WO2004045669A2

WO2004045669A2 - Ventilator method, ventilator and memory medium

Info

Publication number: WO2004045669A2
Application number: PCT/DE2003/003591
Authority: WO
Inventors: Mirko Wagner; Siegfried H�USSLER
Original assignee: Viasys Healthcare Gmbh
Priority date: 2002-11-19
Filing date: 2003-10-29
Publication date: 2004-06-03
Also published as: DE10253946B3; AU2003302001A1

Description

Procedure for a ventilator, ventilator and storage medium

The invention relates to a method for a ventilator according to the preamble of patent claim 1 and a ventilator and a storage medium. In particular, the invention relates to the evaluation of 5 breathing cycles by extracting therapy-relevant information.

Ventilators or respirators for mechanical, artificial respiration in all forms of oxygen deprivation are known. They are used, among other things, for long-term ventilation, with three basic types depending on the switchover mechanism from in to expiration

10, namely pressure-controlled, volume-controlled and timed respirators. The newer type ventilators have technical, mostly electronically controlled, facilities that allow a patient-friendly type of ventilation. For example, the inspiratory time can be extended up to three times the expiration time, a pressure ventilation can be performed as well

15 the respirator are "triggered" by the patient, with already weak breaths impulsing the machine support (Röche Lexicon Medicine, 4th edition, edited by Hoffmann-La Röche AG and Urban & Fischer, Urban & Fischer, Munich, Stuttgart , Jena, Lübeck, Ulm).

Also known are devices for carrying out the CPAP (continuous positive airway 20 pressure) therapy, which are referred to in this application as ventilators. The CPAP therapy is in Chest. Volume No. 110, pages 1077-1088, October 1996 and Sleep, Volume No. 19, pages 184-188. A CPAP device applied by means of a compressor, preferably via a humidifier, via a hose and a nasal mask a positive overpressure up to about 25 30 mbar in the respiratory tract of the patient. This overpressure is intended to ensure that the upper airways remain fully open during the entire night and thus no obstructive respiratory disorders (apnea) occur (DE 198 49571 A1).

Fig. 1 shows CPAP device 1 and a patient 19. The CPAP device in turn

30 includes a compressor 4, a breathing tube 9, a respiratory mask

18, a pressure sensor 11 and a flow sensor 16. To generate a

Overpressure, the compressor contains a turbine 8. The turbine is also called a fan, Fan unit, compressor, fan or blower. These terms are used synonymously in this patent. In the illustrated CPAP device, the pressure sensor 11 is located in the compressor housing. In or near the mask, one or more small holes 2 are attached, so that on average over time an air flow from the compressor to the holes 2 is formed. This prevents the accumulation of CO ₂ in the breathing tube 9 and allows the supply of oxygen to the patient.

The speed of the turbine 8 is controlled by a microcontroller 5 so that the measured with the pressure sensor 11 actual pressure coincides with a predetermined target pressure. The target pressure is conventionally preset under the supervision of a physician and referred to as titration pressure. The flow sensor can, for. Example, be a sensor with heating wire 17, which delivers its measuring signal via a measuring line to the microcontroller in the compressor housing. In another design of the CPAP device, a narrowing in the breathing tube may be provided for the respiratory flow measurement. The microcontroller can also take over the pressure control.

In the course of therapy, a check of the compatibility of the device and the set CPAP pressure is necessary. A patient usually spends a night in a sleep laboratory for this purpose.

It has been found that the patients found the overpressure generated by the CPAP device an unpleasant resistance against which they had to exhale. Therefore, control methods have been developed for CPAP devices that lower the target pressure as much as possible. WO 94/23780 describes such a method for controlling the desired pressure. If no respiratory disturbances occur during sleep, the pressure is gradually lowered. If sleep disorders such as apneas, hypopneas or snoring occur, the pressure is increased.

US 5,335,654, EP 0 612 257 B1, WO 99/24099 and EP 0 934 723 A1 describe similar processes.

In order to reduce the perceived overpressure, further BiPAP devices and multilevel devices were developed. Such a device is described in DE 691 32 030 T2 described. The pressure is raised by a valve during inhalation and lowered during exhalation.

According to US Pat. No. 5,740,795, the respiratory flow signal is supplied to a band-limited differentiator. If the output signal of the differentiator exceeds an inhalation threshold or falls below an exhalation threshold, an exhalation detection signal or a one-event detection signal is determined.

In DE 101 18 968 further a control method for CPAP devices is described. DE 101 18 968 is incorporated by reference into this application. The control method first calculates characteristics from a measured respiratory flow curve and a measured actual pressure curve of a CPAP device. Special combinations of features are combined into detectors. Flags are set in the detectors when they detect an event. The control method then changes the target pressure based on the event flags of the detectors.

Features include expiration time, backward correlation, mean inspiratory volume, mean curvature of inspiratory flow during inspiration, and frequency of zero crossings in the AC component of CPAP actual pressure.

During the transition from inspiration to expiration, a pronounced flank can be seen in the course of the respiratory flow, which is used to detect the individual

Breaths is used. The local maxima of the first derivative of the

Respiratory flow after time corresponds to the maximum slope of the respiratory flow at the transition between inspiration and expiration. From the end of inspiration, the beginning of inspiration is searched for by searching for the first local minimum in the estimated derivative. The expiration time is given as

Time difference between a minimum of the estimated derivative and the previous maximum of the estimated derivative. Due to noise in the

Respiratory flow curve, the respiratory flow curve is not only derived, but also low-pass filtered. The derivative and low pass filtering is done in a filtering step by suitable choice of the coefficients of a digital filter. "Estimation of

Derivation "is derived in this application generic term for and derive with

Low pass filtering used. To calculate the mean curvature of the respiratory flow during inspiration, the estimated first derivative of the respiratory flow during inspiration is used over time. Then, a straight line is fitted to the estimated first derivative. The slope of this fitted straight line gives the mean curvature of inspiration.

According to the teaching of DE 101 18 968, the features calculate a respiratory arrest detector, an apnea detector, a hypopnea detector and a respiratory flow limitation detector as an indication of an increase in pressure as well as a normal detector as an indication of stable respiration and possible pressure reduction ,

For the detection of stable respiration the normal detector uses the backward correlation. Stable breathing is when the set pressure for a given time z. B. 180 sec. Was not changed and during this time the backward correlation, for example,> 0.86.

The object of the invention is to provide a further developed method for a respirator, an advanced ventilator and a storage medium.

This object is solved by the subject matters of the independent claims.

Preferred embodiments of the invention are the subject of the dependent claims.

An advantage of adapting a polynomial to the time course of a respiratory flow curve or its derivation is a considerable data reduction, a low-pass filtering for noise suppression and the extraction therapy-relevant information, ie information that characterizes the condition of the patient. This information can be used in an advantageous manner immediately by the ventilator, for example, to correct a target pressure.

Furthermore, the polynomial can be stored in terms of its coefficients and

Be evaluated offline by a doctor for therapy control. This form of evaluation makes for a little extra work on electronic components Check nights in sleep laboratories redundant, resulting in a cost advantage for the health insurance companies. The data obtained during a control night can thus be recorded in a more comfortable way for the patient in his home environment.

A fourth-degree polynomial adapted to the course of the respiratory flow during an inspiration phase just contains the therapy-relevant information and thus represents a good compromise between data reduction and maintenance of therapy-relevant information.

The adaptation of the polynomial to an inspiratory phase of the respiratory flow path is particularly advantageous for CPAP therapy because only during the inspiratory phase is the pressure in the respiratory tract lower than the ambient pressure and therefore the respiratory tract can collapse and lead to apnea.

The provision of an external storage unit interface makes the ventilator easier to use because the patient does not need to bring the entire device but only the external therapy control storage unit to the doctor.

Even more convenient is the remote data transmission via modem, because here no physical object has to be moved.

Advantageously, the three possibly complex zeros of the derivation of a polynomial of the fourth degree, which was adapted to the temporal course of the respiratory flow, can be used to set the desired pressure. In the same way, the three possibly complex zeros of a polynomial of third degree, which was adapted to the time derivative of the Atemflussverlaufs suitable.

A quality feature of respiration is the imaginary part of the complex conjugate zeros, if any.

An even more stable feature appears to be the area of the triangle spanned by the three zeros in the complex plane.

In the following preferred embodiments of the invention will be explained with reference to the accompanying drawings. Showing: 1 shows a CPAP device,

2 inspiratory phases of a respiratory flow curve with regular breathing,

FIG. 3 inspiration phases of a respiratory flow curve during flow-limited respiration, as well as FIG

4 and 5 are flowcharts of two methods according to the invention.

As mentioned above, a patient is traditionally spending a control night in a sleep laboratory for therapy control. The information obtained during a night of control can essentially be extracted from the recorded flow data. In particular, it must be decided for therapy control based on the recorded flow data, whether the respiratory flow during sleep is limited or not. Therefore, control nights can be saved with a flow data storage device on the CPAP device.

The required amount of data can be estimated as follows: With an average sleep time of 8 hours corresponding to 28800 s, a person breathes about 28,800s / 3 s = 9600 times. At a sampling rate of 100 Hz, the data count is 2.88 - 10 ⁶ data points per night. This amount of data is too large for storage in a conventional CPAP device.

The therapy-relevant information in the different inspiration patterns with normal or flow-limited respiration can be filtered out with a real polynomial of 4th order (equation 1). A 4th order polynomial contains enough information to describe the different inspiratory patterns between normal and flow-limited breathing accurately enough to be suitable for therapy control.

Several inspiration phases of normal and flow-limited breaths are shown in Figs. 2 and 3, respectively. The less smooth curves 81 and 83 represent the measured flux data. The smoother curves 82 and 84 are the 4th order polynomials matched to the flow data. It can be seen clearly that the inspiration phases of normal, regular breaths in FIG. 2 are similar to parabolas that are open at the bottom. In contrast, the inspiration phases shown in FIG. 3 have a more angular, parallelogram-shaped course. After a maximum after the first fifth of the inspiration phase, the respiratory flow drops slowly almost to the end of the inspiration phase. The drop in the respiratory flow often accelerates only in the last tenth of the inspiration phase. As can be seen from the smoother polynomial curves 84, the respiratory flow runs horizontally for a large part of the second half of the inspiratory phases or even has a local maximum in the second half of the inspiration phases. Particularly in the first, third and fourth of the inspiration phases illustrated in FIG. 3, the adjusted polynomials have two maxima and a local minimum lying therebetween.

V (t) = a ₀ + a-, t + a ₂ t ² + a ₃ t ³ + a ₄ t ⁴ (1)

In Equation 1, V (t) is the air flow, t is time and a is ₀ to a *. selectable polynomial coefficients. To illustrate an inspiratory phase, it is sufficient, the 5

Polynomial coefficients a ₀ to a ₄ store. Thus, the reduced

Memory requirement per night for 9,600 breaths to 48,000 polynomial coefficients instead of 2,88 -10 ⁶ data points. The memory requirement is thus reduced by a factor of 60.

The adaptation of the polynomial coefficients a ₀ to a * can be done in a conventional manner by minimizing the sum squares of the deviations between measured and calculated flux values according to Equation 2. For this purpose, there are known algorithms that accomplish a numerically complex minimum search by solving a linear system of equations. In other embodiments, other criteria may be used for fitting a polynomial, in particular a 4th order, to the flow of the respiratory flow. In particular, according to Equation 3, the sum of the absolute values of the differences between measured values and polynomial values can be minimized.

Σ VVii --VV ((ttiijJ == min (3) A 4th order polynomial can have either 1 or 3 extrema. As is known to those skilled in the art, extrema is found by searching for zeros in the derivative. Equation 4 contains the derivation of the 4th order polynomial from Equation 1 by time. It can be represented as 3rd order polynomial with the coefficients b ₀ to b ₃ . The coefficients b ₀ to b ₃ can be related by a coefficient comparison with the coefficients ai to a.

- V (t) = V (t) = a-, + 2a ₂ t + 3a ₃ t ² + 4a ₄ t ³ = b ₀ + b-, t + b ₂ t ² + b ₃ t ³ (4) dt

V (t) = b ₀ + b ₁ t + b ₂ t ² + b ₃ t ³ = 0 (5)

A third-order polynomial with real coefficients has three zeroes ni, n ₂ and n ₃ , two of which may be conjugate complex zeros. Without limiting the generality, the zero ni should always be real. If one finds three real zeros in Equation 5, then the corresponding 4th order polynomial in Equation 1 has two local maxima and a local minimum (see Inspirational Pattern in Figure 3). If one finds only a real of two complex conjugate zeros in Equation 5, then the corresponding 4th order polynomial in Equation 1 has only one maximum. In the latter case, the inspiration phases are similar to parabolas open at the bottom (see inspiration pattern in Fig. 2).

It has been found that the evaluation of the magnitude of the imaginary parts of equal magnitude of the two complex conjugate zeros provides a feature in the sense of DE 101 18 968. The greater the amount of imaginary parts, the more stable is the respiration. From this, another normal detector in the sense of DE 101 18 968 can be obtained by comparing the magnitude of the imaginary parts with a threshold value and determining a normal event if the magnitude of the imaginary parts is above the threshold value. The advantage of such a normal detector over the normal detector based on the backward correlation from DE 101 18 968 is that it delivers a result per breath, ie does not require a large number of breaths.

According to the current state of knowledge, the area of the triangle spanned by the three zeros in the complex plane is even an even more stable feature in the sense of DE 101 18 968. If unstable breathing occurs, there should be three real zeros result, this area is zero. By calculating the area, no case distinction needs to be made between three real or only one real zero.

To define another normal detector, this triangular area can be compared to a threshold, with a normal event being present when the threshold is exceeded. Even a defined normal detector delivers a result per breath.

An advantage of such features is that they can assess the quality of normal breathing. A pressure control for optimum setting of the target pressure in a CPAP device then no longer needs, as in the SEP 20 (law file number: SEP 20, "Method for controlling the pressure supplied by a CPAP device, CPAP device and storage medium", applicant : seleon gmbh) provoke respiratory events to recognize that the target pressure can not be further lowered. By virtue of the features described above, it is still possible to detect in the area of normal respiration below which pressure a respiratory flow limitation is imminent. The patient is then less disturbed in his sleep by provoked repiratory events.

In another embodiment, a third degree polynomial (see Equation 4) may be adjusted to the time derivative or the estimated time derivative of the respiratory flow. The time derivative of the respiratory flow is estimated anyway to determine the transitions between inspiration and expiration so that data on the discharge of the respiratory flow is available. Matching a third degree polynomial is less computationally expensive than fitting a fourth degree polynomial. The fitting of the polynomial to the derivative can be done according to the criteria mentioned in equations 2 and 3 or other criteria. Since fitting polynomials to traces is not a linear operation, interchanging the order of polynomial fitting and derivation will produce slightly different coefficients for the third order polynomials, even assuming identical measurement data. Thus, the zeros will be slightly different. However, this can be compensated by shifting the thresholds in the corresponding normal detectors. Although the third-order polynomials contain less therapy-relevant information. In particular, these polynomials contain no information about the mean inspiratory volume. However, if this is not the case, the coefficients of the third order polynomials can also be recorded and later evaluated by a physician for therapy control.

A ventilator may include a digital signal processor (DSP) and / or a microcontroller 5 to perform the data reduction procedure. For storing the data, an external memory device 7 z. B. in the form of a PCMCIA card, a smart card, a storage dongel or a memory stick may be provided, for which the CPAP device may have a slot 6.

In another embodiment, the ventilator may be equipped with a modem 12 (modulator demodulator) through which the CPAP device may transmit the data to, for example, a public switched telephone network (PSTN) to a physician's computer. Furthermore, emergency calls can also be issued via the modem 12 in ventilators. It is particularly advantageous to temporarily store the flow data in the respirator so as not to have to maintain an ongoing connection via the public telephone network. A data reduction reduces the connection duration and thus the telephone costs.

The invention has been explained in detail above with reference to preferred embodiments. However, it will be apparent to those skilled in the art that various modifications and changes can be made without departing from the spirit of the invention. Therefore, the scope of protection is defined by the following claims and their equivalents.

LIST OF REFERENCE NUMBERS

1 CPAP - device 17 heating wire

2 hole 15 18 respiratory mask

4 Compressor 19 Sleeping 5 Microcontroller 40 Flowchart

6 slot 41 - - 48 steps

7 Storage Medium 50 Flowchart

8 turbine 20 51 - 58 steps

9 Ventilation tube 81 Measured respiratory flow curve 10 Data line 82 Adapted respiratory flow curve

11 Pressure sensor 83 measured respiratory flow curve

12 modem 84 adapted respiratory flow curve

16 flow sensor 25

Claims

claims

1. Method for a ventilator with:

repeatedly measuring (16, 17, 42) a breathing air flow during operation of the ventilator (1) at multiple times; and

Storing the measuring points of the respiratory flow;

marked by:

Fitting a first polynomial (44) to the time course of the measurement points.

2. The method according to claim 1, characterized in that the first polynomial is a polynomial of the fourth degree.

3. The method according to any one of the above claims, characterized in that the measuring points of the respiratory flow are divided into individual inspiratory and Expirationsphasen and the first polynomial is adapted to the belonging to an inspiration phase points.

4. The method according to any one of the above claims, characterized in that the ventilator transmits the polynomial coefficients of the first polynomial via an interface (6) to the external memory unit (7).

5. The method according to any one of the above claims, characterized in that the ventilator transmits the polynomial coefficients of the first polynomial via a modem (12) and a public telephone network (PSTN) to another computer.

6. The method according to claim 2 or claims 3 and 5, as far as they relate to claim 2, with:

Calculating (46) the derivative of the first polynomial to produce a second polynomial of third degree.

7. Method for a ventilator with: repeatedly measuring (16, 17, 42) the respiratory flow during operation of the ventilator (1) at multiple times; and

Storing the measuring points of the respiratory flow;

marked by

Estimating (53) the derivative of the respiratory flow with time;

Fitting (54) a second third order polynomial to the derivative.

8. The method of claim 6 or 7, further comprising:

Determining the three zeros (46, 56) of the second polynomial;

Evaluating (47, 57) the imaginary part of the two conjugate complex zeroes if the second polynomial has only one real root.

The method of claim 8, further comprising the area (47, 57) of the triangle subtended by the three zeros in the complex plane.

A respirator, in particular a CPAP device with a flow sensor (16), a command memory and a central processing unit (5), which executes instructions stored in the command memory such that the ventilator performs a method according to any one of claims 1 to 9.

11. A storage medium for use with a respirator, in particular a CPAP device, which comprises a flow sensor (16) and a central processing unit (5) for processing the instructions stored in the storage medium, wherein the respirator during processing of the instructions stored in the storage medium, a method according to claims 1 to 9 performs.