DE102022109697A1 - Gas mixer and ventilator comprising a gas mixer - Google Patents

Abstract

The invention relates to a gas mixer which, by using two pressure sensors per gas component, enables high measurement accuracy for both low flows and thus pressures of the gas components at low costs. A sensor is designed to measure low pressures and a sensor to measure high pressures. In addition, the invention relates to a medical device comprising such a gas mixer.

Description

The invention relates to a gas mixer with which gases can be mixed in predetermined proportions to form a gas mixture.

In addition, the invention relates to a medical device comprising a gas mixer.

Gas mixers are used in a variety of devices to mix different gases together. It is often important to mix the different gases with one another in predetermined ratios and/or to adjust the proportions of the respective gases in the gas mixture to predetermined values.

For example, such gas mixers are used in medical devices, including in particular in ventilators and/or anesthesia devices. Anesthesia devices within the meaning of this document are devices that enable the anesthesia of a patient using inhalation anesthetics.

In ventilators, gas mixers are used, for example, to set a predetermined oxygen content in the breathing gas.

In anesthesia machines, which are often designed as a combined ventilation and anesthesia device, gas mixers are used, for example, to set predetermined levels of oxygen (O2), a carrier gas (e.g. air) and an anesthetic gas (e.g. N20) in the breathing gas.
With both the ventilator and the anesthesia machine, the fresh gas mixture generated in this way is usually delivered to a patient via a ventilation tube and a patient interface, such as a tube, a ventilation mask or a nasal cannula.

It is very important to adjust the proportions of the different gases in the gas mixture as precisely as possible.

Particularly for applications in the medical technology sector, it is extremely important to be able to adjust the proportions of gases in a gas mixture with high precision. This is particularly true for anesthesia machines, because an overdose of the anesthetic gas used and/or an undersupply of an anesthetized patient with oxygen can have extremely harmful effects on the patient's health.

Various gas mixers are known which, through their mechanical structure and/or with the help of electronic components, enable relatively precise adjustment of the proportions of different gases in a gas mixture.

For example, gas mixers are known with which oxygen, air and an anesthetic gas can be mixed with one another in predetermined proportions, the gas mixer having a plurality of valves with different channel diameters for each of the three components of the gas mixture. These valves can then be controlled individually for each component of the gas mixture, so that certain valves are opened and other valves are closed for each gas component. Depending on the pressure applied to the respective component, the flow and thus also the proportion of the respective component in the gas mixture can be adjusted. The accuracy of the setting options for the proportions of the various gas components in the gas mixture depends on the number of available valves per component. A lot of valves are required to achieve high levels of accuracy, so that such gas mixers are relatively large and require a large number of different components.

In other known gas mixers, proportional valves are used for the various gas components, which can be controlled electronically with a pulse width modulated control signal (PWM) in such a way that the degree of opening of the valve is based on the duty cycle (ratio “on” to “off” in one period) of the PWM is adjustable. As a rule, one proportional valve per gas component is sufficient.
For both types of gas mixers, it is necessary to determine the flow of the individual gas components in the gas mixer in order to determine the proportions of the components in the gas mixture. This is often achieved by measuring the pressure of the individual gas components applied to the gas mixer and calculating the flow (volume flow) of the individual gas components from this.

The pressure of a gas component applied to the gas mixer varies with the degree of opening of the respective valve or, if applicable, the valves assigned to the respective gas component and the resulting flow of the respective gas component. Volume flows in a range from less than 1 1/min to around 10 1/min are common, which are accompanied by a correspondingly large pressure range. According to the prior art, pressure sensors are used to measure the pressure, which can be used over the entire working range of the expected pressures.

In order to achieve a sufficiently high measurement accuracy across the entire working range of the existing pressures, high-quality pressure sensors with a wide measuring range must be used which, however, are very expensive and which may still have lower dynamics and therefore measurement accuracy for particularly high or low pressures.

It is therefore an object of the invention to provide a gas mixer which enables high measurement accuracy of the pressure for each gas component at lower costs.

This object is achieved according to the invention by a gas mixer according to claim 1.

It is a further object of the invention to provide a medical device comprising a gas mixer which solves the aforementioned object.

This task is solved by a medical device according to claim 13.

The features of a gas mixer disclosed below are part of the invention both individually and in all executable combinations.

A gas mixer according to the invention has at least two valves, with at least one valve being assigned to one of at least two gas components to be mixed with one another.

For each gas component, a gas mixer according to the invention has an input connection and an output connection, which are connected to the at least one valve assigned to the respective gas component.

The line system of the gas mixer for the individual gas components is designed in such a way that the gas components flow through the respective inlet port depending on the opening state of the at least one assigned valve and through the outlet port.

In a preferred embodiment of the invention, the gas mixer has exactly one proportional valve for at least one gas component. The use of a proportional valve enables high adjustment accuracy of the respective volume flow with only a few components required and a small space requirement.

In particularly advantageous embodiments, the gas mixer has exactly one proportional valve for each gas component.

However, in other embodiments of the invention, valve banks having a plurality of valves with differently sized through openings in the open state can also be used for the individual gas components.

The output connections of the valves of the gas mixer are connected to one another either directly on the gas mixer itself or in the further course of lines connected to it, for example hoses, so that the gas components are combined to form the desired gas mixture.

To regulate the proportions of the individual gas components in the gas mixture, the gas mixer has a volume flow-based control of the valves. The volume flow of the individual gas components is calculated using a gas mixer according to the invention based on pressure measurements.

A gas mixer according to the invention has two pressure sensors for each gas component, with a first pressure sensor having a high measurement accuracy at low pressures and a second pressure sensor having a high measurement accuracy at high pressures. These pressure sensors are also referred to herein as low-pressure sensors or high-pressure sensors.

Low pressures in the sense of this document are in a range from 0 bar to approximately 100 mbar.
High pressures in the sense of this document are in a range from approximately 100 mbar to approximately 1000 mbar.

The accuracy of the flows of the gas components that can be determined using the pressure measurement values with a gas mixer according to the invention is at least 100 ml/min in embodiments of the invention for flows below 1 l/min, at least 50 ml/min in particularly preferred embodiments of the invention, and for flows greater than or equal to 1 1/min in embodiments of the invention at least 15%, in particularly preferred embodiments of the invention at least 10%.

A sufficiently high measurement accuracy of the pressure sensors for the respective area is achieved by appropriately apportioning the pressures that occur with the flows of the gas components to the specialized pressure sensors. For example, the sensitivity of a sensor can be used as an indicator, which results from the ratio of the output value range (full scale) to the difference between the maximum and minimum measured values. The sensitivity of a 100 mbar pressure sensor in comparison to a 1000 mbar pressure sensor results, for example, for an output value range of 26214 (maximum output value minus the offset) to 262.14 values/mbar (100 mbar sensor) and 26.21 values/mbar (1000 mbar sensor) . The 100 mbar sensor is therefore 10 times more sensitive and therefore more accurate than the 1000 mbar sensor, However, due to the limited measuring range, it is not suitable for pressures above 100 mbar.

In embodiments of the invention, the pressure sensors for the respective gas component are connected to the flow channel of the respective gas component via a Y-piece, so that the pressure drop can be measured simultaneously with the low-pressure and the high-pressure sensor.

Differential pressure sensors are used as pressure sensors in preferred embodiments of the invention. For low pressures, a 100 mbar differential pressure sensor is particularly suitable, with which differential pressures can be measured in a range from 0 to 100 mbar, and for high pressures, a 1000 mbar differential pressure sensor, with which differential pressures in a range from 0 to 1000 mbar can be measured.

The differential pressure that occurs at a differential pressure sensor is proportional to the flow of the gas or the respective gas component flowing through the respective measuring channel.

The low pressures described above are to be expected at low flows in a range of about 0 ml/min to 2 l/min, while the high pressures are to be expected at high flows in a range of about 2 l/min to 20 l/min .

In a preferred embodiment of the invention, the gas mixer is designed to mix three gas components and has at least one valve individually assigned to each gas component and one low-pressure sensor and one high-pressure sensor for each gas component.

In embodiments of the invention, the gas mixer has a mechanical gas mixing block, which includes the valves along with the respective associated input connections and a common output connection for the gas mixture.

In embodiments of the invention, the pressure sensors are arranged on a circuit board, which is advantageously arranged on the mechanical gas mixing block.

With the help of a control unit, the respective pressures for the individual gas components can be recorded and evaluated with regard to the respective flow, and the at least one valve assigned to the respective gas component can be controlled in accordance with a predetermined proportion of the gas component in the gas mixture.

For this purpose, the sensors and the valves are electrically connected to the control unit, so that measurement signals in analog or digital form as well as control signals can be transferred accordingly.

In embodiments with at least one proportional valve, this can be adjusted according to the desired flow, for example by a PWM using the control unit.

The control unit can either be an independent control unit only for the gas mixer or a higher-level control unit that fulfills further functions in a device having a gas mixer according to the invention.

In advantageous embodiments of the invention, the gas mixer has means for ensuring a minimum content of at least one gas component.

This is designed, for example, as a safety device that ensures a proportion of at least 25% O2 in the gas mixture. If the appropriate flow of the respective gas component cannot be provided, an emergency shutdown is integrated, for example, which at least stops the admixture of the anesthetic gas.

In advantageous embodiments of the invention, a differential communication interface is used between the control unit and the circuit board on which the pressure sensors are arranged. This means that communication between the sensors and the control unit is less susceptible to disruption.

For example, a conventional I2C signal (single-ended) is converted into a differential signal using a first buffer, transmitted from the control unit to the sensor circuit board and converted there again into a conventional I2C signal using a second buffer.

In embodiments of the invention, the control unit has an FPGA for reading out the pressure measured values from the pressure sensors and for controlling the valves.

In order to evaluate the pressure measurement values and to calculate the flows of the respective gas component based on predetermined proportions of the gas mixture, the control unit of the gas mixer in embodiments of the invention additionally has an MCU.

In other embodiments of the invention, the functions of the MCU and FPGA can also be implemented by a single processor or by several analog and digital electronic components.

A medical device according to the invention has at least one gas mixer according to the invention according to the above description.

In embodiments of the invention, the medical device is designed as a ventilation and/or anesthesia device.

Both a manual or semi-manual as well as an automated supply of the fresh gas mixture as breathing gas through appropriate ventilation and/or anesthesia devices are possible.

A medical device according to the invention has a patient interface via which the gas mixture can be delivered to a patient.

For the individual gas components, a medical device according to the invention has sources which provide the respective gas component with the required pressure. For example, such sources can be compressed gas bottles or a blower that sucks in ambient air and usually provides it in filtered form.

It should be noted that the features listed individually in the claims can be combined with one another in any technically sensible manner and show further refinements of the invention. The description additionally characterizes and specifies the invention, particularly in connection with the figures.

It should also be noted that a conjunction “and/or” used here between two features and linking them together must always be interpreted in such a way that in a first embodiment of the subject matter according to the invention only the first feature can be present, in a second embodiment only the second feature can be present and in a third embodiment both the first and the second feature can be present.

A ventilator is any device that supports a user or patient in natural breathing, provides ventilation for the user or living being (e.g. patient and/or newborn and/or premature infant) and/or is used for respiratory therapy and/or otherwise affects the breathing of the user or patient. This includes, for example, but is not limited to, CPAP and BiPAP devices, anesthesia or anesthesia devices, respiratory therapy devices, (clinical, out-of-hospital or emergency) ventilators, high-flow therapy devices and cough machines. Ventilators can also be understood as diagnostic devices for ventilation. Diagnostic devices can generally be used to record medical and/or respiratory parameters of a living being. This also includes devices that can record and optionally process medical parameters of patients in combination with breathing or only relating to breathing.

Unless explicitly described otherwise, a patient interface can be understood to mean any peripheral device that is intended for the interaction, in particular for therapy or diagnostic purposes, of the measuring device with a living being. In particular, a patient interface can be understood as a mask of a ventilator or a mask connected to the ventilator. This mask can be a full-face mask, i.e. that encloses the nose and mouth, or a nasal mask, i.e. a mask that only encloses the nose. Tracheal tubes or cannulas and so-called nasal cannulas can also be used as masks or patient interfaces. In some cases, the patient interface can also be a simple mouthpiece, for example a tube, through which the living being at least exhales and/or inhales.

An exemplary embodiment of the invention is shown in the figure explained below.

In 1 a schematic block diagram of an embodiment of a gas mixer (1) according to the invention is shown.

The gas mixer (1) has a valve block (10), a control unit (6) and a sensor board (11) which is arranged on the valve block (10).

Three valves (2) are arranged on the valve block (10), which are designed as proportional valves and are each assigned to a gas component. The inlets of the valves (2) are each connected to an inlet opening (3), via which the respective gas component can be fed to the gas mixer (1) from sources not shown. The outputs of the valves (2) are connected to a common outlet opening (4) through which the gas mixture generated from the gas components can be released.

In the area of the outlets of the valves (2), these are each connected to two pressure sensors (8), with a first pressure sensor (8) acting as a low-pressure sensor (8a) and a second pressure sensor (8) acting as a high-pressure sensor (8b ) is trained.

The sensor board (11) is connected to the control unit (6) via a data line (9), via which the pressure measurements recorded by the pressure sensors (8) can be transferred to the control unit (6).

The control unit (6) has an FPGA (7) and an MCU (12). The FPGA (7) is used to read the pressure measured values from the pressure sensors (8) and to control the valves (2) via control lines (5). The MCU (12) reads the pressure measured values from the FPGA (7), executes the corresponding control algorithm and specifies the parameters for controlling the valves (2) to the FPGA (7).

The following applies to all embodiments: If, for example, a ventilator designed as a ventilator is used to ventilate a patient, it is absolutely necessary to supply the patient with fresh gas that has a certain minimum oxygen content (02). Another example is the use of an anesthesia machine to anesthetize a patient. In addition to a minimum O2 content in the fresh gas mixture, a specification regarding the proportion of anesthetic gas in the fresh gas mixture must also be adhered to. Examples of anesthetic gases are argon, helium, nitrous oxide, chloroform, isoflurane, sevoflurane, desflurane, halothane, enflurane, xenon, carbon dioxide.

The invention therefore also relates to an anesthesia and/or ventilation device with a gas mixer, which enables high measurement accuracy for both low flows and thus pressures of the gas components at low costs through the use of at least one pressure sensor per gas component, with one sensor for measuring each lower Pressures and a sensor is designed to measure high pressures and at least one valve for controlling the gas flows is dynamically controlled.

The invention therefore also relates to an anesthesia and/or ventilator with a gas mixer, characterized in that there is an emergency air device, which is designed, for example, as a valve that opens access to the ambient air, the emergency air device providing access to the ambient air then releases if at least one of the valves and/or the sensors does not work.

Claims (18)

Gas mixer (1) for mixing gas components to form a gas mixture, the gas mixer (1) having at least two valves (2), at least a first valve (2) being assigned to a first gas component and at least a second valve (2) being assigned to a second gas component, further comprising an inlet opening (3) for each gas component and an outlet opening (4) for the gas mixture, the gas mixer (1) having means for measuring the applied pressure of the respective gas component for each gas component, characterized in that the means for measuring the applied pressure of the Gas components are pressure sensors (8), with each gas component having a pressure sensor (8) as a low-pressure sensor (8a) for a pressure range of 0 to 100 mbar and a pressure sensor (8) as a high-pressure sensor (8b) for a pressure range of approximately 0 to 1000 mbar. Gas mixer (1). Claim 1 , characterized in that it has a control unit (6) with which the pressure measurements recorded using the pressure sensors (8) can be converted into flow values of the individual gas components and with which control signals for controlling the valves (2) can be generated in such a way that at least a valve (2) assigned to a gas component can be adjusted according to a predetermined proportion of the respective gas component in the gas mixture. Gas mixer (1) according to one of the Claims 1 and 2 , characterized in that the valves (2) are controlled dynamically. Gas mixer (1) according to one of the Claims 1 until 3 , characterized in that it has exactly one valve (2) for each gas component, this valve (2) being designed as a proportional valve. Gas mixer (1) according to one of the Claims 1 until 4 , characterized in that it is designed to mix three gas components. Gas mixer (1) according to one of the Claims 1 until 5 , characterized in that the valves (2) are integrated into a mechanical valve block (10), on which a sensor board (11) is arranged, on which the pressure sensors (8) are arranged. Gas mixer (1) according to one of the Claims 1 until 6 , characterized in that the signal transmission between the control unit (6) and the sensor board (11) takes place differentially. Gas mixer (1) according to one of the Claims 1 until 7 , characterized in that the pressure sensors (8) are designed as differential pressure sensors. Gas mixer (1) according to one of the Claims 1 until 8th , characterized in that the flows of the gas components can be determined with an accuracy of at least 100 ml/min for flows below 1 1/min and with an accuracy of at least 15% for flows greater than or equal to 1 1/min. Gas mixer (1) according to one of the Claims 1 until 9 , characterized in that the control unit (6) has an FPGA (7) and an MCU (12), the FPGA (7) being designed to retrieve the pressure measured values from the pressure sensors (8) and to control the valves (2) and the MCU (12) is designed to execute a control algorithm based on the pressure measurement values that can be read out by the FPGA (7) and to control the FPGA (7) to specify the parameters for controlling the valves (2). Gas mixer (1) according to one of the Claims 1 until 10 , characterized in that the pressure sensors (8) for each gas component are each connected to the respective flow channel via a Y-piece. Gas mixer (1) according to one of the Claims 1 until 11 , characterized in that it has three valves (2) designed as proportional valves, each of which is designed to adjust the flow of a gas component, with a low-pressure sensor (8a) and a high-pressure sensor (8b) for measuring the applied pressure are connected to the respective flow channel. Gas mixer (1) according to one of the Claims 1 until 12 , characterized in that an emergency air device, which is designed, for example, as a valve, which opens access to the ambient air, is present, the emergency air device releasing access to the ambient air when at least one of the valves and / or the sensors does not work . Use of a gas mixer (1) according to one of Claims 1 until 13 for mixing gas components to form a gas mixture. Medical technology device, characterized in that it has at least one gas mixer (1) according to one of the Claims 1 until 13 having. Medical device according to Claim 15 , characterized in that this is designed as an anesthesia and/or ventilator. Anesthesia and/or ventilator with a gas mixer, which enables high measurement accuracy for both low flows and thus pressures of the gas components at low costs through the use of at least one pressure sensor per gas component, with one sensor for measuring low pressures and one sensor for measuring high pressures and at least one valve for controlling the gas flows is dynamically controlled. Anesthesia and/or ventilator with a gas mixer, characterized in that an emergency air device, which is designed, for example, as a valve, which opens access to the ambient air, is present, the emergency air device releasing access to the ambient air when at least one the valves and/or the sensors are not working.

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