JPH05115554A - Method and device for ratio aid type artificial respiration - Google Patents

Abstract

PURPOSE: To allow a user to completely control his own respiration in all respects by detecting the flow and capacity of gas supplied in response to a pressure gradient generated by respiration effort, amplifying their signals separately, and providing pressure support for the gas in proportion to their sum. CONSTITUTION: A chamber 202 accepts gas via a check valve 203, and the gas moves to a patient 208 via a check valve 204 during inhalation. The coil of a linear drive motor 205 pushes and pulls a piston 201 in proportion to driving potential applied via a cable 207. The flow of gas from the chamber 202 to the patient 208 is measured by the flow system 209 of an intake pipe 210 and is adjusted by an external adjustable gain controller 212. A flow signal produces a signal corresponding to an instantaneous intake 214 via an integrator 213, the signal being adjusted by an external adjustable gain controller 215. Flow and capacity signals 216, 217 produce a composite output signal through the use of an addition amplifier 218.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to methods and apparatus for assisting ventilation of a patient's lungs in proportion to patient effort.

[0002]

Ventilators force a gas, usually air or oxygen-enriched air, into the lungs of a patient who, for some reason, is unable to maintain proper breathing by their own efforts. Is a device used for. The pressure source is a piston device, a built-in blower or a high pressure line. Commercially available ventilators utilize a variety of mechanisms to regulate the pressure exerted on the patient. In each case, breathing is started and a series of operations is started,
Meanwhile, the pressure cycle ends when pressure is applied to reach the target volume or pressure. Once the cycle is initiated, the artificial respiration procedure proceeds in a predetermined manner set by adjusting the dial on the control panel of the device. With the currently available ventilators and breathing methods, as described below,
Patients have limited or no ability to adjust the output of mechanical ventilation with their own efforts. One of the main indications for lung ventilation assist devices is the existence of an unfavorable relationship between patient effort and the resulting ventilation (FIG. 1). This may be due to neuromuscular weakness, which requires more effort to generate some pressure, or an abnormal respiratory mechanism, which requires greater output pressure to perform some lung ventilation, or both. Optimal CO due to this abnormal relationship
The removal of ₂ and / or the patient's ability to control lung ventilation and breathing patterns to ensure oxygen delivery is impaired. Further, intense breathing effort causes pain, and fatigue (respiratory muscle fatigue) is finally produced when the effort is sufficiently intense.

If positive pressure is applied to the airway during inspiration, all current methods of assisting lung ventilation (volume, pressure, or time cycle methods) reduce the load on the respiratory muscles and the patient's effort and the achieved lung ventilation. The relationship between is improved overall. For some inspiratory efforts, the patient will receive a greater amount of air than if not supported by assisted breathing.
However, this support method results in various losses in patient ventilation and respiratory pattern control. The effect is shown in Figure 2
As shown in FIG. In volume cycle ventilation (FIG. 2), pressure is generated during ventilator assisted breathing in the amount and cycle necessary to produce a given flow pattern and cyclic volume. The ventilator operator (i.e., doctor, or clinician), rather than the patient, determines the delivery flow rate and volume. If the patient makes an inspiratory effort during inspiration, the ventilator will simply reduce the delivery pressure so that the delivery flow and volume are at the determined values. As the patient makes more effort, the pressure delivered by the ventilator is correspondingly reduced (FIG. 2, left to right). Conversely, when the patient does not want to accept the determined volume or flow and ceases to work, the ventilator creates a large amount of pressure to compensate for the patient's work. Therefore, there is a conflicting relationship between the patient and the ventilator.

In this volume cycle ventilation, the degree to which the patient loses control of his or her breath depends on the type of ventilation used. Continuous forced ventilation (CMV)
In that case, the patient is completely out of control because he cannot change the flow and volume on each assisted breath, nor can he influence the cycle. In assisted control mode (A / C), the patient can change the frequency of forced breaths, but at each breath the same reciprocal relationship between patient effort and delivery pressure occurs. New synchronized intermittent forced ventilation (SIMV)
Then, natural breathing can be performed between forced breaths. During these breaths, the patient controls the rate and depth of breathing. However, the primary reason for ventilatory support, the anomalous relationship between effort and ventilatory output (FIG. 1), persists. In fact, the situation is exacerbated because the device and the endotracheal tube put more stress on the patient. Therefore, the patient repeats breathing (forced breathing) that has no ventilation result even if he or she makes an effort and abnormally low breathing result of effort.

In the pressure assisted method of assisted ventilation, the delivery pressure is a predetermined function of time and is usually a square wave pressure that begins at the beginning of inspiration and ends when the flow rate drops to a certain volume. Therefore, delivery pressure is independent of how much the patient makes an inspiratory effort during inspiration (FIG. 3). Great flow and volume are obtained no matter how the patient makes inspiratory effort during breathing (FIG. 3, AC). However, since the delivery pressure is independent of effort, the patient's effort ventilation results are still dominated by the abnormal relationship between effort and lung dilation shown by the disease of FIG. Although the overall relationship between effort and ventilation is improved,
The patient's ability to change ventilation in response to changing needs is impaired. In addition, patient effort ramps up during inspiration,
On the other hand, since the delivery pressure of the ventilator is almost constant, the ventilator over-supports in the early stage of inspiration, and the support decreases as the inspiration progresses. With prolonged inspiration, the patient perceives an increase in load, which causes the patient to take a short inspiratory breath, thus reducing tidal volume.

In airway pressure relief ventilation (APRV), airway pressure changes between high and low levels in a time sequence independent of patient effort (FIG. 4). A periodic cycle of pressure ensures minimum ventilation. The patient can also obtain spontaneous breathing independently of the programmed cycle. During this time, the patient is not assisted (similar to SIMV). The relationship between effort and ventilatory performance during these breaths was poor, as demonstrated by illness (Figure 1), limiting the patient's ability to change flow and ventilation in response to changing needs. It In fact, in APRV the volume of active lung increases and the relationship between effort and ventilatory outcomes becomes worse due to the adverse effect of increased lung volume on neuromechanical coupling (ie pressure generation for a given muscle activity). ..

J. Appl. Physiol. 41 : 2
52-255, recorded from respiratory nerves with modifications to commercially available pressure-driven ventilators, as described in Remer et al., "Servo Ventilators Consisting of Positive Pressure Ventilators", 52-255. Prior art is known to produce pressure that fluctuates with the electrical activity of the device. To the extent that activity in the inspiratory nerves reflects effort, for the purposes of this invention, these modifications would allow the ventilator to deliver pressure proportional to effort. Developed with animals that have access to and can take a record of inspiratory nerves, these modifications provide direct measurement of inspiratory muscle or nerve activity that is not performed in humans requiring ventilatory support. Is required. In contrast, the present invention uses an algorithm that can infer the extent of effort from easily measurable variables such as flow rate and volume without the need for direct recording of activity to deliver pressure proportional to patient effort. can do. IEEE Trans.
Biomed. Eng. 33 : 361-365.198.
6, Poon et al., "Mechanical Breathing Apparatus," describes a commercially available volume ventilator with modifications to deliver a pressure proportional to inspiratory flow. This device was originally developed during an experimental study of human movement to simulate and amplify the effect of helium to reduce respiratory resistance, but theoretically provides partial ventilation support for the patient. Can be used for Thus, the device produces pressure in a time pattern similar to the inspiratory flow, which is highest during inspiration and then decreases. Since this pattern does not correlate (rather negatively) with the patient's continuous inspiratory effort during inspiration (rather negative), this support pattern, as described below, makes pressure a function of inspiratory effort throughout inspiration. Is completely different from the method of the present invention. Not only is the method of the present invention (drafting vs. effort proportional to effort) completely different, but the device of the present application described herein does not rely on conventional volumetric systems designed to regulate flow rate rather than pressure. It is far more suitable for the method of the present application (Proportional Assisted Ventilation, PAV) than the modified ventilator device. The design of the present invention allows for unrestricted flow and there is no delay between the start of inspiratory effort and the start of flow from the ventilator to the patient. The system of the present invention can also provide proportional assistance by positive pressure in the airways or negative pressure at the body surface, but a modified positive pressure, gas-operated ventilator performs only the former function.

Various breathing apparatus are described in the prior art patents. U.S. Pat. No. 3,985,124 describes a spirometer that measures expiratory flow and volume and produces a graphical record thereof. This device has a piston type expansion chamber that expands in proportion to the exhaled air. U.S. Pat. No. 3,669,097 describes a device for increasing lung volume and strength. An inflatable bellows chamber is connected to a tube with a mouthpiece. A selectively adjustable valve is provided on the tube to constrict the flow path from the mouthpiece to the inlet of the bellows chamber so that expansion of the bellows requires more than the normal pressure exerted by the lungs. Is becoming U.S. Pat. No. 4,301,810 includes
A ventilator training device is described which comprises a leather bar and a mouthpiece and which expels old air from the leather bar during exhalation and introduces fresh air into the leather bar during inspiration. The airflow through the mouthpiece is monitored to ensure that the device is used in its intended way. US Patent 4,462,410
The publication describes a recording spirometer that performs a respiratory test using a movable push plate that moves in response to the patient's breathing and a recording medium that can record the patient's expiratory volume as a function of time. U.S. Pat. No. 4,487,207 describes a lung training device having a mouthpiece in which a patient inhales. A tube is connected to the air inlet and a valve is located on the tube and biased to a normally closed position. When you inhale, the valve opens and the inspiratory volume is monitored.

Fry's US Pat. No. 4,459,982 describes a lung ventilation system having a chamber for delivering respiratory gas to a patient. One embodiment of this patent describes providing a flow rate that is directly controlled by the patient's instantaneous demand under spontaneous breathing and is therefore considered relevant to the present invention. However, in order to operate and control the device, it is necessary to move the piston within the chamber to maintain the pressure in the patient's airway at a constant value equal to the operator-determined reference pressure. Since the device operates to maintain a constant airway pressure during inspiration, it delivers pressure proportionally to fluctuating patient effort during inspiration, as in the method of the invention (PAV). Obviously not.

British Patent No. 1,541,852 describes a motor driven piston which changes the internal pressure of the piston according to the electric power applied to the motor. This system is designed to deliver pressure according to a predetermined pressure one hour profile, such as a pressure cycle ventilator, or to force a given amount of gas to a patient, such as a volume cycle method. In the method of the present invention, neither pressure nor flow rate and volume are predetermined. Rather, the patient determines his flow pattern and ventilation by his own effort, with the ventilator delivering pressure in parallel with the patient's efforts, which is clearly not predetermined. Other known techniques using motor driven pistons that provide a predetermined pressure versus time or volume versus time pattern include Hillman U.S. Pat. No. 4,036,221, Chu's U.S. Pat. No. 4,617,637 and Apple's U.S. Pat. There is US Pat. No. 4,726,366.

In US Pat. No. 4,448,192 and British Pat. No. 2,121,292 Stwick describes a system having a motor driven piston and an extremely complex controller, the purpose of which is patient and artificial. To alleviate incongruity between respiratory organs. Physician-specified amount (periodic ventilation) that allows the patient to vary in effort
And the control system continuously calculates an ideal pressure-volume curve designed to allow the ventilator to deliver gas at flow rates. While this system allows the patient to ignore inhalation or short-term physician-specified delivery patterns, the control system should readjust the terms in the formula to ultimately meet physician-determined criteria. To Therefore, the control principle is similar to the volume cycle method in that the increased patient effort is matched with the decreased mechanical assistance and returns the ventilator output to the physician-defined value. The major difference from other volume cycle methods is the patient's freedom to transiently ignore physician prescriptions. This principle of operation is the exact opposite of what is carried out by the method of the invention. Thus, in Stwick's system, the physician sets the target volume, flow rate and timing, and the machine alters various parameters of the control system formula to meet the physician's requirements. In contrast, in the present invention, the proportionality between pressure on the one hand and volume and flow on the other hand is a given parameter, and the patient is completely free to choose the volume, flow and flow pattern and timing of each breath. can do.

[0012]

This study shows that prior art patient ventilation systems provide ventilation assistance to the patient primarily according to parameters determined by the physician rather than by the patient. Generally, the prior art requires some target flow rate, target pressure, target volume, and / or target period or inspiratory or expiratory time. Such conditions cause the various problems described above.

The present invention aims at a ventilation support method which is completely different from the above-mentioned prior art. In the present invention, the ventilator delivery pressure increases in direct proportion to the effort of the patient and the proportionality is applied for each inspiration and continuously during breathing. In fact,
The patient's effort is amplified, which normalizes the relationship between effort and ventilation, giving the patient complete control of his breath in all respects. In the present invention, the pressure delivered to the patient from the ventilator reflects not only the temporal pattern of patient effort, but amplitude as well (see Figure 5). There is no target flow rate, target pressure, target volume, and target cycle or inspiration or expiration time as in the prior art. These parameters are determined only by the pattern of patient effort, and the ventilator simply amplifies the ventilator performance. The net effect of this method is to restore the abnormal relationship between effort and ventilation outcomes to normal, and to regain the ability of the patient to change ventilation and flow patterns according to their changing needs, including optimization of respiratory sensation. That is. The ventilation procedure of the present invention can be referred to as proportional assisted ventilation (PAV).

The left graph of FIG. 6 outlines the relationship between patient effort and pressure delivered by the ventilator for various ventilation methods, and the right graph shows the relationship between patient effort and ventilation performance. Show. SIMV, PS, APRV results in minimal ventilation when no effort is made. All effects of patients on their breathing are constrained by illness (SIM
The linear slopes of V, PS and APRV are similar to that of disease). In PAV, on the other hand, the relationship between effort and ventilation performance is normalized at different effort levels.

[0015]

SUMMARY OF THE INVENTION In accordance with one aspect of the present invention, there is provided a novel lung ventilation system for PAV with relatively simple electric drive operation. In the present invention, the gas pressure in the patient's airway is determined by the action of the electric motor acting on the piston that reciprocates in the chamber in connection with any desired command input. The electric motor moves the piston with a force proportional to the magnitude of the applied power. The flow rate (F) and volume (V) of gas traveling from the chamber to the patient is monitored by electronic circuitry that can independently adjust the gain and amplitude of each of the two signals. The electronic circuit supplies power to the motor that is proportional to the sum of the appropriately amplified V and F signals. As will be described below, this procedure allows the device to deliver pressure proportional to patient effort.

The difference between proportional support ventilation and other methods is that the patient has complete control over his breathing pattern. In this way, the device operates on the positive feedback principle, that is, as the volume and flow taken by the patient increases, so does the supply pressure of the device. The adjustable parameter is not the target pressure or target volume, but the degree of support (ie, proportionality) to the patient's breathing pattern.
Therefore, the patient's respiratory stiffness (elastance) is 1
If you need 40 cmH ₂ O for expansion of 〓,
The device is adjusted to give a specific amount of pressure / unit inspiration. In this case, if the proportionality is set to ₂₀ cm H ₂ O / L, the patient will do half of the elastic action and the device will do the other half. The patient does not have to take up a volume or reach a pressure. As soon as the patient reduces his effort, the inflow of air is stopped and the device stops inhaling. Accordingly, as a feature of the present invention, there is provided a method of providing breath support in proportion to a patient's ongoing inspiratory effort, which is provided by an air supply system in response to a pressure gradient generated by the patient's inspiratory effort. Forming a free gas flow to the patient, determining the flow rate and volume of the gas flow to the patient, independently amplifying the signals corresponding to the determined flow rate and volume, and determining the sum of the amplified flow rate and volume. It consists of providing gas pressure support in proportion.

The present invention also provides an apparatus for providing proportionally assisted ventilation to a patient, the apparatus including means for delivering a free gas flow to the patient in response to the patient's inspiratory effort, and an operative gas. Means for producing pressure in the free gas stream in response to the electrical command signal and a separate means for detecting the instantaneous volume and flow rate of the gas stream to the patient and corresponding to the magnitude of each detected value. An electric command signal to the pressure generation means in proportion to the sum of the detection means for generating an electric signal, the means for selectively amplifying each electric signal, and the amplified electric signal corresponding to the instantaneous flow rate and the magnitude of the capacity. It is equipped with a means for transmitting.

There are several advantages to this type of ventilator in relation to prior art ventilators and methods. The first advantage is the comfort because the relationship between the device and the patient is not only synchronous but perfectly harmonious. There is no collision between the patient and the device, in fact the ventilator is an extension of the patient's own muscles. In PAVs, pressure is delivered only in the presence of patient effort, and since pressure is proportional to patient effort during inspiration, the patient must contribute a portion of the pressure used to expand the chest. This ventilator
Less pressure needs to be delivered for a given ventilation compared to other devices. Other forms of ventilator cannot rely on patient contribution and often oppose the opposite. The peak airway pressure required in such devices is higher than in the present invention. Preliminary studies with the ventilator of the present invention show that peak airway pressure at the same ventilation level is SI for PAV.
It was found to be 1/3 to 1/2 of MV. In the present invention, since the required peak pressure is low, it is possible to stop the intubation by performing artificial respiration of the patient with the nose or face mask. Intubation, either directly or indirectly, is one of the leading causes of morbidity or mortality in mechanical ventilation patients. As in the normal body, the intrathoracic pressure becomes negative during inspiration, which reduces the blood circulation complications of artificial respiration. The increased comfort, collision-free, and avoidance of intubation significantly reduce the need for sedation and paralysis that impairs patient protection.

In PAVs, the ventilator is simply an extension of the patient's own muscles, and is therefore subject to any essential control mechanism that regulates ventilation for varying needs and protects against various insults. Such a control mechanism is potentially very beneficial. For example,
The respiratory system has a strong reflex and prevents overexpansion of the lungs. Overexpansion reflexively results in the inhibition of inspiratory effort and the gradual increase in expiratory effort. Overexpansion causes the ventilator to reflexively stop circulation because the ventilator pressure is interrupted when the inspiratory effort ends. The risk of pressure disturbance is also reduced. Furthermore, a patient's metabolic demands sometimes change significantly due to exercise, tremors or changes in temperature. Respiratory control usually changes inspiratory effort to bring ventilation into line with metabolic demand. In PAVs, such adjustment of inspiratory effort is made by machine-assisted harmonic changes. This effect tends to control arterial blood gas pressure within narrow limits.
Furthermore, patients do not fluctuate from over-supported periods to under-supported periods, which makes them feel distressed as their metabolic demands change.

In accordance with the present invention, the PAV method requires a minimum level of inspiratory muscle activity, so that it is less likely that the inspiratory muscles will be depleted. The use of PAV during illness does not result in periods of central control inactivity (lack of breathing). In other ventilatory support methods, central respiratory insufficiency is common during withdrawal, partly due to the prolonged inactivity of the respiratory center caused by devices that promote respiratory insufficiency. Let's see Withdrawal is facilitated because there is less chance of central and peripheral muscle dysfunction.

The efficiency of negative pressure ventilation is improved. The ability of the negative pressure device to reduce intrathoracic pressure is limited and is greatly reduced for patients with significant organ abnormalities such as chronic pulmonary obstruction (COPD) or pulmonary fibrosis. In addition, pump pressure and upper airway dilator muscle activity are compromised, promoting airway collapse. When the negative pressure applied to the human body surface is coordinated with the patient's own inspiratory effort, the upper airway stenosis is reduced and the combined pump pressure and patient generated pressure is suitable for ventilation.
These two factors allow heavy lung disease patients to be ventilated during sleep using the present invention. Currently, chest ventilation for these patients (COPD) can only be performed when awake.

The essential and salient features of the procedure of the invention are:
Rather than the generated pressure of the ventilator guiding or initiating the exchange of gas from the device to the patient as in conventional devices,
It is to obey it. The flow rate and volume must first be changed before the ventilator changes its output pressure. Although the ventilator of the present invention is specifically designed to produce this proportional support mode, the design principle used to achieve this goal is that the design of any desired input can be accomplished with only a few additional electronics. The machine can deliver a pressure proportional to This versatility allows us to meet future needs with minor modifications.

[0023]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a patient's inspiratory effort is detected and responded to. The inspiratory effort is the maximum possible activation (E
It can be defined as the inspiratory muscle activation degree (E _i ) with respect to _max . The inspiratory pressure (P _mus ⁱ ) generated as a result of inspiratory activity is expressed by the following equation.

[E _max ] P _mus ⁱ = fE _i / E _max where f is the function governing the conversion of activity into pressure. This function is mainly affected by muscle strength, lung volume (V) and ventilation flow (F) (see I. Th, which is shown here for reference).
eory, J .; Appl. Physiol. 51:96
3-978, 1981, Younes et al., Model of Relationship between Respiratory Nerve and Mechanical Output). Since the maximum inspiratory pressure is not affected by the resting periodic volume range, and the resting flow rate is associated with a very low muscle shortening speed relative to the maximum possible speed (the aforementioned Younes et al.), The relationship between effort and P _mus. The function that governs is primarily governed by muscle strength at resting ventilation levels. This is very often abnormal for patients who require pulmonary ventilation support, primarily as a result of overexpansion in the case of neuromyopathy, secondarily nutritional or metabolic disorders, or severe asthma or chromium disordered lung disease patients (CORD). That is. In such a situation, the pressure from a given effort will be subnormal and therefore less dilated.

At any instant during breathing, the pressure applied to the respiratory system (P _appl ) is dissipated to the elastic and resistive elements of the respiratory system because the inertial loss of resting ventilation levels is negligible. Therefore, P _appl = P _el + P _res , and P
_el is a function of lung volume above the passive functional residual capacity (FRC) (P _el = fV) indicated by the pressure-volume relationship of the respiratory system, and P _res is indicated by the pressure-flow relationship of the respiratory system. It is a flow rate function. Both functions are complex and non-linear, but for convenience, a linear function is used here. Therefore, P _appl =
V. E _rs + F. R _rs , where V is the capacity above ERC, E _rs is the elastance (cmH ₂ O / l) that indicates the resilience of the respiratory system within the linear range, F is the flow rate, and E _rs is the ventilator. , Respiratory system resistance (cmH ₂ O / L / sec). During spontaneous breathing, the pressure (P
_mus ) is the only source of P _appl . Pressure applied to a patient fitted with a ventilator is the sum of the generated pressure and machine generated pressure of the patient (P _{ve nt).} The latter takes the form of positive pressure in the respiratory tract or negative pressure (on the chest or chest) on the human surface. During assisted ventilation, the relationship between opposing forces is P _mus
+ P _vent = V. E _rs + F. R _rs (1) or P _mus =
V. E _rs + F. R _rs −P _{ve nt} (2). Since V, F and P _vent can be continuously measured and E _rs and R _rs can be measured or estimated, P _mus can be continuously calculated based on the measured values by an arbitrary and simple calculator. , The ventilator is made to change the pressure in proportion to the instantaneous P _mus . That is, P _vent = A. P _mus here,
A is a proportional coefficient between P _vent and P _mus (cmH ₂ O / cm
H ₂ O). A simpler and applicable method is to design the ventilator to generate pressure according to the following equation: That is, P _vent = K ₁ V + K ₂ F (3), where K ₁ is the gain factor (cmH ₂ O /
L) and K ₂ are gain factors (cmH ₂ O / L /
Seconds). Although constants are used in this analysis, non-linear functions can be used if applicable. If A is given by the desired proportionality factor P _mus of P _mus (2) _equation, P _vent = A. V. E _rs + A. F. R _rs = A. P
_vent , and thus P _vent (1 + A) = A. _Ers・ V
+ A. R _rs · F, that is, P _vent = [A / (1 + A)]
E _rs · V + [A / (1 + A)] R _rs · F. The last equation has the same form as equation (3) above, where K ₁ is the fraction of elastance (ie A / (1 + A)) and K ₂ is the same fraction of respiratory resistance. Therefore, P _vent can be made proportional to P _mus without actually calculating P _mus according to the equation (2). Therefore, 3 of P _mus (A = 3)
To generate double P _vent , set K ₁ to 0.75E
_rs and K ₂ is 0.75R _rs . Equation (2) or equation (3) can be used to control P _vent . However, the expression (3) is advantageous for the following reasons. In the case of the expression (2), P _vent is used to derive a command signal to the pressure generating mechanism, which itself is a controlled variable. In particular, the delay between the command signal and P _vent is unavoidable, which causes vibrations and is difficult to filter. In the case of equation (3), the use of individually adjustable gain factors for flow rate and volume allows different relaxation of resistance and elastic properties, which is advantageous in certain clinical situations. Furthermore, although E _rs and R _rs are often difficult or unreliable to measure, the gain factors of V and F can be adjusted separately to make the patient comfortable using equation (3). , E _rs and R _rs need not be known. An example of a system that operates according to this principle is described below.

An essential and distinctive feature of proportional assisted ventilation (PAV) according to the present invention is that the ventilator generated pressure follows the gas flow from the machine to the patient, prior to the gas flow. It does not happen. The flow rate and volume must first be changed before the ventilator changes its output pressure. Therefore, any device that delivers a PAV to the patient must pass a free air stream from the device to the patient in response to changes in the patient's pressure, a condition that can be easily illustrated by breathing with an easily movable bellows. At any given time, elasticity and resistance pressure loss (right side of equation (1)) are balanced by the sum of P _mus and P _vent , so P
Any increase in _mus changes the total applied pressure and changes the corresponding flow rate and volume. The device then responds by varying its pressure, causing large changes in flow rate and volume.

Systems operating according to this sequence exhibit positive feedback. Such a system is inherently unstable in itself and is prone to "runaway" as some air is forced out of the system to create pressure, which in turn causes more air to be released. is there. However, the positive feedback inherent in a ventilator when attached to a patient is counteracted by the patient's mechanical properties, ie, negative feedback due to elastance and resistance. It is schematically shown in Figure 7 that the interaction between the PAV system and the patient eliminates the possibility of "runaway" and the system simply amplifies the ventilatory outcome of the patient's effort. A brief description of meeting the criteria for a PAV air supply system is given at the top of FIG. A freely moving piston is connected to the patient. The movement of air from the piston to the patient is sensed by the flow meter to generate flow and volume signals. This signal is used to control a motor that exerts a force on the back of the piston that is proportional to the flow and volume signals. Separate gain controls, on the one hand, determine the proportionality between flow and capacity,
On the other hand, the applied force or pressure is determined. Such gain capacitance is similar to the K ₁ and K ₂ terms of equation (3).

To facilitate the explanation of the interaction between the patient and the PAV system, all changes (P _mus and P _vent ) occur in separate sequence steps, as shown in the bottom three graphs of FIG. And consider the case where all the generated pressure is added to the elastance of the respiratory system (ie, resistance is zero). Patient elastance is expressed in arbitrary units,
Assign a value of 1 (ie 1 unit pressure / unit capacity). Before inspiration starts, that is, when P _mus = 0, the airway and volume are stable and show a positive expiratory pressure value (0 in the figure). The patient shall change 4 units of P _mus in steps. A volume of 4 units is transferred from the ventilator to the patient according to the patient's elastance. As can be seen from the spacing between the first pair of vertical lines, the airway pressure is still zero. However, the movement of gas (volume or flow rate) is detected,
The pressure in the system (ie, P _aw ) then increases according to the capacitive signal and the selected gain factor. Gain rate of 0.5
When set to pressure units / unit volume, the ventilator will increase P _aw by 2 pressure units in response to the first 4 unit volumes and increase the total pressure (P _appl = P _mus + P _aw ) to 6 units and 2 more. Volume units will be transferred. This increase in capacity is then sensed, and P _vent is increased by one more unit according to the gain factor, and so on, causing one more volume unit to be transferred, and so on.

Since the gain factor is smaller than the patient's elastance, there is no tendency for the step size to taper and "runaway". In fact, if P _mus is constant, the capacity approaches the asymptote. This effect is shown in Figure 7, where the volume asymptote is twice the value generated by unassisted patients. For example, in FIG.
Like the second step of P _mus , due to the large step change of P _mus , the volume exchanged by the patient's own force increases and the response of the ventilator also increases, but again there is no tendency to runaway, so in this second step The exchanged capacity has the same proportionality to P _{mus as the} small first step. Since the elastic recoil at any point in time is supported together by the patient and the ventilator, when the contribution of the patient as indicated by the arrow in FIG. 7 decreases, the pressure applied to the respiratory system, namely P _mus
+ P _vent is no longer sufficient to maintain the elastic recoil of the system. A decrease in P _{mus at} the end of inspiration, as in spontaneous breathing, initiates exhalation with a positive gradient from the alveoli to the airways. The amplification of the elastic component of P _mus is a function of the gain of the ventilator volume signal (K ₁ ) with respect to the patient's own elastance (E _rs ). Total elastic pressure (V.
E _rs) Since some also by the elastic component of the part _{P mus (P mus (el)} ) is balanced by the elastic support of the ventilator (V.K _1), as it follows.

P _mus (el) = V. _Ers- P _vent (el) = V. _Ers- V. K ₁ = V (E _rs −K ₁ ) Therefore, the total elastic applied pressure, V. _Ers , and elastic amplification factor (F
(El)) the patient's developed pressure (P _mus (el)) is given by the following equation. F (el) = V. E _rs / V [E
_{rs -K 1] = E rs /} [E rs -K 1] Thus, as in the example of FIG. 7, the amplification factor if K ₁ is 1 / 2E _rs becomes 2.
For K ₁ = 0.75E _rs , the amplification factor is 4, and so on. If K ₁ is greater than or equal to _Ers , then
The amplification becomes infinite and a runaway condition occurs. But _Ers
Since it gradually increases with increasing lung volume, the runaway condition caused by a gain factor that happens to be greater than E _rs, which is close to functional residual capacity, will soon cease as lung volume increases and E _rs increases.

The example of FIG. 7 is highly simplified to illustrate the principles associated with the present invention. For example, the resistance is 0
_However, a portion of P _mus is spent on the resistive element of the (patient plus device) system. However, it is possible to similarly analyzed and taken into consideration also the resistance component of P _mus, i.e. P _mus (res). At any given time, the total pressure used to offset the flow-related pressure gradient is F.S. It is given by R, where R is the total resistance of the airflow from the ventilator to the chest wall and also includes the resistance of the device. This pressure is partly due to the ventilator (FK ₂ ) and partly to P
It is provided by the resistance component of _mus (P _{mu s} (res)).
By the same analysis as for elastic resistance, the amplification of the resistance component of P _mus (F (res)) is a function of the ventilator's flow gain (K ₂ ) with respect to total resistance (R) according to the following relationship: That is, F (res) = R / [R−K ₂ ].
Capacity during inhalation is gradually increased, but the flow rate is to reduce the inspiratory late peaked early distribution between the elastic and resistive components of P _mus significantly vary with inspiration time. P _mus (r
es) contributes to the majority of P _{mus in} the inspiratory phase, which falls to almost zero at the end of inspiration. Instantaneous flow or P _mus (res) and instantaneous effort or total P
The correlation between _mus is extremely low, and in fact becomes negative in the latter part of inspiration. Thus, support related only to flow amplifies the effort during the early inspiration periods when less effort is exerted and leaves the muscle essentially unassisted during the late inspiration periods when maximum effort is exerted. Similarly,
Since P _mus (el) constitutes different parts of the total P _{mus at} different times of inspiration, the container is not completely correlated with effort, but during inspiration both P _mus and volume increase, so the correlation is Better than with flow. However, with volume-only support, P _mus amplification occurs predominantly in late inspiration and remains essentially unsupported during early inspiration. In this case, since the relationship between the effort in the early inspiration and the ventilation result is normal and support is not required, there is no particular disadvantage if the resistance is normal. However, since R is abnormal for all artificial respiration patients due to at least endotracheal resistance and device resistance, failure to amplify P _mus during early inspiration causes the patient to feel stress and lead to dyspnea. The increase in inspiratory resistance is not so great even in severe obstruction, and the patient's own resistance is also high because the main load is mainly the elasticity exhibited by dynamic overdilation.

The flow rate or volume only Another consideration with respect to providing support in proportion to the one element of P _mus, i.e. P _mus (el) or P _mus (re
Amplifying s) will inevitably increase the contribution to the other unsupported element. Therefore, the flow rate proportional support first increases the flow rate. The lung volume, and thus the elastic component of P _mus , rises rapidly. As a result, P _mus (res)
As a result, the support subsequently declines. From this examination, it is necessary to support both the flow rate and the volume according to the equation (3) in order to normalize the relationship between the effort and the ventilation result. In this way, P _mus is amplified no matter how it is distributed between the elastic and resistive components. The example of FIG. 7 should not be construed as the control being performed sequentially. The analog control circuit functions similarly. Whether analog or digital, the command signal to the pressure generator changes following, but not after, changes in flow and volume, making the ventilator useful to the patient. Contrary to a gas driven ventilator where the pressure is changed only by flow control, there is a direct and direct relationship between the command signal and the output pressure,
For PAVs, motor driven bellows are the preferred basic design. The relationship between flow rate and system pressure is extremely complex. Subtle servo control is important, and unless severe filtering is done, it is prone to oscillations in the PAV method and significantly reduces the response as described above.

The embodiment of FIG. 8 using a motor driven bellows is suitable when the relationship between the power applied to the motor and the pressure within the bellows is linear within the range required for ventilation. It has a mechanical design that minimizes inertial and resistive losses during piston or bellows movements, ensuring that the motor has a linear range (i.e. power and output power) over the entire clinically useful range of piston or bellows capacity. This is achieved by ensuring that they operate in a fixed relationship). This mechanical design eliminates the need to control the motor using pressure feedback and error signals. As mentioned above, the use of pressure feedback in the PAV method results in device instability (because the desired pressure itself is variable rather than a constant criterion or function and is subject to system influence). Therefore, if the pressure feedback is removed from the command signal, the system becomes more stable. Filtering can be minimized as the device is more responsive.
The operation of such a device is error-free in nature.

FIG. 8 shows the currently best mode for implementing the invention (PAV). A low inertia, low resistance rolling seal piston 201 is free to move within chamber 202. The chamber 202 receives gas during the exhalation phase via a check valve 203 having an appropriate opening pressure value, and during inspiration gas travels from the chamber 202 to the patient 208 via another check valve 204. .. The piston 201 is connected to the coil of the linear drive motor 205, and is itself fixed magnet 20.
Move freely within 6. Coil 205 is cable 207
The piston 201 is pushed and pulled in proportion to the magnitude of the driving potential applied to the coil 205 via the. Obviously, any other type of bellows and motor combination is also suitable, provided that the free gas flow to the patient flows under the pressure gradient generated by the patient. This condition is met by the mechanical properties (ie, low inertia, low resistance) inherent in prior art bellows and motor combinations or proper servo control of the bellows position. The gas flow rate from the chamber 202 to the patient 208 is measured by the flow meter 209 mounted on the intake pipe 210. Alternatively, the gas flow rate can be measured using a velocity transducer (not shown) that monitors the velocity of movement of the piston. The position of piston (201) is also monitored using potentiometer 211 or other suitable device.

The flow signal is adjusted by an external adjustable gain controller 212. This is equal to K ₂ in equation (3). The amplification can be constant or variable, taking into account the non-linear behavior of the pressure-flow relationship of the patient and / or the external conduit. The flow rate signal is integrated via integrator 213 to produce a signal corresponding to the instantaneous inspiratory volume 214. The latter is also adjusted by the external adjustable gain controller 215. This is equivalent to K _{1 in} equation (3), and the gain can be made constant or variable in consideration of the nonlinear elastic characteristic of the respiratory system. The flow and capacity signals 216 and 217 are summed using summing amplifier 218 to produce a combined output signal. The summing amplifier may also receive another input 219 to operate the device in a non-proportional support mode. During the latter part of the inspiratory phase and expiratory phase, the switch mechanism 220 outputs the output of the summing amplifier 218 to the motor 2.
Send to 05. During early exhalation, this switch 220 sends a constant negative voltage 221 to return the piston 210 to a preset position as determined by potentiometer signal 211. In either case, the command signal 222 is first properly amplified using the power amplifier and power supply 224. Exhalation tube 2
25 and the exhalation valve 226 ensure the gas flow from the patient to the atmosphere during the exhalation phase. Any of the various exhalation valves commercially available can be used. The exhalation valve 226 is opened and closed by its valve control mechanism 228.

A differential pressure transducer 227 measures the pressure gradient between the upstream and downstream points of the check valve 204, which directs flow into the intake line 210. The downstream point may be as close as possible to the patient to increase the flow sensitivity of the transducer 227 and the upstream point may be conveniently located in the chamber 202. The inspiratory phase can be defined as any time when the upstream pressure is higher than the pressure at a point near the patient. The expiratory phase is when the patient side pressure of valve 204 is higher than in chamber 202. The output of the differential pressure transducer 227 is passed to the exhalation-valve control mechanism 228 and the switching mechanism 220 of the motor drive 205. At the transition from inspiration to expiration determined by the output of transducer 227, integrator 213 is reset to return capacitive signal 214 to 0 and prepare for the next cycle. The other input 219 to the summing amplifier 218 can include any of a variety of functions. Two preferred functions are a constant voltage, which optionally provides continuous positive airway pressure (CPAP), and an input designed to counteract the effects of inspiratory resistance. In the latter case, the differential pressure transducer 22
The output of 7 is passed to summing amplifier 218 after proper amplification and rectification (positive slope from chamber to patient only). In this way, the piston produces a positive pressure component equal to the pressure gradient between the chamber and the patient, essentially eliminating the tube resistance effect at all flow rates.

Other inputs 219 include a back-up function such as, for example, a repetitive slope or square wave voltage versus time function that ensures ventilation in the case of apnea. Alternatively, using these other inputs, the manufacturer may add various conventional ventilation methods to the machine performing the PAV, such as airway pressure relief ventilation (APR).
These additional methods, such as D) or Synchronous Intermittent Active Ventilation (SIMV) or Pressure Assistance (PS) can be made available for use with or selectively with PAD.
At the start of the expiratory phase, the piston 201 retracts under the influence of the negative voltage 221 and obtains fresh gas of the desired composition via the check valve 203 until it reaches a predetermined value. Next, the switching mechanism 2
20 disconnects the negative voltage and passes the output of summing amplifier 218 to motor 205. At this point, the adjusted flow signal 216 is zero and the capacitive signal 217 adjusted by resetting the integrator 213 is also zero. The only drive is from the other input 219. When a constant voltage is applied via the other input 219, the motor 205 pressurizes the piston 201 to a constant level to prepare for the next inspiration. The constant pressure level is typically set to a level just below the desired positive end expiratory pressure (PEEP), which is an exhalation valve controller or other suitable P
Determined by EEP device. In this way, the airway pressure is P
Flow from the chamber to the patient occurs immediately below the EEP level. As the flow begins, the output of the summing amplifier changes according to the regulated flow 216 and capacitance 217 signals and the sum of the constant voltage, if any, through the other input 219. This increases the pressure inside the chamber 202. As mentioned above, as long as the gain factors of flow rate 212 and volume 215 are lower than the resistance and patient elastance values, chamber pressure alone is not sufficient to fully support elastic recoil and resistance pressure loss, and thus patient Contribute to the total pressure and flow and volume continue to respond to patient effort. When the patient terminates his or her respiratory effort, there is insufficient pressure to maintain the elastic recoil of the respiratory system. The airway pressure exceeds the chamber pressure, which opens the expiratory valve 226 via the differential pressure transducer 227, resets the integrator 223 and thus the chamber pressure loss and the cycle repeats. In summary, the present invention provides a new ventilator device and method (Proportional Assisted Ventilation, PAV) that can deliver air to the patient in proportion to the patient's ongoing inspiratory effort. Modifications are possible within the scope of the invention.

[Brief description of drawings]

1 is a graphical representation of patient effort and respiratory flow and volume.

FIG. 2 Volumetric circulation ventilation (VC) according to prior art procedures.
The graph figure of V).

FIG. 3 is a graphical representation of pressure assisted ventilation (PSV) according to another prior art method.

FIG. 4 is a graphical representation of airway pressure relief ventilation (APRV) according to yet another prior art method.

FIG. 5 is a graphical representation of proportional assisted ventilation (PAV) according to the present invention.

FIG. 6 is a graph showing a comparison of proportional assisted ventilation (PAV) according to the present invention and prior art methods.

FIG. 7 is a block diagram of a proportional assist ventilator and a graphical representation of ventilator gain and patient elastance.

FIG. 8 is a schematic diagram of a ventilator providing proportional assisted ventilation according to another embodiment of the present invention.

[Explanation of symbols]

 201 piston (bellows means) 202 chamber (gas feeding means) 203, 204 check valve 205 linear drive motor (pressure generation means) 206 fixed magnet (electric drive motor) 207 electric signal (electric command signal) 209 flow meter (detection) 210) Intake pipe (tube) 211 Potentiometer 212, 215 Controller (amplifying means) 213 Integrator (electric circuit means) 214 Instantaneous intake amount 216 Flow rate signal 217 Capacity signal 218 Summing amplifier (adding means) 220 Switch mechanism 221 Negative Voltage 222 Command signal 223 Power amplifier 227 Differential pressure transducer 228 Exhalation valve control mechanism

Claims (16)

[Claims] 1. A proportional assist ventilation method for providing breathing assistance in proportion to a patient's inspiratory effort, the gas delivery system to the patient in response to a pressure gradient generated by the patient's inspiratory effort. Providing a free gas stream, detecting the flow rate and volume of the gas stream to the patient, separately amplifying the signals corresponding to the detected flow rate and volume of the gas stream, and A proportionally assisted artificial respiration method comprising the step of pressure-supporting the gas in proportion to the sum of the flow rate and the volume of the amplified gas flow. 2. The pressure support is of the formula: P _vent = K ₂ V + K ₂ F
( _Where P _vent is the magnitude of pressure support, K ₁ is the gain factor applied to the continuously varying volume signal V, and K ₂ is the gain factor applied to the continuously varying flow signal F). The proportionally assisted ventilation method of claim 1 determined. 3. The proportional assist ventilation method of claim 2, wherein a non-linear function is used instead of K ₁ and K ₂ . 4. The pressure support is of the formula: P _vent = A. P _mus (where P _vent is the magnitude of pressure support, A is an independent coefficient that determines the proportionality between pressure support and patient-generated pressure, P _mus is an expression, P _mus
= V. E _rs + F. It is an instantaneous evaluation value of the patient-generated pressure determined by R _rs −P _vent , where V is the magnitude of the variable capacitance signal in progress, F is the magnitude of the continuously changing flow signal, and E _rs is the patient. Respiratory system elastance, R _rs is the resistance to the patient's respiratory system). 5. The flow rate and volume of gas is determined by continuously sensing the flow of gas to a patient, generating an electrical signal corresponding to each sensed flow rate and volume of gas to provide pressure support. To continuously amplify each signal separately to the extent necessary to perform, calculate the sum signal of each of these amplified signals, and apply the sum signal continuously to the gas delivery system to generate pressure. The proportional support type artificial respiration method according to any one of claims 1 to 4, which performs support. 6. The flow of gas is sensed to generate an electrical signal corresponding to the flow rate of the gas through the tube connecting the gas delivery system to the patient, and the electrical signal is integrated to flow the gas through the tube. 6. The proportional assist ventilation method of claim 5, wherein the electrical signal corresponding to the volume of 7. The gas delivery system comprises bellows means and a motor operatively connected to the bellows means for producing a pressure of a magnitude corresponding to the magnitude of the sum signal applied to the motor. 7. The proportional support artificial respiration method according to any one of items 6 to 6. 8. The proportional assist system according to claim 1, wherein the gas delivery system generates a negative pressure for supporting the breathing of the patient by applying a negative pressure to the body surface of the patient. Artificial respiration method. 9. Used in conjunction with ventilatory assistance using a predetermined relationship of pressure, flow and / or volume versus time, such as continuous positive airway pressure (CPAP), intermittent mandatory ventilation (IMV), pressure assisted ventilation (PSV), And a proportional assisted artificial respiration method according to any one of claims 1 to 8, which further comprises airway pressure relief ventilation (APRV). 10. A device for proportionally assisted ventilation of a patient, said gas delivery means (202) operatively delivering a free gas flow to the patient in response to the patient's inspiratory effort. A pressure generating means (205) connected to the means (202) for generating a pressure in the free gas flow in response to an electric command signal (207), and detecting the instantaneous gas volume and flow rate to the patient, the detected values Detecting means (209) for generating separate electric signals of a magnitude corresponding to the magnitude of, and amplifying means (212, 215) for selectively amplifying the electric signals.
In proportion to the sum of the amplified electrical signals corresponding to the instantaneous flow rate and volume magnitude, the electrical command signal (2
07) and an addition means (218) for generating the pressure generation means (205) to the pressure generation means (205). 11. Gas feed means (202) comprises bellows means (201) and pressure generating means (205) comprises an electric drive motor (206) operatively connected to said bellows means (201). The proportional support type artificial respiration device according to claim 10. 12. The proportional assist ventilation apparatus of claim 11, wherein the bellows means (201) comprises a rolling seal piston. 13. A detection means (209) is operatively connected to a tube (210) connecting the gas delivery means (202) to a patient and produces an electrical signal indicative of the gas flow rate through said tube (210). A detection means (209), and an electric circuit means (213) for generating an electric signal indicating the capacity of the flow through the pipe (210) from the electric signal indicating the gas flow rate as the detected value of the capacity. 1 to 12
A proportional support type artificial respiration device according to the paragraph. 14. An adding means (2) for adding an electric signal whose capacity and gas flow rate are amplified by an electric command signal generating means.
18. The proportional assist system according to claim 13, further comprising: 18), and having means (223) for applying the command signal to the electric motor means, for supporting ventilation of the patient in accordance with the magnitude of the sum signal. Artificial respiration equipment. 15. The proportional support type artificial respiration device according to claim 10, wherein the ventilation support is performed by applying a negative pressure to a human body surface. 16. Ignoring the means for generating electrical command signals, continuous positive airway pressure (CPAP), intermittent mandatory ventilation (I).
MV), pressure assisted ventilation (PSV) and airway pressure relief ventilation (APRV) including electrical circuit means for providing alternate command signals corresponding to operator predetermined pressure, flow and / or volume versus time relationships. Claim 10
15. The proportional support type artificial respiration device according to any one of 15.