Title:
Process and device for controlling the pressure course of a respirator
United States Patent 3923055


Abstract:
A process and apparatus are disclosed for controlling the pressure course of a respirator connected to a patient, in which the pressure of the respiration gas is momentarily decreased, under the control of a pulse-synchronized signal waveform derived from physiological data taken from the patient, for example, the ECG, during the propagation time of each pulse wave in the alveolar flow path of the patient. Following each decrease there is immediately effected a substantial re-establishment of the pressure of the respiration gas. Disclosed apparatus suitable for performing this operation comprises a timer circuit responsive to the pulse-synchronized signals generated from the patient's physiological data and a valve arrangement which is coupled into the patient respirator line and controlled by the output pulse waveform of the timer circuit.



Inventors:
HAMMACHER KONRAD
Application Number:
05/524172
Publication Date:
12/02/1975
Filing Date:
11/15/1974
Assignee:
HOFFMANN-LA ROCHE INC.
Primary Class:
International Classes:
A61M16/00; (IPC1-7): A61M16/00
Field of Search:
128/145
View Patent Images:
US Patent References:



Other References:

Hilberman et al., On-Line Assessment of Cardiac and Pulmonary Pathophysiology in the acutely ill. .
Journal of the Association for the Advancement of Medical Instrumentation, Vol. 6 No. 1 Jan., Feb. 1972, p. 65-69..
Primary Examiner:
Michell, Robert W.
Assistant Examiner:
Recla, Henry J.
Attorney, Agent or Firm:
Welt, Samuel Leon Bernard Hopkins Mark L. S. L.
Claims:
What is claimed is

1. A process for controlling the pressure course of a respirator comprising momentarily decreasing the pressure of the respiration gas under the control of a pulse-synchronized signal derived from a measurement of impulses produced by the heart of the patient associated with the respirator in each case during the propagation time of the pulse wave in the pulmonary alveolar blood vessel flow paths of the patient and immediately thereafter causing substantially a re-establishment of the pressure of the respiration gas.

2. A process according to claim 1 wherein the pulse-synchronized signal is derived from the patient's ECG.

3. A process according to claim 1 wherein the pulse-synchronized signal is generated from a patient-derived blood-pressure signal.

4. A process according to claim 1 further comprising delaying the pulse-synchronized signals and reforming same into impulses corresponding to the duration of the passage of the pulse wave through the pulmonary alveolar blood vessel flow paths.

5. A process according to claim 1 further comprising producing a control signal from the pulse-synchronized signal and superimposing same on the pressure course of a respirator via a valve means connected into the respiration line.

6. A process according to claim 5 further comprising coupling the patient line to a reduced pressure via a valve means for the duration of the control impulse.

7. A process according to claim 1 further comprising generating a control signal from the pulse-synchronized signal and using same for controlling the time cycle of a respirator.

8. A process according to claim 1 further comprising providing additional pneumatic means for shortening the pressure increase following the reduction in pressure.

9. Apparatus for controlling the pressure course of a respirator, in which the pressure of the respiration gas is momentarily decreased, under the control of a pulse synchronized signal derived from a measurement of impulses produced by the heart taken from a patient associated with the respirator, during the propagation time of the pulse wave in the pulmonary alveolar blood vessel flow paths of the patient and is immediately substantially re-established thereafter, comprising first means for deriving the pulse synchronized signal from said measurement taken from a patient, second means contained in the line from a respiration gas source to the patient for controllably reducing the pressure momentarily in the patient line, and timer means responsive to the pulse synchronized signals generated by said first means for controlling said second means, said timer means including means for delaying said second means for a time period which elapses between the measuring incident and the arrival of the pulse wave in the alveolar blood vessels.

10. A device according to claim 9 wherein said second means is a valve arrangement which in one position connects the respiration gas source with the patient and in its other position connects the patient with the atmosphere.

11. A device according to claim 10 wherein said valve arrangement is connected with a reduced pressure chamber in said other switching position.

12. A device according to claim 10 wherein said valve arrangement connects the patient line with a suction pump in said second switching position.

13. A device according to claim 9 wherein said second means is a pump arrangement.

14. A device according to claim 9 wherein said second means is comprised of the control valve of a valve-controlled respirator.

Description:
BACKGROUND OF THE INVENTION

This invention concerns a process and a device for controlling the pressure course of a respirator.

The functioning of most hitherto available respirators is based on periodically delivering a respiration gas to the lungs of the patient with a frequency lying in the magnitude of the natural respiration frequency. There are essentially two types of control being used: Regarding the so-called pressure-controlled systems, a specified maximum pressure is built up in the lungs of the patient in every respiration cycle and subsequently released. In the so-called volume-controlled systems, a volumetrically measured quantity of respiration gas is delivered to the patient in every respiration cycle. In addition, there are also systems known in which during every respiration cycle or with the consideration of certain criteria, the system switches from one type of control to the other.

Common with the pressure-controlled and volume-controlled systems is the fact that during a considerable part of the respiration cycle, a relatively high pressure continuously exists in the lungs of the patient. This gives rise to the disadvantage that during the phase of high pressure, the propagation of the pulse wave in the pulmonary alveolar blood vessels is impaired. This disadvantage is especially serious in patients with weak circulation, such as, for example, in the new or prematurely born or in the presence of circular diseases.

SUMMARY OF THE INVENTION

The present invention is based on the task of eliminating this disadvantage and producing a control for a respirator with which an improved artifical respiration is made possible, especially in the case of patients with weak circulation.

This is accomplished in accordance with the invention by a control process in which the pressure of the respiration gas is momentrarily decreased with the aid of a pulse-synchronized signal in each case during the propagation time of the pulse wave in the alveolar flow path, and then immediately re-increased.

There is suitable for carrying out this process an apparatus comprising a timer responsive to a pulse-synchronized signal and a valve, the latter of which is connected to the patient line and controlled by an output impulse of the timer, for reducing the pressure in the patient line.

The pulse-synchronized signal which is brought into use for the pressure control can be produced in various ways. One possibility consists, for example, in using the so-called ECG-trigger impulse of an ECG apparatus which gives the R-peak of the electrocardiogram. Other possibilities consist in taking the control signal from a plethysmograph or from devices for rheographically determining the heartbeat volume or the detection of blood flow by means of an ultrasonic process. In general, there is suitable for the production of the control signal, any measurement of action currents or potentials of the heart, as well as sanguinous and non-sanguinous measurements of pressure, flow, flow velocity, acceleration, etc. of the blood by means of a pressure transducer, as well as such in catheters, optical sensors, ultrasonic apparatus, acoustic transducers and the like. The thus obtained impulses have to be delayed by the time which elapses between the measuring instant and the arrival of the pulse wave in the alveoles. This time span depends, for example, on the measuring point when using a signal derived from a plethysmograph or a signal produced by a rheographical measurement and in other respects is influenced by physiological factors, so that it can be of different duration from patient to patient.

After suitable forming, the delayed impulse is delivered to the respiration system where it effects the reduction of the respiration pressure. For this purpose, there can also be provided in the pneumatic system of the respirator, various options such as valves, pumps, etc., some of which are described in the following.

After the passage of the pulse wave through the alveolar flow paths, the respiration pressure is re-increased, an additional acceleration impulse being imparted to the blood flowing back to the left heart with appropriate construction of the pressure curve and the action of an auxiliary lung-circulation pump being accordingly produced.

Embodiments of the invention are described in the following in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic representation of an embodiment of the device in accordance with the invention in interaction with the patient line of a respirator;

FIGS. 1A and 1B are enlarged schematic representations of a valve element in the arrangement of FIG. 1;

FIG. 1C is a schematic representation of the timing circuit portion of the arrangement of FIG. 1;

FIGS. 2a-2e are graphical representations which show the functioning at various points of the device and the influence thereof on the respiration pressure;

FIGS. 3a-3d are graphical representations for another operating method.

FIG. 4 is a schematic representation of another embodiment of the invention; and

FIG. 5 is a schematic representation of a further embodiment of the invention.

As shown in FIG. 1, a patient 1 is respired with a respirator 2 which is connected with the patient via a line 3. The patient 1 can be a new or prematurely born child or also an adult. Depending on the particular patient, a different respirator 2 is employed, the control of the respirator, however, generally being insignificant. The device in accordance with the invention is equally well suited to volume-controlled, pressure-controlled or hybrid systems.

In the patient line 3 is inserted a valve 4 which depending on the disposition of the patient is connected with the respirator 2 or with the open air. The two positions of the valve are shown in enlarged scale and in a schematic form with I and II in FIGS. 1A and 1B. By the valve 4 in the present embodiment there is provided an electromagnetic valve in which a switching is effected by an electronic impulse. The electronic impulse required for switching proceeds to the valve 4 via the electric line 5.

The switching signal for the valve is produced in the present embodiment from the ECG of the patient. For this purpose, the patient carries the usual ECG electrodes 6, which are connected via lines 7 with the inputs of an electrocardiograph 8. In the electrocardiograph, the so-called ECG-trigger impulse is obtained from the R-peak of the ECG. This ECG-trigger is usually available in the patient monitoring anyhow, so that the ECG device according to the invention is not further concerned with the derivation of same.

The ECG-trigger signal is delivered to a timer circuit 9, a preferred example of which is illustrated in greater detail in FIG. 1c. The timer circuit 9 serves for producing a rectangular signal with a certain delay with respect to the ECG-trigger signal. For this purpose, the timer circuit contains, for example, two monostable sweep circuits, normally connected in series, the first of which produces an impulse whose length determines the time delay of the output impulse of the timer circuit with respect to the ECG-trigger signal and controls the second sweep circuit with its declining flank. Such timer circuits are available in the trade as integrated components. There exists, for example, the component XR-2556 of the Firm Exar-Integrated Systems Inc., which contains two timer stages, with which the functioning of the timer contained in the present embodiment can be realized by suitable conventional switching.

Since not only the spacing of the control impulse for the magnetic valve from the ECG-carrier impulse, but also the duration of the control impulse is to be adjustable, two potentiometers are contained in the timer circuit 9, with which the impulse lengths of the monostable sweep circuits can be varied. The output signal of the timer 9 is amplified in an amplifier 10 until it is suitable for switching the electromagnetic valve 4.

The functioning of the arrangement shown in FIG. 1 is as follows.

The patient 1 is respired by the respirator 2 with a permanently set frequency, i.e. at constant intervals a specific amount of respiration gas is pumped into the lungs of the patient and in each case subsequently released or evacuated. The ECG of the patient is simultaneously measured, that is with a measuring apparatus which produces an impulse indicating the R-peak. With this so-called ECG-trigger impulse, the control impulse for the valve 4 is produced in the timer 9. For the duration of this control impulse, the valve switches from the I position shown in FIG. 1A into the II position shown in FIG. 1B, in which the respiration gas line from the respirator to the patient is blocked and a connection between the patient and the open air exists. Since the pressure in the lungs of the patient lies above the atmospheric pressure for practically an entire respiration cycle, at the moment in which the valve produces a connection between the patient's lungs and the open air, a sudden pressure decrease occurs in the lungs.

At the end of the control signal, the valve again switches to position I, the patient is accordingly reconnected to the respirator, by which means the pressure in his lungs again increases to the respiration pressure.

It is readily seen from the foregoing, that the time spacing between the ECG-trigger signal and the beginning of the control impulse for the valve 4 should correspond essentially to the time-span between the occurrence of a QRS-complex (or more precisely the R-peak) and the arrival of the respective or, if possible, a following pulse wave in the pulmonary alveolar vessel system, in order to achieve optimal relief of the alveolar circulation. On the other hand, the duration of the control impulse has to correspond to the time which the pulse wave requires to pass through the alveolar vessel system in order to subsequently be able to very rapidly re-increase the pressure and accordingly achieve the desired effect of a back-flow acceleration impulse.

The functioning of the device in accordance with the invention is seen particularly well in its time cycle by way of the impulse diagram shown in FIGS. 2a-2e. The curve FIG. 2e shows the electrocardiogram. From the R-peaks 100 of same there is derived the ECG-trigger impulse (e.g. pulse 40) which is shown in the curve of FIG. 2a. The ECG-trigger impulse waveform is introduced into the timer circuit 9, in which the impulses 11 shown in the curve of FIG. 2b are produced by the first monostable sweep circuit and the impulses 12 shown in the curve c are produced by the second sweep circuit, the impulses 12 representing the control impulses for the electromagnetic valve. Thus, the curve of FIG. 2c shows the output pulse waveform of the timer 9. For the duration of an impulse 12, the valve 4 is switched into position II, in which the connection from the respirator 2 to the patient is blocked and the air under pressure can escape from the lungs of the patient. At the end of the impulse 12, the valve 4 is again switched back into position I and the connection between the respirator 2 and the lungs of the patient is again provided.

The curve of FIG. 2d shows the course of the respiration pressure. The dotted line 13 gives the respiration pressure as it is produced from the respirator without the device in accordance with the invention. At the point 14, the valve switches into position II by which means, after a short delay dependent on the compliance of the lungs, the pressure decreases. The point 15 corresponds to the end of an impulse 12 and accordingly to the switching of the valve 4 back into position I. Thus, at the point 15 the curve changes into a new pressure increase with a short delay. At the point 16, the valve is again switched, by which means the pressure again falls. At the point 17, a switching back of the valve into position I is effected, which results in a new pressure increase. The same process repeats itself several times during each respiration cycle, the number of switchings per respiration cycle depending on the ratio of respiration frequency to heart frequency.

In order to achieve a more rapid pressure relief of the patient's lungs with arrival of the pulse wave, the patient can be connected to a reduced pressure instead of the atmospheric pressure for the duration of the impulse 12. This is shown in dotted lines in FIG. 1 by the connection of the valve 4 to a negative pressure chamber 18. The chamber 18 is kept constantly at reduced pressure by a pump 19. Another possibility consists in connecting the valve 4 directly to the pump 19.

FIGS. 3a-3d are graphical illustrations or impulse diagrams which show the application of the process in accordance with the invention to a respiration method which is at present employed repeatedly for the respiration of the new-born. In this method, the lungs of the patient are kept continuously at a positive final expiratory pressure above which the patient breathes spontaneously. By pulse-synchronized modulation of the pressure, there can also be produced in this method a substantially improved perfusion as well as, above all, the effect of a back-flow auxiliary pump. In the diagrams shown, the electrical impulse plots of FIG. 3a and FIGS. 3b-3d correspond respectively to those of FIG. 2a and FIGS. 2c-2e.

In FIG. 4, an alternative arrangement is shown wherein in place of the valve 4 a pump 20 is provided which for the duration of the impulse 12 extracts respiration gas from the line from the respirator 2 to the patient 1 and redelivers it at the end of the impulse 12. By suitable design of the pump, a rapid pressure decrease and, in particular, also a rapid pressure increase at the end of the impulse 12 can be obtained. This is particularly favorable for the additional action of the device in accordance with the invention as a back-flow auxiliary pump.

The hitherto described embodiments of the device in accordance with the invention serve as supplementary apparatus for existing respirators. The pressure relief functioning of the device in accordance with the invention is superimposed on the pressure curves of the respirators. As a further development of the invention, the entire control of a respirator can be carried out by pulse synchronization. A corresponding embodiment is shown in FIG. 4. In this case, the respiration frequency is not specified independently, but it is a multiple of the heart frequency. Likewise, the inspiration and expiration phases are multiples of the heart cycle.

Such a respirator (e.g. FIG. 5) consists of a respiration gas source 21 in which respiration gas is available at an elevated pressure, a regulation valve 22 for regulating the flow of the respiration gas and for switching between inspiration and expiration and a pneumatic switch 23 which leads off the expired gas from the patient line. Such a respirator is described, for example in the U.S. Pat. application Ser. No. 341,432, filed Mar. 15, 1973. The patient line 3 leads through a measuring head 26 for measuring the flow and pressure of the respiration gas directly in the tracheal tube which serves for the intubation of the patient. Electric signals are produced in the measuring head 26, which reproduce the flow and/or pressure course of the respiration gas. An electric lead 27 serves for transmitting the obtained signals to an electronic regulation device 28. There are also introduced into the regulation device 28 via the lines 29 and 30 standard signals for pressure and/or flow of the respiration gas and via the line 31 the delayed time control signal (produced from the ECG-trigger) for the synchronous control of the respiration cycles with the ECG. With the aid of these input parameters, a respiration cycle similar to the pressure course shown in FIGS. 2a-2e is produced, but with the respiration cycles now running synchronously with multiples of the heart frequency. The pressure in the patient's lungs is build up in a series of stages with a specified pressure course, the pressure and/or flow being regulated according to the input parameters by the feedback via the measuring head 26.

Although a respirator such as the previously described respirator regulated entirely with the aid of a valve is especially well suited for a combination with the respiration method in accordance with the invention, respirators based on other principles can also be adapted to operation with the pulse-synchronized control. With a respirator operating with a pump, the pressure characteristic of the pump must therefore by synchronized with the heartbeat. Depending on the pump, this can be carried out in a relatively simple manner either mechanically or also electronically.

The already mentioned delay between the measured parameters of the blood circulation, inclusive of ECG, and the control impulse for the pressure reduction can also be automatically regulated independently of the pulse frequency. Since the delay times in bradycardia and in tachycardia have to be of a different magnitude, a non-linear regulation characteristic is advantageously chosen, for example, the function t = (l/f), t being the delay time and f being the heart frequency.

As already mentioned, rheographical processes for measuring the perfusion are also suitable for producing the control signal. A device for such a process could be arranged to be directly associated with the tracheal tube, which has the advantage that the signal is obtained in the immediate vicinity of the alveolar vessel system and errors caused by variations of the propagation time of the pulse wave can be excluded. For the purpose of this measurement, the tracheal tube is provided, for example, with electrodes at both its ends, which are connected to a suitable measuring circuit. The second electrode could alternatively also be applied externally to the thorax.