DE10253946B3 - Procedure for a ventilator, ventilator and storage medium - Google Patents

Abstract

The invention relates to a method for a ventilator. Here, a first polynomial is adapted to the time course of a respiratory flow. Furthermore, the invention relates to a method for a ventilator, in which the derivation of the respiratory flow is estimated over time and a second polynomial is adapted to the derivative. Furthermore, the invention relates to a ventilator, in particular a CPAP device, for carrying out these methods and a storage medium containing corresponding programs.

Description

The invention relates to a Procedure for a respirator according to the generic term of claim 1 and a ventilator and a storage medium. In particular The invention relates to the evaluation of respiratory cycles extracting therapy-relevant information.

Are known ventilators or Respirators for mechanical, artificial Ventilation in all forms of hypoxia. you will be for, among other the long-term ventilation used, depending on the switching mechanism be differentiated from in- to expiration three basic types, namely pressure-controlled, Volume-controlled and timed respirators. The ventilators newer Type have technical, usually electronically controlled devices that are patient-friendly Allow ventilation type. For example, the inspiratory time be extended to three times the Expirationszeit, a pressure ventilation carried out being as well as the respirator "triggered" by the patient, being already weak breaths impulsive for the machine support are (Roche Lexicon Medicine, 4th edition, edited by the Hoffmann-La Roche AG and Urban & Fischer, Urban & Fischer, Munich, Stuttgart, Jena, Lübeck, Ulm).

Also known are devices for carrying out the CPAP (continuous positive airway pressure) therapy, which are also 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 applies by means of a compressor, preferably via a humidifier, via a hose and a nasal mask a positive overpressure up to about 30 mbar in the respiratory tract of the patient. This overpressure is intended to ensure that the upper respiratory tract remains fully open throughout the night and thus no obstructive respiratory disorders (apnea) occur ( DE 198 49 571 A1 ).

1 shows CPAP device 1 and a patient 19 , The CPAP device in turn includes a compressor 4 , a breathing tube 9 , a respiratory mask 18 , a pressure sensor 11 as well as a flow sensor 16 , To generate an overpressure, the compressor includes a turbine 8th , The turbine is also referred to as fan, fan unit, compressor, fan or blower. These terms are used synonymously in this patent. The illustrated CPAP device contains the pressure sensor 11 in the compressor housing. In or near the mask are one or more small holes 2 attached so that on average over time an air flow from the compressor to the holes 2 arises. This prevents the accumulation of CO ₂ in the breathing tube 9 and allows the patient to be supplied with oxygen.

The speed of the turbine 8th is through a microcontroller 5 so regulated that with the pressure sensor 11 measured 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. B. a sensor with heating wire 17 be, 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 is a review of compatibility of the device and the set CPAP pressure. Usually a patient spends for this purpose, a night of control in a sleep laboratory.

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. The WO 94/23780 describes such a procedure for controlling the target 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.

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

To reduce the perceived overpressure, BiPAP devices and multilevel devices have also been developed. Such a device is in the DE 691 32 030 T2 described. The pressure is raised by a valve during inhalation and lowered during exhalation.

According to the US 5,740,795 the respiratory flow signal is fed 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 the DE 101 18 968 Further, a control method for CPAP devices is described. The 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 based on the Er Event flags of the detectors the target pressure.

The features include the expiration time, a backward correlation, a mean inspiratory volume, a mean curvature of the Respiratory flow during the inspiration as well as frequency from zero crossings in the Alternating part of the CPAP actual pressure.

In the transition from inspiration to Expiration is a pronounced flank in the course of the respiratory flow to detect which used for the detection of individual breaths becomes. The local maxima of the first derivative of the respiratory flow the time correspond to the maximum slope of the respiratory flow at the transition between inspiration and expiration. From the end of inspiration the beginning of the inspiration is searched for, after the first local Minimum in the estimated Derivation is sought. The expiration time is a time difference between a minimum of the estimated Derivative and the preceding maximum of the estimated derivative. Due to noise in the respiratory flow curve, the respiratory flow curve does not only derived, but additionally low-pass filtered. The Derivation and low-pass filtering takes place in a filtering step suitable choice of the coefficients of a digital filter. "Estimation of Derivative "is in this application generic term for Derive and derive used with low pass filtering.

To calculate the mean curvature of the Respiratory flow during the inspiration becomes the valued first Derivation of the respiratory flow during used the inspiration after the time. Subsequently, will to the esteemed first derivative adapted a straight line. The slope of this adapted The straight line gives the mean curvature of inspiration.

According to the teaching of DE 101 18 968 From the features a respiratory arrest detector, an apnea detector, a hypopnea detector and a Atemflußlimitations detector are calculated as an indication of an increase in pressure and a normal detector as an indication of stable breathing and possible pressure reduction.

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

The object of the invention is a advanced method for a respirator, an advanced ventilator and a storage medium specify.

This task is accomplished by the objects of independent claims solved.

Preferred developments of the invention are the subject of the dependent Claims.

Beneficial to fitting a polynomial on the time course of a respiratory flow curve or its derivation is a significant data reduction, a low-pass filtering for noise reduction as well as the extraction of therapy-relevant information, ie information, which characterizes the condition of the patient. This information can advantageously immediately from the ventilator, for example be used to correct a target pressure.

Furthermore, the polynomial in the form of his Coefficients are stored and Oftline by a doctor Therapy control are evaluated. This form of evaluation makes for a small extra effort on electronic components Sleep laboratories superfluous, causing itself a cost advantage for the health insurance companies. The data gained during a control night can, can so on for the patient more pleasantly recorded in his home environment become.

An on the respiratory flow during a Inspiratory phase adapted fourth degree polynomial contains straight nor the treatment-relevant information and thus provides a good Compromise between data reduction and maintaining therapy-relevant Information is.

Adapting the polynomial to a Inspiration phase of the respiratory flow is especially for CPAP therapy advantageous because only during the inspiratory phase the pressure in the airways is less than that Ambient pressure is and therefore the airways collapse and shut to lead an apnea can.

The provision of an interface for one external storage unit makes the ventilator more easy to use because the patient does not use the whole device, but only the external memory unit for therapy control for Doctor must bring.

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

Advantageously, the three possibly complex zeros of the derivation of a polynomial of the fourth degree, which was adapted to the temporal flow flow, for adjustment the target pressure are used. In the same way are suitable the three possibly complex zeros of a third degree polynomial, the was adapted to the time derivative of the respiratory flow course.

A quality feature for breathing is the imaginary part the conjugate complex zeros, if any.

An even more stable feature seems the area of the three zeros spanned in the complex plane To be a triangle.

The following are preferred embodiments the invention explained with reference to the accompanying drawings. there demonstrate:

1 a CPAP device,

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

3 Inspiratory phases of a respiratory flow curve with flow-limited respiration, as well

4 and 5 Flowcharts of two methods according to the invention.

As mentioned above, traditionally spends a patient for therapy control every now and then a night of control in a sleep laboratory. The information in a control night can be obtained essentially from the recorded Extract flow data. In particular, for therapy control be decided on the basis of the recorded flow data, whether the Respiratory flow during of sleep is limited or not. That's why you can take control nights with you a storage device for Flow data on the CPAP device save.

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 in normal or flow-limited respiration can be determined with a real polynomial 4 , Filter out order (equation 1). A polynomial 4 , Order contains enough information to describe the different inspiratory patterns between normal and flow-limited breathing accurately enough to be suitable for therapy control.

Several inspiratory phases of normal and flow-limited breaths are in the 2 respectively. 3 shown. The less smooth curves 81 and 83 represent the measured flow data. The smoother curves 82 and 84 are the polynomials adapted to the flow data 4 , Order. It can be clearly seen that the inspiration phases of normal, regular breaths in 2 resemble parabolas that are open at the bottom. In contrast, the in 3 shown inspiratory phases on a more angular, parallelogram course. After a maximum after the first fifth of the inspiratory phase, the respiratory flow slowly drops 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. How to look at the smoother polynomial curves 84 The respiratory flow is horizontal over a large part of the second half of the inspiratory phases or even has a local maximum in the second half of the inspiratory phases. Especially in the first, third and fourth of in 3 shown inspiration phases, the adjusted polynomials have two maxima and an intermediate local minimum.

In Equation 1, V (t) is the air flow, t is time, and a ₀ through a _{4 are} selectable polynomial coefficients. To represent an inspiration phase, it is sufficient to store the 5 polynomial coefficients a ₀ to a ₄ . Thus, the memory requirement per night with 9 600 breaths is reduced 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 ₄ can be carried out 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.

A polynomial 4 , Order can have either 1 or 3 extremes. As is known to those skilled in the art, extrema is found by searching for zeros in the derivative. Equation 4 contains the derivative of the polynomial 4 , Order from equation 1 after time. It can be called a polynomial 3 , Order with the coefficient b ₀ to b ₃ are shown. The coefficients b ₀ to b ₃ can be related by a coefficient comparison with the coefficients a ₁ to a ₄ .

A polynomial 3 , Order with real coefficients has three zeros n ₁ , n ₂ and n ₃ , of which two may be conjugate complex zeros. Without limiting the generality, the zero point n _{1 should} always be real. If we find three real zeros in Equation 5, then we have the corresponding polynomial 4 , Order in Equation 1 two local maxima and one local minimum (see inspiration pattern in 3 ). If one finds only a real of two complex conjugate zeros in Equation 5, then the corresponding polynomial has 4 , Order in equation 1 only one maximum. In the latter case, the phases of inspiration are similar to parabolas open at the bottom (see inspiration pattern in 2 ).

It has been found that the evaluation of the magnitude of the equal-magnitude imaginary parts of the two complex conjugate zeros is a feature in the sense of DE 101 18 968 supplies. 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 are obtained by comparing the amount of imaginary parts with a threshold and determining a normal event if the amount of imaginary parts is above the threshold. Advantageous in such a normal detector over the based on the backward correlation normal detector DE 101 18 968 is that he delivers a result per breath, so 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 results in three real zeros, 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 can this triangular area are compared to a threshold, where a normal event is present when the threshold is exceeded. Also a Thus 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 optimal setting of the target pressure in a CPAP device then no longer needs, as in the SEP 20 (Attorney's reference: SEP 20 , "Method for controlling the pressure supplied by a CPAP device, CPAP device and storage medium", applicant: seleon gmbh) provoke respiratory events to detect 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 can be a third degree polynomial (see equation 4) to the temporal Derivative or the estimated temporal derivative of the respiratory flow to be adjusted. The temporal Derivation of the respiratory flow is used to determine the transitions between Inspired and Expiration anyway, so that data on the Derivation of the respiratory flow are present. The fitting of a polynomial third degree is less computationally expensive than the adaptation of a Polynom's fourth degree. Adapting the polynomial to the derivative can according to the in Equations 2 and 3 or other criteria. Because fitting polynomials to waveforms is not a linear operation is, by interchanging the order of polynomial fitting and derivative slightly different coefficients for the polynomials third order, even if assumed identical measurement data becomes. Thus, the zeros will be slightly different. However, this can be done by moving the thresholds into the corresponding normal detectors are compensated.

Contain the third-order polynomials Although less treatment-relevant information. In particular included these polynomials have no information about the mean inspiratory volume. If it does not matter, then the coefficients can also be used the polynomials of the third order are recorded later and later be evaluated by a doctor for therapy control.

A ventilator may use a digital signal processor (DSP) and / or a microcontroller to perform the data reduction procedure 5 contain. For storing the data, an external storage device 7 z. In the form of a PCMCIA card, a smartcart, a storage dongle or a memo stick for which the CPAP device has a slot 6 can have.

In another embodiment, the ventilator may be connected to a modem 12 be equipped (modulator demodulator) over which the CPAP device, the data can be transmitted via a public switched telephone network (PSTN), for example, to a computer of a physician. In addition, respirators can also make emergency calls via the modem 12 be delivered. It is particularly advantageous, the Caching flow data first in the ventilator in order not to have to maintain an ongoing connection over the public telephone network. A data reduction reduces the connection duration and thus the telephone costs.

The invention has been described above of preferred embodiments explained in more detail. For a specialist However, it is obvious that various modifications and modifications can be made without departing from the spirit of the invention. Therefore, the scope of protection by the following claims and their equivalents established.

1

CPAP device hole

2

hole

4

compressor

5

microcontroller

6

slot

7

storage medium

8th

turbine

9

breathing tube

10

data line

11

pressure sensor

12

modem

16

flow sensor

17

heating wire

18

breathing mask

19

Sleeping

40

Flow chart

41-48

steps

50

Flow chart

51-58

steps

81

measured Respiratory flow curve

82

customized Respiratory flow curve

83

measured Respiratory flow curve

84

customized Respiratory flow curve

Claims (11)

Procedure for a ventilator with: repeated measurement ( 16 . 17 . 42 ) of a breathing air flow during the operation of the ventilator ( 1 ) at several times; and storing the measuring points of the respiratory flow; characterized by : fitting a first polynomial ( 44 ) on the time course of the measuring points. A method according to claim 1, characterized in that it is the first polynomial is a fourth degree polynomial. Method according to one of the above claims, characterized that the measuring points of the respiratory flow in individual inspiratory and Expirationsphasen be divided and the first polynomial to the belonging to an inspiratory phase Points is adjusted. Method according to 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 storage unit ( 7 ) transmits. Method according to one of the preceding claims, characterized in that the ventilator transmits the polynomial coefficients of the first polynomial via a modem ( 12 ) and a Public Switched Telephone Network (PSTN) to another computer. Method according to claim 2 or claims 3 and 5, as far as they relate to claim 2, comprising: calculating ( 46 ) of the derivative of the first polynomial, resulting in a second polynomial of third degree. Procedure for a ventilator with: repeated measurement ( 16 . 17 . 42 ) of the respiratory flow during the operation of the ventilator ( 1 ) at several times; and storing the measuring points of the respiratory flow; characterized by treasures ( 53 ) the derivative of the respiratory flow with time; To adjust ( 54 ) of a second third degree polynomial to the derivative. The method of claim 6 or 7, further comprising: determining the three zeros ( 46 . 56 ) of the second polynomial; Evaluate ( 47 . 57 ) of 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 spanned by the three zeros in the complex plane. Ventilator, especially CPAP device with a flow sensor ( 16 ), a command memory and a central processing unit ( 5 ) executing instructions stored in the instruction memory so that the ventilator performs a method according to any one of claims 1 to 9. Storage medium for use with a respirator, in particular a CPAP device containing a flow sensor ( 16 ) and a central processing unit ( 5 ) for processing the instructions stored in the storage medium, the respirator performing a method according to claims 1 to 9 during the execution of the instructions stored in the storage medium.