The following four possible asynchrony types are time asynchrony types, i.e. a ventilation stroke is triggered depending on an inspiratory effort, but too early or too late:

- A ventilation stroke triggers an inspiratory effort (reverse triggering).
- A ventilation stroke is triggered too late (late triggering).
- A ventilation stroke is ended too late (late cycling off).
- A ventilation stroke is ended too early (premature cycling off).

The remaining four possible asynchrony types are event asynchrony types, i.e. a ventilation stroke is falsely triggered (no inspiratory effort) or falsely not triggered (inspiratory effort not detected):

- A ventilation stroke is triggered without an inspiratory effort (auto triggering).
- An inspiratory effort does not trigger a ventilation stroke (missed effort).
- A first inspiratory effort is completed during one breath and a second inspiratory effort is started during the same breath (missed expiration).
- A first breath is completed during an inspiratory effort and a second breath is started during the same inspiratory effort (double triggering).

Preferably, at least one presentation is generated and output in a form perceptible by a human, for example visually on a display unit. The monitoring unit automatically generates the or each such presentation. Preferably, the presentation is continuously updated as the ventilator performs a sequence of ventilation strokes. The or at least one presentation refers, for example, to the entire history of artificial ventilation up to now, or to the history since the ventilator was last calibrated or changed, or since a parameter of the artificial ventilation was changed, or alternatively to a rolling period of time prior to the current time point. The or each generated presentation shows at a glance how often and/or how long at least two of the predetermined possible asynchrony types have actually occurred in each case. Preferably, the presentation is additionally provided with a textual description of each of the possible asynchrony types for which a measure is output.

This presentation allows a user to quickly grasp, virtually at a glance, how well the ventilation strokes are synchronized with the patient's inspiratory efforts. This effect is achieved in many cases even if the display surface of the display unit is relatively small and/or not optimally illuminated or is positioned angularly relative to a user. The presentation makes it easier for a user to assign a target setpoint to a parameter of the artificial ventilation wherein the target setpoint is more suitable for this patient than the currently used setpoint, if the synchronization is not sufficient.

In one embodiment, the monitoring unit generates both a measure for the respective frequency and a measure for the respective duration for at least two asynchrony types, preferably for each predetermined asynchrony type. Preferably, in the embodiment just described, both measures for the two asynchrony types are presented, for a total of at least four measures. In many cases, this presentation makes it even easier for a user to assess how well the ventilation strokes are synchronized with the patient's inspiratory efforts. In particular, based on the illustration showing the asynchrony types and the two measures per asynchrony type, a user can select between different possible remedies to obtain indications on how to improve synchronization or can improve the synchronization. In particular, a user may weight in the situation that one asynchrony type can be reduced by assigning a larger setpoint to a parameter and another asynchrony type by assigning a smaller setpoint to that parameter.

The following embodiment leads in many cases to a particularly clear presentation, even if the display unit on which the presentation is output is relatively small and/or poorly illuminated or oriented angularly to a user. According to this embodiment, for each presented asynchrony type two respective measures are determined, namely one for the frequency and one for the duration. The presentation is generated using two axes. These two axes are perpendicular or oblique to each other and are, for example, an x-axis and a y-axis. On one axis the determined measure for the frequency of an asynchrony type is plotted, for example the absolute number or the relative number in relation to the number of ventilation strokes. On the other axis, the determined measure for the duration of the asynchrony type is plotted, for example the absolute duration or the relative duration related to the total duration of artificial ventilation, in particular since the last setting or adjustment of the ventilator. In the plot, a two-dimensional area is shown for each asynchrony type. If the two axes are perpendicular to each other, this area has the shape of a rectangle. If they are at an angle to each other, this area has the shape of a trapezoid. The two dimensions of this area depend on the measure for frequency and the measure for duration, respectively. Preferably, the larger a dimension of the area is, the larger that dimension is.

This presentation shows a user even more intuitively which asynchrony types are currently relevant. Both a frequently occurring asynchrony type and a long-lasting asynchrony type result in a large area, and thanks to the embodiment just described a user can quickly grasp this.

The various forms of presentation just described thus lead to particularly ergonomic configurations for displaying information about the state and operation of the ventilator in a form that can be perceived by a human being.

Particularly preferably, two presentations are generated and continuously updated, and the display unit selectively displays one or the other presentation. For example, a user may switch between one presentation and the other presentation. One presentation shows how long and/or how often the four possible time asynchrony types occurred. The other presentation shows how long and/or how often the four possible event asynchrony types occurred. Preferably, each presentation comprises four quadrants, each quadrant representing one asynchrony type. In each quadrant an area is shown. At least one dimension of this area depends on the determined measures for this asynchrony type. It is also possible to output both presentations simultaneously. In this way, a user is quickly informed about the current state of the ventilator.

Furthermore, the invention relates to a computer program. This computer program is executable on a signal processing monitoring unit. This signal processing monitoring unit comprises a processor and a data memory. Preferably, the computer program can at least temporarily be stored in the data memory. The computer program is provided as a non-transitory computer-readable medium that is physical, transferable, and reproducible. The processor is adapted to execute the computer program.

A data connection with a ventilator can be or is established permanently or at least temporarily. This ventilator is able to perform supportive artificial ventilation for a patient, whereby the patient performs his/her own inspiratory efforts. The embodiment of such a ventilator has been described above. The data link allows data and/or signals to be transmitted from the ventilator to the monitoring unit, and optionally messages to be transmitted from the monitoring unit to the ventilator. In one embodiment, the monitoring unit is able to assign a setpoint to a parameter of the ventilator, and the ventilator uses this parameter setpoint to perform the supportive artificial ventilation. In one embodiment, the monitoring unit is adapted to control a display unit of the ventilator and to cause a presentation described above to be output on said display unit.

When a data link is established between the ventilator and the monitoring unit, preferably the processor of the monitoring unit executes the computer program, the monitoring unit causes a monitoring procedure according to the invention to be performed.

The invention further relates to a process of supportive artificial ventilation of a patient by a ventilator, wherein the ventilator performs a sequence of ventilation strokes with the aim that the ventilation strokes in the supportive artificial ventilation are ideally synchronized with the patient's own inspiratory efforts. A signal processing monitoring unit monitors how well the ventilation strokes are synchronized with the patient's own inspiratory efforts, and determines, for each predefined possible asynchrony type, a measure for how often and/or how long that asynchrony type actually occurred. This monitoring unit is configured according to the invention. Advantageous embodiments of the monitoring process according to the invention are also advantageous embodiments of the ventilation process.

The invention further relates to a ventilator arrangement. The ventilator arrangement comprises a ventilator, a sensor arrangement comprising at least one respiratory sensor and a monitoring unit according to the invention. The sensor arrangement (the respiratory sensor or each respiratory sensor) is capable of measuring an indicator (one or more indicators) that correlates with the patient's own inspiratory efforts. The ventilator is capable of providing supportive artificial ventilation to a patient and is configured as described above.

In the following, the invention is described with reference to example of embodiments. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic view showing an example with an artificially ventilated patient, a ventilator, and several sensors;

FIG. 2a is a view of an example of an electrical sum signal obtained by measurements;

FIG. 2b is a view of an example of a pneumatic respiratory signal obtained by measurements;

FIG. 3 is a schematic view showing an exemplary course for a sequence of breaths of the patient and a sequence of ventilation strokes of the ventilator;

FIG. 4 is a schematic view showing a time course of four different situations during supportive ventilation;

FIG. 5 is an exemplary presentation of the frequency of four asynchrony sequences, which are time asynchronies; and

FIG. 6 is an exemplary presentation of the frequency of four asynchrony sequences, which are event asynchronies.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, in an embodiment, the invention is used to artificially ventilate a patient and thereby support the patient's own respiratory activity. The patient's own respiratory activity can be brought about by the patient's spontaneous breathing and/or by external stimulation of the patient's respiratory muscles.

A fluid connection is established between the patient's airway and a ventilator. Through this fluid connection, the ventilator supplies the patient with breathing air or another gas mixture containing oxygen. This gas mixture may comprise at least one anesthetic. In particular, when the patient is anesthetized, the fluid connection may be part of a ventilation circuit between the patient and the ventilator.

FIG. 1 shows an example of a patient Pt who is being artificially ventilated. The lungs Lu, the esophagus Sp, the stomach Ma and the diaphragm Zw of the patient Pt are shown schematically. In the mouth of the patient Pt, during artificial ventilation, there is a flexible connector 4 belonging to a patient-side coupling unit. In one embodiment, a flexible measurement catheter 6 is placed in the esophagus of the patient Pt, wherein the measurement catheter 6 starts in the connector 4. The patient-side coupling unit is at least temporarily attached in/or to the body of the patient Pt, and in an embodiment comprises the connector 4 and the measurement catheter 6.

A ventilator 100 with a display and control unit 12 and a signal processing unit 10 artificially ventilates the patient Pt. A fluid connection is established between the ventilator 100 and the patient-side coupling unit 4, 6. The ventilation tubing between the ventilator 100 and the patient Pt is not shown.

Various respiratory sensors measure various pneumatic or electrical or mechanical vital parameters of the patient Pt and/or parameters of the gas flow between the ventilator 100 and the lungs Lu of the patient Pt or of the gas delivered to the patient-side coupling unit 4, 6. To carry out the invention, not all of these respiratory sensors necessarily need to be present. The following respiratory sensors are shown as examples in FIG. 1:

- A sensor 15 in or on the ventilator 100 measures an indicator of the volumetric flow, that is, the volume Vol′ per unit time, of the flow of the gas mixture from the ventilator 100 to the patient Pt (for example, inspiratory volumetric flow or inspiratory minute volume) and/or back from the patient Pt to the ventilator 100 (for example, expiratory volumetric flow or expiratory minute volume).
- An optional pneumatic sensor 2 comprises a transducer 2.1 having an aperture located near the patient's mouth Pt and tapping a sample of gas from the fluid connection. The tapped air is transmitted to a pressure sensor 2.2 via a tube not shown, and the pressure sensor 2.2 measures an indicator of airway pressure P_aw(pressure in airway) in the fluid connection and optionally an indicator of volumetric flow Vol′. In one embodiment, the measurement sensor 2.1 is arranged in or on a Y-piece close to the connector 4, i.e. close to the mouth of the patient Pt. Preferably, the tapped gas sample is fed back into the fluid connection.
- An optional probe 3 in the esophagus Sp of the patient Pt, preferably comprising a measuring balloon, measures an indicator of the time-varying pneumatic pressure P_es(pressure in esophagus) in the esophagus Sp. The probe 3 is in fluid communication with the connector 4 via the measuring catheter 6 or is a component of the measuring catheter 6.
- An optional further measuring balloon of probe 3 or an optional gastral probe 7 in the form of a measuring balloon placed in the stomach Ma measure an indicator for gastral pressure P_gain the stomach Ma.
- Several measuring electrodes are attached to the chest of the patient Pt. FIG. 1 shows an example of a pair 5.1.1, 5.1.2 of measuring electrodes near the heart and a pair 5.2.1, 5.2.2 of measuring electrodes near the diaphragm. Using measured values of these optional measuring electrodes 5.1.1, . . . , 5.2.2 as well as a reference electrode for electrical ground, which is not shown, an electrocardiogram (ECG) and/or an electromyogram (EMG) of the patient Pt are generated, which are two different respiratory signals. It is possible that an ECG/EMG generated close to the heart is generated on the basis of measured values of the pair 5.1.1, 5.1.2 close to the heart and an ECG/EMG generated close to the diaphragm is generated on the basis of measured values of the pair 5.2.1, 5.2.2 close to the diaphragm.

The signal processing unit 10 is capable of automatically determining when air or another gas mixture flows into the respiratory system of the patient Pt and when a gas mixture flows out of the respiratory system again. Thus it is ideally capable of detecting each inspiration phase and each expiration phase of the patient Pt's own respiratory activity. For this purpose, the signal processing unit 10 uses measured values from at least one of the sensors 2, 3, 7 and 15 and optionally from the measuring electrodes 5.1.1 to 5.2.2.

The ventilator 100 performs a sequence of ventilation strokes. The signal processing unit 10 repeatedly automatically triggers the two steps of starting a ventilation stroke and ending it during the supportive artificial ventilation. The signal processing unit 10 controls a corresponding actuator (not shown) of the ventilator 100, for example a pump or at least one valve interacting with a blower. During each ventilation stroke, the ventilator 100 feeds breathing air or other gas mixture into the fluid connection, and this gas mixture flows to the patient Pt.

In the embodiment, the patient Pt's own respiratory muscles draw in a gas mixture, i.e. the patient Pt inhales a gas mixture from the fluid connection. The inhalation may be caused by the spontaneous breathing of the patient Pt. Optionally, the patient's respiratory muscles are externally stimulated. The ventilator 100 assists the patient Pt's own breathing activity by the ventilator 100 delivering a gas mixture to the lungs Lu, said gas mixture comprising oxygen.

In the following, a distinction is made between the terms “inhalation process” and “inspiratory effort” of patient Pt. The patient's own respiratory musculature Pt, which is stimulated in the patient Pt's body itself and/or externally stimulated, attempts to suck in a gas. This attempt is called an inspiratory effort. If this attempt succeeds, i.e. a relevant amount of the aspirated gas actually flows into the lungs Lu, then the patient Pt has actually taken a breath and therefore also performed an inhalation process. However, it is also possible that an inspiratory effort does not cause an inhalation event that results in a measurable/relevant volume flow into the airway of the patient Pt. In particular, this situation may occur when the lungs Lu of the patient Pt are not very elastic and therefore a relatively large amount of used air remains in the lungs Lu after an exhalation event, leaving little room for new gas. Furthermore, in some situations, the ventilator 100 performs an occlusion. During an occlusion, the patient Pt is briefly prevented from actually breathing in. During such an occlusion, in many cases a lung mechanical parameter of the patient Pt can be better measured than in a situation where gas flows into the lungs Lu of the patient Pt.

Ideally, any inspiratory effort performed by the patient Pt with the patient's own respiratory muscles immediately triggers a ventilation stroke of the ventilator 100, in one embodiment except during an occlusion. Ideally, this ventilation stroke is immediately terminated when the patient Pt ceases the inspiratory effort. Thus, each inspiratory effort of the patient Pt ideally triggers exactly one ventilation stroke of the ventilator 100, and each ventilation stroke is triggered by exactly one inspiratory effort. The ventilation strokes of the ventilator 100 are thus ideally fully synchronized with the patient Pt's own respiratory activity.

The patient's own respiratory muscles Pt perform breaths in which air or another gas mixture first flows into the lungs (inspiration) and then flows out of the lungs again (expiration). In the following, the term “inspiration” is also used for an inspiratory effort that does not result in a measurable breath and thus does not result in a measurable inhalation process.

The respiratory sensors described above are each capable of providing measured values. From measured values from at least one respiratory sensor, the signal processing unit 10 generates a signal that correlates with the patient Pt's own respiratory activity. This signal is referred to as a “respiratory signal” and is denoted by Sig_res. Typically, readings from different respiratory sensors will result in different respiratory signals. Typically, the actual respiratory activity of patient Pt differs at least some of the time from the respiratory signal or each respiratory signal Sig_resobtained, such that the respiratory signal or each respiratory signal Sig_resis only an approximation of patient Pt's own actual respiratory activity.

In one embodiment, the signal processing unit 10 detects, by evaluating at least one respiratory signal Sig_res, that the patient Pt's own respiratory muscles have started an inhalation process or at least an inspiratory effort (start of an inspiration phase). The readings leading to this respiratory signal Sig_rescome from the or at least one pneumatic respiratory sensor, for example the pneumatic sensor 2 in front of the patient Pt's mouth, the probe 3 in the patient Pt's esophagus Sp or the gastral probe 7 in the patient Pt's stomach. The readings from these pneumatic respiratory sensors each result in a pneumatically obtained respiratory signal Sig_res.

In a preferred embodiment, at least one pneumatic respiratory signal Sig_resis used which correlates with the patient's inspiratory efforts Pt and not only with the breaths actually taken. The pneumatic respiratory sensors 15, 3 and 7 are capable of providing measured values from which such a respiratory signal Sig_resis generated. The respiratory signal Sig_res, which is generated from the measured values of the pneumatic respiration sensor 2, on the other hand, correlates with the breaths actually taken by the patient Pt.

In another embodiment, the fact that the patient Pt's own respiratory muscles are stimulated to move by a sequence of electrical pulses generated in the patient Pt's body and/or optionally by a stimulating device is exploited. These electrical impulses can be measured and result in an electrical signal. This electrical signal for the respiratory muscles correlating with the internal and/or external stimulation is referred to as an “electrical respiratory signal” and can be measured approximately. The cardiac activity of the patient Pt is triggered by another sequence of electrical signals generated in the body of the patient Pt. From this sequence, a signal for cardiac activity can be generated, which is referred to as a “cardiogenic signal”.

For the measured values of the measuring electrodes 5.1.1 to 5.2.2 as well as the measured values of the reference electrode not shown, a signal preprocessing is carried out in one embodiment, which preferably comprises a summation and a smoothing of the measured electrical measured values and provides a so-called envelope. This envelope is or provides a sum signal Sig_Sum, which results from a superposition of the electrical respiratory signal with the cardiogenic signal and may be influenced by interfering signals. Interfering signals can come from the patient Pt's body and from the environment. The influence of the cardiogenic signal on the sum signal Sig_Sumis at least approximately compensated by calculation. For example, in the sum signal Sig_Sumthose sections are detected which originate from one heartbeat each, for example one so-called QRS section each. Or a standardized course of the cardiogenic signal in the course of a single heartbeat is subtracted from the sum signal, a so-called ECG template. The computational compensation provides an approximation for the electrical respiratory signal Sig_res. The estimate for the electrical respiratory signal Sig_resobtained in this way also indicates when the patient Pt begins an inspiratory effort and when the patient Pt ends it.

It is possible that a first electrical respiratory signal Sig_resis obtained from measured values of the pair 5.1.1, 5.1.2 near the heart and a second electrical respiratory signal is obtained from measured values of the pair 5.2.1, 5.2.2 near the diaphragm. As a rule, these two electrical signals differ from each other.

FIG. 2a shows an example of an electrical sum signal Sig_Sum, which was obtained from measured values of the two pairs 5.1.1, 5.1.2 and 5.2.1, 5.2.2 of measuring electrodes as well as measured values of the non-generated reference electrode. On the x-axis the time t is plotted, on the y-axis the respective value of the sum signal Sig_Sum. The respective effect of a sequence of heartbeats, e.g. the heartbeats Hz(x) and Hz(y), and a sequence of breaths, e.g. the breaths Atm(1), . . . , Atm(4), can be seen. From this electrical sum signal Sig_Suman electrical respiratory signal Sig_rescan be generated, preferably by compensating the influence of the cardiogenic signal on the sum signal Sig_Sumby calculation. FIG. 2b shows an exemplary pneumatic respiratory signal Sig_res, which was generated by evaluating measured values from one of the sensors 3, 7, 15.

In a further embodiment not shown, readings from a mechano-myographic sensor provide a mechanical respiratory signal that correlates with the activity of the patient's own respiratory muscles Pt.

The signal processing unit 10 detects in at least one respiratory signal Sig_resthe respective start and the respective end of each inspiratory effort. The embodiments just described for generating respiratory signals in different ways can be combined with each other. In one embodiment, at least two different respiratory signals are present. These respiratory signals ideally match, but in practice generally differ from each other and from the actual inspiratory efforts. In one embodiment, the signal processing unit 10 generates an averaged respiratory signal Sig_resfrom a plurality of respiratory signals and uses this averaged respiratory signal Sig_res, to detect the patient Pt's inspiratory efforts. On the other hand, in another embodiment, the signal processing unit 10 uses a plurality of respiratory signals to detect the inspiratory efforts of the patient Pt.

Ideally, each inspiratory effort or at least each inhalation event of the patient Pt is visible in the or each respiratory signal Sig_res, furthermore each exhalation event. Ideally, the signal processing unit 10 detects each inspiratory effort in each respiratory signal Sig_resand always detects those times at which the inspiratory effort starts or ends. Ideally, the respiratory strokes of the ventilator 100 are synchronized with the inspiratory efforts of the patient Pt.

In practice, an inspiratory effort may not be detected at all in the or at least one respiratory signal Sig_res. Furthermore, it is possible that the signal processing unit 10 detects the same inspiratory effort of the patient Pt in multiple respiratory signals Sig_res, but with different times for the start and/or for the end of the inhalation. The different estimates may be combined at the wrong time or even misclassified as two different inspiratory efforts. It is also possible that the signal processing unit 10 in the respiratory signal or a respiratory signal Sig_ressupposedly detects an inspiratory effort, although the patient Pt has not performed an inspiratory effort at that time. Indeed, the respiratory signal or each respiratory signal Sig_resinevitably deviates from the patient Pt's own actual respiratory effort. Some reasons for this are: a distance occurs between the diaphragm Zw and other regions of the patient Pt's body that cause the inspiratory efforts and the measurement point at which the measurement values for a respiratory signal Sig_resare measured, whereby interfering signals may become effective. In addition, measurement inaccuracies and measurement errors of the sensors used usually occur, and further signals generated in the patient Pt's body or even outside may affect the respiratory signal Sig_resobtained. It is also possible that the signal processing unit 10 does not detect an inspiratory effort of the patient Pt at all.

Preferably, the signal processing unit 10 detects an inspiratory effort of the patient Pt when this inspiratory effort becomes visible in the respiratory signal or at least one respiratory signal Sig_res, even when this inspiratory effort does not become visible in another respiratory signal Sig_res. If the same inspiratory effort is visible in several respiratory signals, the signal processing unit 10 preferably detects in at least two of these respiratory signals the respective time for the start and the end of the inhalation. If multiple respiratory signals are present, in one embodiment the signal processing unit 10 averages over the detected times for the start of the inspiratory effort and averages over the detected times for the end of the inspiratory effort, thereby determining an averaged start time and an averaged end time for each inspiratory effort. In this averaging, weight factors are taken into account in one embodiment, where a weight factor is greater the more reliable a particular respiratory sensor and/or the more reliable the derivation of the respiratory signal from that sensor. It is also possible that the time points in the respiratory signal that currently has the highest reliability are used.

As a rule, a period of time elapses between the time at which the patient Pt begins or ends an inspiratory effort and the time at which this event is detected in a pneumatic respiratory signal Sig_res, in particular if the pneumatic respiratory sensor used is located outside the body of the patient Pt. One reason is that the inspiratory effort must have resulted in a sufficiently large volume flow at the respective measuring point of a pneumatic respiratory sensor before the inspiratory effort is detected in the respiratory signal Sig_resfrom this respiratory sensor. Moreover, time also elapses between the time when the patient Pt's body or even a stimulating device generates electrical impulses which activate the patient's own respiratory muscles and which are measured, and the time when the patient's own respiratory muscles actually begin an inspiratory effort. This time span may depend on the so-called neuromuscular efficiency of the patient's own respiratory musculature, i.e. how quickly and how well the patient's own respiratory musculature Pt responds to stimulating electrical impulses. These two time spans can be estimated in many cases, but any estimate may be subject to uncertainty.

The patient's actual own respiratory activity and therefore the respiratory signal or each respiratory signal Sig_resgenerally oscillate, and generally the amplitude and frequency of this oscillation varies over time. The signal processing unit 10 of the ventilator 100 automatically applies a decision rule to the or each respiratory signal Sig_resobtained to detect in the respiratory signal Sig_resthe start and end of an inspiratory effort of the patient Pt, and to start and end a ventilation stroke depending on the detected start and end of the detected inspiratory effort. This decision rule applies parameters in many cases, for example the following operating parameters:

- If a measure for the volume flow of respiratory air to the lungs Lu of the patient Pt is greater than a predetermined barrier x, optionally greater than the barrier x within a predetermined time period T, it is decided that the patient Pt has started an inspiratory effort, and a new ventilation stroke is started.
- If the measure for this volume flow becomes less than a percentage y of the last measured maximum volume flow, i.e. the maximum volume flow at this inspiratory effort, it is decided that the patient Pt has completed the inspiratory effort, and the current ventilation stroke is terminated.

Setpoints for these operating parameters x, y are determined on the basis of the following conflicting requirements:

- Every inspiratory effort should be detected.
- The start and end of each inspiratory effort that the patient Pt actually performs should be detected as accurately as possible.
- During supportive ventilation, a ventilation stroke should only be performed if patient Pt is also making an effort to breathe in. It should be avoided that a ventilation stroke is erroneously executed due to a supposed inspiratory effort, although the patient Pt is not inhaling. In particular, it is generally intended to avoid the ventilator 100 performing a ventilation stroke while the patient Pt is exhaling.

FIG. 3 illustrates by means of an exemplary schematic diagram a situation in which the ventilation strokes of the ventilator 100 “lag behind” the patient's own respiratory activity Pt. The time in [sec] is plotted on the x-axis. Time periods in which the patient Pt's own respiratory musculature causes an inspiratory effort, i.e. attempts to suck in air, are coded with a 1 in the course S.Pt (shown dashed), the other time periods with a 0. Correspondingly, time periods in which the ventilator 100 delivers breathing air to the patient Pt, i.e. executes a ventilation stroke, are coded with a 1 in the course S.100 (shown solid), the other time periods with a 0.

In the example shown, the ventilation strokes are started and ended depending on a pneumatic respiratory signal Sig_res, i.e. depending on readings from at least one pneumatic sensor 15, 3, 7. In the example shown, each ventilation stroke starts and ends later than the inspiratory effort that triggers that ventilation stroke. Various possible reasons for the supportive artificial ventilation “lagging behind” the patient's own respiratory activity have already been mentioned above.

It is also possible that a ventilation stroke begins earlier than the inspiratory effort that triggers that ventilation stroke. In particular, this situation may occur if the ventilation stroke is triggered by an estimate for an electrical respiratory signal Sig_res, where this electrical signal Sig_resis generated depending on electrical pulses generated in the patient Pt's body and not by the start of an executed inspiratory effort. One possible cause of a ventilation stroke starting too early is the following: a threshold to detect an electrical respiratory signal Sig_resfor a patient Pt inspiratory effort is set too low, i.e., the sensor is too sensitive. Possible reasons for supportive artificial ventilation to precede the patient's own respiratory effort have also been mentioned above.

At each sampling time, the following four situations may occur, which in a preferred embodiment are encoded with four different values. The following table 1 shows these four situations and exemplary their respective coding.

TABLE 1

Ventilation stroke performed
Inspiratory effort performed

(air flows from ventilator
(own respiratory muscles

Coding
100 to patient Pt)?
trying to draw in breath)?

0
No
No

1
Yes
No

2
No
Yes

3
Yes
Yes

Of course, other codings than the digits 0, 1, 2, 3 are also possible.

In the following, the designations “Situation 0” to “Situation 3” are used as abbreviations. These codings are entered as an example under the x-axis in FIG. 3.

In the following, a sequence of three situations is referred to as a “sequence”, provided that two situations immediately following each other are different from each other.

If the ventilator 100 is ideally synchronized with the patient Pt's own respiratory activity, only situations 0 and 3 occur. An ideally synchronized ventilation stroke leads to the situation sequence [0, 3, 0]. In practice, situations 1 and 2 usually occur as well. These situations mean asynchrony.

As a rule, it is completely harmless for the patient Pt if the start and end of a ventilation stroke does not deviate from the start and end of the inspiratory effort that triggers this ventilation stroke by more than a predefined duration limit. This duration limit may be fixed for all patients Pt and all situations and may be, for example, 100 msec. The duration limit may also depend on measured vital parameters of the patient Pt and/or on the way in which the ventilation strokes differ from the inspiratory efforts. Therefore, in the following, a situation 1 or 2 is only registered if this situation 1 or 2 lasts longer than the predetermined duration limit. This can be ensured, for example, with a sufficiently large sampling frequency or with signal preprocessing.

Situations 1 and 2 are referred to as “asynchrony situations”. FIG. 4 shows the time course of the four situations 0, 1, 2, 3 for the course of FIG. 3. In addition, FIG. 3 shows some exemplary time periods in which one of these four situations occurs. On the x-axis of FIG. 4 again the time tin [sec] is plotted, on the y-axis the value 0, 1, 2, 3 for the respective situation.

A sequence of sampling time points is predefined. For each sampling time point it is automatically determined which of the four possible situations 0, 1, 2, 3 is present at this sampling time point. This procedure provides a sequence of situations. As explained earlier, a section of the situations sequence consisting of three situations in immediate succession is called a “sequence”, provided that two situations in immediate succession are different from each other. Examples of situation sequences are [0,1,0], [2,3,0] and [1,0, 3]. With n=4 different possible situations there are

n*(n−1)*(n−1)=36

various possible situation sequences.

An “asynchrony sequence” is defined as a situation sequence in which the situation in the middle is an asynchrony situation, i.e. equal to 1 or equal to 2. The invention makes it possible to selectively detect the asynchrony sequences during supportive artificial ventilation of the patient Pt. With n=4 different possible situations and m=2 asynchrony situations, there are

(n−1)*m*(n−1)=18

various possible asynchrony sequences.

The following Table 2 shows by way of example which of these 18 possible asynchrony sequences have which technical meanings.

TABLE 2

Sequence
technical importance

[0, 1, 0]
Ventilation stroke performed without a temporally

overlapping inspiratory effort

[0, 1, 2]
First neither ventilation stroke nor inspiratory effort, then

only ventilation stroke performed, then only inspiratory

effort performed

[0, 1, 3]
Ventilation stroke started before inspiratory effort

[0, 2, 0]
Inspiratory effort performed without a temporally

overlapping ventilation stroke

[0, 2, 1]
First only inspiratory effort, immediately afterwards only

ventilation stroke performed

[0, 2, 3]
Inspiratory effort started before ventilation stroke

[1, 2, 0]
Ventilation stroke terminated before inspiratory effort

[1, 2, 1]
Inspiratory effort started and ended during a ventilation

stroke

[1, 2, 3]
Ventilation stroke started before inspiratory effort

[2, 1, 0]
Inspiratory effort terminated before ventilation stroke

[2, 1, 2]
Ventilation stroke started and ended during inspiratory effort

[2, 1, 3]
Inspiratory effort started before ventilation stroke

[3, 1, 0]
Inspiratory effort terminated before ventilation stroke

[3, 1, 2]
First inspiratory effort finished before ventilation stroke,

then second inspiratory effort started without ventilation

stroke

[3, 1, 3]
First inspiratory effort completed during one breath and

second inspiratory effort started during the same breath.

[3, 2, 0]
Ventilation stroke terminated before inspiratory effort

[3, 2, 1]
First ventilation stroke completed before inspiratory effort,

second ventilation stroke started without inspiratory effort.

[3, 2, 3]
First ventilation stroke completed during an inspiratory

effort and second ventilation stroke started during the

same inspiratory effort.

Table 3 below shows the clinical meanings for eight relatively common asynchrony type sequences. These eight asynchrony type sequences function as eight possible asynchrony types within the meaning of the claims.

TABLE 3

clinical significance

Sequence
clinical significance (details)
(terms)

[0, 1, 0]
Ventilation stroke triggered by itself
Auto Triggering

[0, 1, 3]
Ventilation stroke triggers inspiratory
Reverse Triggering

effort

[0, 2, 0]
Inspiratory effort missed
Missed Effort

[0, 2, 3]
Ventilation stroke triggered too late
Late Triggering

[3, 1, 0]
Ventilation stroke ended too late
Late Cycling Off

[3, 1, 3]
End of an inspiratory effort missed
Missed Expiration

(exhalation missed)

[3, 2, 0]
Ventilation stroke ended too early
Premature Cycling Off

[3, 2, 3]
new ventilation stroke triggered
Double Triggering

during inspiratory effort

Two classes of asynchrony sequences can be distinguished, namely time asynchronies and event asynchronies (desynchronies). In a time asynchrony, the ventilation stroke starts later or earlier than the inspiratory effort that triggers this ventilation stroke. If only time asynchronies occur during supportive artificial ventilation, each inspiratory effort of the patient Pt triggers exactly one ventilation stroke of the ventilator 100. In an event asynchrony, an inspiratory effort does not trigger a ventilation stroke at all, or a ventilation stroke is triggered without an inspiratory effort. Or, an inspiratory effort by the patient Pt is supported by a ventilation stroke, but the patient interrupts the inspiratory effort, or the ventilator 100 interrupts the supporting ventilation stroke. The four relatively frequent asynchrony sequences [0,1,3], [0,2,3], [3,2,0], and [3,1,0] are time asynchronies, and the remaining four relatively frequent asynchrony sequences [0,2,0], [3,1,3], [0,1,0], and [3,2,3] are event asynchronies.

A signal processing monitoring unit 11, which monitors the supportive artificial ventilation by the ventilator 100 and which comprises a processor and a data memory, receives the generated respiratory signal Sig_res, optionally each individual respiratory signal Sig_resfrom different respiratory sensors, and detects in the or each respiratory signal Sig_resobtained the inspiratory efforts of the patient Pt and for each inspiratory effort its respective start and its end. Because this monitoring unit 11 monitors the ventilator 100 but does not itself initiate any ventilation stroke, the monitoring unit 11 can evaluate a longer section of the or each respiratory signal Sig_res. For this evaluation, the monitoring unit 11 has a greater computing time available than is available to the signal processing unit 10 to trigger ventilation strokes. The monitoring unit 11 may be a component of the ventilator 100 or may be arranged outside the ventilator 100. However, it is also possible that the same signal processing device performs both the functions of the signal processing unit 10 and the functions of the monitoring unit 11.

In one embodiment, the monitoring unit 11 applies a learning method to each temporally last portion of the respiratory signal Sig_resto detect the start and the end of an inspiratory effort. In one embodiment, the learning method is applied to the N temporally last detected inspiratory efforts, where N is a predetermined number. In another embodiment, the learning method is applied to the temporally most recent portion of the respiratory signal Sig_res, where this most recent portion has a predetermined time duration T. In many cases, the application of a learning method increases the reliability with which the respective start and the respective end of the inspiratory efforts are detected in the respiratory signal Sig_res.

In addition, for each ventilation stroke, the monitoring unit 11 receives from the signal processing unit 10 an identification of those two times at which this ventilation stroke was started and ended, respectively.

The monitoring unit 11 compares the respiratory signal Sig_res, received or generated by averaging or by any other suitable type of signal processing, which correlates with the patient Pt's own respiratory activity, with the time course of the ventilation strokes performed by the ventilator 100, exemplified by the curve S.100 shown in FIG. 3. By comparing the two curves, the monitoring unit 11 detects any possible asynchrony sequence, exemplarily shown in Table 3. Preferably, an asynchrony situation 1 or 2 is only taken into account here if it lasts longer than the predefined time duration limit of, for example, 100 msec or of variable duration. The monitoring unit 11 generates a temporal sequence n1 n2 n3 . . . , where n1, n2, n3 are codes for the possible situations, in this case a number 0, 1, 2 or 3 respectively. This series is hereinafter referred to as the “series of situations”.

Preferably, the monitoring unit 11 automatically counts how often in the series of situations which asynchrony sequence occurs. In some cases, a certain asynchrony sequence is only relevant if its frequency in the series of sequences is above a predetermined frequency limit or follows a certain occurrence pattern in the series of situations. This applies in particular to the asynchrony sequence [0,1,3] (reverse triggering), i.e. a ventilatory effort triggers an inspiratory effort instead of an inspiratory effort triggering a ventilatory effort.

As has been explained, the signal processing unit 10 applies a decision rule to detect in the respiratory signal Sig_resthe respective start and the respective end of each inspiratory effort. This decision rule depends on at least one parameter. In one embodiment, the monitoring unit 11 automatically assigns a setpoint to this parameter or modifies an already assigned setpoint, depending on how often and/or how long a possible asynchrony sequence has actually occurred. For example, if individual inspiratory efforts are not detected, a lower bound for the volume flow in the decision rule is preferably lowered. Conversely, if individual ventilation strokes are triggered without a corresponding inspiratory effort, this lower volume flow barrier is raised.

In the embodiment example, the monitoring unit 11 causes the result of the monitoring to be output on the display and control unit 12. In many cases, at least one of the boundary conditions that frequently occur in everyday clinical practice is to be observed, namely that

- the display and control unit 12 is relatively small,
- nevertheless relatively much information must or should be output,
- sometimes there is no optimal lighting and
- a user should be able to quickly grasp the presented results, even under high stress and/or stimulus overload, both of which often occur in everyday clinical practice.

FIG. 5 and FIG. 6 show examples of how a result obtained by the monitoring unit 11 is output on the display and control unit 12. The upper half of the illustration shows inspiratory asynchrony sequences, and the lower half shows expiratory asynchrony sequences. In an inspiratory asynchrony sequence, an inspiratory effort is not completely overlapped in time by a ventilation stroke, and in an expiratory asynchrony sequence, a ventilation stroke is not completely overlapped in time by an inspiratory effort. The left half of the illustration refers to asynchronies caused by an activity of the ventilator 100 triggered too early or incorrectly. Accordingly, the right half refers to too late or no activity caused by the ventilator 100. The terms “too early”, “too late”, “erroneously” and “absent” refer to the view of the patient Pt.

FIG. 5 shows an example of how the four event asynchronies are output. FIG. 6 shows an example of how the four time asynchronies are output. In the example shown, the display area used is divided into four quadrants Q1 to Q4. In both FIG. 5 and FIG. 6, quadrants Q1 and Q4 represent two different inspiratory asynchrony sequences, while the other two quadrants Q2 and Q3 represent two different expiratory asynchrony sequences. Of course, the asynchrony sequences can also be distributed differently among the four quadrants.

Quadrants Q3 and Q4 in