High-frequency jet breathing machine system and control method

Abstract

The invention discloses a high-frequency jet breathing machine system and a control method. The control method comprises the steps that oxygen flow and air flow in an oxygen path and an air path are obtained through a first flow sensor and a second flow sensor respectively; the oxygen concentration monitoring system is used for monitoring the current oxygen concentration in the air and oxygen mixing device in real time; after the monitored current oxygen concentration is compared with the target oxygen concentration, oxygen output parameters and air output parameters are determined through an optimal oxygen concentration prediction model; according to the determined oxygen output parameters and air output parameters, an air proportional valve, an oxygen proportional valve and a mixed gas proportional valve are regulated and controlled, and stable control over the target oxygen amount is achieved. Through real-time monitoring, intelligent feedback adjustment and multi-parameter optimization, the patient can obtain appropriate and constant oxygen supply in the whole respiratory cycle, and the stability and accuracy of oxygen supply are further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ventilators, and particularly relates to a high-frequency jet ventilator system and a control method thereof. Background Art

[0002] High-frequency jet ventilators (HFV) are widely used in fields such as intensive care, first aid, and anesthesia, and are mainly used for assisting ventilation of patients with respiratory system dysfunctions. Compared with traditional ventilators, HFV can deliver gas to patients at a higher frequency and with a smaller jet volume, and is suitable for improving pulmonary gas exchange and ventilation function.

[0003] However, a major challenge of HFV lies in the stable control of oxygen concentration. Especially during high-frequency jetting, fluctuations in oxygen concentration may affect the oxygenation level of patients. Moreover, current HFV technologies still have instability problems in the control of oxygen concentration. Traditional adjustment methods often rely on preset oxygen concentration values and lack dynamic feedback and real-time adjustment mechanisms.

[0004] Therefore, how to achieve appropriate and constant oxygen supply for patients throughout the breathing cycle through precise and stable control technologies is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In order to solve the above technical problems, the present application proposes the following technical solutions:

[0006] In a first aspect, an embodiment of the present application provides a control method for a high-frequency jet ventilator system, including:

[0007] Obtaining the oxygen flow rate and air flow rate in the oxygen gas path and the air gas path respectively through a first flow sensor and a second flow sensor;

[0008] Using an oxygen concentration monitoring system to monitor the current oxygen concentration in the air-oxygen mixing device in real time;

[0009] After comparing the monitored current oxygen concentration with the target oxygen concentration, determining the oxygen output parameter and the air output parameter through an optimal oxygen concentration prediction model;

[0010] Adjusting an air proportional valve, an oxygen proportional valve, and a mixed gas proportional valve according to the determined oxygen output parameter and air output parameter to achieve stable control of the target oxygen amount.

[0011] In a possible implementation manner, the obtaining the oxygen flow rate and air flow rate in the oxygen gas path and the air gas path respectively through a first flow sensor and a second flow sensor includes:

[0012] Filter the oxygen output from the first controllable pressure gas source through a gas source filter and then input it into the oxygen gas path;

[0013] Filter the air output from the second controllable pressure gas source through a gas source filter and then input it into the air gas path;

[0014] Obtain the oxygen flow rate and air flow rate in the oxygen gas path and the air gas path respectively through the first flow sensor and the second flow sensor.

[0015] In a possible implementation manner, after comparing the monitored current oxygen concentration with the target oxygen concentration, determining the oxygen output parameter and the air output parameter through the optimal oxygen concentration prediction model includes:

[0016] Collect multiple groups of oxygen proportional valve parameters, air proportional valve parameters, and mixed oxygen concentration parameters in advance;

[0017] Input the collected multiple groups of data into a convolutional neural network for training to form an optimal oxygen concentration prediction model;

[0018] When there is an error after comparing the monitored current oxygen concentration with the target oxygen concentration, input the target oxygen concentration into the optimal oxygen concentration prediction model;

[0019] Determine the oxygen output parameter and the air output parameter through the optimal oxygen concentration prediction model.

[0020] In a possible implementation manner, regulating the air proportional valve, the oxygen proportional valve, and the mixed gas proportional valve according to the determined oxygen output parameter and air output parameter to achieve stable control of the target oxygen amount includes:

[0021] Obtain the total flow rate demand ejected by the high-frequency jet ventilator system;

[0022] Regulate the air proportional valve, the oxygen proportional valve, and the mixed gas proportional valve according to the determined oxygen output parameter, air output parameter, and the ejected total flow rate demand to achieve stable control of the target oxygen amount.

[0023] In a possible implementation manner, regulating the air proportional valve, the oxygen proportional valve, and the mixed gas proportional valve according to the determined oxygen output parameter, air output parameter, and the ejected total flow rate demand to achieve stable control of the target oxygen amount includes:

[0024] When the total flow rate demand ejected by the high-frequency jet ventilator system remains unchanged, if the current oxygen concentration is higher than the target oxygen concentration, then control the proportional opening of the oxygen proportional valve to decrease and the proportional opening of the air proportional valve to increase through the driver;

[0025] Alternatively,

[0026] When the current oxygen concentration is lower than the target oxygen concentration, the driver controls the proportional opening of the oxygen proportional valve to increase and the proportional opening of the air proportional valve to decrease;

[0027] When the total flow demand ejected by the high-frequency jet ventilator system decreases, if the current oxygen concentration is higher than the target oxygen concentration, the driver controls the proportional openings of the mixed gas proportional valve and the oxygen proportional valve to decrease respectively, and the proportional opening of the air proportional valve remains unchanged;

[0028] Alternatively,

[0029] When the current oxygen concentration is lower than the target oxygen concentration, the driver controls the proportional openings of the mixed gas proportional valve and the air proportional valve to decrease respectively, and the proportional opening of the oxygen proportional valve remains unchanged;

[0030] When the total flow demand ejected by the high-frequency jet ventilator system increases, if the current oxygen concentration is higher than the target oxygen concentration, the driver controls the proportional openings of the mixed gas proportional valve and the air proportional valve to increase respectively, and the proportional opening of the oxygen proportional valve remains unchanged;

[0031] Alternatively,

[0032] When the current oxygen concentration is lower than the target oxygen concentration, the driver controls the proportional openings of the mixed gas proportional valve and the oxygen proportional valve to increase respectively, and the proportional opening of the air proportional valve remains unchanged.

[0033] In a second aspect, an embodiment of the present application provides a high-frequency jet ventilator system, including:

[0034] A main controller and a ventilation control system, an oxygen concentration monitoring system, a feedback regulation system, an alarm system, and a jet needle electrically connected to the main controller;

[0035] The ventilation control system is used to ensure the normal ejection of oxygen and air in the ventilator;

[0036] The oxygen concentration monitoring system is used to monitor the oxygen concentration during the ejection process in real time;

[0037] The feedback regulation system is used to adjust the oxygen supply flow rate and ejection frequency to ensure that the oxygen concentration output by the ventilator always remains within the set range;

[0038] The alarm system is used to give an alarm prompt for abnormal situations that occur during the operation of the ventilator.

[0039] In a possible implementation, the ventilation control system includes an oxygen gas path, an air gas path, and a mixed gas path. The output ends of the oxygen gas path and the air gas path are both connected to the input end of the mixed gas path, and the output end of the mixed gas path is connected to the main controller outlet.

[0040] In a possible implementation, the intake end of the oxygen gas path is externally connected to a first controllable pressure gas source. The output end of the first controllable pressure gas source is connected to the input end of a first gas source filter. The output end of the first gas source filter is respectively connected to the first pressure sensor and the first end of a first pressure reducer. The second end of the first pressure reducer is connected to the first end of an oxygen proportion valve. The second end of the oxygen proportion valve is connected to the first end of a first flow sensor. The second end of the first flow sensor is connected to the first end of an air-oxygen mixing device.

[0041] In a possible implementation, the intake end of the air gas path is externally connected to a second controllable pressure gas source. The output end of the second controllable pressure gas source is connected to the input end of a second gas source filter. The output end of the second gas source filter is respectively connected to the second pressure sensor and the first end of a second pressure reducer. The second end of the second pressure reducer is connected to the first end of an air proportion valve. The second end of the air proportion valve is connected to the first end of a second flow sensor. The second end of the second flow sensor is connected to the first end of the air-oxygen mixing device.

[0042] Compared with the prior art, the beneficial effects of the present application are as follows:

[0043] The present application dynamically tracks the oxygen concentration during the injection process through an oxygen concentration real-time monitoring system, and can accurately record the change trend in each breathing cycle, providing data support for subsequent adjustment.

[0044] The present application forms an optimal oxygen concentration prediction model through a convolutional neural network, calculates the most appropriate adjustment amount through the model, and timely adjusts the oxygen supply flow rate and injection frequency to ensure that the oxygen concentration output by the ventilator always remains within the set safe range. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is an overall schematic diagram of a high-frequency jet ventilator system provided by an embodiment of the present application;

[0046] Figure 2 It is an internal structure schematic diagram of the high-frequency jet ventilator system provided by an embodiment of the present application;

[0047] Figure 3 It is a flowchart of a control method for a high-frequency jet ventilator system provided by an embodiment of the present application;

[0048] Figure 4 It is a training diagram of a convolutional neural network provided by an embodiment of the present application;

[0049] Figure 5 It is a schematic diagram of a control system based on a convolutional neural network provided by an embodiment of the present application. Specific implementation manners

[0050] The following elaborates on this solution in combination with the accompanying drawings and specific implementation manners.

[0051] Figure 1 It is an overall schematic diagram of a high-frequency jet ventilator system provided by an embodiment of the present application. Refer to Figure 1 , in this embodiment of the high-frequency jet ventilator system, it includes: a main controller and a ventilation control system, an oxygen concentration monitoring system, a feedback regulation system, an alarm system, and a jet needle electrically connected to the main controller. Among them, the ventilation control system is used to ensure the normal spraying of oxygen and air in the ventilator, the oxygen concentration monitoring system is used to monitor the oxygen concentration in real time during the spraying process, the feedback regulation system is used to adjust the oxygen supply flow rate and spraying frequency to ensure that the oxygen concentration output by the ventilator always remains within the set range, and the alarm system is used to give an alarm prompt for abnormal situations that occur when the ventilator is working.

[0052] Refer to Figure 2 , in this embodiment, the ventilation control system includes an oxygen gas path, an air gas path, and a mixed gas path. Among them, the output ends of the oxygen gas path and the air gas path are both connected to the input end of the mixed gas path, and the output end of the mixed gas path is connected to the outlet of the main controller.

[0053] Specifically, the intake end of the oxygen gas path is externally connected to a first controllable pressure gas source, the output end of the first controllable pressure gas source is connected to the input end of the first gas source filter, the output end of the first gas source filter is respectively connected to the first pressure sensor and the first end of the first pressure reducer, the second end of the first pressure reducer is connected to the first end of the oxygen proportion valve, the second end of the oxygen proportion valve is connected to the first end of the first flow sensor, and the second end of the first flow sensor is connected to the first end of the air-oxygen mixing device. The intake end of the air gas path is externally connected to a second controllable pressure gas source, the output end of the second controllable pressure gas source is connected to the input end of the second gas source filter, the output end of the second gas source filter is respectively connected to the second pressure sensor and the first end of the second pressure reducer, the second end of the second pressure reducer is connected to the first end of the air proportion valve, the second end of the air proportion valve is connected to the first end of the second flow sensor, and the second end of the second flow sensor is connected to the first end of the air-oxygen mixing device.

[0054] The feedback regulation system in this embodiment has a built-in convolutional neural network, and through cooperation with the oxygen concentration monitoring system, it realizes intelligent and stable oxygen concentration control.

[0055] In this embodiment, the pressure of the filtered air and oxygen is maintained within the range of 400 - 1000 Kpa. When the air and oxygen pressures within this range are determined, they can enter the system. After passing through the proportional valve, the proportional valve adjusts the proportional opening according to the current oxygen concentration and the target oxygen concentration. The control of the proportional opening is adjusted by relying on the duty cycle of the driving PWM wave, and the proportional adjustment division is carried out depending on the concentration difference between the target concentration and the current concentration. The flow sensor obtains the current gas flow rate and then adjusts the flow rate towards the target flow rate according to the gap from the target flow rate.

[0056] Corresponding to the high-frequency jet ventilator system provided in the above embodiment, the present application also provides an embodiment of a control method for a high-frequency jet ventilator system.

[0057] See Figure 3 , the flowchart of the control method for a high-frequency jet ventilator system provided in this embodiment. The control method for a high-frequency jet ventilator system in this embodiment includes:

[0058] S101, obtain the oxygen flow rate and air flow rate in the oxygen gas path and the air gas path respectively through the first flow sensor and the second flow sensor.

[0059] In this embodiment, the oxygen output from the first controllable pressure gas source is filtered through a gas source filter and then input into the oxygen gas path, and the air output from the second controllable pressure gas source is filtered through a gas source filter and then input into the air gas path. The first flow sensor and the second flow sensor are used to obtain the oxygen flow rate and air flow rate in the oxygen gas path and the air gas path respectively.

[0060] S102, use the oxygen concentration monitoring system to monitor the current oxygen concentration in the air-oxygen mixing device in real time.

[0061] The oxygen concentration monitoring system in this embodiment adopts a monitoring system integrating an oxygen concentration sensor and a microprocessor, which can measure and feedback the oxygen concentration in the airway in real time during high-frequency jetting.

[0062] S103, after comparing the monitored current oxygen concentration with the target oxygen concentration, determine the oxygen output parameters and air output parameters through the optimal oxygen concentration prediction model.

[0063] See Figure 4, in this embodiment, according to the optimization method of the convolutional neural network, an optimization algorithm based on adaptive moment estimation gradient descent is used to optimize the weights and biases of the deep learning neurons of the three-layer convolutional neural network, and the optimal control effect is calculated. According to the target oxygen concentration and flow rate, the optimal control signals of the oxygen gas path and the air gas path are obtained by using the trained optimal oxygen concentration prediction model. 1000 groups of oxygen proportional valve parameters, air proportional valve parameters and mixed oxygen concentration parameters are pre-collected as input data, and the collected multi-group data are input into the convolutional neural network for training to form an optimal oxygen concentration prediction model, so as to ensure that the output oxygen concentration is consistent with the target oxygen concentration. When there is an error after comparing the monitored current oxygen concentration with the target oxygen concentration, the target oxygen concentration is input into the optimal oxygen concentration prediction model, and the oxygen output parameters and air output parameters are determined by the optimal oxygen concentration prediction model.

[0064] In this embodiment, the input data is convolved through the convolutional layer to extract the eigenvalue of the sample data. The Relu activation function reduces overfitting, and the fully connected layer combines the convolutional data part to form an output model. The training process of the convolutional neural network of this system includes two parts: forward propagation and backward propagation. Forward propagation calculates the input data from the bottom layer to the high layer, and the input of each layer of data is the output of the previous layer. Backward propagation calculates the gradient of the convolutional neural network, and updates the parameters of the convolutional neural network by using the adaptive moment estimation gradient descent algorithm according to the calculated gradient, so as to minimize the loss function.

[0065] Among them, the mean square error loss function is used as the loss calculation method in the calculation process of the convolutional neural network, y i is the true value (the control signal parameters of the oxygen and air gas paths), y i is the model prediction value, n is the number of samples of the sample, and MSE is the loss value.

[0066]

[0067] S104. According to the determined oxygen output parameters and air output parameters, the air proportional valve, oxygen proportional valve and mixed gas proportional valve are regulated to achieve stable control of the target oxygen amount.

[0068] In this embodiment, the oxygen output parameters correspond one by one to the opening of the oxygen proportional valve, and the air output parameters correspond one by one to the opening of the air proportional valve. The convolutional neural network will adjust the opening according to the concentration to form concentration control. See Figure 5, in this embodiment, the total flow rate requirement ejected by the high-frequency jet ventilator system is obtained, and the air proportional valve, the oxygen proportional valve, and the mixed gas proportional valve are regulated according to the determined oxygen output parameter, air output parameter, and the total flow rate requirement ejected, so as to achieve stable control of the target oxygen amount. When the total flow rate requirement ejected by the high-frequency jet ventilator system remains unchanged, if the current oxygen concentration is higher than the target oxygen concentration, the proportional opening of the oxygen proportional valve is controlled to decrease and the proportional opening of the air proportional valve is controlled to increase by the driver; if the current oxygen concentration is lower than the target oxygen concentration, the proportional opening of the oxygen proportional valve is controlled to increase and the proportional opening of the air proportional valve is controlled to decrease by the driver.

[0069] When the total flow rate requirement ejected by the high-frequency jet ventilator system decreases, if the current oxygen concentration is higher than the target oxygen concentration, the proportional opening of the mixed gas proportional valve and the proportional opening of the oxygen proportional valve are controlled to decrease respectively by the driver, and the proportional opening of the air proportional valve remains unchanged; if the current oxygen concentration is lower than the target oxygen concentration, the proportional opening of the mixed gas proportional valve and the proportional opening of the air proportional valve are controlled to decrease respectively by the driver, and the proportional opening of the oxygen proportional valve remains unchanged.

[0070] When the total flow rate requirement ejected by the high-frequency jet ventilator system increases, if the current oxygen concentration is higher than the target oxygen concentration, the proportional opening of the mixed gas proportional valve and the proportional opening of the air proportional valve are controlled to increase respectively by the driver, and the proportional opening of the oxygen proportional valve remains unchanged; if the current oxygen concentration is lower than the target oxygen concentration, the proportional opening of the mixed gas proportional valve and the proportional opening of the oxygen proportional valve are controlled to increase respectively by the driver, and the proportional opening of the air proportional valve remains unchanged.

[0071] In the embodiments of the present application, "a plurality of" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent the situation where A exists alone, A and B exist simultaneously, or B exists alone. Wherein A and B may be singular or plural. The character " / " generally represents an "or" relationship between the front and rear associated objects.

[0072] It should be noted that in this article, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0073] The above are only specific embodiments of the present application. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. The protection scope of the present application shall be subject to the protection scope of the claimed rights.

Claims

1. A control method for a high-frequency jet ventilator system, characterized in that: include: The oxygen flow rate and the air flow rate in the oxygen gas path and the air gas path are acquired respectively by means of a first flow sensor and a second flow sensor; The oxygen concentration monitoring system is used to monitor the current oxygen concentration in the air-oxygen mixing device in real time; After comparing the monitored current oxygen concentration with the target oxygen concentration, the oxygen output parameters and the air output parameters are determined by the optimal oxygen concentration prediction model; The air proportional valve, oxygen proportional valve and mixed gas proportional valve are regulated according to the determined oxygen output parameters and air output parameters to achieve stable control of the target oxygen amount.

2. The control method of the high-frequency jet ventilator system according to claim 1, characterized in that: The method of obtaining the oxygen flow rate and the air flow rate in the oxygen gas path and the air gas path respectively by using the first flow sensor and the second flow sensor comprises: The oxygen outputted by the first controllable pressure gas source is filtered through the gas source filter and then inputted into the oxygen gas circuit; The air outputted from the second controllable pressure air source is filtered through an air source filter and then inputted into the air path; The oxygen flow rate and the air flow rate in the oxygen gas path and the air gas path are acquired respectively by the first flow sensor and the second flow sensor.

3. The control method of the high-frequency jet ventilator system according to claim 1, characterized in that: After comparing the monitored current oxygen concentration with the target oxygen concentration, the oxygen output parameter and the air output parameter are determined by the optimal oxygen concentration prediction model, including: Collect multiple sets of oxygen proportion valve parameters, air proportion valve parameters and mixed oxygen concentration parameters in advance; Input multiple sets of collected data into a convolutional neural network for training to form an optimal oxygen concentration prediction model; When there is an error after comparing the monitored current oxygen concentration with the target oxygen concentration, the target oxygen concentration is input into the optimal oxygen concentration prediction model; The oxygen output parameter and the air output parameter are determined by the optimal oxygen concentration prediction model.

4. The control method of the high-frequency jet ventilator system according to claim 1, characterized in that: The method of regulating the air proportional valve, the oxygen proportional valve and the mixed gas proportional valve according to the determined oxygen output parameter and air output parameter to achieve stable control of the target oxygen amount includes: Obtain the total flow demand of the high-frequency jet ventilator system; The air proportional valve, oxygen proportional valve and mixed gas proportional valve are regulated according to the determined oxygen output parameters, air output parameters and total ejection flow requirements to achieve stable control of the target oxygen amount.

5. The control method of the high-frequency jet ventilator system according to claim 4, characterized in that: The air proportion valve, the oxygen proportion valve and the mixed gas proportion valve are regulated according to the determined oxygen output parameter, the air output parameter and the total flow rate requirement of the ejection to achieve stable control of the target oxygen amount, including: When the total flow demand of the high-frequency jet ventilator system remains unchanged, if the current oxygen concentration is higher than the target oxygen concentration, the proportional opening of the oxygen proportional valve is controlled by the driver to decrease, and the proportional opening of the air proportional valve is increased; or, If the current oxygen concentration is lower than the target oxygen concentration, the proportional opening of the oxygen proportional valve is increased and the proportional opening of the air proportional valve is decreased by controlling the driver; When the total flow demand of the high-frequency jet ventilator system decreases, if the current oxygen concentration is higher than the target oxygen concentration, the proportional opening of the mixed gas proportional valve and the proportional opening of the oxygen proportional valve are respectively controlled to decrease through the driver control, and the proportional opening of the air proportional valve remains unchanged; or, If the current oxygen concentration is lower than the target oxygen concentration, the proportional opening of the mixed gas proportional valve and the proportional opening of the air proportional valve are respectively controlled to decrease through the driver control, and the proportional opening of the oxygen proportional valve remains unchanged; When the total flow demand of the high-frequency jet ventilator system increases, if the current oxygen concentration is higher than the target oxygen concentration, the proportional opening of the mixed gas proportional valve and the proportional opening of the air proportional valve are respectively controlled to increase through the driver control, and the proportional opening of the oxygen proportional valve remains unchanged; or, If the current oxygen concentration is lower than the target oxygen concentration, the proportional opening of the mixed gas proportional valve and the proportional opening of the oxygen proportional valve are respectively controlled to increase through the driver control, and the proportional opening of the air proportional valve remains unchanged.

6. A high-frequency jet ventilator system, characterized in that: include: A main controller and a ventilation control system, an oxygen concentration monitoring system, a feedback regulation system, an alarm system and an air jet needle electrically connected to the main controller; The ventilation control system is used to ensure the normal spraying of oxygen and air in the ventilator; The oxygen concentration monitoring system is used to monitor the oxygen concentration in real time during the injection process; The feedback regulation system is used to adjust the oxygen supply flow rate and injection frequency to ensure that the oxygen concentration output by the ventilator is always maintained within a set range; The alarm system is used to issue an alarm prompt for abnormal situations that occur when the ventilator is working.

7. The high-frequency jet ventilator system according to claim 6, characterized in that: The ventilation control system comprises an oxygen gas circuit, an air gas circuit and a mixed gas circuit, the output ends of the oxygen gas circuit and the air gas circuit are both connected to the input end of the mixed gas circuit, and the output end of the mixed gas circuit is connected to the outlet of the main controller.

8. The high-frequency jet ventilator system according to claim 7, characterized in that: The air inlet end of the oxygen gas circuit is externally connected to a first controllable pressure air source, the output end of the first controllable pressure air source is connected to the input end of a first air source filter, the output end of the first air source filter is respectively connected to the first ends of a first pressure sensor and a first pressure reducer, the second end of the first pressure reducer is connected to the first end of an oxygen proportional valve, the second end of the oxygen proportional valve is connected to the first end of a first flow sensor, and the second end of the first flow sensor is connected to the first end of an air-oxygen mixing device.

9. The high-frequency jet ventilator system according to claim 7 or 8, characterized in that: The air inlet end of the air circuit is externally connected to a second controllable pressure air source, the output end of the second controllable pressure air source is connected to the input end of a second air source filter, the output end of the second air source filter is respectively connected to the first end of a second pressure sensor and a second pressure reducer, the second end of the second pressure reducer is connected to the first end of an air proportional valve, the second end of the air proportional valve is connected to the first end of a second flow sensor, and the second end of the second flow sensor is connected to the first end of an air-oxygen mixing device.

Images