Ventilation system with oxygen pre-filled chamber

Abstract

The present disclosure relates to a ventilation system (1) for supplying an oxygen-containing breathing gas to a patient (3) via a gas delivery line (5), comprising a flow generator (7) for generating a flow of air from an air inlet (11) of the gas delivery line (5) towards the patient (3). The system (1) comprises an oxygen pre-filled chamber (9) arranged downstream of the air inlet (11) such that air from the air inlet (11) flows through the oxygen pre-filled chamber (9) on its way towards the patient (3). The system (1) is configured such that oxygen can be delivered to the patient (3) and the oxygen pre-filled chamber (9) via the oxygen valve (13). The system (1) is able to deliver up to 100% oxygen to the patient (3) by delivering oxygen to the oxygen pre-filled chamber (9) before the start of a high flow period of the inspiration phase, even if the oxygen valve (13) is unable to deliver an oxygen flow matching the peak inspiration flow produced by the flow generator.

Description

Technical Field

[0001] The present disclosure relates to a ventilation system for supplying oxygen-containing breathing gas to a patient, and to a method and a computer program for controlling the oxygen content of oxygen-containing breathing gas, as stated in the preambles of the appended independent claims. Background Art

[0002] Blower ventilation systems are typically configured to ventilate a patient by supplying a breathing gas mixture comprising air and oxygen to the patient's airway. The ventilation system's blower typically generates a gas flow that causes air to be drawn from the ventilation system's environment through an air inlet of a gas delivery line used to deliver the breathing gas mixture to the patient. In the gas delivery line, the air can be mixed with oxygen from an oxygen source supplied to the gas delivery line via a controllable oxygen valve. The air and oxygen are typically mixed in a mixing chamber of the ventilation system to obtain a uniform breathing gas mixture, and the oxygen valve is typically controlled so that the oxygen concentration of the breathing gas mixture corresponds to a set target oxygen concentration. Examples of such blower ventilation systems are disclosed in US 2003 / 0084900 A1 and US 2016 / 0082220 A1.

[0003] The blower in a blower-type ventilation system is typically capable of producing a peak flow rate of 180 lpm or higher. Some blowers are even capable of producing a peak flow rate of 240 lpm or higher. The high peak flow rate of the blower places high demands on the oxygen valve, as the oxygen valve must be able to deliver a corresponding oxygen flow rate so that the ventilation system can deliver 100% oxygen to the patient, which is sometimes desired. Even for more moderate oxygen concentrations, the oxygen valve must be able to deliver a high flow rate of oxygen to maintain the set target oxygen concentration in the respiratory gas reaching the patient, especially during the high-flow period of inspiration.

[0004] Oxygen valves capable of delivering such high flow rates are typically bulky and expensive to manufacture. Particularly for blower-type ventilation systems, which are often mobile and specifically intended for use in environments where a pressurized air source is generally unavailable, bulky and expensive system components should be avoided.

[0005] Therefore, there is a need for a ventilation system that allows the use of a flow generator having a high peak flow rate while being able to deliver breathing gas having a high oxygen concentration without the use of a high volume flow valve as an additional expensive system component. Summary of the Invention

[0006] It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the above-mentioned deficiencies and disadvantages in the prior art.

[0007] It is a specific object of the present disclosure to provide a ventilation system using a flow generator that is capable of generating and delivering a high flow of oxygen-enriched breathing gas to a patient without requiring high-capacity flow valves or other expensive system components.

[0008] These and other objects, which will become apparent in view of the detailed description below, are achieved by a ventilation system, a method and a computer program as defined in the appended claims.

[0009] According to one aspect of the present disclosure, a ventilation system for supplying oxygen-containing breathing gas to a patient via a gas delivery line is provided. The ventilation system includes a flow generator for generating an air flow flowing from an air inlet of the gas delivery line toward the patient. The ventilation system includes an oxygen pre-fill chamber forming part of the gas delivery line, the oxygen pre-fill chamber being arranged downstream of the air inlet such that air from the air inlet flows through the oxygen pre-fill chamber on its way to the patient. The ventilation system also includes a controllable oxygen valve for regulating the flow of oxygen through the oxygen inlet of the gas delivery line, the oxygen inlet being arranged in fluid communication with the oxygen pre-fill chamber, and a controller for controlling the oxygen valve so that an average oxygen concentration of the breathing gas delivered to the patient during inspiration substantially corresponds to a set target oxygen concentration. The controller is further configured to control the oxygen valve so that the oxygen pre-fill chamber is pre-filled with a certain volume of oxygen before the start of a high-flow period during an inspiratory phase.

[0010] By pre-filling the oxygen pre-fill chamber with a certain volume of oxygen before the high flow period of the inspiratory phase begins, a high concentration of oxygen (up to 100%) can be delivered to the patient even if the oxygen valve is unable to deliver an oxygen flow that matches the peak inspiratory flow produced by the flow generator.

[0011] This is most easily understood by examining an exemplary scenario where a target oxygen concentration of 100% is set. In this scenario, in a ventilation system without an oxygen pre-fill chamber, when the oxygen flow rate from the oxygen valve drops below the inspiratory flow rate generated by the flow generator, air will inevitably be drawn into the gas delivery line via the air inlet and delivered to the patient. Therefore, such a ventilation system will not be able to deliver 100% oxygen unless the oxygen valve is capable of delivering an oxygen flow rate that matches the peak inspiratory pressure of the flow generator. By using the proposed oxygen pre-fill chamber and pre-filling it with a certain amount of pure oxygen before the high-flow period of the inspiratory phase, the flow rate required to compensate for the difference between the flow rate generated by the flow generator and the maximum flow rate through the oxygen valve during the high-flow period is withdrawn from the oxygen pre-fill chamber, enabling the delivery of breathing gas containing 100% oxygen to the patient.

[0012] Thus, the proposed ventilation system enables the use of oxygen valves that are not matched to the capacity of the flow generator in terms of maximum flow rate.Thus, less complex, smaller and less expensive oxygen valves can be used while the peak inspiratory flow capacity of the ventilation system remains unchanged.

[0013] Thus, the flow generator and the oxygen valve can advantageously be configured such that the gas flow rate generated by the flow generator during the high flow period of the inspiratory phase exceeds the maximum oxygen flow rate that can be delivered via the oxygen valve. In some embodiments, the flow generator can be a high flow generator capable of generating a gas flow rate of at least 120 lpm, preferably at least 180 lpm, and most preferably at least 240 lpm, while the oxygen valve can deliver a maximum oxygen flow rate of no more than 60 lpm.

[0014] In the event that the oxygen concentration of the respiratory gas delivered to the patient falls below a set target oxygen concentration, the controller can be configured to first apply an oxygen valve control strategy in which the oxygen concentration of the respiratory gas is increased to above the set target oxygen concentration during at least one low flow period of one or more upcoming inspiratory phases. As used herein, a low flow period refers to a period during which the gas flow rate generated by the flow generator is less than the maximum flow rate of oxygen that can be delivered through the oxygen valve. If increasing the oxygen concentration above the set target oxygen concentration during the low flow period is insufficient to achieve the set target oxygen concentration, or if the oxygen concentration of the respiratory gas cannot be further increased during the low flow period (e.g., when 100% oxygen is to be delivered), the controller switches to an oxygen valve control strategy in which the oxygen valve is controlled to pre-fill the oxygen pre-fill chamber with oxygen before the start of a high flow period during one or more upcoming inspiratory phases. In other words, the controller may be configured to control the oxygen valve such that the oxygen pre-fill chamber is pre-filled with oxygen before the start of the high-flow phase of the at least one inspiratory phase in response to a failure to bring the average oxygen concentration substantially to correspond to the set target oxygen concentration by controlling the oxygen valve such that the oxygen concentration of the breathing gas increases above the set target oxygen concentration during the at least one low-flow period of the at least one inspiratory phase.

[0015] The controller can be configured to control the oxygen valve so that the oxygen pre-fill chamber is pre-filled with a certain volume of oxygen during the low flow period of the respiratory cycle. The low flow period of the respiratory cycle can occur during any one or any combination of the final stage of the inspiratory phase, the initial stage of the inspiratory phase, and the expiratory phase. Therefore, in the case where the oxygen pre-fill chamber must be used to reach a set target oxygen concentration during the inspiratory phase, the controller can control the oxygen valve so that the oxygen pre-fill chamber is pre-filled during the final stage of the preceding inspiratory phase, during the expiratory phase before the inspiratory phase, during the initial stage of the inspiratory phase itself, or during any combination thereof. The oxygen inlet of the gas delivery line can be arranged relative to the oxygen pre-fill chamber so that an excess oxygen flow exceeding the current gas flow generated by the flow generator flows into the oxygen pre-fill chamber. In this way, the oxygen pre-fill chamber can be pre-filled with oxygen during any period when the inspiratory flow generated by the flow generator is less than the maximum flow of oxygen delivered via the oxygen valve.

[0016] The controller can be configured to determine whether to pre-fill the oxygen pre-fill chamber based on a measured oxygen concentration of the respiratory gas delivered to the patient and a set target oxygen concentration. For example, the controller can be configured to determine an average oxygen concentration of the respiratory gas delivered to the patient during one or more previous breaths based on the measured oxygen concentration, and determine whether to pre-fill the oxygen pre-fill chamber before the start of one or more high-flow periods of the upcoming inspiratory phase based on a comparison between the average oxygen concentration and the set target oxygen concentration. For example, if the average oxygen concentration delivered during the one or more previous breaths is below a threshold (which may correspond to the set target oxygen concentration) or gradually decreases over the course of the plurality of previous breaths, the controller can determine to increase the average oxygen concentration of the respiratory gas delivered during the upcoming inspiratory phase by controlling the oxygen valve such that the oxygen pre-fill chamber is pre-filled with a certain volume of oxygen before the start of the one or more high-flow periods of the upcoming inspiratory phase.

[0017] According to some embodiments, the oxygen pre-fill chamber includes an elongated gas channel that serves as an oxygen reflector and is configured such that oxygen flowing into the oxygen pre-fill chamber from the oxygen inlet pushes air contained in the gas channel out of the oxygen pre-fill chamber in the direction of the air inlet, and such that air flowing into the oxygen pre-fill chamber from the air inlet pushes oxygen contained in the gas channel out of the oxygen pre-fill chamber in the direction of the patient. In this way, oxygen can be delivered to, retained in, and delivered from the oxygen pre-fill chamber to the patient without requiring upstream or downstream valves, pressurized gas tanks, or other expensive or energy-consuming circuit components. The oxygen pre-fill chamber thus forms a non-pressurized, open-ended gas channel that serves as an oxygen reflector for receiving and retaining a certain amount of oxygen during low-flow periods of ventilation and for reflecting a certain amount of oxygen back to the patient during high-flow periods of ventilation.

[0018] According to some embodiments, the oxygen inlet is positioned downstream of the elongated gas passage, or at the downstream end of the elongated gas passage. This creates a well-defined gas interface between the oxygen and air in the oxygen pre-fill chamber and prevents or at least mitigates mixing of the oxygen and air, thereby preventing oxygen leakage from the air inlet and improving oxygen delivery control. Furthermore, the well-defined gas interface between the oxygen and air in the oxygen pre-fill chamber serves to effectively propel oxygen and air back and forth within the oxygen pre-fill chamber while minimizing gas mixing. Furthermore, the downstream location of the oxygen inlet allows oxygen to flow into the oxygen pre-fill chamber only when the flow through the oxygen valve exceeds the current flow generated by the flow generator. Thus, the controller can control the degree of pre-filling of the oxygen pre-fill chamber by controlling the oxygen flow through the oxygen valve relative to the current inspiratory flow generated by the flow generator.

[0019] According to some embodiments, the length of the elongated gas channel of the oxygen pre-filled chamber is at least five times greater than the width or diameter of the elongated gas channel. Preferably, the length of the elongated gas channel is at least ten times greater than its width or diameter. In this way, a laminar flow is achieved in the oxygen pre-filled chamber, which further facilitates maintaining a well-defined gas interface between the oxygen column and the air column moving back and forth in the oxygen pre-filled chamber, thereby further preventing mixing of oxygen and air.

[0020] The size of the elongated gas channel can be adapted to the requirements of the patient being ventilated. Typically, the volume of the elongated gas channel is 200 ml to 3000 ml. According to some embodiments, the volume of the elongated gas channel of the oxygen pre-filled chamber is 200 ml to 2000 ml, preferably 250 ml to 1500 ml, more preferably 300 ml to 1000 ml, and most preferably 400 ml to 800 ml.

[0021] The controller can be configured to prefill all or part of the oxygen prefill chamber with oxygen before the high-flow period of the inspiratory phase begins. The volume of oxygen prefilled into the oxygen prefill chamber before the high-flow period of inspiratory phase begins (hereinafter referred to as the prefill oxygen volume) should at least correspond to the volume of oxygen that needs to be delivered to the patient during the high-flow period so that the average oxygen concentration of the respiratory gas delivered during the entire inspiratory phase reaches a set target oxygen concentration. Therefore, the controller can be configured to determine the prefill oxygen volume based on the flow profile of the inspiratory flow generated by the flow generator and the set target oxygen concentration. Preferably, in order to deliver 100% oxygen to the patient, the prefill oxygen volume should correspond to or exceed the maximum flow volume, which corresponds to the volume of respiratory gas delivered to the patient at a flow rate that exceeds the maximum flow rate of oxygen delivered via the oxygen valve.

[0022] In some embodiments, the oxygen pre-fill chamber can be comprised of a section of tubing forming an elongated gas passage. In other embodiments, the oxygen pre-fill chamber can include a housing having an air inlet port for receiving air from the air inlet and an oxygen inlet port for receiving oxygen from the oxygen inlet. The air inlet port and the oxygen inlet port are fluidly connected to each other within the housing via a section of tubing or a gas conduit extending between the air inlet port and the oxygen inlet port. The oxygen pre-fill chamber can be detachably connected to the gas delivery line between the air inlet and the oxygen inlet.

[0023] According to some embodiments, the oxygen pre-filling chamber and the oxygen inlet are arranged upstream of the flow generator along the gas delivery line. This is advantageous from a noise point of view. Flow generators such as blowers typically generate a large amount of noise. Downstream of the flow generator, this noise is captured within the gas delivery line, and the piping and circuit components between the flow generator and the patient act as a sound trap, effectively preventing the noise from reaching high sound levels outside the gas delivery line. On the other hand, on the upstream side of the flow generator, the noise escapes the gas delivery line via the air inlet, which typically produces high sound levels in the area behind the flow generator. By placing the oxygen pre-filling chamber upstream of the flow generator, between the flow generator and the air inlet, the volume and gas passage of the oxygen pre-filling chamber will act as a sound trap with a damping effect on the noise in a manner similar to the piping and circuit components downstream of the flow generator.

[0024] According to another aspect of the present disclosure, a method for controlling the oxygen content of oxygen-containing breathing gas delivered to a patient by a ventilation system is provided. The ventilation system includes: a flow generator for generating a flow of air from an air inlet of a gas delivery line to the patient via an oxygen pre-fill chamber of the gas delivery line; and a controllable oxygen valve for regulating the flow of oxygen through the oxygen inlet of the gas delivery line, the oxygen inlet being arranged in fluid communication with the oxygen pre-fill chamber. The method includes the steps of pre-filling the oxygen pre-fill chamber with a volume of oxygen to be delivered to the patient during a subsequent high-flow period of an inspiratory phase.

[0025] All features and advantages disclosed herein with respect to the ventilation system also apply to the method of controlling the oxygen content of breathing gas delivered to a patient via such a ventilation system.

[0026] As described above, the method aims to control the oxygen content of the respiratory gas so that the average oxygen concentration of the respiratory gas delivered to the patient during inspiration substantially corresponds to a set target oxygen concentration. As will also be apparent from the above, the step of pre-filling the pre-fill chamber with oxygen may be performed in response to a failure to achieve an average oxygen concentration corresponding to the set target oxygen concentration during one or more inspiration phases.

[0027] According to some embodiments, the oxygen inlet is arranged downstream of the elongated gas passage of the oxygen pre-filled chamber, or at the downstream end of the elongated gas passage, whereby the oxygen pre-filled chamber can be pre-filled during low flow periods, during which the gas flow rate generated by the flow generator is lower than the maximum flow rate of oxygen that can be delivered via the oxygen valve.

[0028] According to some embodiments, the low flow period occurs during any one or any combination of the final portion of the inspiratory phase, the initial portion of the inspiratory phase, and the expiratory phase.

[0029] According to some embodiments, the step of pre-filling the oxygen pre-fill chamber before the start of the high-flow period of the at least one inspiratory phase is performed in response to a failure to bring the average oxygen concentration to substantially correspond to the set target oxygen concentration by increasing the oxygen concentration of the breathing gas above the set target oxygen concentration during at least one low-flow period of the at least one inspiratory phase.

[0030] The method may be a computer-implemented method executed by the controller described above for controlling an oxygen valve of a ventilation system when executing a computer program.

[0031] Therefore, according to another aspect of the present disclosure, there is provided a computer program for controlling the oxygen content of respiratory gas delivered to a patient by a ventilation system, the ventilation system comprising: a flow generator for generating an air flow from an air inlet of a gas delivery line toward the patient; an oxygen pre-fill chamber forming part of the gas delivery line and arranged downstream of the air inlet such that air from the air inlet flows through the pre-fill chamber on its way to the patient; a controllable oxygen valve for regulating the flow of oxygen through the oxygen inlet of the gas delivery line, the oxygen inlet being arranged in fluid communication with the pre-fill chamber; and a controller for controlling the oxygen valve such that an average oxygen concentration of the respiratory gas delivered to the patient during an inspiratory phase substantially corresponds to a set target oxygen concentration. The computer program comprises computer-readable instructions that, when executed by a processor of the controller, cause the controller to perform the above-described method.

[0032] According to yet another aspect of the present disclosure, a computer program product is provided, which includes a non-transitory data storage medium storing a computer program.

[0033] The present disclosure will become apparent from the detailed description below. The detailed description and specific examples disclose preferred embodiments of the present disclosure by way of illustration only. Those skilled in the art will appreciate from the guidance of the detailed description that changes and modifications may be made to the teachings of the present disclosure within the scope of the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above objects and other objects, features and advantages of the present disclosure will be more fully understood by referring to the following illustrative and non-limiting detailed description of example embodiments of the present disclosure when taken in conjunction with the accompanying drawings.

[0035] Figure 1 A ventilation system for supplying oxygen-containing breathing gas to a patient is illustrated in accordance with an exemplary embodiment of the present disclosure.

[0036] Figure 2 A ventilation system for supplying oxygen-containing breathing gas to a patient according to another exemplary embodiment of the present disclosure is illustrated.

[0037] Figure 3 A ventilation system for supplying oxygen-containing breathing gas to a patient according to yet another exemplary embodiment of the present disclosure is illustrated.

[0038] Figure 4 An oxygen pre-fill chamber component of a ventilation system according to an exemplary embodiment of the present disclosure is illustrated.

[0039] Figure 5is a flow chart illustrating a method for controlling the oxygen content of oxygen-containing breathing gas delivered to a patient, according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION

[0040] The present disclosure will now be described with reference to the accompanying drawings, in which preferred exemplary embodiments of the present disclosure are shown. However, the present disclosure may be implemented in other forms and should not be construed as limited to the embodiments disclosed herein. The disclosed embodiments are provided solely to fully convey the scope of the present disclosure to those skilled in the art.

[0041] It should be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. It should be noted that, as used in the specification and the appended claims, unless the context clearly indicates otherwise, the expressions "a," "an," "the," and "said" are intended to mean the presence of one or more elements. Thus, for example, a reference to a "unit" or "the unit" may include several devices, etc. Furthermore, the terms "comprises," "comprising," "including," and similar words are intended to be open transition terms and do not exclude the possibility of additional elements or steps.

[0042] Figure 1 A ventilation system 1 for supplying oxygenated breathing gas to a patient 3 is schematically illustrated. In particular, the ventilation system 1 is configured to deliver breathing gas comprising air, oxygen, or a mixture of air and oxygen. The ventilation system 1 comprises a gas delivery line 5, which includes a flow generator 7 for generating an air flow from an air inlet 11 of the gas delivery line 5 toward the patient 3. The breathing gas is delivered to the airway of the patient 3 via a patient connector 12, which may comprise a mask, an endotracheal tube, a nasal cannula, or any other type of patient connector known in the art of mechanical ventilation. The gas delivery line 5 is the inspiratory limb of the ventilation system 1 for delivering breathing gas, also referred to herein as inspiratory gas, to the patient 3. The ventilation system 1 typically also includes an expiratory limb, which includes ventilation circuit components, such as an expiratory valve, one or more flow and pressure sensors, etc., which has been omitted from the drawings to avoid obscuring them with unnecessary detail.

[0043] The air inlet 11 constitutes the open end of the gas delivery line 5 and is arranged to communicate directly with the air surrounding the ventilation system 1, so that when the flow generator 7 is in operation, the surrounding air is drawn into the gas delivery line 5 via the air inlet 11, thereby generating a negative pressure in the gas delivery line 5. An air filter (not shown) is typically located downstream of the air inlet 11 in the gas delivery line 5 for filtering the air entering the ventilation system 1. The air inlet 11 constitutes the upstream end of the gas delivery line 5. The directional terms "upstream" and "downstream" herein refer to the flow of gas through the gas delivery line 5 in the direction of the patient 3, meaning that the air inlet 11 constitutes the upstream end of the gas delivery line 5 and the patient connector 12 constitutes the downstream end of the gas delivery line 5.

[0044] The flow generator 7 can be any type of flow generator that is capable of generating sufficient inspiratory flow or air from the air inlet 11 toward the patient 3 without the need for any additional flow generating components or pressurized air source. In the illustrated example, the flow generator 11 is a blower. The term "blower" herein is intended to include the terms "fan," "compressor," and "turbine," which are exemplary terms for flow generating devices that are often used interchangeably with "blower" in the field of mechanical ventilation. Similarly, the term "blower" is intended to include various types of blower devices, including but not limited to conventional ventilation blower devices and piezoelectric microblowers. The ventilation system 1 can therefore constitute what is sometimes referred to as a blower-type ventilation system or a blower-based ventilation system, a blower-ventilated or blower-based ventilation device, or simply a blower ventilation device. The flow generator 7 is preferably configured to generate a peak inspiratory flow rate of at least 120 liters per minute (lpm), more preferably at least 180 lpm, and most preferably at least 240 lpm.

[0045] Ventilation system 1 also includes a gas reservoir, functionally referred to herein as an oxygen pre-fill chamber 9, which forms part of gas delivery line 5. Oxygen pre-fill chamber 9 is arranged downstream of air inlet 11, such that air drawn into air inlet 11 from the surroundings of ventilation system 1 by operation of flow generator 7 flows through oxygen pre-fill chamber 9 on its way to patient 3. In the illustrated embodiment, oxygen pre-fill chamber 9 is arranged upstream of flow generator 7. In other embodiments, oxygen pre-fill chamber 9 may be arranged downstream of flow generator 7.

[0046] The ventilation system 1 also includes a controllable oxygen valve 13 for regulating the flow of oxygen through an oxygen inlet 17 of the gas delivery line 5. The oxygen inlet 17 is arranged in fluid communication with the oxygen pre-fill chamber 9 and is preferably located downstream of the oxygen pre-fill chamber 9 or at the downstream end of the oxygen pre-fill chamber, as will be discussed in more detail below. Oxygen is supplied by an oxygen source 15, which can be an oxygen outlet at a hospital facility, an oxygen pressurized cylinder, or any other type of oxygen source suitable for delivering oxygen for medical applications. The oxygen valve 13 is typically a low-flow valve, which in this context means that the flow capacity of the oxygen valve 13 is less than the flow capacity of the flow generator 7. The oxygen valve 13 is preferably configured so that it can deliver a maximum flow of no more than 60 lpm at a valve inlet pressure of between 4 bar and 5 bar. This flow rate allows the oxygen valve to deliver a constant oxygen concentration throughout the inspiratory phase for all breaths as defined in Table 201.104 of ISO 80601-2-12:2020, while ensuring that the flow rate does not exceed 60 lpm averaged over 10 seconds at a pressure of 280 kPa measured at the oxygen inlet 17 of the gas delivery line 5, as required by 201.4.11.101.2 of the ventilation device compatibility requirements of ISO 7396-1:2016. In addition to allowing the use of small, cost-effective, and energy-efficient oxygen valves that meet the compatibility requirements due to their technical limitations, the maximum flow rate of 60 lpm improves patient safety by eliminating the risk of delivering a very high flow rate to the patient in the unexpected and potentially harmful event of a valve failure.

[0047] It is noteworthy that the ventilation system 1 does not include any valve or pressure regulating device for controlling the pressure in the oxygen pre-fill chamber 9. The oxygen pre-fill chamber 9 is always in fluid communication with the surrounding air via the air inlet 11, and gas is allowed to flow freely through the oxygen pre-fill chamber 9 during inspiration and expiration. In this way, an open, non-pressurized ventilation system 1 is obtained with system components that minimize complexity, volume, and energy consumption.

[0048] The ventilation system 1 also includes a control module or controller 19 for controlling the oxygen valve 13. By controlling the oxygen valve 13, the controller 19 indirectly controls the flow rate of oxygen flowing through the oxygen valve 13. The controller 19 is typically a computerized controller that controls the oxygen valve 13 by following computer-readable instructions. Unless otherwise specified, any steps described below involving the control of the oxygen valve 13 are performed by the controller 19 when a computer program including computer-readable instructions is executed by the controller's processor 23. The computer program may be stored in a data storage medium 25 of the controller 19, such as a non-transitory storage hardware device.

[0049] The controller is configured to control oxygen valve 13 such that the oxygen concentration of the respiratory gas delivered to patient 3 during inspiration substantially corresponds to a set target oxygen concentration. As will be described in more detail below, this does not necessarily mean that the instantaneous oxygen concentration is constant and corresponds to the set target oxygen concentration at any given time during the inspiration phase. Rather, it means that at least the average oxygen concentration of the respiratory gas delivered during the entire inspiration phase, or the average oxygen concentration of the respiratory gas delivered during a plurality of inspiration phases, substantially corresponds to the set target oxygen concentration, i.e., the volumetric concentration of oxygen in the respiratory gas delivered to the patient during the course of one or more inspiration phases substantially corresponds to the set target oxygen concentration.

[0050] According to the principles of the present disclosure, in order for ventilation system 1 to deliver a large tidal volume with a high oxygen concentration at a high peak inspiratory flow rate, the controller is configured to selectively utilize oxygen pre-fill chamber 9 by controlling oxygen valve 13 so that oxygen pre-fill chamber 9 is pre-filled with a certain volume of oxygen before the start of a high-flow period during the inspiratory phase. As used herein, a high-flow period is a period during which the gas flow generated by flow generator 7 is higher than the maximum flow rate of oxygen that can be delivered via oxygen valve 13.

[0051] Controller 19 can be configured to detect an undesirable decrease in delivered oxygen concentration, for example, by detecting whether the oxygen concentration delivered to patient 3 falls below a predetermined threshold, which can correspond to a preset target oxygen concentration or a value within a predetermined tolerance range of the target oxygen concentration, or by detecting whether the delivered oxygen concentration decreases over time. The undesirable decrease in delivered oxygen concentration can be detected based on oxygen measurements obtained by oxygen sensor 20. Oxygen sensor 20 is typically positioned downstream of flow generator 7 and can, for example, be positioned in or near a Y-piece connecting the illustrated inspiratory and expiratory limbs (not shown) of ventilation system 1. When controller 19 detects an undesirable decrease in delivered oxygen concentration, it can be configured to pre-fill oxygen pre-fill chamber 9 with oxygen prior to the onset of one or more high-flow periods of inspiration. Thus, controller 19 is configured to pre-fill the oxygen pre-fill chamber, enabling ventilation system 1 to increase the oxygen concentration of the respiratory gas delivered during subsequent high-flow periods of inspiration.

[0052] The oxygen pre-fill chamber 9 can be pre-filled with oxygen during a low-flow period, during which the gas flow rate generated by the flow generator 7 is less than the maximum flow rate of oxygen that can be delivered by the oxygen valve 13 via the oxygen inlet 17. The low-flow period can occur during the final stage of the inspiratory phase, the initial stage of the inspiratory phase, the expiratory phase, or any combination thereof. During the low-flow period, the controller 19 controls the oxygen valve 13 so that the flow rate of oxygen flowing into the gas delivery line 5 through the oxygen valve 13 via the oxygen inlet 17 exceeds the relatively low flow rate generated by the flow generator 7 during the low-flow period. A first portion of the oxygen flow corresponding to the current gas flow rate generated by the flow generator 7 will then flow downstream in the gas delivery line 5 and further to the patient 3, while a second portion of the oxygen flow, which may be referred to herein as excess oxygen flow, will flow upstream in the gas delivery line 5 to the oxygen pre-fill chamber 9. The excess oxygen flow pushes the gas already contained in the oxygen pre-fill chamber 9 out of the chamber in the direction of the air inlet 11. By controlling the flow of oxygen through the oxygen valve 13 based on the current flow rate produced by the flow generator 7, the controller 19 can control the excess oxygen flow into the oxygen pre-fill chamber 9 and thus the pre-fill volume of oxygen with which the chamber is pre-filled.

[0053] During a high-flow period following priming of oxygen pre-fill chamber 9, when the inspiratory flow rate generated by flow generator 9 exceeds the flow rate of oxygen delivered via oxygen valve 13 (typically corresponding to the maximum flow rate of oxygen that can be delivered by oxygen valve 13), a pre-fill volume of oxygen is withdrawn from the oxygen pre-fill chamber to compensate for the difference between the flow rate generated by flow generator 7 and the flow rate of oxygen delivered via oxygen valve 13. In this way, the average oxygen concentration of the inspiratory gas delivered to patient 3 during the high-flow period can be controlled by pre-filling oxygen pre-fill chamber 9 with an oxygen pre-fill volume that is adapted to the volume of inspiratory gas delivered to the patient during the high-flow period and the volume of oxygen delivered via oxygen valve 13 during the high-flow period. In view of the foregoing description, it will be readily understood that, for each inspiratory phase, by pre-filling oxygen pre-fill chamber 9 with an oxygen pre-fill volume that at least corresponds to the maximum flow volume of inspiratory gas delivered to the patient at a flow rate exceeding the maximum flow rate of oxygen valve 13, ventilation system 1 is capable of achieving up to 100% oxygen delivery to patient 3.

[0054] As described above, in response to the average oxygen concentration of the delivered breathing gas failing to reach the set target oxygen concentration, the controller 19 may apply a "priming strategy" according to which the oxygen pre-fill chamber 9 is pre-filled with oxygen prior to the high flow period of the subsequent inspiratory phase. The controller 19 may be configured to apply different oxygen valve control strategies depending on the set target oxygen concentration and / or the ability of the oxygen valve 13 to deliver the set target oxygen concentration given the flow profile of the inspiratory flow generated by the flow generator 7.

[0055] The first control strategy may be a conventional proportional control strategy, according to which the oxygen valve 13 is controlled so that the oxygen flow rate through the oxygen valve 13 is proportional to the current inspiratory flow rate generated by the flow generator 7. In this way, as long as the oxygen valve 13 is able to deliver the proportional flow rate required to achieve the set target oxygen concentration, a constant oxygen concentration substantially corresponding to the set target oxygen concentration will be delivered to the patient 3 throughout the inspiratory phase. If the controller 19 detects that the average oxygen concentration of the delivered respiratory gas is lower than the set target oxygen concentration, which is most likely due to the oxygen valve 13 being unable to deliver a proportional oxygen flow rate that matches the inspiratory flow rate during the high-flow period of inspiration, the controller 19 may switch to the second control strategy.

[0056] According to a second control strategy, controller 19 controls oxygen valve 13 such that the oxygen concentration delivered to patient 3 during one or more low-flow inspiratory periods is above the set target oxygen concentration to compensate for the lower oxygen concentration delivered during high-flow inspiratory periods. This allows the average oxygen concentration of the respiratory gas delivered to patient 3 during the entire inspiratory phase—which corresponds to the volumetric concentration of oxygen delivered to the patient during the entire inspiratory phase—to still correspond to the set target oxygen concentration. For example, according to this second control strategy, controller 19 can be configured to control oxygen valve 13 such that the oxygen concentration of the respiratory gas is above the set target oxygen concentration during the initial and / or final phases of inhalation. If the controller detects that the oxygen concentration cannot be increased above the set target oxygen concentration during the low-flow periods of inhalation (as would be the case if the set target oxygen concentration were 100%), or that an average oxygen concentration substantially corresponding to the set target oxygen concentration is insufficient, controller 19 can switch to a third control strategy. According to the teachings of the present disclosure, the third control strategy may be a “pre-fill strategy” according to which the oxygen valve 13 is controlled such that the oxygen pre-fill chamber 9 is pre-filled with oxygen before the start of the high flow period of one or more inhalation phases.

[0057] Preferably, the oxygen valve 13 is a control valve capable of delivering a variable flow of oxygen to the gas delivery line 5 via the oxygen inlet 17. However, in some embodiments, the oxygen valve 13 may be an on-off valve that either allows unimpeded flow through the valve or is configured to completely prevent flow. In this case, the controller 19 may control the opening and closing times of the oxygen valve 13 so that pulses of oxygen are delivered to the gas delivery line 5 via the air inlet 17. The pulsed oxygen flow results in an average oxygen flow through the oxygen valve 13, which can be controlled by controlling the opening and closing times of the control valve 13 according to the principles described above. Therefore, it should be understood that, according to the principles of the present disclosure, the "controllable oxygen valve for regulating the flow of oxygen through the oxygen inlet 17" as used herein may be any of a control valve, an on-off valve, or any other type of valve that can be controlled to deliver oxygen to the gas delivery line 5.

[0058] Now refer to Figure 2 , oxygen inlet 17 is preferably located downstream of oxygen pre-fill chamber 9 along gas delivery line 5. In this way, the entire volume of oxygen pre-fill chamber 9 can be used as a reservoir of oxygen, which is delivered to the patient during a subsequent high-flow inspiratory period. Therefore, according to some embodiments, oxygen pre-fill chamber 9 is arranged downstream of air inlet 11 and upstream of oxygen inlet 17. Oxygen inlet 17 and oxygen pre-fill chamber 9 are located on the same side of flow generator 7. Preferably, but not necessarily, oxygen pre-fill chamber 9 and air inlet 17 are located upstream of flow generator 7.

[0059] Now refer to Figure 3 The oxygen pre-fill chamber 9 may include an elongated gas channel 21 that serves as an oxygen reflector and is configured such that oxygen flowing into the oxygen pre-fill chamber 9 from the oxygen inlet 17 pushes the gas contained in the gas channel out of the oxygen pre-fill chamber 9 in the direction of the air inlet 11, and such that air drawn into the gas delivery line 5 under the negative pressure generated by the flow generator 7 and flowing into the oxygen pre-fill chamber 9 from the air inlet 11 pushes the oxygen contained in the gas channel out of the oxygen pre-fill chamber 9 in the direction of the patient 3. The configuration in which the upstream end of the elongated gas channel 21 is arranged in fluid communication with the air inlet 11 and the downstream end is arranged in fluid communication with the oxygen inlet 17 facilitates the formation of a well-defined gas interface between the oxygen and the air in the oxygen pre-fill chamber 9. The well-defined gas interface serves to minimize mixing of the oxygen and air in the oxygen pre-fill chamber 9 and simultaneously serves to propel the oxygen column and the air column back and forth in the oxygen pre-fill chamber 9.

[0060] The length of the elongated gas channel 21 of the oxygen pre-filled chamber 9 can be at least ten times the width or diameter of the elongated gas channel 21. This dimensional relationship facilitates laminar flow through the oxygen pre-filled chamber, which in turn facilitates maintaining a well-defined gas interface between oxygen and air in the oxygen pre-filled chamber 9 and further reduces gas mixing within the chamber. The dimensions of the elongated gas channel 21 can be adapted to the respiratory capacity of the patient 3 and the flow profile of the inspiratory flow generated by the flow generator 7. In some examples, the length of the gas channel 21 can be in the range of 0.5 meters to 4 meters. In some examples, the width or diameter of the gas channel can be in the range of 8 millimeters to 25 millimeters. In some examples, the total volume of the gas channel 21 can be in the range of 200 ml to 3000 ml, 200 ml to 2000 ml, 250 ml to 1500 ml, 300 ml to 1000 ml, or 400 ml to 800 ml. In some embodiments, the oxygen pre-filled chamber 9 is adapted to accommodate as many patient types as possible, in which case the total volume of the gas channel 21 can be 800 ml to 1200 ml. By enabling oxygen pre-filled chambers of different sizes to be connected to the gas delivery line 5, the oxygen pre-filled chamber 9 can be adapted to the needs of different patients in a simple and effective manner. In the exemplary case of ventilation for adult patients, the gas channel 21 may have a volume of approximately 1 liter and a length of approximately 2.5 meters.

[0061] In order for ventilation system 1 to deliver 100% oxygen to patient 3 during inspiration, oxygen pre-fill chamber 9 should have a minimum volume corresponding to the volume of respiratory gas delivered during the high-flow period of inspiration, and should be delivered at an inspiratory flow rate that exceeds the maximum oxygen flow rate that can be delivered via oxygen valve 13. This volume (hereinafter referred to as the maximum flow volume) corresponds to the volume of gas extracted from the oxygen pre-fill chamber during the high-flow period of inspiration if oxygen valve 13 is left fully open to deliver the maximum oxygen flow that can be delivered via oxygen valve 13. Preferably, the volume of oxygen pre-fill chamber 9 should be slightly larger than the high-flow volume to account for any minor mixing of air and oxygen at or near the gas interface between the air column and the oxygen column.

[0062] Gas channel 21 can be a length of tubing, such as that typically used in ventilation circuits. The tubing can be folded or coiled to minimize the space occupied by oxygen pre-fill chamber 9 in ventilation system 1, and can optionally be retained in a housing suitable for retaining the tubing's shape. In other embodiments, gas channel 21 can be formed from a hollow gas conduit manufactured, for example, by a molding process or additive manufacturing technique, which is assembled into a housing to form an oxygen pre-fill chamber component configured to connect to gas delivery line 5.

[0063] Figure 4An exemplary embodiment of such a component is illustrated. In this embodiment, the oxygen pre-fill chamber 9 includes an elongated gas passage 21 in the form of a hollow, rigid gas conduit. The gas conduit is housed in a housing 29, which includes an air inlet port 31 for receiving air from the air inlet 11 and an oxygen inlet port 33 for receiving oxygen from the oxygen inlet 17. The air inlet port 31 and the oxygen inlet port 33 are fluidly coupled to each other within the housing 29 via the hollow, rigid gas conduit extending between the air inlet port 31 and the oxygen inlet port 33. The oxygen pre-fill chamber can be detachably connected to the gas delivery line 5 between the air inlet 11 and the oxygen inlet 17.

[0064] The rigid gas conduit constituting the gas passage 21 of the oxygen pre-filling chamber 9 can be designed in various ways so as to provide a well-defined gas interface between the air column and the oxygen column moving back and forth in the gas conduit. The gas conduit can have a substantially circular cross section, or a rectangular cross section with rounded corners, or an elliptical or approximately elliptical cross section. The cross-sectional area of ​​the conduit, i.e. the cross-sectional area in a plane perpendicular to the flow direction, is preferably in the range of 300 mm. 2 Up to 450mm 2 within the range, more preferably within 350mm 2 Up to 400mm 2 range, and most preferably about 370 mm 2 The length and total volume of the gas conduit may be the same as discussed above with respect to the gas channel 21 .

[0065] In the illustrated example, the rigid gas conduit has an integral, single-piece molded structure. The gas conduit can be a single, continuous gas conduit comprising a straight portion and a curved portion. The shape of the rigid gas conduit can be similar to that of a folded tube. The air inlet port 31 and the oxygen inlet port 33 can be located adjacent to each other on the same side of the housing 29, and the free end of the folded gas conduit can be connected to a corresponding one of the air inlet port 31 and the oxygen inlet port 33. The two portions of the folded gas conduit, respectively extending from the air inlet port 31 and the oxygen inlet port 33, can extend side by side with each other within the housing 29 and spirally wound inwardly toward the center of the housing, with the two portions meeting at the center, as illustrated in the accompanying drawings.

[0066] The present disclosure also relates to a method for controlling the oxygen content of oxygen-containing breathing gas delivered to a patient by a ventilation system, the ventilation system comprising: a flow generator for generating a flow of air from an air inlet of a gas delivery line to the patient via an oxygen pre-fill chamber of the gas delivery line; and a controllable oxygen valve for regulating the flow of oxygen through the oxygen inlet of the gas delivery line, the oxygen inlet being arranged in fluid communication with the oxygen pre-fill chamber. In accordance with the teachings of the present invention, the method includes the step of pre-filling the oxygen pre-fill chamber with a volume of oxygen to be delivered to the patient during a subsequent high-flow period of an inspiratory phase.

[0067] As described above, the controller 19 of the ventilation system 1 is typically configured to control the oxygen valve 13 so that the oxygen pre-fill chamber is pre-filled with oxygen only when other control strategies fail to result in an average oxygen concentration delivered to the patient 3 that substantially corresponds to a set target oxygen concentration.

[0068] Figure 5 is a flow chart illustrating a method comprising the method described above with reference to Figure 1 The method is thus a computer-implemented method that is executed by the controller 19 of the ventilation system 1 when the processor 23 executes a computer program. The method aims to control the oxygen valve 13 so that the average oxygen concentration of the respiratory gas delivered to the patient 3 substantially corresponds to the set target oxygen concentration.

[0069] In a first step S1, the controller 19 controls the oxygen valve 13 according to a proportional control strategy such that the oxygen flow rate through the oxygen valve 13 is proportional to the current inspiratory flow rate generated by the flow generator 7. In this way, as long as the oxygen valve 13 is able to deliver the proportional flow rate required to achieve the set target oxygen concentration, a constant oxygen concentration substantially corresponding to the set target oxygen concentration will be delivered to the patient 3 at any given time during the inspiratory phase.

[0070] In step S2, if the controller 19 detects that the average oxygen concentration delivered to the patient during inspiration is below the set target oxygen concentration, most likely due to the oxygen valve 13 being unable to deliver a proportional oxygen flow during the high flow period of inspiration, the method proceeds to step S3.

[0071] In step S3, controller 19 checks whether the set target oxygen concentration is less than 100%. If so, according to the current proportional control strategy, the oxygen flow rate delivered through oxygen valve 13 during the low-flow period of inspiration is less than the inspiratory flow rate generated by flow generator 7. This means that by increasing the oxygen flow rate during the low-flow period, i.e., by increasing the oxygen concentration to above the set target oxygen concentration during the low-flow period, it is still possible to make the average oxygen concentration delivered to the patient during the inspiratory phase meet the set target oxygen concentration, whereupon the method proceeds to step S4. On the other hand, if the set target oxygen concentration is 100%, the oxygen flow rate delivered during the low-flow period already corresponds to the inspiratory flow rate generated by flow generator 7, and the method proceeds to step S6.

[0072] In step S4, the controller 19 applies a control strategy according to which the respiratory gas is pressurized with oxygen during the low-flow period of ventilation. This is achieved by the controller 19 controlling the oxygen valve 13 so that the oxygen flow through the oxygen valve 13 is increased to a proportional oxygen flow rate higher than that specified by the previous proportional control strategy, thereby ensuring that an oxygen concentration higher than the set target oxygen concentration is delivered during the low-flow period of ventilation.

[0073] In step S5, if the controller 19 detects that the average oxygen concentration delivered to the patient 3 during inspiration is below the set target oxygen concentration, which is most likely due to the fact that the increase in oxygen concentration during the low flow periods is insufficient to compensate for the ability of the oxygen valve 13 to deliver high oxygen concentrations during the high flow periods of inspiration, the method proceeds to step S6.

[0074] According to the teachings of the present invention, in step S6 , the controller 19 controls the oxygen valve 13 so that the oxygen pre-fill chamber 9 is pre-filled with oxygen before the start of the high flow period of one or more inhalation phases.

[0075] Those skilled in the art will recognize that the present disclosure is not limited to the embodiments described above. Those skilled in the art will also recognize that modifications and variations are possible within the scope of the appended claims.

Claims

1. A ventilation system (1) for supplying oxygen-containing breathing gas to a patient (3) via a gas delivery line (5), the ventilation system (1) comprising a flow generator (7) for generating an air flow flowing from an air inlet (11) of the gas delivery line (5) towards the patient (3), characterized in that The ventilation system (1) comprises: an oxygen pre-fill chamber (9), said oxygen pre-fill chamber (9) forming part of said gas delivery line (5), said oxygen pre-fill chamber (9) being arranged downstream of said air inlet (11) such that air from said air inlet (11) flows through said oxygen pre-fill chamber (9) on its way towards said patient (3); - a controllable oxygen valve (13) for regulating the flow of oxygen through an oxygen inlet (17) of the gas delivery line (5), the oxygen inlet (17) being arranged in fluid communication with the oxygen pre-filled chamber (9), and a controller (19) for controlling the oxygen valve (13) such that the average oxygen concentration of the respiratory gas delivered to the patient (3) during inspiration substantially corresponds to a set target oxygen concentration, The controller (19) is configured to control the oxygen valve (13) so that the oxygen pre-fill chamber (9) is pre-filled with a certain volume of oxygen before the high flow period of the inhalation phase begins.

2. The ventilation system (1) according to claim 1, wherein The oxygen pre-filled chamber (9) comprises an elongated gas channel (21) serving as an oxygen reflector, the oxygen reflector being configured to: The oxygen flowing from the oxygen inlet (17) into the oxygen pre-filled chamber (9) pushes the air contained in the gas channel (21) out of the oxygen pre-filled chamber (9) in the direction of the air inlet (11), and the air flowing from the air inlet (11) into the oxygen pre-filled chamber (9) pushes the oxygen contained in the gas channel (21) out of the oxygen pre-filled chamber (9) in the direction of the patient (3).

3. The ventilation system (1) according to claim 2, wherein The oxygen inlet (17) is arranged downstream of the elongated gas channel (21), or at the downstream end of the elongated gas channel (21).

4. The ventilation system (1) according to any one of claims 2 to 3, wherein: The length of the elongated gas channel (21) of the oxygen pre-filled chamber (9) is at least ten times the width or diameter of the elongated gas channel (21).

5. The ventilation system (1) according to any one of claims 2 to 4, wherein The volume of the elongated gas channel (21) of the oxygen pre-filled chamber (9) is 200ml to 3000ml.

6. The ventilation system (1) according to any one of the preceding claims, wherein The oxygen pre-fill chamber (9) and the oxygen inlet (17) are arranged upstream of the flow generator (7) along the gas delivery line (5).

7. The ventilation system (1) according to any one of the preceding claims, wherein The controller (19) is configured to control the oxygen valve (13) such that the oxygen pre-fill chamber (9) is pre-filled during a low flow period, during which the gas flow rate generated by the flow generator (7) is lower than the maximum flow rate of oxygen that can be delivered via the oxygen valve (13).

8. The ventilation system (1) according to claim 7, wherein The low flow period occurs during any one of the last phase of the inspiratory phase, the initial phase of the inspiratory phase, and the expiratory phase, or any combination thereof.

9. The ventilation system (1) according to any one of the preceding claims, wherein The controller (19) is configured to control the oxygen valve (13) so as to pre-fill the oxygen pre-fill chamber with oxygen before the start of a high flow period of at least one inspiratory phase in response to a failure to bring the average oxygen concentration substantially to correspond to the set target oxygen concentration by controlling the oxygen valve (13) so as to increase the oxygen concentration of the respiratory gas above the set target oxygen concentration during at least one low flow period of at least one inspiratory phase.

10. A method for controlling the oxygen content of oxygen-containing breathing gas delivered to a patient (3) by a ventilation system (1), the ventilation system (1) comprising a flow generator (7) for generating an air flow from an air inlet (11) of a gas delivery line (5) via an oxygen pre-fill chamber (9) of the gas delivery line (5) towards the patient (3), and a controllable oxygen valve (13) for regulating the flow of oxygen through an oxygen inlet (17) of the gas delivery line (11), the oxygen inlet (17) being arranged in fluid communication with the oxygen pre-fill chamber (9), the method comprising the following steps: - Pre-filling (S6) the oxygen pre-fill chamber (9) with a volume of oxygen that will be delivered to the patient (3) during a subsequent high flow period of the inspiratory phase.

11. The method according to claim 10, wherein: The oxygen inlet (13) is arranged downstream of the elongated gas passage (21) of the oxygen pre-filling chamber (9), or at the downstream end of the elongated gas passage (21), and wherein the oxygen pre-filling chamber (9) is pre-filled during a low flow period, during which the gas flow rate generated by the flow generator (7) is lower than the maximum flow rate of oxygen that can be delivered via the oxygen valve (13).

12. The method according to claim 10 or 11, wherein: The low flow period occurs during any one of the final stage of the inspiratory phase, the initial stage of the inspiratory phase, and the expiratory phase, or any combination thereof.

13. The method according to any one of claims 10 to 12, wherein: The step of pre-filling the oxygen pre-fill chamber (9) before the start of the high flow period of the at least one inspiratory phase is performed in response to a failure to bring the average oxygen concentration substantially to correspond to the set target oxygen concentration by increasing (S4) the oxygen concentration of the respiratory gas above the set target oxygen concentration during at least one low flow period of the at least one inspiratory phase.

14. A computer program for controlling the oxygen content of oxygen-containing breathing gas delivered to a patient (3) via a ventilation system (1), the ventilation system (1) comprising: a flow generator (7) for generating a flow of air from an air inlet (11) of a gas delivery line (5) toward the patient (3); an oxygen pre-fill chamber (9) forming part of the gas delivery line (5), the oxygen pre-fill chamber (9) being arranged downstream of the air inlet (11) such that air from the air inlet (11) flows through the oxygen pre-fill chamber (9) on its way towards the patient (3); - a controllable oxygen valve (13) for regulating the flow of oxygen through an oxygen inlet (17) of the gas delivery line (11), the oxygen inlet (17) being arranged in fluid communication with the oxygen pre-filled chamber (9), and a controller (19) for controlling the oxygen valve (13) such that the average oxygen concentration of the respiratory gas delivered to the patient (3) during inspiration substantially corresponds to a set target oxygen concentration, The computer program comprises computer-readable instructions, which, when executed by a processor (12) of the controller (19), cause the controller (19) to perform the method according to any one of claims 10 to 13.

15. A computer program product comprising a non-transitory data storage medium (25) storing a computer program according to claim 14.

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