

[0005] In principle, this problem can be solved or at least significantly reduced by arranging the fresh gas connections as far as possible from the gas outlet in the ventilator. The greater the distance that respiration-induced pressure waves have to travel before they reach a differential pressure sensor, the lower the disturbance. The disadvantage of this arrangement, however, is that it takes significantly longer for a change in the setting of the control valves to lead to a change in the composition of the breathing gas supplied to the patient at the gas outlet. In order to be able to react quickly, the fresh gas connections are therefore preferably arranged as close as possible to the gas outlet. There, the differential pressure sensor and thus the specific fresh gas flow are also exposed to particularly strong disturbances.

[0006] US 6,945,123 B1 discloses a ventilator with a fresh gas port and a gas outlet for connecting a supply line for a patient. The fresh gas port includes several control valves and a differential pressure sensor, which is part of a flow sensor. The differential pressure sensor is formed by two absolute pressure sensors arranged on opposite sides of a constricted section of a line in the direction of flow. The two absolute pressure sensors each measure the absolute pressure against vacuum. They are connected to a differential pressure circuit to determine the pressure difference across the constricted section of the line.

[0007] US 2006 / 0 283 450 A1 discloses a ventilation device with a gas source for generating breathing gas, a gas supply system, and a breathing circuit. The gas supply system comprises a pressure generator for generating a constant flow, a control valve whose inlet is connected to a differential pressure sensor, and a flow sensor. The differential pressure sensor is designed to measure the pressure difference between the breathing gas at the control valve and the ambient pressure in order to detect a pressure increase caused by the pressure generator.

[0008] WO 2011 / 147 438 A1 discloses a ventilation device with a gas channel comprising a breathing circuit. The breathing circuit is connected to a patient via an inspiration and expiration branch. Pressure is determined at different flow points in the gas channel. For this purpose, pressure sensors are provided outside the gas channel and are connected to a data processing device. The data processing device determines an estimated pressure in the gas channel as the average of the pressure values ​​present at the two flow points. The estimated pressure is transmitted to a flow determination unit for determining the flow between the two flow points.

[0009] WO 2011 / 147 438 A1 discloses a method for controlling the differential pressure in a CPAP (continuous positive airway pressure) device, wherein the differential pressure is adjusted depending on a measured ambient air pressure and / or the measured ambient temperature. The device comprises a differential pressure sensor located directly upstream of a connector element that connects the device to an inspiratory branch. The differential pressure at the differential pressure sensor is determined as the pressure difference between the pressure in the ventilation mask and the ambient pressure.

[0010] In view of the problems known from the prior art, it is an object of the present invention to provide a ventilation device and a method in which a fresh gas flow can be determined as free as possible from ventilation-induced, narrowband disturbances.

[0011] In a first aspect, the object underlying the invention is achieved by a ventilation device in which the data processing device is connected to the absolute pressure sensor and the differential pressure sensor in order to receive and record the absolute pressure measured by the absolute pressure sensor at a plurality of times and the differential pressure measured by the differential pressure sensor at a plurality of times. The data processing device is configured to determine a fresh gas flow through the fresh gas connection at a specific time from the differential pressure measured at the specific time, the absolute pressure measured at the specific time, and one or more absolute pressures measured at times prior to the specific time.

[0012] The ventilation device according to the invention, which can also be an anesthesia device, comprises a gas outlet and a fresh gas connection which are connected via an inspiration branch. An inspiration branch is understood to be a part of a ventilation device through which a breathing gas flows before it is made available at the gas outlet to a patient who is connected to the gas outlet, for example, via a breathing mask or a differently designed supply line. An absolute pressure sensor is arranged in or on the inspiration branch, with which the absolute pressure in the inspiration branch, i.e. the pressure of the breathing gas in the inspiration branch, can be measured or determined. An absolute pressure is understood here to be the pressure of a gas in relation to a constant or only slowly changing reference pressure, for example vacuum or ambient pressure.

[0013] Preferably, the absolute pressure is measured against vacuum, since the absolute pressure measured in this way can be used directly as a reference value for the fresh gas flow measurement.

[0014] The fresh gas connection is designed to be connected to a fresh gas supply, for example in the form of a gas cylinder, a central gas supply, or a redundant gas supply. A redundant gas supply is a shared connection for a central gas supply and a gas cylinder, which is designed so that fresh gas is only drawn from the gas cylinder when the pressure in the central gas supply falls below a required pressure. The fresh gas connection also includes a control valve with which the fresh gas flow from a fresh gas supply connected to the fresh gas connection into the ventilator can be adjusted. The control valve can, for example, be a mechanical control valve that must be adjusted manually by a user. In this case, a user must manually set the desired fresh gas flow.However, it is also conceivable for the control valve to be adjusted electronically by the data processing device, with a user simply entering a desired fresh gas flow into the data processing device and the data processing device adjusting the control valve. A differential pressure sensor is also installed between the control valve of the fresh gas connection and the inspiration branch to measure a differential pressure between the control valve and the inspiration branch. In an exemplary, preferred embodiment, the differential pressure sensor is a measuring orifice in which the pressure difference, i.e., the differential pressure, across the measuring orifice is proportional to the square of the mass flow and the volume flow.

[0015] The data processing device, for example, a conventional PC or an integrated circuit, is connected to the differential pressure sensor and the absolute pressure sensor, the sensors or pressure sensors. The connection can be established, for example, via data lines, through which digital measured values ​​from the sensors are transmitted. Alternatively, the connection can also be established via analog measuring lines, through which a current or voltage signal corresponding to the measured pressures is transmitted. The differential and absolute pressures measured by the sensors at specific times are received and recorded by the data processing device. For example, the data processing device can record the differential and absolute pressures measured at 10 ms intervals.In particular in the case of an analogue transmission between the sensors and the data processing device, but also in the case of a digital transmission, it is possible to understand the specific point in time at which a differential pressure or an absolute pressure was measured as the point in time at which the differential pressure or absolute pressure was received by the data processing device.

[0016] The data processing device is configured to determine a fresh gas flow through the fresh gas connection at a specific point in time. To do so, the data processing device first uses the differential pressure measured at the specific point in time. The absolute pressure measured at the specific point in time and at least one other absolute pressure measured at a point in time prior to the specific point in time are also included in the determination of the differential pressure.

[0017] The present invention advantageously makes it possible to incorporate at least two absolute pressure measurements, at least one of which was taken prior to the specific time, into the determination of the fresh gas flow, in addition to the differential pressure. This allows the influence of breathing-induced disturbances to be taken into account when determining the fresh gas flow. These disturbances propagate as pressure waves from the gas outlet of the ventilator toward the fresh gas connection through the inspiratory branch. Before the pressure waves can impact the differential pressure sensor and disrupt the differential pressure measurement, they inevitably first pass through the absolute pressure sensor and influence the measured absolute pressure before the measured differential pressure is affected.In this way, the subsequent influence on the differential pressure can be estimated from the influence of the pressure waves on the measured absolute pressure, and this influence can be taken into account when determining the fresh gas flow. The fresh gas flow determined in this way can be displayed on a display device for a user of the ventilator who wishes to manually adjust the fresh gas flow using a mechanical control valve. The displayed fresh gas flow is advantageously free of narrow-band, breathing-induced disturbances, which makes it significantly easier for the user to set the desired fresh gas flow. Even if the control valve is adjusted electronically, determining a corrected fresh gas flow is advantageous because the time required to correctly adjust the control valve is significantly reduced.

[0018] In a preferred embodiment, the ventilation device has at least one further fresh gas connection, wherein the at least one further fresh gas connection is connected to the gas outlet via the inspiration branch and is configured to connect a fresh gas supply, wherein the at least one further fresh gas connection comprises a control valve and a differential pressure sensor, wherein a gas flow from a fresh gas supply connected to the at least one further fresh gas connection to the inspiration branch can be adjusted via the control valve and the differential pressure sensor is arranged and configured to measure a differential pressure in the at least one further fresh gas connection between the control valve and the inspiration branch, wherein the data processing device is connected to the differential pressure sensor of the at least one further fresh gas connection,to receive and record the differential pressure measured by the differential pressure sensor at a plurality of times, and wherein the data processing device is configured to determine a fresh gas flow through the at least one further fresh gas connection at the specific time from the differential pressure measured at the specific time by the differential pressure sensor of the at least one further fresh gas connection, the absolute pressure measured at the specific time, and one or more absolute pressures measured at times prior to the specific time.

[0019] In the preferred embodiment, the device has at least one additional fresh gas connection, which is arranged parallel to the first fresh gas connection and has a similar structure. For these fresh gas connections, too, the data processing device can advantageously determine a fresh gas flow at a specific time from the differential pressure measured for the specific time by the differential pressure sensor of the respective fresh gas connection and the already known absolute pressures. In addition to the advantages known for a single fresh gas connection, this also offers the additional advantage that the absolute pressure measured once can be used to correct multiple differential pressures.

[0020] It is preferred that the data processing device is configured to determine, for each point in time at which an absolute pressure was measured, an average value of the absolute pressure from absolute pressures measured at a plurality of points in time prior to that point in time, and to additionally determine the fresh gas flow(s) from the average values ​​of the absolute pressure determined for those points in time at which an absolute pressure was measured that is used to determine the fresh gas flow(s). In the preferred embodiment, a moving average of the absolute pressure is formed, for example, over the last 20 seconds prior to a specific point in time. For this purpose, the data processing device continuously records the absolute pressures measured by the absolute pressure sensor and stores the values ​​for as long as necessary.

[0021] Furthermore, it is preferred that the data processing device be configured to determine the fresh gas flow(s) from the differences between the absolute pressures and the mean values ​​of the absolute pressure measured and determined for the same time points. By forming the difference, short-term fluctuations in the absolute pressure can be advantageously determined, which propagate in the form of pressure waves in the ventilation device.

[0022] The data processing device is configured to determine the fresh gas flow(s) from a corrected differential pressure(s), wherein the corrected differential pressure(s) is / are determined using a transfer function from the measured differential pressure(s) and the absolute pressures used to determine the respective fresh gas flow. Thus, the known relationship between the differential pressure and the fresh gas flow can advantageously be used without modification by correcting the measured differential pressure using the measured absolute pressures. This correction is preferably performed using a transfer function, for example, a transfer function for time-discrete systems.

[0023] Preferably, the transfer function is of the form dPcorr(z)=dP(z)−b1P˜(z)+b2P˜(z−1)+b3P˜(z−2)a1P˜(z)+b2P˜(z−1)+a3P˜(z−2), where z is the specific time, dP(z) is the differential pressure at time z, dP corr (z) is the corrected differential pressure at time z, P̃(z) is the difference between the absolute pressure measured for time z and the mean value of the absolute pressure determined for time z, z -1 and z - 2 are times before the specific time z, and a1, a2, a3, b1, b2 and b3 are coefficients. In the preferred embodiment, a discrete time signal is used, and to correct the differential pressure at a specific time, in addition to the absolute pressure measured for the specific time, the absolute pressures measured at the two immediately preceding times are used.

[0024] The coefficients a1, a2, a3, b1, b2, and b3 are determined by recording the differential pressures and the absolute pressure for different points in time during a typical pressure surge during inspiration with a constant fresh gas flow, i.e., with fixed control valves and thus an initially fixed, predetermined differential pressure. The required mean-adjusted values ​​are determined from the measured and recorded values. The coefficients can then be determined, for example, using the least squares method, since the individual differential pressure values ​​are fixed by the constant, respective fresh gas flow.

[0025] The preferred transfer function is quick to calculate and allows a correction of the differential pressure and thus also of the determined fresh gas flow with sufficiently high accuracy to correct the disturbances in the differential pressure caused by the changing breathing phases of a patient connected to the ventilator.

[0026] In a preferred embodiment, the control valve(s) is / are mechanical control valves that are manually adjusted by a user of the ventilator, and the data processing device comprises a display device on which the previously determined fresh gas flow(s) can be displayed to a user of the ventilator.

[0027] In a further aspect, the object of the invention is achieved by a method for determining a fresh gas flow at a specific time through a fresh gas connection of a ventilator from a differential pressure and a plurality of absolute pressures which have been measured at different times, wherein the differential pressure between a control valve of the fresh gas connection, with which the fresh gas flow through the fresh gas connection is adjusted, and an inspiration branch of the ventilator is measured, wherein the fresh gas connection is connected at least in sections via the inspiration branch to a gas outlet for connecting a supply line for a patient, wherein the absolute pressure in the inspiration branch is measured and wherein the fresh gas flow at the specific time from the differential pressure measured for the specific time,the absolute pressure measured for the specific time and at least one absolute pressure measured for a time prior to the specific time.

[0028] Preferably, for each point in time at which an absolute pressure taken into account in determining the fresh gas flow has been measured, an average value of the absolute pressure is determined from absolute pressures measured at a plurality of points in time preceding the point in time, and the fresh gas flow or flows are additionally determined from the average values ​​of the absolute pressure determined for those points in time at which an absolute pressure was measured which is included in determining the fresh gas flow or flows.

[0029] It is preferred that the fresh gas flow is determined from the differences of the absolute pressures and the mean values ​​of the absolute pressure that have been measured or determined for the same time points.

[0030] The fresh gas flow is determined from a corrected differential pressure, whereby the corrected differential pressure is determined using a transfer function from the measured differential pressure and the absolute pressures used to determine the fresh gas flow. The transfer function is preferably of the form dPcorr(z)=dP(z)−b1P˜(z)+b2P˜(z−1)+b3P˜(z−2)a1P˜(z)+b2P˜(z−1)+a3P˜(z−2), where z is the specific time, dP(z) is the differential pressure at time z, dP corr(z) is the corrected differential pressure at time z, P̃(z) is the difference between the absolute pressure measured for time z and the mean value of the absolute pressure determined for time z, z -1 and z - 2 are times before the determined time z and a1 , a2 , a3 , b1 b2 and b3 are coefficients.

[0031] The embodiments of the method according to the invention are advantageous for the same reasons as the embodiments of the ventilation device according to the invention, which have corresponding method and device features.

[0032] The present invention will be explained below with reference to a drawing showing only a preferred embodiment, in which Fig. 1 shows an embodiment of a ventilation device according to the invention.

[0033] With reference to Fig. 1, an embodiment of a ventilation device 1 according to the invention is described. Fig. The ventilator 1 shown in Figure 1 is an anesthesia device with a closed breathing circuit. However, the invention is by no means limited to ventilators 1 with a closed breathing circuit, but can also be used in ventilators 1 with a semi-open breathing circuit.

[0034] A patient who is to be ventilated with the ventilator 1 is connected to the gas outlet 3 of the ventilator 1 via a supply line, e.g., a breathing mask. Breathing air exhaled by the patient flows through the gas outlet 3 into an expiratory branch 5, which includes a flow sensor 7. The flow sensor 7 measures the volume or mass flow of the breathing air exhaled by the patient. From the expiratory branch 5, the exhaled breathing air is passed through a soda lime cartridge 9, which binds the carbon dioxide contained in the breathing air. A resuscitation bag 11 and an expiratory control valve 13 are arranged between the expiratory branch 5 and the soda lime cartridge 9. Breathing air can be temporarily stored in the resuscitation bag 11 before it is processed and fed back to the patient.The expiratory control valve 13 closes whenever the patient inhales, thus preventing the patient from re-inhaling used and untreated breathing air. Furthermore, the ventilation device 1 includes a blower 15 to generate the pressure required for ventilation in the treated breathing air.

[0035] The conditioned breathing air is then fed back to the gas outlet 3 via an inspiration branch 17 and then to a patient connected to the gas outlet 3 via a supply line. A further flow sensor 19 is arranged in the inspiration branch 17, with which the volume or mass flow of the conditioned breathing air inhaled by the patient can be measured. An absolute pressure sensor 21 is also arranged along the inspiration branch 17, with which an absolute pressure of the breathing gas in the inspiration branch 17 can be measured. Absolute pressure here refers to the pressure of the breathing gas in the inspiration branch 17 relative to a vacuum or a slowly changing reference pressure, such as ambient pressure.

[0036] Three fresh gas connections 23, 25, 27 are arranged between the blower 15 and the inspiratory branch 17. The three fresh gas connections 23, 25, 27 are identically constructed. Therefore, the same reference numerals are used for elements of the fresh gas connections 23, 25, 27 with the same name, and only one of the fresh gas connections 23, 25, 27 is described in detail here as representative of the remaining fresh gas connections 23, 25, 27.

[0037] Each of the fresh gas connections 23, 25, 27 has a connection element 29 for connecting a fresh gas supply, for example in the form of a gas cylinder, a central gas supply, or a redundant gas supply. A mechanical control valve 31 is arranged between the connection element 29 and the inspiration branch 17, with which a user of the ventilation device 1 can manually adjust the gas flow from a connected fresh gas supply into the ventilation device 1. In order to be able to monitor the fresh gas flow from the fresh gas supply into the ventilation direction 1 and, more precisely, into the inspiration branch 17, a differential pressure sensor 33 in the form of a measuring orifice is also arranged between the control valve 31 and the inspiration branch 17 in each of the fresh gas connections 23, 25, 27. The differential pressure sensor 33 measures a differential pressure, which can also be referred to as a pressure difference.The differential pressure is proportional to the square of the mass or volume flow of the fresh gas - the fresh gas flow - through the differential pressure sensor 33 and thus from the fresh gas supply into the ventilator 1.

[0038] In the prior art, it had proven problematic that the differential pressure measured by a differential pressure sensor 33 and the resulting fresh gas flow were disrupted by the constant pressure changes in the inspiratory branch 17 and the expiratory branch 5 of the ventilator 1. In other words, the differential pressure sensor 33 measures, in addition to the differential pressure corresponding to the actual fresh gas flow, a narrowband disturbance generated, for example, by the patient's breathing rhythm or the closing and opening of the expiratory control valve 13. However, this disturbance causes the fresh gas flow displayed to a user attempting to adjust a fresh gas flow using the control valve 31 to constantly fluctuate, making correct adjustment extremely difficult.

[0039] To counteract this interference, the present invention provides for connecting the absolute pressure sensor 21 and the differential pressure sensor 33 to a data processing device 37 via data lines 35. Data transmission between the sensors 21, 33 can be digital or analog, i.e., the sensors 21, 33 can transmit the measured pressures either as digital data to the data processing device 37 or transmit an analog voltage or current signal corresponding to the measured pressure to the data processing device 37, which converts this analog signal into a digital value. The data processing device 37 records the received absolute and differential pressures and assigns them to a plurality of points in time.The plurality of points in time can either be the points in time at which the respective pressure was actually measured or the points in time at which a measured pressure was received by the data processing device 37. In either case, it is a discrete time signal, so that a measured absolute pressure can generally be assigned to a point in time, and a measured differential pressure can be assigned to each differential pressure sensor 33.

[0040] For a specific point in time, usually the most recent point in time, the data processing device 37 determines a fresh gas flow through the fresh gas connection 23, 25, 27 from the differential pressure measured for the specific point in time by the differential pressure sensor 33 of the respective fresh gas connection 23, 25, 27, the absolute pressure measured for the specific point in time by the absolute pressure sensor 21, and at least one absolute pressure measured at a previous point in time. For this purpose, a corrected differential pressure is first formed, from which a corrected fresh gas flow can be calculated. The corrected differential pressure is determined from the measured differential pressure, three measured absolute pressures, and moving averages of the absolute pressure using a transfer function. The transfer function is dPcorr(z)=dP(z)−b1P˜(z)+b2P˜(z−1)+b3P˜(z−2)a1P˜(z)+b2P˜(z−1)+a3P˜(z−2), where z is the specific time, dP(z) is the differential pressure measured by the differential pressure sensor 33 at time z, dP corr (z) is the corrected differential pressure at time z, P̃(z) is the difference between the absolute pressure measured by the absolute pressure sensor 21 for time z and the mean value of the absolute pressure determined for time z, z - 1 and z - 2 are times prior to the determined time z, and a1, a2, a3, b1, b2, and b3 are coefficients. From the corrected differential pressure, the data processing device 37 determines the fresh gas flow through the respective fresh gas connection 23, 25, 27 in a manner known from the prior art. The determined fresh gas flow is output to a display device 39 for a user of the ventilation device 1, so that the user can easily set the respective fresh gas flow to the desired value on the manual control valves 31.

[0041] In other words, an embodiment of a method according to the invention is carried out with the embodiment of a ventilation device 1 according to the invention. For this purpose, the absolute pressure is first measured by the absolute pressure sensor 21 in the inspiration branch 17 of the ventilation device 1 at a plurality of points in time. In addition, a differential pressure is measured at the plurality of points in time in each of the three fresh gas connections 23, 25, 27 by a differential pressure sensor 33. The measured pressures are transmitted via data lines for further processing to the data processing device 37, which determines a fresh gas flow for a specific point in time from the differential pressure measured at the specific point in time, the absolute pressure measured at the specific point in time, and an absolute pressure measured at a point in time prior to the specific point in time.

[0042] The determination is made by first determining a moving average of the absolute pressure for each point in time at which an absolute pressure was measured that is to be considered when determining the fresh gas flow, for example, over the last 20 seconds prior to that point in time. In the further determination of the fresh gas flows, the difference between the absolute pressure and the moving average of the absolute pressure determined for that point in time is then taken into account for each point in time. These differences are processed together with the differential pressure measured for the specific point in time in a transfer function to determine a corrected differential pressure. The corrected differential pressure is calculated using the formula: dPcorr(z)=dP(z)−b1P˜(z)+b2P˜(z−1)+b3P˜(z−2)a1P˜(z)+b2P˜(z−1)+a3P˜(z−2), where z is the specific time, dP(z) is the differential pressure measured by the differential pressure sensor 33 at time z, dP corr(z) is the corrected differential pressure at time z, P̃(z) is the difference between the absolute pressure measured by the absolute pressure sensor 21 for time z and the mean value of the absolute pressure determined for time z, z -1 and z - 2 are times prior to the determined time z, and a1, a2, a3, b1, b2, and b3 are coefficients. From the corrected differential pressure, a corrected fresh gas flow is subsequently determined which is largely free of short-term disturbances that propagate through the inspiration branch 17 as pressure waves to the fresh gas connections 23, 25, 27. The corrected fresh gas flow is displayed to a user on the display device 39.

[0043] The exemplary embodiment of the ventilation device 1 according to the invention and also the exemplary embodiment of the method according to the invention, which is carried out by the ventilation device 1, are advantageous for various reasons. First and foremost, they make it possible to determine a fresh gas flow through the fresh gas connections 23, 25, 27 that is largely free of narrowband disturbances caused by the changing respiratory pressures of a patient. Since the changing respiratory pressures propagate in the form of pressure waves through the ventilation direction 1 and in particular the inspiration branch 17, they first pass through the absolute pressure sensor 21 before being detected by the differential pressure sensor 33, so that the pressure measured by the absolute pressure sensor can advantageously be used to correct a pressure measured by the differential pressure sensor 33.

Claims

[1] Ventilation device (1) with a fresh gas connection (23, 25, 27), a gas outlet (3), an absolute pressure sensor (21) and a data processing device (37), wherein the gas outlet (3) is designed to connect a supply line for a patient and is fluidically connected to the fresh gas connection (23, 25, 27) via an inspiration branch (17), wherein the absolute pressure sensor (21) is arranged and configured to measure an absolute pressure in the inspiration branch (17), and wherein the fresh gas connection (23, 25, 27) is configured for connecting a fresh gas supply and comprises a control valve (31) and a differential pressure sensor (33), wherein a gas flow from the fresh gas supply to the inspiration branch (17) can be adjusted via the control valve (31) and the differential pressure sensor (33) is arranged and configured to measure a differential pressure in the fresh gas connection (23, 25, 27) between the inspiration branch (17) and the control valve (31), wherein the data processing device (37) is connected to the absolute pressure sensor (21) and the differential pressure sensor (33) to receive and record the absolute pressure measured by the absolute pressure sensor (21) at a plurality of times and the differential pressure measured by the differential pressure sensor (33) at a plurality of times, wherein the data processing device (37) is designed to determine a fresh gas flow through the fresh gas connection (23, 25, 27) at a specific time from the differential pressure measured at the specific time, the absolute pressure measured at the specific time and one or more absolute pressures measured at times prior to the specific time, wherein the data processing device (37) is configured to determine the fresh gas flow or the fresh gas flows from a corrected differential pressure or corrected differential pressures, wherein the corrected differential pressure or the corrected differential pressures are determined by means of a transfer function from the measured differential pressure or the measured differential pressures and the absolute pressures used in determining the respective fresh gas flow. [2] Ventilation device (1) according to claim 1, characterized bythat the ventilation device (1) has at least one further fresh gas connection (23, 25, 27), wherein the at least one further fresh gas connection (23, 25, 27) is connected to the gas outlet (3) via the inspiration branch (17) and is designed to connect a fresh gas supply, wherein the at least one further fresh gas connection (23, 25, 27) comprises a control valve (31) and a differential pressure sensor (33), wherein a gas flow from a fresh gas supply connected to the at least one further fresh gas connection (23, 25, 27) to the inspiration branch (17) can be adjusted via the control valve (31), and the differential pressure sensor (33) is arranged and configured to measure a differential pressure in the at least one further fresh gas connection (23, 25, 27) between the control valve (31) and the inspiration branch (17), wherein the data processing device (37) is connected to the differential pressure sensor (33) of the at least one further fresh gas connection (23, 25, 27) in order to receive and record the differential pressure measured by the differential pressure sensor (33) at a plurality of times, and wherein the data processing device (37) is configured to determine a fresh gas flow through the at least one further fresh gas connection (23, 25, 27) at the specific time from the differential pressure measured at the specific time by the differential pressure sensor (33) of the at least one further fresh gas connection (23, 25, 27), the absolute pressure measured at the specific time, and one or more absolute pressures that were measured at times prior to the specific time. [3] Ventilation device (1) according to claim 1 or 2, characterized by that the data processing device (37) is designed to for each point in time at which an absolute pressure has been measured, to determine an average value of the absolute pressure from absolute pressures measured at a plurality of points in time preceding that point in time, and to determine the fresh gas flow(s) additionally from the mean values ​​of the absolute pressure determined for those points in time at which an absolute pressure was measured which is used to determine the fresh gas flow(s). [4] Ventilation device (1) according to claim 3, characterized by that the data processing device (37) is designed to determine the fresh gas flow or flows from the differences between the absolute pressures and the mean values ​​of the absolute pressure which have been measured and determined for the same points in time. [5] Ventilation device (1) according to one of the preceding claims, characterized bythat the transfer function is of the form dPcorr(z)=dP(z)−b1P˜(z)+b2P˜(z−1)+b3P˜(z−2)a1P˜(z)+b2P˜(z−1)+a3P˜(z−2) where z is the specific time, dP(z) is the differential pressure at time z, dP corr (z) is the corrected differential pressure at time z, P̃(z) is the difference between the absolute pressure measured for time z and the mean value of the absolute pressure determined for time z, z -1 and z - 2 are times before the determined time z and a1 , a2 , a3 , b1, b2 and b3 are coefficients. [6] Ventilation device (1) according to one of the preceding claims, characterized by that the control valve (31) or the control valves (31) are mechanical control valves (31) which are manually adjusted by a user of the ventilation device (1), and that the data processing device (37) comprises a display device (39) on which the previously determined fresh gas flow or the previously determined fresh gas flows can be displayed to a user of the ventilation device (1). [7] Method for determining a fresh gas flow at a specific time through a fresh gas connection (23, 25, 27) of a ventilator (1) from a differential pressure and a plurality of absolute pressures which have been measured at different times, wherein the differential pressure between a control valve (31) of the fresh gas connection (23, 25, 27), with which the fresh gas flow through the fresh gas connection (23, 25, 27) is adjusted, and an inspiration branch (17) of the ventilator (1) is measured, wherein the fresh gas connection (23, 25, 27) is connected at least in sections via the inspiration branch (17) to a gas outlet (3) for connecting a supply line for a patient, wherein the absolute pressure in the inspiration branch (17) is measured, wherein the fresh gas flow at the specific time is determined from the differential pressure measured for the specific time, the absolute pressure measured for the specific time and at least one absolute pressure measured for a time prior to the specific time, and wherein the fresh gas flow is determined from a corrected differential pressure, wherein the corrected differential pressure is determined by means of a transfer function from the measured differential pressure and the absolute pressures used to determine the fresh gas flow. [8] Method according to claim 7, characterized bythat for each point in time at which an absolute pressure taken into account in determining the fresh gas flow has been measured, an average value of the absolute pressure is determined from absolute pressures measured at a plurality of points in time preceding that point in time, and the fresh gas flow or flows are additionally determined from the mean values ​​of the absolute pressure which have been determined for those points in time at which an absolute pressure has been measured which is used to determine the fresh gas flow or flows. [9] Method according to claim 8, characterized by that the fresh gas flow is determined from the differences between the absolute pressures and the mean values ​​of the absolute pressure measured or determined for the same time points. [10] Method according to claim 7, 8 or 9, characterized by that the transfer function is of the form dPcorr(z)=dP(z)−b1P˜(z)+b2P˜(z−1)+b3P˜(z−2)a1P˜(z)+b2P˜(z−1)+a3P˜(z−2) where z is the specific time, dP(z) is the differential pressure at time z, dP corr (z) is the corrected differential pressure at time z, P̃(z) is the difference between the absolute pressure measured for time z and the mean value of the absolute pressure determined for time z, z -1 and z - 2 are times before the determined time z and a1 , a2 , a3 , b1, b2 and b3 are coefficients.

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