Respirator

(54) Designation: Volume Controlled Respiratory Device The present invention relates to respirators and more particularly relates to a volume controlled respirator for gas delivery to patients under controlled conditions when considering the particular pathological problems associated with each patient's lung system. The respirator device is of the kind that includes displaceable gas delivery means for periodically supplying a patient with gas under pressure.

A respirator thus forces or presses gas into the lungs of; a patient who is unable to breathe normally by himself. In general, normal breathing is impaired either because of pathological problems associated with the patient's lungs, such as high airway resistance or lung stiffness, or due to other physiological problems present outside the lungs, such as paralysis due to polyomyelitis, head injuries and the like. that the patient receives proper air exchange.

Previously known volume controlled respirators usually provide the opportunity to 'regulate both the number of times per minute. as gas is forced into the patient's lungs, such as the volume of gas left during each cycle. However, such respirators do not sufficiently control the delivered gas volume but as a function of time during the inhalation cycle to achieve a toll-related volume flow profile that is best suited for each patient considering his particular pathological breathing problems. For example, known respirators give little or no precision in terms of control and accommodation for optimizing breathing in inhalation and achieving maximum possible gas distribution within the lungs without undesirable premature build-up of airway pressure. Thus, there is a risk that excessive pressure can occur in the lungs of a patient who has problems with high airway resistance or pulmonary stiffness, which can damage the patient's lungs or cause extreme discomfort when the patient is using a respirator.

In order to solve this problem, in previously known respirators, a safety or pressure relief valve has usually simply been used for immediate release of the gas in the respirator to the room air upon detection of excessive pressure. However, this has the disadvantage of wasting gas that should be conveyed to the patient to maintain proper air exchange.

In accordance with the present invention, there is provided a volume controlled respirator which controls the gas flow to a patient's lungs so that the gas delivered during the inhalation cycle is in the best conceivable accordance with the patient's particular pathological breathing problems.

As mentioned, the respirator device according to the invention comprises previously displaceable gas delivery means for periodically forcing gas under pressure into the patient's lungs. Preferably, a piston movable piston is used to deliver gas to the patient, although an expandable and compressible bellows or other similar gas flow generating devices may be used. The operation of the respirator is controlled by means of drive means corresponding to a waveform (in the form of a reference signal) representing a desired gas volume to be delivered to the patient as a function of time. The desired volume waveform is preferably an ideal time flow of gas to be delivered during each inhalation cycle considering the particular physiological properties of the patient's lung system, although other parameters such as gas pressure versus time or gas flow rate versus time could be used to define the ideal gas flow. The desired volume waveform could be a fixed waveform, but the waveform is preferably generated by an adjustable waveform control and accumulation device to provide a selected volume waveform under given pathological conditions.

In accordance with the invention, said respirator drive means is controlled by feedback means provided in a closed loop which comprise

7306024-6 means for sensing the gas volume, which is in fact emitted from the respirator as a function of time, by sensing the position of said gas delivery means. Said sensing means thus generates a position feedback signal which is compared to the desired volume waveform for generating an error signal to control the movement of said respirator drive means, so that the ideal time flow of gas is delivered to the patient during each moment of the inhalation cycle.

In one embodiment of the invention, a separate accommodation or buffer container or space is in gas communication with the respirator. During the early part of the inhalation cycle, the buffer container receives from the respirator all gas that cannot be accepted by the patient due to high respiratory resistance and / or pulmonary stiffness problems such as emphysema and / or pulmonary fibrosis. The buffer container includes drive means, such as a piston which is controlled by a feedback control system, to force the gas stored in the buffer container back into the patient's lungs under ideal and optimized conditions at the end of the inhalation cycle.

At an altar. In carrying out the invention, accommodation can be provided without storing gas in a buffer space or container by generating an accommodation signal which seeks to limit the force applied to the respirator's piston when premature buildup of overpressure in the patient's lungs is detected during the previous portion. of the inhalation cycle. Thus, the accommodation or buffer container acts as an override to modify the desired waveform in accordance with known pressure build-up in the patient to deliver a predetermined gas volume, under ideal conditions, at the end of the inhalation cycle.

Preferably, an inhalation extension system senses excessive accommodation and extends the inhalation time of the cycle in order to allow more time for receiving the given gas volume.

Thus, the respirator of the present invention is continuously controlled during inhalation to ensure that the predetermined volume of gas is delivered to the patient during each inhalation cycle.

If pathological problems are associated with the patient's lungs or coughing, or the patient deliberately resists the respirator's efforts to provide inhalation, the buffer space prevents excessive pressure from building up in the patient's lungs during the early part of the inhalation cycle. Any part of the predetermined

7306024-6 gas volume to be delivered is not lost through the usual safety valve but is stored and delivered to the patient again, under ideal conditions, during the latter part of the inhalation cycle. The system thus provides the greatest possible chance that the entire predetermined volume of gas will be delivered to the patient before the end of the inhalation cycle. This avoids the 'pre-existing problem', which means that gas is often released into the surrounding room atmosphere, thereby preventing the patient from getting the necessary air volume.

The above and other aspects of the invention will become more apparent from the following detailed description in connection with the accompanying drawing. In this, Fig. 1 shows a schematic block diagram illustrating a respirator in which a driving piston forms part of a feedback control system. FIG. 2 is a diagram showing a waveform representing ideal gas pressure in a normal patient during an inhalation cycle as well as a pair of waveforms representing gas pressure in abnormal patients with common types of abnormal pressure ulcer building. Fb.g. 3 is a diagram showing a waveform representing an ideal volume of gas delivered to a normal patient during an inhalation cycle and a waveform representing the volume of gas delivered to an abnormal patient. FIG. 4 is a diagram showing a waveform representing ideal gas flow rate delivered to a normal patient during an inhalation cycle and a waveform representing gas flow rate delivered to an abnormal patient. Fig. 5 is a schematic block diagram showing a preferred embodiment of a feedback control system for controlling the position of a respirator piston. FIG. 6 is a schematic block diagram showing a system for controlling the gas flow to a patient from a respirator having a buffer space as well as a system for controlling the volume of gas in the buffer space. Fig. 6A is a schematic block diagram showing the system of Fig. 6 modified to include an overall or auxiliary system for prolonging the inhalation. Fig. Is a diagram showing a waveform representing the piston displacement in dependence on the auxiliary system shown in Fig. 6A. Fig. 7 is a diagram showing a time-dependent pressure build-up for an abnormal patient utilizing the respiratory system of Fig. 6, in which the pressure build-up is accommodated by the pressure accommodation system, and in which the accommodated pressure build-up is compared with an ideal pressure build-up for a normal patient. Fig. 8 is a diagram showing a time-dependent pressure build-up for an abnormal patient using the respiratory system

7306024-6 according to Fig. 6, in which the pressure build-up is not accommodated by the pressure accommodation system, and in which the pressure build-up in the system is compared with an ideal pressure build-up for a normal patient. Fig. 9 is a diagram representing the volume shift of the accommodation piston in the pressure accommodation system of Fig. 6, in which both larger and smaller volume shifts occurring early during respiration are returned to a programmed zero volume at the end of the inhalation cycle. Fig. 10 is a diagram representing the volume shift of the accommodation piston of the pressure accommodation system of Fig. 6, in which both larger and smaller volume shifts occurring late during respiration are returned to a programmed zero volume at the end of the Inhalation cycle.

Fig. 11 is a graph comparing the composite volume shift in the pressure accommodation system of Fig. 6 for two patients, a curve describing sufficient pressure accommodation with progressive return of the volume of space to zero and a curve describing insufficient pressure accommodation but still with a corresponding progressive return the space to zero volume at the end of the inhalation. FIG. 12 is a diagram showing a composite volume shift in the pressure accommodation system of Fig. 6, in which sufficient pressure accommodation occurs early during inhalation and insufficient pressure accommodation occurs late during inhalation but where the volume is progressively returned to zero at the end of the inhalation cycle. FIG. 13 is a schematic view illustrating the respiratory system of FIG. 6 during a late part of the inhalation cycle, where the accommodation space accommodates premature pressure build-up and where exhaustive resistance effects of the space have occurred. Fig. 14 is a schematic view. The illustrative respirator system of Fig. 6 during the exhalation cycle with return of the accommodation space to zero volume. Fig. 15 is a schematic block diagram showing a respirator with an alt. accommodation system, whereby a pooled propeller and accommodation container is programmed to deliver an optimized gas volume to a patient during inhalation. Fig. 16 is a schematic block diagram showing an alt. electrical control method for achieving accommodation with the pooled piston-buffer space system shown in Fig. 15 · Fig. 16A is a schematic block diagram showing an alt. embodiment of the system of FIG. 16. FIG. 16B is a schematic block diagram showing a method of modifying the system of FIG. 16 to include an overall or auxiliary system for providing

7306024-6 inhalation extension. Fig. 17 shows schematically an alt. execution of the accommodation space during an early part of the Inhalation cycle, when space accommodation has taken place. Fig. 18 schematically shows the accommodation space or container of Fig. 17 during a late part of the inhalation cycle, when emptying of the space has taken place.

Fig. 19 is a schematic block diagram showing means for providing a periodic artificial sigh during inhalation. Fig. 20 is a graph showing a volume-time ratio for normally generated inhalation tags, and where the volume-time ratio is exceeded by the artificial suction system shown in Fig. 19. Fig. 21 is a schematic block diagram of an alt. embodiment of the artificial suction system shown in Fig. 19 · Figs.

is a graph showing a volume-time ratio of inhalation tags generated by the artificial suction system shown in Fig. 21.

In accordance with Fig. 1, a respirator 30 comprises a piston 32 which is arranged in a cylinder 34. The piston is driven back and forth in the cylinder by suitable drive means 36, preferably a translation motor (such as a linear actuator or linear motor) coupled to the piston. via suitable means (not shown). However, it is possible to use other types of motors or piston drive means, such as a mechanical drive device including rack and pinion or a fluid amplifier, within the scope of the invention. Likewise, one could use a bellows device instead of the piston to periodically force gas into a patient's lungs.

A conduit 3θ feeds gas, usually air or a suitable mixture of air and oxygen, into the cylinder. As said piston drive means .36 pushes the piston forward in the direction of arrow 4o in Fig. 1, gas supplied through line 3θ is forced out of cylinder 34 by means of suitable valves (not shown) and through line 42 conventionally connected to a patient (schematically represented at 44) so ​​that the gas is passed to the patient's lungs. The piston reciprocating movement periodically pumps the gas into the patient's lungs to stimulate the inhalation cycle in nohmal respiration and allow for a suitably set time for exhalation. The exhalation cycle takes place each time the plunger is retracted, the patient breathing out passively, through a separate conduit (not shown) or where there are exhalation assistive devices or # 0 inhibitory devices (not shown), as is well known in connection with re-sprouting pi.

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The present invention includes means for controlling the movement of the plunger to deliver a controlled gas volume to the patient during each inhalation cycle. A computer and waveform generator 46 receive Input data, which affects the operator's time-related gas volume to be delivered during inhalation. Such data include an adjustable order signal 48 for respiration rate, an adjustable order signal 50 for the time relationship between inhalation and exhalation, and an adjustable order signal 52 for the volume passing to and from the lungs.

The computer 46 is preferably an analog special computer and signal generator, although other special purpose or computer generating devices can be utilized within the scope of the invention. The computer is programmed to process data and generate a voltage signal or reference output 54 which is proportional to the desired volume of gas which is cold delivered to the patient as a function of time. The output 54 is preferably a position signal which provides instructions regarding the movement of the piston, such that the piston forces a given gas volume into the patient's lungs as a function of the inhalation time. In a preferred embodiment of the invention, the output 54 may be manually set by an operator to provide an input 56 for the desired waveform or automatically through an input 58 representing a desired waveform generated internally in the computer. For example, the operator may select a particular waveform representing the time-dependent volume of gas that can best be accommodated considering the patient's particular breathing condition. Thus, it is possible to choose waveforms representing normal patients or patients with relief of airway obstruction, severe airway obstruction, reduced pulmonary resilience or the like. Preferably, reference output 54 describes an optimal, time-related volume of gas to be delivered during each inhalation cycle.

However, one can also generate a time-related pressure function or a time-related flow rate function to achieve the same purpose, which is to deliver gas to the patient under ideal conditions considering the particular pathological problems associated with the patient's lung system.

The ideal time-volume function produced by the computer may be intended for normal conditions, that is, for a patient whose lungs are not ill but which is temporarily unable to breathe normally by himself, or for abnormal patients having such conditions as high air resistance (soBom asthma or emphysema) or low pulmonary resilience (pulmonary stiffness, such as pulmonary fibrosis).

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Figures 2-4 show curves describing the lung dynamics of a normal patient compared to the lung dynamics of abnormal patients. The curve 60 in Figure 2 represents a typical pressure build-up in the lungs of a normal patient during inhalation. Curve pairs 62 and 64 of FIG. 2 represents two common types of pressure build-up in the lungs of abnormal patients, whose resistance or compliance problem causes pressure to build up more quickly during the early part of the inhalation cycle compared to that of a normal patient. When a respirator forces gas into a patient's lungs, care must be taken to prevent the build-up of excessive pressure, as such pressure could damage the patient's lungs, such as by rupture. It is also desirable to deliver a predetermined, fixed volume of gas to any given patient during each inhalation cycle. Previously known respirators often have the disadvantage that they allow the build-up of excessive pressure in situations with abnormal patients when a predetermined, necessary gas volume is delivered to the patients, which triggers a safety valve and releases the gas into the atmosphere, making gas necessary for proper air exchange is wasted.

The respirator according to the present invention is arranged to drive the piston 32 in such a way that gas is released under ideal conditions that substantially prevent the build-up of excessive pressure in abnormal patients (as represented by curves 62 and 64) and provide the greatest possible chance of a predetermined necessary gas volume will be delivered to the patient during each cycle. As will be clear from the following detailed description, the respirator of the present invention is designed to provide an optimal distribution of gas within the lung with minimal risk of release of necessary gas into the atmosphere.

As described above, the ideal pressure build-up during inhalation is preferably achieved by controlling the volume of gas delivered to the patient during each inhalation cycle. In Figure 3, curve 66 shows how a normal patient's lungs are filled as a predetermined volume of gas is forced into them. The curve 68 in Fig. 3 represents a volume-time ratio for an abnormal patient, where the filling of the patient's lungs is initially lower than that of the normal patient. However, the filling rate is greater for the abnormal patient during the latter part of the cycle, and both patients have received the same gas volume at the end of the inhalation cycle, unless excessive pressure develops in the lungs of the abnormal patient with consequent release of gas into the atmosphere.

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The following detailed description will show that the respirator is arranged to emit gas under ideal conditions generally represented by the volume curve 66. However, for more abnormal patients, the volume-time waveform 54 may be changed, either manually or automatically by the input signal 56, respectively. 58, in order to better conform to waveform 68 and thereby optimize the delivery of gas to the patient having more unfavorable dynamic conditions with respect to the lungs.

The respirator of the present invention may alternatively. be arranged to provide ideal pressure build-up by controlling the flow rate of gas delivered to the patient during each breathing cycle. In Figure 4, curve 70 shows the gas flow rate into the lungs of a normal patient. Curve 72 in Fig. 4 illustrates the flow rate as a function of time for an abnormal patient, for which the filling rate is initially lower than for the normal patient. However, the final flow rate is greater for the abnormal patient, so that the same gas volume has been delivered to both patients at the end of the inhalation cycle.

The position of the piston 52 is preferably accurately controlled by a closed loop feedback system which continuously controls the position of the piston so that the desired gas flow represented by the computer output 54 is maintained. The feedback control system includes a suitable converter 74 for measuring the controlled variable of the system, which is preferably the volume of gas actually delivered to the patient as a function of time. Alt. For example, converter 74 can measure the gas volume remaining in cylinder 54. Converter 74 is preferably a position transducer which determines the instantaneous actual position of piston 52 in cylinder 54 and generates a control signal or position feedback signal 76 proportional to the actual volume of gas delivered by piston 52. The feedback control system also includes means, represented by a summation point 78, to compare the signal 54 of the desired position with the feedback signal 76 to provide a position error signal 80 representing the deviation between the desired volume and actual volume of gas delivered by the piston as a function of time. The position error is fed to the piston drive 56 to control its movement by continuously adjusting the position of the piston to maintain the desired volume-time flow of gas from the piston to the patient.

Thus, the feedback control system servo controls the piston accurately to provide the desired gas volume time

7306024-6 generated by the computer. . In addition, suitable signals for both normal and abnormal patients can be processed or generated for the correct piston setting, either manually or automatically.

Fig. 5 shows a system for electrically actuating the piston 52. This system is shown only as an example, since it is also possible to control the piston by mechanical or fluid control means.

A desired waveform, represented by the signal 54, is generated by the computer 46 and measured to a differential amplifier 82. The differential amplifier also receives a feedback signal 76 representing the actual position of the piston 14 as a function of time. The differential amplifier produces an error signal 8o, which is a voltage whose size and polarity represents the algebraic difference between the positions of the position signals 54 and 6.

The piston is preferably actuated by a translational motor which is schematically represented at 84. The motor is designed to push the actuating arm of the piston in the direction either to the right or

In the left-hand side of Fig. 5, depending on which control phase of the motor is energized. The error signal 8o is applied to a power amplifier 86 which supplies a variable amount of energy to the translation motor for driving the piston. The amount of energy supplied depends on the size of the error signal 8o. The greater the fault voltage, the more energy is supplied to the translation motor and the longer and faster the motor moves. Positive fault voltages cause the translation motor to move in one direction and negative voltages cause the motor to move in the opposite direction. The translation engine can be operated with alternating or direct voltage and be of high power or low power type. At low power and alternating current or direct current operation, the power amplifier 86 is a linear amplifier which directly feeds energy to the translation motor. In cases of high power, dictated by the power requirements of some translation motors, the power amplifier 86 consists of gate circuits 88 and 90 for thyristor drive circuits generally represented at 92. In conjunction with AC powered translation motors, the thyristors are bi-directional, so-called Triacs. As is well known, each such thyristor is a gate electrode controlled silicon switch for full wave alternating voltage arranged to be switched from a locked state to a conductive state for both polarities of applied voltage. The term Triac is the trade name for such a switching device. Each of the thyristors acts as a switch and varies the effective value of the motor voltage to vary the length of time the AC voltage is connected to a given control phase of the motor. The error voltage 8o is thus converted to a time-dependent signal by the thyristor driver circuits 92 which supply current either to the gate 88 or gate 90 depending on the polarity of the error signal 80. The gate opened opens energy to the motor for driving it in the direction and with such force as dictated by the polarity and magnitude of the error voltage 80.

In conjunction with DC motors, the thyristors used are so-called controlled silicon rectifiers (SGR). As is well known, these gate gates are controlled half-wave switches. The operation of the control circuit for the DC voltage case is analogous to that for the AC voltage case. The control or gate circuits are generally represented at 88 and 90, and each controlled silicon inverter acts as a switch to vary the time during which a rectified AC voltage is connected to the motor. Positive or negative error voltages are converted to time-dependent signals that trigger either gate 88 or gate 90 to cause the piston to move to the left or right position of Fig. 1.

The position of the piston as it moves in response to the influence of the translational motor is detected by the position transducer or transducer 74, which is preferably a precision potentiometer or linear variable differential transformer. The feedback voltage signal 76 is proportional to the position of the piston. By supplying this voltage to one side of differential amplifier 82, the position of the piston is continuously adjusted to correspond to the desired waveform represented by signal 54.

Fig. 6 shows a separate accommodation system 94 which can be used in conjunction with the basic respirator of Fig. 1 for delivering gas to a patient under conditions ideal to compensate for the particular pathological condition of the patient's lung system or in some cases to compensate for incorrect setting of the basic respirator itself. The accommodation system comprises a second space or accommodation space 96 which is in gas communication with the cylinder 54 of the primary piston 52. Briefly, the accommodation space from the primary piston receives all gas which cannot be accepted due to either high airway resistance or lung compliance problem. Such problems cause premature or inappropriate pressure buildup in the patient's lungs, and gas which cannot be received by the patient due to the pressure buildup is stored in the accommodation space during the early part of the inhalation cycle. During the latter part of the inhalation cycle, the accommodated gas is forced back into the patient's lungs under controlled and optimized conditions by a piston 98 in said space. The accommodation system thereby improves the possibility for an abnormal patient to be able to accommodate a certain volume of gas which is necessary for proper air exchange, instead of gas that cannot be immediately accepted being released into the room air.

Fig. 6 shows a preferred system for operating the primary piston and the space or secondary piston for delivering gas to the patient either under conditions controlled in response to the particular technical pathological problems associated with the patient's lung system. A data processor 100, preferably a special purpose analogue computer, receives information such as the instantaneous or instantaneous gas pressure in the cylinder 54 and the instantaneous or instantaneous position of the secondary piston 98.

The gas pressure in the cylinder 54 and the patient's lungs is measured by a pressure transducer or transducer 102, which produces a computer input 104 proportional to the instantaneous pressure. A position transducer or transducer 106 produces a detector input 108 which is proportional to the instantaneous position of the piston 98.

The computer 100 includes an adjustable pressure-time waveform generator

110, which is programmed to provide an output 112 representing a waveform describing ideal time-dependent pressure build-up in the lungs of a normal patient for each inhalation cycle. The computer is programmed to produce, in dependence on signal 104 and other programmed information, which will be described in more detail below, an output signal 114 which affects appropriate piston drive means 116, preferably a translation engine, for controlling the position of the secondary piston 98.

5θ The elapsed time for each inhalation cycle is calculated internally in the computer 100 by a program logic 118 depending on a data signal 119 from the computer 46 representing the patient's breathing rate and inhalation / exhalation ratio. (For clarity, FIG.

that signal 119 is generated by speed / ratio data 120 in response to a signal 121 from computer 46. The signal 119 is in fact generated by the computer 46 depending on the speed / ratio data supplied to the computer.) The program 118 generates an output 122 representing the instant elapsed time, and this signal is applied to an internal logic program 124 in the computer together with the pressure signal 104 for effecting of an output 126 repre7306024-6 centering a waveform for the actual pressure build-up as a function of time. The actual pressure signal 126 is compared with the Ideal pressure-time waveform 112 at a summation point 128 to produce a pressure error signal 130. The pressure error signal 130 is applied to an internal program logic 131 for converting the pressure signal to a corresponding piston position error signal 132 representing the displacement of the piston 78 as is required to accommodate the pressure represented by the pressure error signal. The position error signal 132 partially controls the movement of the secondary piston 98 via the output 114.

Thus, if the patient's breathing is normal, the error signal will come

132 to be zero, and the pressure in the patient's lungs will be allowed to increase during the inhalation cycle without filling the accommodation space. In this case, the accommodation piston 98 will remain in a fixed position, as shown by dashed lines in Fig. 6, thereby blocking the gas flow into the accommodation space. Thus, the output 114 of the computer instructs the accommodation pistons actuating means 116 to maintain the secondary piston 98 in its position which blocks the accommodation space as long as the pressure build-up is normal. Thus, all gas boom is supplied by the primary piston to the patient, as long as the pressure build-up in the system remains normal during the inhalation cycle.

However, if the patient has high airway resistance or lung compliance problems or if the patient coughs or deliberately opposes gas being delivered to the lungs, the pressure in the system exceeds the normal, and consequently, at a given time, the pressure feedback signal represented by the signal 119 will be greater than the ideal pressure. is represented by signal 112. In this case, the pressure error signal 130 becomes greater than zero and instructs via the output 114 the piston driving means 116 to retract the piston 98 from the position shown by dashed lines in Fig. 6 so that the volume of space 96 increases, thereby increasing the total pressure in the patient's lungs and the primary piston system decreases. The size of the accommodation, i.e. the displacement of the piston 98 away from zero volume in the space, is proportional to the size of the unsuitable pressure build-up and therefore to the size of the pressure error signal 83. Fig. 6 shows the movement of the accommodation piston 98 under excessive pressure build-up as the piston strives to move. in the direction of arrows 133 to allow gas which cannot be accepted by the patient to fill the accommodation space.

The computer 100 is further programmed to affect the secondary piston

7306024-6 '>. out-Lil ·

98 so that it will be pushed back with sufficient force and the total predetermined volume of gas represented by signal 54 will be forced back into the patient at the end of the inhalation cycle. To achieve this result, the position of the secondary piston during inhalation is measured by the position sensor 106, which supplies to the computer 100 the signal 1θ8 proportional to the displacement of the piston from its space-blocking position. The computer is programmed to instruct translation engine 116 to push back with a force proportional to both the gas volume in the accommodation space and the time elapsed from the beginning of the inhalation cycle. Thus, the overpressure in the system is relatively small, the gas volume in the accommodation space is relatively small and is instructed | the accommodation piston to push back with a small force sufficient to push the gas in the space back into the patient's 45 lungs at the end of the inhalation cycle. This movement of the piston 98 is represented by the arrows 134 in Fig. 13.

⁴ Because the built-up overpressure in the system is relatively large, the gas volume in the accommodation space is also large, so the output 114 will instruct the actuator 116 to push ²⁰ return the secondary piston with great force to ensure that the gas in the space will have been delivered to the patient at the end of the cycle.

The force applied by the secondary piston is also dependent on the elapsed time during the inhalation cycle. This means that underneath it²5 early part of the bicycle accommodation piston is instructed to push back with relatively little force. However, as the end of the inhalation cycle approaches and less time remains to empty the space, the output 114 instructs the piston actuator 116 to push back harder to ensure that the preset gas volume will be delivered to the patient at the end of the cycle.

Thus, the pressure accommodation system is programmed to receive all gas which cannot initially be accepted by the patient due to abnormal conditions in the patient's lung system. Gas stored in the accommodation space is squeezed back into the patient's lungs during the remaining portion of the inhalation cycle under conditions that give the greatest possible chance of total preset gas volume. accepted before the end of the cycle. Thus, when excessive pressure builds up in the system, the gas is not released to the atmosphere but stored and returned under controlled conditions so selected as to allow the patient to accommodate the desired gas volume.

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Fig. 14 shows the accommodation piston 98 in its desired position at the end of the inhalation cycle. During the following exhalation cycle, the primary piston 32 is returned in the direction of the arrows 136 so that it is ready for the next inhalation cycle.

The above aspects of the invention are best understood by reference to the graphic presentations and waveforms shown in Figures 7-12. Fig. 7 shows a graphical representation of a signal 112 for ideal pressure build-up compared to a signal 126 for actual pressure build-up. An error signal 130 is built up during the initial stage of the inhalation up to a relatively high value, represented at 130a, to instruct the secondary piston 9θ to accommodate.

Later during the inhalation, when the allowable pressure has increased, the error signal 130 has a relatively small size, represented at 130b.

In this situation, the accommodation system has provided pressure accommodation, so that the actual pressure 1 system at the end of the inhalation cycle is substantially equal to the desired pressure, represented by the signal 112.

Fig. 8 is a graphical representation of an actual pressure build-up signal 126 when the ideal pressure accommodation situation described in Fig. 7 does not occur. In the state represented by Fig. 8, the pressure in the piston / patient system remains high, and a relatively large pressure error signal 130c during the early stage of the inhalation remains until the end of the inhalation cycle, as represented by the error at 130d.

As described above, the error signals 130c and 130d are arranged to instruct the translation engine 116 to move the accommodation piston 98 from left to right in Fig. 6 to increase the volume. However, this movement of the piston is allowed to occur late during the inhalation cycle, the undesirable situation arises in which gas remains in the space 96 and prevents the patient from getting the gas volume necessary to ensure proper air exchange. To avoid this undesirable situation, computer 100 is programmed to disable or cancel the pressure accommodation system during the latter part of the inhalation cycle to ensure that the preset gas volume, represented by signal 54, is delivered to the patient in connection with each breath. The secondary flask is programmed to return in an optimal manner for prevailing room volume conditions and elapsed time for the inhalation cycle to ensure that the patient receives the preset volume under conditions that are safe and comfortable to accommodate.

7306024-6, 16 ί The disconnection system is best understood by reference to Fig. 6 in combination with the graphic representations shown in Figs. 9-12. The position signal 108 and the time signal 122 are both applied to a program logic 138 in the computer 100, which logic produces an output signal.

- 140 representing the actual position of the secondary piston 98 at any given point in time during the inhalation cycle. The position signal '140 is applied to an internal program logic 142 which is arranged to provide a piston position signal 144 which constantly instructs the secondary piston to return to zero at the end of the inhalation cycle. Prior to 10, program 142 instructs the piston to return to zero in a substantially asymptotic manner, which depends on the magnitude of the position feedback signal 1θ8 and the time remaining (time signal 122) until the end of the inhalation. The position signal 144 and the pressure accommodation signal 132 are both fed to signal balancing B and discriminator means, preferably an alternating time sampling device 146,^! which alternately allows signal 144 and signal 132 to pass to motor 116 as signal 114, i.e., a composition of signals * 132 and 144.

The operation of the signal sampling device 146 is best understood by referring to Figs. 9-12. Fig. 9 shows two conditions in which the position signal 108 arises during the early part of the inhalation. 0m space volume is relatively small, occurs

- a small position signal 108a early during the inhalation. At a suitable real-time point 90a, determined by the timing signal 122, a position return instruction received from logic 142 instructs secondary piston 98 to gradually return to zero volume at the end of the inhalation cycle.

On the other hand, the space volume is relatively large, a large position signal 108b occurs during the early part of the inhalation cycle. At a suitable real-time point 90b, determined by the time signal 122, a position signal l44b instructs the piston 98 to return to zero volume at a greater rate than that obtained with the position signal l44a.

Fig. 10 shows the mode of operation of program logic 142 in a situation in which a similar secondary piston displacement occurs during a later part of the inhalation cycle. At appropriate real-time35 points, represented by 90c and 90d, program 142 generates a position instruction 144c rep. l44d for return of accommodationBj the piston to zero volume at greater speed than instructed 'by the position instruction lones 144a and l44b. The reason for this is that there is less time for the same volume to return to zero.

Figs. 11 and 12 illustrate how the signal sampling device 146

7306024-6 attenuates the pressure accommodation signal 152 with position signals 144 for resetting the volume of volume to zero at the end of the inhalation cycle. Fig. 11 shows how a small pressure accommodation signal is attenuated by periodic position return signals l44e (shown with dashed lines), so that the secondary piston 98 gradually returns to zero volume at the end of the inhalation. This volume of gas returned to the patient / piston system is well accepted without additional pressure build-up, as represented by signal 152e in solid lines. A typical pressure-time response of this kind is illustrated by curve 126 of FIG. 7 On the other hand, composite curve IL4f, IL2f of FIG. 11 illustrates a situation in which gas delivered by the main drive piston 52 is not well accepted by the patient, whereby the a high pressure error signal is generated at the end of the inhalation. In this case, the pressure accommodation instruction 152f instructs the piston 98 to accept larger and larger space volumes. As a result, the program generates 142 position instructions 1444f, which periodically attenuate signal 152f to progressively increase to ensure that the secondary piston 98 will return to zero at the end of the inhalation.

After all, even if the space volume return is optimized, there may be clinical situations in which the pressure build-up produced by the composite signal 114 will be too strong for a particular patient. This overpressure is released into the atmosphere through an adjustable safety valve 148 which is connected to the conduit 42. The pressure safety valve may be a simple weighted spring loaded device or in a more advanced embodiment an electronic or fluid controlled device coupled to the pressure input 112 to allow pressure release at the particular inhalation time.

Fig. 12 illustrates how computer program logic 102 is capable of correcting for sudden changes in pressure during the inhalation cycle. A curve for such an inhalation cycle comprises a portion 150 which falls early during the inhalation and which is similar to curve 152e, l44e of Fig. 11. In other words, the initial displacement of the piston 98 is relatively small, and gas stored in the space is favorably returned to the patient / piston system by the piston 9θ · At a time 90e, however, a high pressure problem is experienced, such as in connection with coughing. The response of the program 142 to the high pressure state is illustrated by a portion 151 of the curve of Fig. 12, which bet

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In response, curve 132f, l44f is similar to Fig. 11. Pressure accommodation represented by curve 132f is not sufficient due to the high pressure condition, but the piston displacement correction i is more powerful, as represented by curves l44f, to ensure that the secondary piston returns to the zero position at the end! of the inhalation cycle.

• Excessive accommodation situations can sometimes occur: which the accommodation system described in Figures 7-12 does not have

- ability to handle within the available inhalation time.

⁵ io This usually occurs during a cough, a series of coughs; or when the patient is struggling and exhaling as the respirator tries to force air into his lungs. Under these conditions, it could be dangerous for the respirator to force large volumes of air into the patient's lungs near the end of the inhalation cycle, as there may be insufficient time to accomplish this task without damaging the patient's lungs.

Accordingly, in exaggerated accommodation situations, the inhalation time of the particular cycle is extended by modifying the system of Fig. 6 to include an inhalation extension computer 152 shown in Fig. 6a. The computer comprises an extension initiation logic program 153a, which receives a position signal 108 from the position sensor 106 to instruct the program that the accommodation piston has moved from its ideal zero volume position. The program 153a also receives the output 54 from the waveform generator

46 indicating the desired piston position (or volume) for the particular time interval during the inhalation cycle. Program 153a evaluates the input information obtained, and when a piston position deviation <greater than a predetermined value is exceeded during the particular interval of the inhalation cycle, an extension time logic program 153b is extended for the inhalation time. A control 153c controls the value of the position deviation at which the extension; triggered.

A position deviation signal 153e is generated by program 153a for activating the extension time program 153b, the magnitude of signal 153e being proportional to the piston's deviation from the predetermined acceptable deviation. Program logic 153b controls the elongation time in accordance with the magnitude of piston position deviation detected by program 153a. As the piston position deviation from the ideal represented by signal 153e increases, the program extends

153b extension time. Program 153b produces an output 154,

7306024-6 which seizes the inhalation time signal 54 from the waveform generator 46 to extend the inhalation time of the particular cycle.

The diagram shown in Fig. 6b illustrates the function of the inhalation extension system. The piston displacement initially follows a curve 108a up to the point tp when a strong first coughing triggers the system to extend the inhalation time from the original time t_Q at the time the piston displacement nip follows curve 108b as the piston continues its movement and again forces air into the patient's lungs. At time t₂triggers a second powerful hosting system to extend the inhalation cycle from time to time tg. The piston displacement then follows curve 108c as the piston continues its movement and forces air into the patient's lungs until the time tg is reached, at which time the exhalation cycle begins.

Fig. 15 shows an alt. electric accommodation system, which can be added to the primary piston drive system of Fig. 1 without requiring any accommodation space. As described above, computer output 54 represents a desired volume-time waveform which can be adjusted according to the particular physiological state of each patient's lung system. The signal 54 is supplied together with the position signal 76 from the converter 74 to a special purpose analogue computer 155, in which the signals are compared at a summing point 156 to provide a position error signal 158. The analog computer 155 performs essentially the same function as the computer 100, i.e. it provides accommodation logic depending on pressure accommodation instructions and position accommodation instructions. The pressure accommodation for the computer 155 is substantially the same as that previously described for the computer 100. This means that a pressure transducer 160 generates an output 162 representing the instantaneous pressure inside the main drive piston 52. The signal 162 is fed to a summing point 164 in the computer 155, where it is compared with a desired pressure-time waveform 166 generated by a waveform generator 168. (Preferably, the pressure signal 162 is converted to a pressure-time waveform in a manner identical to that previously described for signal 126. However, these steps have been shortened in the system shown in FIG. ·) The pressure signals 166 and 162 are compared to produce a pressure error signal 170 which is applied to an internal program logic 172 for converting the pressure error signal to a corresponding piston position signal 174 representing the displacement of the piston 52 required to correct the pressure error.

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The pressure accommodation signal 174 is compared to the volume offset error signal 158 at a summing point 176 to provide a composite piston position error signal 178 Comparable to the position error signal 114 30m described above in connection with the system shown in Fig. 6. The position error signal 178 is balanced either in its pressure component or in its volume offset component in a manner similar to, but not necessarily identical to, the time balance obtained by means of sampling device 146 described above. (The sampling device for signals 158 and 174 is not shown in FIG.

for shortening purposes.) The composite piston displacement error signal 178 is fed to a summation point 108, where it is compared to the basic piston position error signal 80 to provide an accommodation error signal 182 for driving the piston 52.

Thus, because excessive pressure build-up does not occur in the piston 52, the waveform represented by the signal 182 is substantially identical to the waveform of the main position error signal 80, so the piston will operate as described in connection with the system of Fig. 1. However, if the piston / patient is too high pressure build-up is detected, the position signal 178 instructs the piston driver 56 to reduce the relative movement of the piston 52 forward, thereby providing time for pressure accommodation. Should the pressure build-up become relatively strong, the same logic will either stop or, if necessary, retard the movement of the piston 52 forward to provide pressure accommodation. The desired volume-time waveform represented by the position signal 54 is continuously compared to the actual piston position signal 76 to instruct the piston driving means 56 to force substantially all of the necessary gas volume into the patient at the end of the inhalation cycle. Thus, accommodation is provided by pressure and volume displacement in the pooled piston / buffer space system of Figure 15 in a manner similar to that provided by the separate accommodation buffer space described in conjunction with the system of Figure 6.

· Fig. 16 shows an alt. The pressure inside the space of the piston 52 is measured by the pressure transducer 160, which in turn produces the pressure output 162 representing the instantaneous pressure in the piston. A waveform generator 184 corresponding to the waveform generator 168 provides an output 186 representing a desired time-dependent pressure build-up in the pressure / patient system. A comparator 188 compares signals 162 and 186. About the actual pressure, represented

7306024-6 of the signal 162, is equal to or greater than the desired pressure, represented by the signal 186, an electric accommodation signal 190 is generated by the comparator and fed to the drive amplifier 86 to grip the position information from the differential amplifier 82. This overall limits the force applied to the plunger by the drive means 56, so that the plunger temporarily lags or returns from the desired volume waveform represented by the signal 54. As the desired maximum pressure increases later during the cycle, the actual volume reaches the desired volume.

If the actual pressure is instead less than the desired pressure, the accommodation signal 190 grips the position signal 82 and instructs the piston force to temporarily increase to allow the volume delivered to the patient to reach the desired volume.

Thus, as the maximum pressure builds up during the inhalation cycle, the entire gas volume preset by the signal 54 is forced into the patient's lungs before the end of the cycle. The accommodation signal prevents excessive pressure being generated, which increases the possibility that the patient will be able to accept the entire preset gas volume.

Fig. 16A shows an alt. arrangement of the system of FIG.

16, in which the actual pressure signal 162 is fed directly to the waveform generator and the computer. In this embodiment of the accommodation system, the generator of the desired pressure-time waveform and the comparator of Fig. 16 are internally programmed in the computer 46 to provide a signal equivalent to the signal 190 of Fig. 16 for attenuating the desired waveform and generating a damped output signal. 54a, which is fed to the differential amplifier 82.

Fig. 16b shows a method of modifying the system shown in Fig. 16 to extend the inhalation time for excessive accommodation problems. The system shown in Fig. 16B and its mode of operation are substantially identical to the auxiliary system shown in Fig. 6a.

Figures 17 and 18 show an alt. accommodation system comprising a mechanical or fluid controlled accommodation space 192 of variable size. The accommodation or buffer space is preferably constituted by a bellows 194 or other suitable means which expands and contractes in response to internal gas pressure.

A spring or series of springs 196 applies a rigid and suitably variable and adjustable biasing force on the outside of the

7306024-6 the expandable accommodation space, which force strives to keep the space compressed when the pressure build-up inside the system is below the predetermined value. If the pressure build-up during the early part of the inhalation cycle becomes too high, gas that is not accepted by the patient is forced into the accommodation space and causes the spring 196 to be compressed (as shown in Fig. 17)> which allows the space to expand and receive the excess gas volume. . As shown in Figure 18, the biasing force applied by the spring 196 attempts to compress the gas stored in the compartment into the patient during the latter part of the inhalation cycle. To ensure that the space is completely emptied at the end of the inhalation, a mechanical device (not shown) is activated with sufficient force to automatically overcome any patient resistance during the latter part of the inhalation phase.

If necessary, the spring force 196 is supplemented to ensure that the space is emptied. This can be done by means of a device (not shown) comprising rack and pinion and which is mechanically synchronized with the inhalation, but other devices could be utilized within the scope of the invention.

Fig. 19 shows a preferred embodiment of a device 198 for providing an artificial sigh. As is well known, normal air exchange requires inhalation of an extra gas volume, ie, a sigh, with regular recurring time intervals to supplement the normal gas volume going to and from the lungs, which prevents the lungs from increasingly collapsing. The device 198 simulates a periodic sigh by generating a function that exceeds the normal gas volume delivered by the primary piston 32. The device generates a voltage signal 200 representing a gas volume of gas to be delivered to the patient at specific time intervals controlled by a timing device 202. At predetermined time intervals, the timing device 202 generates a timing signal 203 which opens a gate 204 so that the voltage 200 can pass to the waveform generator and the computer 46. Under normal conditions, the computer 46 generates the piston drive signal 54 representing the normal breathing volume to be delivered to the patient. However, at the specific times when the suction volume signal 200 is generated, the computer 46 generates a signal 205 which activates signal gate means 206, preferably an exel type gate, to cut off signal 54 and instead introduce a suction volume offset signal 208 to apply additional force to the piston and thereafter. an extra sack of gas to the patient. '

The volume and time reference of the circuit for providing an artificial sigh can be varied relative to the time and volume of the normal waveform represented by the signal 54. For example, a larger and slower breath can be generated for simulation of a periodic sigh. Such a breath is illustrated by the volume-time curve shown in FIG. 20, in which a series of normal volume time signals 54 is followed by a suction volume time signal 208 which has both greater volume and longer duration but has the same general form as the normal volume time signal.

Fig. 21 shows a more advanced embodiment of the device for providing an artificial suction according to Fig. 19. The system shown in Fig. 21 includes a separate suction computer and waveform generator 210. A timing device 212, which determines the number of suction cycles, is arranged to alternately activating either computer 46 or computer 210 to transmit either waveform signal 54 or sigh waveform signal 214 to signal gate means 216. As previously described in connection with the system of Fig. 19, said signal gate means is a gate of the exceller type which allows either signal 54 or signal 214 to pass to the piston drive means.

The timing device 212 forms part of an artificial suction control panel 218, which also includes the following control means: a sigh volume control means 220 for adjusting the volume of the normal breath and the added volume of the sigh;

a control means 222 for adjusting the number of sucks to be delivered during each suction cycle determined by the timing device 212 ·, a control means 224 which allows setting the length of the inhalation suction time, which may, for example, be two or three times the length of the breathing volume inhalation time, a manually adjustable control means 226 for changing the waveform of the suction volume time waveform, which is of importance, since the volume-time waveform for the suction volume may have different technical requirements compared to the volume-time waveform for the normal breath; an automatic control means 228 for adjusting the suction volume waveform, which is used as an alternative to the manual setting control means 226 and a control means 230 for providing a signal 232, which sets the pressure safety limits for the safety valve 148. The safety limits provided by the safety valve 148 are usually different from and higher than the emission limits required for the normal breath. The pressure limit setting may be a fixed pressure point operating through the safety valve 148 and controlled by mechanical, fluid or electrical means. Alt. For example, the pressure release may be variable, following a time-related pressure build-up during inhalation, as represented by curve 60 in FIG. 2 for example, but where the safety valve is set to open at a variable pressure level that is higher than the normal pressure generated by normal breath.

Fig. 22 shows a typical volume-time waveform represented by the signal supplied to the piston drive means by the signal gate means 216.

Normal breath 54 is interrupted by a sighing day 214a and a different pair of sighing days 214b. The suction days 2,4a and 2,4b differ from each other in terms of volume, waveform, inhalation length and number of breaths per cycle according to the settings of the parameters on the control panel 218.