CN102451506A

CN102451506A - Method and device for controlling airflow of respirator

Info

Publication number: CN102451506A
Application number: CN2010105171499A
Authority: CN
Inventors: 袁含光
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-10-19
Filing date: 2010-10-19
Publication date: 2012-05-16
Anticipated expiration: 2030-10-19
Also published as: CN102451506B

Abstract

The invention discloses a method for controlling the airflow of a respirator. The method comprises the following steps of: introducing continuous airflow with a stable flow rate into a respirator system through an air source; and dynamically adjusting ventilation rhythm and ventilation strength in an air passage by controlling the valve movement frequency and distance of an airflow outlet end so as to support the respiration of a patient. In the method, a command ventilation mode and an autonomous respiration operating mode are utilized; if respiration is stopped in the autonomous respiration mode, autonomous respiration can be maintained in a mode of reducing target tidal volume; and the respiration is still stopped when the tidal volume is reduced to a preset value, so that central pathological changes are determined, and the autonomous respiration operating mode is converted into the command ventilation operating mode. The invention also discloses a device for controlling the airflow of the respirator. In the method and the device, an independent and integral respirator system which completely uses positive pressure switching ventilation of the air passage as a technical basis is formed by a series of matched regulation modes such as a target tidal volume automatic regulation mode, the autonomous respiration mode, the command ventilation operating mode, a respiration pause automatic processing mode and the like.

Description

Ventilator airflow control method and control device

Technical Field

The invention relates to an artificial respirator, in particular to a continuous airflow control method and a continuous airflow control device for a respirator.

Background

A ventilator is a critical life support device that provides ventilatory and oxygenation support for respiratory failure patients. At present, the work of the mainstream ventilator adopts the simulated breathing action, namely, the ventilator carries out periodic positive pressure airflow perfusion on the airway of a patient to provide respiratory power support for lung filling. In the case of ventilator technology, to improve the quality of respiratory support and to minimize the airway pressure and work of breathing during respiratory support, it is necessary to improve the synchronization and coordination of ventilator operation with the patient's spontaneous breathing. Modern ventilators have made some technological advances in these areas, but because analog ventilation is performed with periodic patient breathing and periodic ventilator airflow output, to operate the ventilator completely in compliance with the patient's spontaneous breathing, the two highly dynamic processes must be completely synchronized and coordinated, which requires rather complex airflow control techniques and expensive manufacturing costs, and complete synchronization and coordination between the two is difficult to achieve.

Volume-type ventilation and pressure-type ventilation in the prior art are two basic types of ventilatory support mechanisms for modern mainstream ventilators. Both types of ventilation are pressure-supported by a ventilator operating air supply that periodically delivers a positive pressure flow of air into the airway. Because the patient's breathing is periodic and the patient's airway and lungs are a complex system of conduits, the ventilator airflow output must be tailored to the patient's inspiratory needs, to follow the instantaneous changes in the frictional resistance of the patient's airway and the compliance of the thoracic and lung tissues in various aspects of the stimulation of the airflow output, the setting and variation of flow, the time-phased transitions, the airway pressure and tidal volumes, etc.; improper setting of any of these indicators may cause patient discomfort, excessive airway pressure, and even opposition to the ventilator.

These disadvantages are particularly pronounced in volume-type ventilation regimens, particularly in patients with complex and severe airway lesions, because the flow output of volume-type ventilation is set and does not vary with changes in airway conditions and patient inspiratory requirements. It is now clear that excessive airway pressure is the primary cause of lung injury in ventilators. Improving the safety, ventilation efficiency and comfort of ventilator therapy has been the focus of attention in ventilator technology and ventilator therapy for the purpose of and as a result of its exploration, it is the reduction in airway pressure.

The widespread use of pressure-based ventilation, including pressure-supported ventilation and pressure-controlled ventilation, has been the most important technological advance in mechanical ventilation over the last two decades. The airflow output of the pressure-type ventilation can better follow the airway condition and the performance required by inspiration, the airway pressure of the patient is obviously reduced, and the comfort of the patient is improved, otherwise, if the constant volume ventilation is still adopted, the respiratory support is more difficult to deal with for most cases, particularly for patients with serious lung and airway diseases.

Whether volume-type ventilation or pressure-type ventilation, the ventilation effect depends on the interaction between positive pressure airflow and the airway condition, the generation and output of the positive pressure airflow are periodic, and the mismatch between the positive pressure airflow and the airway condition and the inspiration requirement of a patient can not be completely avoided in the process of periodically pressing the positive pressure airflow into the airway.

In recent years, a new mode of operation has emerged in some ventilators, known as Bi-level. Bi-level can very easily and very quickly relieve dyspnea of a patient with a breathing machine without the help of sedative drugs; meanwhile, on the premise of obtaining the same level of ventilation capacity, the airway pressure caused by Bi-level is obviously lower than that of the conventional ventilation mode, even the pressure support ventilation mode and the pressure control ventilation mode. The practical expression of the clinical application of Bi-level reflects the good ventilation quality of the Bi-level.

The present inventors have proposed a concept of a positive airway pressure switching type ventilation system based on the operation of Bi-level. The positive airway pressure switching ventilation is a ventilation mode which is completely different from two types of mainstream ventilation modes of current volume type ventilation and pressure type ventilation and is based on a continuous airflow terminal flow limiting mechanism. The positive airway pressure switching ventilation working air supply provides high-flow continuous air flow to the pipeline system, and when the air flow is limited by resistance generated on a pressure valve arranged at the terminal opening of the system, the pressure in the whole pipeline system is correspondingly increased. When the air flow movement in the air passage at the end of inspiration and the end of expiration stops, the pressure of the air passage in the system is at the same level, so the system pressure represents the pressure in the air passage and the lung; the switching of system pressure due to positive airway pressure switching ventilation is actually the switching of intra-airway pressure and intra-pulmonary pressure. As an elastic cavity, the change in lung volume always varies with the pressure in the lung, and the relationship between the two is expressed as a pressure-volume curve. On the pressure-volume curve, higher airway pressures and intrapulmonary pressures always represent greater lung volume. When the positive airway pressure switches to ventilation, the switching of the intra-pulmonary airway pressure at two different levels also causes a corresponding shift in lung volume at two different levels, which means that ventilation is proceeding.

Improving ventilation and oxygenation are two basic goals of ventilator therapy, physiologically, these two processes are related to ventilation volume and lung functional residual capacity, respectively. When the positive airway pressure switches to ventilation, the ventilation pressure determines the size of the ventilation volume, and the airway basal pressure determines the size of the residual capacity of the lung function, so the two indexes are the most important indexes in respiratory support.

The principle of positive airway pressure switching ventilation is similar to the change of water level in a reservoir, riverway water flow is blocked and stored by a dam, the upstream water level is naturally improved, and the height of a gate determines the water level in the reservoir. When the positive airway pressure is switched to ventilation, the volume change of the lung is not directly caused by intermittent airflow sent into the lung, but is accompanied by an indirect result of the pressure change of the whole breathing machine pipeline, and the volume change caused by the ventilation of the breathing machine is not influenced by the breathing action of a patient, so that the problem of matching of the airflow output of the breathing machine with the airway condition and the inspiration requirement of the patient is solved.

In recent years, Bi-level has been installed as a relatively minor operation mode in advanced mainstream ventilators based on the volume-type ventilation and the pressure-type ventilation, and the pressure switching is also simple time switching, that is, switching control is performed at a preset frequency and time ratio.

The progress of modern critical illness rescue medicine is leading more and more patients with serious lung and airway pathological changes to have the opportunity of breathing and life support, so the requirements on the safety, effectiveness and comfort of the treatment of a breathing machine are higher and higher; the airway pressure during the ventilation support is reduced as much as possible, the autonomous respiration of the patient is led to the work of the breathing machine as much as possible, the work of the breathing machine can better meet the requirements of the patient, and the breathing machine is becoming a new trend in the treatment of the breathing machine and is also a new requirement for the development of the breathing machine technology. The practical performance of Bi-level shows that the positive airway pressure switching type ventilation is a new technical direction for supporting ventilation; further development and improvement of the positive airway pressure switching type ventilation mode into an independent novel ventilator will be a need for technical and clinical development.

Disclosure of Invention

The invention aims to overcome the defects in the prior art, and an independent and complete respirator system completely based on the technology of positive airway pressure switching ventilation is formed by a series of matched regulation and control of instruction ventilation and autonomous respiration working modes, automatic target tidal volume regulation and control, automatic apnea treatment and the like.

The invention provides a ventilator airflow control method, which inputs continuous airflow with stable flow into a ventilator system from an air source, and dynamically adjusts the ventilation rhythm and the ventilation strength in an airway by controlling the movement frequency and the distance of a valve at an airflow outlet end, thereby realizing the respiratory support of a patient, and the method comprises the following two working modes: a commanded ventilatory mode of operation for use when the patient's breathing pulse is unstable or a specified level of ventilatory support is provided to the patient, wherein in the commanded ventilatory mode of operation the central processor controls the valve to move between the base position A of the valve and the dynamic adjustment of the valve's travel distance B at a predetermined frequency to maintain a set target tidal volume during ventilation to provide a commanded ventilatory support to the patient; the spontaneous respiration working mode is characterized in that the starting and the ending of the inspiration action of a patient are determined through the dynamic pressure and flow detection of an airway interface section, the correction of a basic position A point of a valve and the dynamic adjustment of a moving distance B of the valve are realized, a central processing unit controls the valve to move between two points according to the correction and adjustment result and the spontaneous respiration rhythm of the patient, so that the pressure switching in the airway completely follows the respiration action of the patient, and the set target tidal volume is maintained in the ventilation process or the target tidal volume is adaptively reduced when the patient has respiratory pause so as to maintain the ventilation support of spontaneous respiration.

Wherein, the instruction ventilation working mode comprises the following steps: setting parameters of the command ventilation frequency, the breathing time ratio, the target tidal volume and the basic airway pressure, and converting the set target tidal volume and the basic airway pressure into displacement elements of the valve, wherein the displacement elements of the valve are a basic position A and a moving distance B; according to the displacement element of the valve, the central processing unit controls the starting of the primary ventilation; in the initial ventilation process, detecting the instantaneous flow and the airway pressure of the airway interface section, analyzing and calculating according to actually measured pressure and flow data, respectively obtaining the position of a calibrated point A and the moving distance B of an adjusted valve, and taking the position of the point A and the moving distance B as a valve displacement element of the initial ventilation of the target tidal volume; the central processing unit controls and starts the initial ventilation of the target tidal volume, and executes the initial ventilation according to the position of the calibrated A point and the adjusted valve moving distance B which are determined in the initial ventilation process and the preset ratio of the instruction ventilation frequency to the breathing time; after the initial ventilation, the ventilation of the target tidal volume is continued and the calibration of the position of the a point of the valve and the adjustment of the movement distance B of the valve are repeated on a cycle-by-cycle basis, with this dynamic calibration and adjustment throughout the ventilation support process until a change or termination of the commanded ventilation.

The spontaneous respiration working mode comprises the following steps: carrying out parameter setting on a target tidal volume, a basic airway pressure, inspiratory phase trigger sensitivity and expiratory phase conversion sensitivity, and converting the set target tidal volume and the basic airway pressure into displacement elements of a valve, wherein the displacement elements of the valve are a basic position A and a moving distance B; detecting and processing the spontaneous respiration inhalation flow; when the detected flow change characteristic of the start of the autonomous inspiration meets the set inspiration phase trigger sensitivity threshold within set time, judging the start of inspiration, controlling the starting of the initial ventilation by a central processing unit according to the displacement element of the valve, and moving the valve from the point A to the point B; when the detected flow rate is reduced to a set expiratory phase conversion sensitivity threshold, judging that expiration starts, and instructing the valve to return to the point A instantly by the central processing unit at the moment; in the initial ventilation process, detecting the instantaneous flow and the airway pressure of the airway interface section, analyzing and calculating according to actually measured pressure and flow data, respectively obtaining the position of a calibrated point A and the moving distance B of an adjusted valve, and taking the position of the point A and the moving distance B as a valve displacement element of the initial ventilation of the target tidal volume; when the flow change characteristic of the start of spontaneous respiration is detected to meet the set inspiratory phase trigger sensitivity threshold again in the set time after the initial ventilation is started, the central processing unit controls to start the initial ventilation of the target tidal volume, and the initial ventilation of the target tidal volume is executed according to the calibrated A point position and the adjusted valve moving distance B determined in the initial ventilation process and the breathing rhythm of the patient; after the initial ventilation, continuing the ventilation at the target tidal volume and repeating the calibration of the position of the A point of the valve and the adjustment of the movement distance B of the valve on a cycle-by-cycle basis, this dynamic calibration and adjustment throughout the ventilatory support course of spontaneous breathing until the spontaneous breathing work process is changed or terminated.

In the spontaneous respiration working mode, when respiration pause occurs for the first time in a set time, one instruction ventilation is implemented according to a valve displacement element in the previous spontaneous respiration working mode, and the originally set target tidal volume ventilation of the spontaneous respiration mode is continued when the spontaneous respiration rhythm is stable; when breathing pause occurs again in the set time, performing one-time instruction ventilation according to the target tidal volume after the downward regulation by a certain proportion, calculating and modifying the valve displacement element according to the proportion, and continuing to maintain the downward regulated target tidal volume ventilation in the spontaneous breathing mode when the spontaneous breathing rhythm is recovered to be stable; when apnea still occurs in the set time, the target tidal volume is further adjusted downwards in a certain proportion to implement one-time instruction ventilation, the valve displacement element is still calculated and modified in proportion at the time, and if the spontaneous breathing rhythm is stable, the spontaneous breathing mode is continued to maintain the target tidal volume which is adjusted downwards again to ventilate; if the apnea can not be eliminated, the apnea is judged to be caused by central lesion, and at the moment, the instruction ventilation working mode is started immediately and instruction ventilation is carried out according to the initially set basic airway pressure and target tidal volume parameters.

The invention also provides a ventilator airflow control device, which comprises an air source capable of providing continuous airflow, a central processing unit, a resistance valve and a valve controller, an instruction ventilation control chip and an autonomous respiration control chip, wherein the resistance valve and the valve controller are positioned at the outlet end of an air passage; the method comprises the steps that a ventilation control chip is instructed to control the moving frequency and the breathing time ratio of a valve according to set parameters, and the position of the A point of the valve is dynamically corrected and the moving distance B of the valve is adjusted in the ventilation process according to the pressure of an airway interface section of a patient and the pressure and flow data detected by a flow sensor in real time; the central processor controls the valve to move between two points through the valve controller according to the correction and adjustment results at each time and at a preset frequency, so that a set target tidal volume is maintained during the ventilation process to provide instruction ventilation support for the patient; the spontaneous respiration control chip determines the start and the end of the inspiration action of a patient through the setting of parameters, the pressure at the airway interface section of the patient and the pressure and flow data detected by the flow sensor in real time, and realizes the correction of the basic position A point of the valve and the dynamic adjustment of the moving distance B of the valve.

Compared with the prior art, the ventilator airflow control method and the ventilator airflow control device have two working modes, different respiratory support can be provided for patients, and the problems of asynchrony with respiration and more complex equipment caused by intermittent airflow are avoided by using continuous airflow, which are specifically as follows:

1. in the demand ventilation mode, the central processing unit sends a command to the controller of the resistance valve of the ventilator according to the basic position A point of the valve and the moving distance B of the valve, and the valve moves between the two points at a preset frequency, so that the patient is provided with a demand ventilation support. The mode is the mode of operation that should be selected when providing ventilatory support to a patient with unstable breathing impulses to ensure that the patient does not experience respiratory pauses on the ventilator; alternatively, this controlled mode of operation is indispensable to the ventilator as a life support device, selected to provide a particular level of ventilatory support to the patient depending on the condition and the need for treatment.

2. In the autonomous breathing mode, the central processing unit sends an instruction to a controller of a resistance valve of the breathing machine by detecting the flow change entering an airway of a patient, so that the ventilation action of the machine keeps synchronous with the breathing action of the patient, and the tidal volume provided by the breathing machine for the patient is maintained at a set target level by automatically regulating and controlling the position of the valve; if the breathing is judged to be stopped for a long time in the mode, spontaneous breathing can be supported by reducing the target tidal volume, and if the phenomenon of spontaneous breathing does not exist by reducing the target tidal volume, the mode can be switched to the instruction ventilation mode to support the breathing of the patient.

Drawings

FIG. 1 is a schematic diagram of the operation of the ventilator flow control of the present invention;

FIG. 2 is a flow chart of the ventilator instruction ventilation mode of operation of the present invention;

fig. 3 is a flow chart of the autonomous respiration mode of the ventilator of the present invention.

Detailed Description

Several embodiments of the present invention will be described in detail below with reference to the drawings, but it should be understood that the scope of the present invention is not limited to the embodiments.

Firstly, the ventilation working principle of the breathing machine of the invention is introduced:

the high-flow airflow with stable flow is output from an air source (namely, air supplied by a fan) to enter the system, and the airflow is limited to flow out by a resistance valve at the airflow outlet end, so that positive pressure higher than the atmosphere is formed in the system. Thus, by varying the degree of opening and closing of the resistance valve (i.e. controlling the resistance change of the resistance valve), two pressure switches of different heights can be created in the system including the main airway and the lungs accordingly. Because the lungs of the human body are flexible, different levels of intra-pulmonary pressure mean different lung volume levels. When the resistance valve moves towards the outlet end of the main airway, the pressure of the main airway rises, the pressure and the volume in the lung correspondingly rise, and the lung is inflated; once the resistance valve is quickly returned to the initial position, the pressure in the main airway is quickly reduced, the pressure in the lung is also correspondingly and quickly reduced, at the moment, the airflow in the lung returns to the main airway under the elastic retraction and compression of lung tissues, and the airflow evacuation process of the expiratory phase is started until the airflow evacuation stops. The continuous switching of the system pressure at the respective two levels causes a continuous alternation of the pulmonary filling and emptying states, which is physiologically called the ventilation process; the change in volume during filling and emptying is the volume in and out of the lung, i.e. tidal volume.

The switching control of the resistance valve comprises rhythm control and force control, wherein the rhythm control refers to the control of resistance switching mode, frequency and rhythm; the strength control refers to the control of the difference between high resistance and low resistance, which reflects the strength of ventilation support and is expressed as the size of tidal volume.

As shown in fig. 1, the degree of opening and closing of the resistance valve, i.e., the main control valve of the ventilator (hereinafter referred to as the valve), determines the change of the main airway pressure inside the system. For example: the valve is open at a maximum at point a, so the pressure of the air pressure maintained inside the system is at a minimum when the valve is in this position, this pressure being referred to as the "base airway pressure"; when the valve moves from a to B, the valve opening is reduced, the resistance generated by the valve and the corresponding pressure inside the system are increased, and the movement between the two points of the valve opening A, B directly controls the change of the system pressure. Thus, the location of point a determines the height of the base airway pressure; the distance between the point A and the point B determines the change height (namely the change amplitude) of the airway pressure, namely the ventilation strength or the ventilation intensity; the time interval between the switching of points a to B determines the rhythm control of the switching. Namely the aforementioned force control and tempo control.

The following describes two operation modes of the ventilator of the present invention based on the above ventilation principle: namely a commanded ventilation mode of operation and a spontaneous breathing mode of operation.

The instructed ventilation mode of operation is the commanded control of the patient over the strength of ventilatory support and the rhythm of fill-empty. The mode is the mode of operation that should be selected when providing ventilatory support to a patient with unstable breathing impulses to ensure that the patient does not experience respiratory pauses on the ventilator; alternatively, this controlled mode of operation is indispensable to the ventilator as a life support device, selected to provide a particular level of ventilatory support to the patient depending on the condition and the need for treatment. Specifically, in the command ventilation mode, the frequency and time ratio of the position change of the valve at A, B position is controlled by a command ventilation control chip; and the conversion distance between A, B of the valve is regulated and controlled by a target tidal volume regulation and control module.

The spontaneous breathing mode is a mode of controlling the level of positive airway pressure by controlling the switching of outflow resistance through spontaneous breathing of a patient. This mode is implemented by determining the beginning and end of the patient's inspiratory effort from the flow changes in the patient interface segment and thereby controlling the degree of opening of the resistance valve. When the autonomous respiration mode is adopted, the switching of the airway pressure completely follows the respiration action of the patient, and the most comfortable ventilation support can be provided for the patient. Specifically, the mode selects a particular change in flow into the patient's airway as an indicator to determine the start and end points of a breathing cycle; the valve is controlled to move between A, B by a 'spontaneous respiration control chip', and the frequency and time ratio of the 'spontaneous respiration control chip' are changed along with the spontaneous respiration of the patient; and the shifting distance between the A, B of the valve is still regulated by a target tidal volume regulating module.

Therefore, whether the operation mode of the instruction ventilation or the operation mode of the spontaneous respiration, the rhythm and the strength of the ventilation need to be controlled through the action of the valve. Wherein the ventilation rhythm (how) is determined by the time point (or action change time) when the valve moves between the AB; the moving displacement of the valve determines the magnitude of the ventilation strength (how much the valve moves), and the position to which the valve moves, which is performed by the target tidal volume control chip, and is used for controlling the ventilation strength (or ventilation strength). The two indexes are combined to determine the reciprocating motion rule and track of the valve between the two indexes.

The following is a detailed description of the commanded ventilation mode:

instructional ventilation mode embodiment

The command ventilation mode mainly comprises three working modules, namely a time phase control module, a basic airway pressure (PEEP) control module and a target tidal volume regulation and control module, wherein the three working modules finish operation control tasks under the coordination management of a central processing unit. The following will refer to fig. 2 to specifically describe the implementation steps of this mode:

step 1, selecting to enter a command ventilation working mode by a control panel;

step 2, setting working parameters:

and (4) setting the parameters item by item according to the panel prompt displayed after the step 1 is finished. The parameters to be set include: "ratio of commanded ventilation frequency to breathing time", "target tidal volume", and "basal airway pressure";

the base position of the valve may be determined based on the set base port pressure. After the basic air passage pressure is set, the basic air passage pressure control module calculates the corresponding basic valve position, namely an A0 point according to preset design data in the module, namely the position A of the air passage pressure of 10 cm water column;

the time phase control module sets the moving frequency and the round-trip time ratio of the valve between A, B points according to the setting of the command ventilation frequency and the breathing time ratio;

step 3, starting primary ventilation:

and (3) sending an instruction by the central processing unit, and carrying out primary ventilation according to the valve displacement factors set in the step (2). At this time, the process of the present invention,

the time phase control module provides time control for moving from the point A to the point B and then returning to the point A according to the instruction ventilation frequency and the breathing time ratio set in the step 2;

the position of the valve A point is calculated and given by a basic air channel pressure module according to the setting of the step 2. The valve moves to the basic position according to the position of the A0 point calculated by the basic air channel pressure module in the step 2;

the moving distance of the valve (namely the distance from A to B, hereinafter referred to as the moving distance B) is given by a target tidal volume regulating module according to preset data. The design data is preset in the module, so that a normal person can obtain the tidal volume of about 300 to 500 milliliters, and the moving distance B takes the position A0 as a starting point;

and 4, detecting the flow and pressure in the primary ventilation process:

the flow sensor and the pressure sensor which are positioned in the air passage interface section detect the instantaneous flow and the air passage pressure entering the air passage interface section in the whole ventilation process;

the flow sensor sends the instantaneous flow signal to a "flow processing module" which decomposes the instantaneous flow signal into two components, flow curve data actually entering the airway and base flow data due to possible leaks. Filtering the flow signal, namely decomposing the filling phase curve of each ventilation cycle into an upper sawtooth wave and a possibly existing rectangular bottom, wherein the upper sawtooth wave is the airflow signal really entering the air flue, and the height of the rectangular bottom is a basic flow value and reflects the possible leakage flow at the interface part of the pipeline. The sawtooth wave is transmitted to a tidal volume operation module, and the total volume of the air passage entering the filling process, namely the tidal volume, is obtained through the operation of the tidal volume operation module;

the pressure signal detected by the pressure sensor is sent to a basic air passage pressure control module to give an actual basic air passage pressure value;

step 5, determining the valve moving distance of the initial ventilation of the target tidal volume:

after the initial ventilation valve returns to the point A, the target tidal volume regulating module immediately calculates an initial value B0 of the valve moving distance required by the set target tidal volume according to the set target tidal volume and the preset valve moving distance executed by the initial ventilation and the actual result of the initial ventilation tidal volume measured and calculated by the tidal volume calculating module in the step 4;

step 6, calibrating the basic gas channel pressure:

and (4) calibrating the position of the A point by the basic air passage pressure control module according to the actual basic air passage pressure measured in the step (4). The actual basal airway pressure is the pressure measured by the pressure sensor at the airway interface segment of the patient immediately before the "time phase control module" issues the valve movement instruction to point B, and the pressure at this point should be the lowest level in the whole ventilation cycle. The calibration of the basic air channel pressure is realized by adjusting the position of the A point of the valve in the figure 1, and the specific process is as follows:

the detected pressure signal is input into a basic air channel pressure control module to be compared with the basic air channel pressure set in the step 2: if the error of the two is less than or equal to +/-3%, simply adopting the A0 calculation result in the step 2; if the error of the two is > +/-3%, recalculating according to the measured pressure and the position of the A point of the initial ventilation and moving the valve plate to the Ax position;

step 7, starting target tidal volume initial ventilation:

and (4) calculating the adjusted A point position and displacement distance B0 according to the step 5 and the step 6, and sending an instruction by the central processing unit to perform target tidal volume initial ventilation.

The initial ventilation is the implementation of the target tidal volume, and the most critical patient actual data, namely the basic quantitative relation between the patient tidal volume and the valve moving distance, is obtained, and the control of the target tidal volume is therefore the approximate basis for implementation. The target tidal volume initial ventilation is guided by a target tidal volume regulation module, and the elements of the ventilation are as follows:

a. the standard basic air channel pressure, namely a basic air channel pressure control module, determines the initial position Ax of the valve movement according to the calibration result of the step 6;

b. the preset target tidal volume valve moving distance, namely a target tidal volume control module calculates a valve moving distance B0 required for obtaining the set target tidal volume according to the initial ventilation tidal volume calculated in the step 5 and the initial ventilation valve moving distance B;

c. starting the initial ventilation action of the target tidal volume of the valve, wherein the set frequency and breathing time ratio is that the valve moves B0 from the Ax point and then returns to the Ax point under the set frequency and time ratio command of the time phase control module;

step 8, continuing the target tidal volume ventilation:

and after the target tidal volume is ventilated initially, the construction of working elements of the ventilation valve is instructed to be completed. However, due to the influence of many factors such as respiratory tract movement, static resistance, respiratory conditions and the like, the quantitative relation between the tidal volume of the patient and the airway filling pressure is constantly changed, the moving distance of the valve needs to be correspondingly adjusted at any time to adjust the airway filling pressure when the target tidal volume is maintained to be stable, the adjustment needs to be continued in the whole ventilation support process of the patient receiving the treatment of the breathing machine, and the target tidal volume module is a microcomputer technology which embodies the gradual automatic calculation and adjustment.

After step 7, repeating step 4 to step 7 continuously and periodically, and adjusting the next valve moving distance Bx according to the previous valve moving distance and the actual tidal volume, that is, dynamically repeating the adjustment of the valve moving distance and the calibration of the basic airway pressure during the target tidal volume ventilation process. From this step, the process of ventilator operation enters a cycle of "action-measure-calculate-adjust-re-action", i.e. repeats: flow and pressure sensing-recalibration of basal airway pressure-readjustment of valve travel distance to perform the next commanded ventilation of target tidal volume;

step 9, commanding a change or termination of ventilation:

namely, until any parameter setting is changed, corresponding adjustment is carried out again according to the setting; or at a point on any of the preceding steps.

In summary, in the commanded ventilation mode, the cpu sends a command to the controller of the resistance valve of the ventilator according to the base position a of the valve and the moving distance B of the valve, and the valve is moved between the two points at a predetermined frequency, thereby providing a commanded ventilation support to the patient. The mode is the mode of operation that should be selected when providing ventilatory support to a patient with unstable breathing impulses to ensure that the patient does not experience respiratory pauses on the ventilator; alternatively, this controlled mode of operation is indispensable to the ventilator as a life support device, selected to provide a particular level of ventilatory support to the patient depending on the condition and the need for treatment.

Spontaneous breathing mode of operation embodiment:

the autonomous respiration system mainly comprises five working modules in an autonomous respiration working mode, namely a basic airway pressure (PEEP) control module, a target tidal volume regulation and control module, an inspiratory phase conversion module, an expiratory phase conversion module and a respiration pause automatic treatment module, wherein the five working modules finish operation control tasks under the coordination management of a central processing unit. The following will refer to fig. 3 to specifically describe the implementation steps of this mode:

step 1, selecting to enter a spontaneous respiration working mode by a control panel;

step 2, setting working parameters and providing valve motion elements:

the parameter setting of the autonomous respiration working mode comprises the following steps: "target tidal volume", "basal airway pressure", and "inspiratory phase trigger sensitivity" and "expiratory phase transition sensitivity".

Step 201, "base air duct pressure control module" specifies the position of a0 point of the valve:

after the basic air duct pressure is set, the basic air duct pressure control module calculates the position of A0 point corresponding to the set value of the basic air duct pressure according to the design data of the position of A point of 10 cm water column preset in the module;

step 202, a preset initial ventilation valve travel distance is given:

the 'target humidity control module' gives design data of the moving distance B of the primary ventilation valve preset in the module;

step 203, setting inspiratory phase trigger zero sensitivity:

the inspiratory trigger sensitivity is automatically set at 2 liters/minute, with a selected range of 1-12 liters/minute, representing a flow value relative to the basal flow immediately prior to the start of inspiration, i.e., the inspiratory flow of the patient's airway interface segment.

When the flow processing module detects that the inhalation flow entering the patient airway interface section meets the flow rising change characteristic of the spontaneous breathing inhalation and the flow reaches the set triggering threshold, the central processing unit gives an instruction to trigger the valve to start moving;

step 204, setting expiratory phase conversion sensitivity:

the expiratory phase switching sensitivity is automatically set at 0 litres/min, with a range of 0-10 litres/min being chosen, representing the flow value relative to the filling immediately before the start of inspiration.

When the flow processing module detects that the filling flow in the airway interface section of the entering patient is reduced to a value relative to the flow immediately before the start of inspiration, the central processing unit sends out an instruction, and the valve immediately retracts to the point A;

step 3, connecting the airway of the patient with the pipeline of the breathing machine;

and 4, detecting and processing the suction flow:

a flow sensor disposed within the patient interface segment begins to sense the in-out flow within the segment;

the detected instantaneous flow signal is input into a flow processing module to filter the flow curve, and the filling phase curve of each ventilation period can be decomposed into an upper sawtooth wave part and a possibly existing rectangular bottom part. The sawtooth wave at the upper part is an airflow signal really entering the air passage, and the sawtooth wave signal is subjected to integral operation by a tidal volume operation chip to calculate the total air volume entering the lung, namely the tidal volume; the height of the rectangular bottom is a basic flow value and reflects the leakage flow which possibly appears at the pipeline interface part;

and 5, primary ventilation and subsequent adjustment:

if the flow processing module detects the flow variation characteristic of the beginning of the autonomous inspiration defined in step 203 and the set valve movement trigger threshold (i.e. 2 liters/minute) within 10 seconds, the central processing unit instructs the valve to start moving and perform airway filling, and the parameters of the initial ventilation are determined in steps 201, 202, 203 and 204;

subsequently, when the filling flow drops to the expiratory transition flow value defined in step 204 (i.e., reaches 0 liters/minute), the central processor commands the valve to momentarily retract back to point A.

During the initial ventilation process, the flow and pressure sensors collect measured data as the basis for adjusting the next ventilation, namely the initial ventilation action of the target tidal volume:

step 501, calibrating the base airway pressure:

the calibration of the base gas channel pressure is realized by adjusting the position of the A point of the valve plate in the figure 1 through a base gas channel pressure control module, and the process is as follows:

immediately before the "flow processing module" detects the onset of spontaneous breathing, the pressure measured by the pressure sensor at the patient's airway interface segment is the actual base airway pressure, which should be at the lowest level throughout the ventilation cycle. This pressure signal is input to the "base airway pressure control module" and compared to the base airway pressure set in step 201: if the error between the two is less than or equal to +/-3%, executing the base gas channel pressure set in the step 201; if the error of the pressure and the air is > +/-3%, recalculating according to the measured pressure and the position of the A point of the initial ventilation and moving the valve to the Ax position;

step 502, providing of the initial ventilation valve travel distance for the target tidal volume:

through the initial ventilation, the approximate data of the correlation between the patient tidal volume and the airway pressure change controlled by the valve moving distance is obtained, and the target tidal volume control module can calculate the valve moving distance required by the target tidal volume according to the approximate data, so that the ventilation process of the target tidal volume can be started. The method comprises the following specific steps:

after the valve returns to the point A, the flow processing module inputs an inspiratory phase flow integral operation result after filtering processing into a target tidal volume control module to carry out initialization operation, and calculates a valve moving distance B0 required by a set target tidal volume according to the valve moving distance B of initial ventilation and an actually obtained tidal volume in proportion to serve as a valve moving parameter of initial ventilation of the next ventilation, namely the target tidal volume;

step 6, initially ventilating the target tidal volume:

if the flow change characteristic of the beginning of spontaneous respiration and the set valve movement trigger threshold value are detected again within 10 seconds after the beginning of the initial ventilation, the central processing unit gives an instruction to start to instruct the valve to move according to the set target tidal volume (namely, the initial ventilation process is started, the valve motion factors at the moment, namely the point A is arranged as Ax, the point B moves for a distance B0;)

601, repeating 501 in the initial ventilation process, and calibrating the basic air passage pressure, namely the basic valve position Ax;

step 602, repeating step 502 in the initial ventilation process, and regulating and controlling the valve moving distance Bx to maintain the set target tidal volume;

and 7, continuing the target tidal volume ventilation in the spontaneous breathing mode:

if the spontaneous breathing rhythm is stable, continuously repeating the step 6 until the working parameters are changed or the working mode of the breathing machine is changed;

step 8, automatic treatment of respiratory pause:

step 801, if the first respiratory pause occurs, automatically replacing ventilation once according to a set target tidal volume:

after step 7, when the flow processing module cannot detect the flow change characteristic marking the start of autonomous inspiration and the set valve movement trigger threshold value according to the flow signal of the flow sensor in the 10 th second of the previous valve plate movement, the flow processing module immediately sends a signal to the breath pause automatic processing module, the breath pause automatic processing module immediately sends an instruction to start the movement of the valve to the point B, namely, one instruction ventilation is implemented, and the position of the point A and the movement distance of the point B both repeat the parameters of the previous autonomous respiration working mode;

step 802, if the spontaneous breathing rhythm is stable, continuing to ventilate the originally set target tidal volume in the spontaneous breathing mode:

i.e. after step 801, if the next spontaneous breath starts within 10 seconds, step 7 is repeated;

at step 803, if a respiratory pause occurs again, the instruction is implemented to replace ventilation once with 80% of the target tidal volume:

if the flow change characteristic marking the start of autonomous inspiration and the set valve movement trigger threshold cannot be detected again according to the flow signal of the flow sensor after the step 801, the module immediately sends a signal to the 'breathing pause automatic treatment module' again, and the 'breathing pause automatic treatment module' immediately sends a valve movement instruction, but the moving distance of the point B is proportionally calculated and modified again according to 80% of the set target tidal volume by the 'target tidal volume regulating module' according to the tidal volume and the moving distance of the point B actually obtained in the step 801;

step 804, the spontaneous breathing rhythm is recovered to be stable, and ventilation with lower tidal volume is maintained:

after the breathing is performed once according to 80% of the set target tidal volume, if the breathing pause does not appear any more, the 'breathing pause automatic treatment module' sends out an instruction, modifies the set value of the target tidal volume into 80% of the original set value and repeats the step 7;

if apnea is still present, step 805, the tidal volume setting is again attempted to be lowered:

if the tidal volume is reduced by 80%, and the apnea still occurs, the breathing pause automatic treatment module carries out the replacement instruction ventilation once again, and the Bx moving distance is calculated and modified by a target tidal volume regulating module according to 60% of the originally set target tidal volume;

step 806, if apnea still occurs, redirecting to the ventilatory mode of operation:

if the tidal volume is reduced by 60%, the respiratory pause cannot be eliminated, and the reason is not physiologically excessive dynamic support but is caused by central lesion, so that the autonomous respiration operation mode is not suitable. The 'breathing pause automatic treatment module' immediately and automatically converts the work mode of the breathing machine into the command ventilation work mode, and maintains the originally set basic airway pressure and target tidal volume setting, and the ventilation frequency and time ratio are set to be 12 times/minute and 1: 2, so as to ensure the ventilation safety of the patient on the breathing machine. After the ventilation is converted into the instruction, the working parameters can be additionally adjusted.

In conclusion, in the spontaneous breathing mode, the central processing unit sends an instruction to the controller of the resistance valve of the breathing machine by detecting the flow change entering the airway of the patient, so that the ventilation action of the machine keeps synchronous with the breathing action of the patient, and the tidal volume provided by the breathing machine for the patient is maintained at a set target level by automatically regulating and controlling the position of the valve; if the breathing is judged to be stopped for a long time in the mode, spontaneous breathing can be supported by reducing the target tidal volume, and if the sign of spontaneous breathing does not exist by reducing the target tidal volume, the mode is switched to the instruction ventilation mode to support the breathing of the patient.

The above disclosure is only for a few specific embodiments of the present invention, but the present invention is not limited thereto, and any variations that can be made by those skilled in the art are intended to fall within the scope of the present invention.

Claims

1. A method for controlling the airflow of a breathing machine is characterized in that continuous airflow with stable flow is input into a breathing machine system from an air source, and the ventilation rhythm and the ventilation strength in an airway are dynamically adjusted by controlling the moving frequency and the distance of a valve at an airflow outlet end, so that the breathing support of a patient is realized, and the method comprises the following two working modes:

a commanded ventilatory mode of operation for use when the patient's breathing pulse is unstable or a specified level of ventilatory support is provided to the patient, wherein in the commanded ventilatory mode of operation the central processor controls the valve to move between the base position A of the valve and the dynamic adjustment of the valve's travel distance B at a predetermined frequency to maintain a set target tidal volume during ventilation to provide a commanded ventilatory support to the patient;

the spontaneous respiration working mode is characterized in that the starting and the ending of the inspiration action of a patient are determined through the dynamic pressure and flow detection of an airway interface section, the correction of a basic position A point of a valve and the dynamic adjustment of a moving distance B of the valve are realized, a central processing unit controls the valve to move between two points according to the correction and adjustment result and the spontaneous respiration rhythm of the patient, so that the pressure switching in the airway completely follows the respiration action of the patient, and the set target tidal volume is maintained in the ventilation process or the target tidal volume is adaptively reduced when the patient has respiratory pause so as to maintain the ventilation support of spontaneous respiration.

2. The method of ventilator flow control according to claim 1, wherein said commanded ventilation mode of operation comprises the steps of:

setting parameters of the command ventilation frequency, the breathing time ratio, the target tidal volume and the basic airway pressure, and converting the set target tidal volume and the basic airway pressure into displacement elements of the valve, wherein the displacement elements of the valve are a basic position A and a moving distance B;

according to the displacement element of the valve, the central processing unit controls the starting of the primary ventilation;

in the initial ventilation process, detecting the instantaneous flow and the airway pressure of the airway interface section, analyzing and calculating according to actually measured pressure and flow data, respectively obtaining the position of a calibrated point A and the moving distance B of an adjusted valve, and taking the position of the point A and the moving distance B as a valve displacement element of the initial ventilation of the target tidal volume;

the central processing unit controls and starts the initial ventilation of the target tidal volume, and executes the initial ventilation according to the position of the calibrated A point and the adjusted valve moving distance B which are determined in the initial ventilation process and the preset ratio of the instruction ventilation frequency to the breathing time;

after the initial ventilation, the ventilation of the target tidal volume is continued and the calibration of the position of the a point of the valve and the adjustment of the movement distance B of the valve are repeated on a cycle-by-cycle basis, with this dynamic calibration and adjustment throughout the ventilation support process until a change or termination of the commanded ventilation.

3. The method of claim 2, wherein the analyzing and calculating according to the actual measured flow is specifically:

the actually measured flow data consists of two parts, namely flow curve data actually entering an airway and basic flow data caused by possible leakage, the two parts are respectively represented as two waveform signals of a sawtooth wave at the upper part and a rectangular wave at the bottom part, the sawtooth wave signals are retained and the actual tidal volume is calculated according to the waveform signals through filtering processing, and the difference value of the actual tidal volume and the target tidal volume is used as the adjusting basis of the valve moving distance B.

4. The method for controlling the flow of a ventilator according to claim 2 or 3, wherein the analyzing and calculating according to the actually measured pressure data is specifically:

comparing the actually detected pressure data with the basic air passage pressure set in the parameter setting process, and if the error between the actually detected pressure data and the basic air passage pressure is less than or equal to +/-3%, adopting the position of a valve A point of primary ventilation corresponding to the original basic air passage pressure; if the error of the pressure and the air is > +/-3%, proportionally calculating the position of the updated valve A according to the measured pressure and the position of the valve A of the initial ventilation again.

5. The method of ventilator flow control of claim 2 wherein said commanding a change or termination of ventilation specifically refers to:

the change of the instruction ventilation means that the parameters set in the parameter setting process are changed according to the requirements, and at the moment, corresponding adjustment is carried out according to the reset parameters;

termination of commanded ventilation refers to shutting off operation at any point during ventilation.

6. The method of claim 2, wherein the set target tidal volume is 300 to 500 milliliters.

7. The method of ventilator flow control of claim 1 wherein said spontaneous breathing mode of operation comprises the steps of:

carrying out parameter setting on a target tidal volume, a basic airway pressure, inspiratory phase trigger sensitivity and expiratory phase conversion sensitivity, and converting the set target tidal volume and the basic airway pressure into displacement elements of a valve, wherein the displacement elements of the valve are a basic position A and a moving distance B;

detecting and processing the spontaneous respiration inhalation flow;

when the detected flow change characteristic of the start of the autonomous inspiration meets the set inspiration phase trigger sensitivity threshold within set time, judging the start of inspiration, controlling the starting of the initial ventilation by a central processing unit according to the displacement element of the valve, and moving the valve from the point A to the point B; when the detected flow rate is reduced to a set expiratory phase conversion sensitivity threshold, judging that expiration starts, and instructing the valve to return to the point A instantly by the central processing unit at the moment;

when the flow change characteristic of the start of spontaneous respiration is detected to meet the set inspiratory phase trigger sensitivity threshold again in the set time after the initial ventilation is started, the central processing unit controls to start the initial ventilation of the target tidal volume, and the initial ventilation of the target tidal volume is executed according to the calibrated A point position and the adjusted valve moving distance B determined in the initial ventilation process and the breathing rhythm of the patient;

after the initial ventilation, continuing the ventilation at the target tidal volume and repeating the calibration of the position of the A point of the valve and the adjustment of the movement distance B of the valve on a cycle-by-cycle basis, this dynamic calibration and adjustment throughout the ventilatory support course of spontaneous breathing until the spontaneous breathing work process is changed or terminated.

8. The method of claim 7, wherein when a respiratory pause occurs for the first time within the set time, performing a commanded ventilation according to the valve displacement element of the previous spontaneous breathing mode, and continuing the ventilation of the originally set target tidal volume of the spontaneous breathing mode when the spontaneous breathing rhythm is stabilized.

9. The method as claimed in claim 8, wherein when the breathing pause occurs again within the set time, the target tidal volume is adjusted down by a certain ratio to perform a commanded ventilation, the valve displacement component is proportionally modified, and the adjusted target tidal volume ventilation is maintained in the spontaneous breathing mode when the spontaneous breathing rhythm is stabilized.

10. The method of claim 9, wherein when apnea still occurs within the set time, further decreasing a proportion of the target tidal volume to perform a commanded ventilation, wherein the valve displacement element is still proportionally modified, and if the spontaneous breathing rhythm is stable, continuing to maintain the spontaneous breathing mode and continuing to perform the target tidal volume ventilation after the decreased proportion; if the apnea can not be eliminated, the apnea is judged to be caused by central lesion, and at the moment, the instruction ventilation working mode is started immediately and instruction ventilation is carried out according to the initially set basic airway pressure and target tidal volume parameters.

11. The method as claimed in claim 10, wherein when the spontaneous breathing mode is switched to the commanded ventilation mode due to the central lesion, the ventilation frequency and the breathing time ratio of the commanded ventilation mode are set to 12 times/min and 1: 2, respectively, to ensure the ventilation safety.

12. The method of claim 7, wherein the set time is 10 seconds.

13. The method of claim 7, wherein the inspiratory trigger sensitivity threshold is selected to be in a range of 1-12 liters/minute.

14. The method of claim 13, wherein the inspiratory trigger sensitivity threshold is specifically 2 liters/minute.

15. The method of claim 7, wherein the expiratory phase transition sensitivity threshold is selected to be in a range of 0-10 liters/minute.

16. The method of ventilator flow control of claim 15 wherein said expiratory phase transition sensitivity threshold is specifically 0 liters/minute.

17. The method of claim 7, wherein the analyzing and calculating according to the actual measured flow is specifically:

18. The method of claim 7, wherein the analyzing and calculating according to the actual measured pressure data is specifically:

19. The ventilator airflow control device is characterized by comprising an air source capable of providing continuous airflow, a central processing unit, a resistance valve and a valve controller, an instruction ventilation control chip and a self-breathing control chip, wherein the resistance valve and the valve controller are positioned at the outlet end of an airway; wherein,

the method comprises the steps that a ventilation control chip is instructed to control the moving frequency and the breathing time ratio of a valve according to set parameters, and the position of the position A of the valve and the moving distance B of the valve are dynamically corrected and adjusted in the ventilation process according to pressure at the airway interface section of a patient and pressure and flow data detected by a flow sensor in real time; the central processor controls the valve to move between two points through the valve controller according to the correction and adjustment results at each time and at a preset frequency, so that a set target tidal volume is maintained during the ventilation process to provide instruction ventilation support for the patient;

the spontaneous respiration control chip determines the start and the end of the inspiration action of a patient through the setting of parameters, the pressure at the airway interface section of the patient and the pressure and flow data detected by the flow sensor in real time, and realizes the correction of the basic position A point of the valve and the dynamic adjustment of the moving distance B of the valve.

20. The ventilator flow control device of claim 19 wherein said commanded ventilation control chip comprises:

the basic air passage pressure control module is used for dynamically calibrating a basic position A point of the valve according to a set basic air passage pressure parameter and actual pressure data detected by the pressure sensor in the ventilation process;

the target tidal volume regulating and controlling module is used for dynamically regulating the moving distance B of the valve according to the set target tidal volume parameters and the actual flow data detected by the flow sensor in the ventilation process;

and the time phase control module is used for providing frequency and time control for the valve to return to the point A instantly after moving a distance B from the point A according to the set instruction ventilation frequency and breathing time ratio.

21. The ventilator flow control device of claim 20, wherein said target tidal volume adjustment module comprises:

the flow processing module is used for decomposing the detected flow data into actual flow curve data which are expressed as sawtooth waves and enter the air flue and basic flow data which are expressed as rectangular bottoms, and filtering and reserving the sawtooth waves;

and the tidal volume operation module is used for receiving the sawtooth wave signals and calculating the actual tidal volume in the airway filling process.

22. The ventilator airflow control device of claim 19 wherein said spontaneous breathing control chip comprises:

the inspiratory phase conversion module is used for setting an inspiratory phase trigger sensitivity threshold, judging the start of inspiration when detecting that the inspiratory flow entering the airway interface section of the patient has flow change characteristics which accord with the start of spontaneous respiration inspiration and the flow reaches the set inspiratory phase trigger sensitivity threshold, and transmitting a signal of the start of inspiration to the central processing unit so as to trigger the valve to start moving from the point A;

the expiratory phase conversion module is used for setting an expiratory phase conversion sensitivity threshold, judging the start of expiration and transmitting a signal of the start of expiration to the central processing unit when detecting that the inhalation flow entering the airway interface section of the patient has flow change characteristics which accord with the end of spontaneous respiration and inspiration and the flow reaches the set expiratory phase conversion sensitivity threshold so as to trigger the valve to return to the point A instantly;

the automatic respiratory pause treatment module is used for conducting one-time instruction ventilation according to the initially set target tidal volume when the first respiratory pause occurs; when respiration pause occurs for the second time, regulating the target tidal volume down by a certain proportion and then carrying out primary instruction ventilation; when the respiration pause appears for the third time, continuously reducing the target tidal volume by a certain proportion and then carrying out one-time instruction ventilation; after each instruction ventilation, if the spontaneous respiration rhythm is stable, maintaining the target tidal volume set by the instruction ventilation to continue the ventilation in the spontaneous respiration working mode; and if the apnea still occurs after the target tidal volume is adjusted twice, judging that the apnea is caused by central lesion, and immediately starting the instruction ventilation working mode.

23. The ventilator flow control device of claim 22, wherein said target tidal volume adjustment module comprises:

the flow processing module is used for decomposing the detected flow data into actual flow curve data which are expressed as sawtooth waves and enter the air flue and basic flow data which are expressed as rectangular bottoms, and filtering and reserving the sawtooth waves; the automatic respiratory pause treatment module is also used for judging whether a respiratory pause occurs in the ventilation process and sending a signal of the respiratory pause to the automatic respiratory pause treatment module;

24. The ventilator flow control device of any one of claims 19 to 23 wherein said resistance valve is an iris-type resistance valve.