WO2003059426A2

WO2003059426A2 - Method for determining a mask pressure, air flow and/or air pressure in a cpap device, cpap device and corresponding test equipment

Info

Publication number: WO2003059426A2
Application number: PCT/DE2003/000015
Authority: WO
Inventors: Martin Baecke; Harald Genger
Original assignee: Seleon Gmbh
Priority date: 2002-01-04
Filing date: 2003-01-02
Publication date: 2003-07-24
Also published as: DE10390059D2; AU2003235692A1; AU2003235692A8; DE10200183A1; WO2003059426A3

Abstract

The invention relates to a method for pressure regulation in a CPAP device (1). In order to adjust the actual pressure in a mask (5) to a therapeutical pressure, the pressure drop produced by an airflow in a respiratory tube (4) is calculated and from this value a desired pressure for a pressure sensor (3) accommodated in the housing of the CPAP device is repeatedly calculated. The invention further relates to a method for calculating an airflow from the excess pressure produced by the ventilator (2) of a CPAP device (1) and the engine voltage of the blower, thereby eliminating the need for a pressure sensor (3). Finally, the invention relates to a CPAP device (1) and to corresponding test equipment.

Description

Method for determining a mask pressure for pressure regulation in a CPAP device, method for determining the air flow and / or air pressure in a CPAP device, CPAP device and test apparatus therefor

According to a first aspect, the invention relates to a method for pressure regulation in a CPAP device according to the preamble of patent claim 1.

According to a second aspect, the invention relates to a method for determining the air flow in a CPAP device according to the preambles of claims 6 and 7 and a CPAP device according to the preamble of claim 13 and a test apparatus according to claim 14. Obstructive respiratory disorders lead to apneas (Respiratory arrest) through which the sleeper awakens. Frequent apneas prevent the sleeping person from relaxing in deep sleep. People who suffer apneas during sleep are therefore no sleep during the day, which can lead to social problems in the workplace and in the worst case to fatal accidents, for example in professional drivers. For the treatment of apneas, continuous positive airway pressure (CPAP) therapy was developed in Chest. Volume No. 110, pages 1077-1088, October 1996 and Sleep, Volume No. 19, pages 184-188. A CPAP device generates a positive overpressure of up to about 30 mbar by means of a blower, which is also referred to as a compressor, compressor or turbine, and preferably applies this via a humidifier, via a breathing tube and a face or nose mask in the patient's airways , CPAP devices intended to be used with a nasal mask are also referred to as nCPAP devices, where n stands for "nasal."

This overpressure is intended to ensure that the upper respiratory tracts remain completely open during the entire night and thus no apneas occur (DE 198 49 571 A1). The required overpressure depends, among other things, on the sleep stage and the body position of the sleeping person.

In all known CPAP devices and in the patent literature, two methods have hitherto been used to determine the pressure in the face mask of CPAP devices.

In one, a differential pressure sensor detects the pressure of the air delivered to the patient directly in the device. By default, the pressure difference is measured for a commonly used combination of breathing tube and mask at a medium flow rate. This difference value is subtracted from the pressure measured in the device and the result is interpreted as a mask pressure. Inevitably there are errors in the pressure setting, because the air flow fluctuates constantly through the breathing and thus varies the pressure loss in the breathing tube. Especially annoying for the patients is that the pressure in the face mask or nasal mask during inhalation is lower than during exhalation. Therefore, especially in this form of pressure control, the patient has the feeling of having to breathe against resistance.

A change in the face mask due to compatibility issues, additional leakage due to damage, change in breathing tube length when replacing the breathing tube, and kinking in the tube will not cause the device to react, i. the mask pressure is not set correctly.

In the other method, one of which is described in WO 00/66207, the pressure detection takes place in the vicinity of the end of the breathing tube in front of the mask or in the mask. Here, the pressure detection is very accurate, the pressure control compensates even leaks etc. The pressure measurement itself can be carried out with a pressure sensor, the electrical connection wires with the breathing tube to the ventilator must be performed. Especially with devices from MAP, a separate thin tube from the measuring point to a pressure sensor located in the CPAP device. A disadvantage of these variants is that special hoses are needed to allow the return of the connecting wires or the hose into the CPAP device. These custom-made products are more expensive than normal breathing tubes. Furthermore, their use with other CPAP devices is limited. Finally, the cleaning is more complicated.

DE 96 101 100 T2 discloses two embodiments for a long-term ventilatory support device. Both embodiments differ essentially by the position of the pressure measurement, namely according to the first embodiment in the mask and according to the alternative embodiment approximately in the middle of the air supply hose and by the flow measurement by a Pneumotachograp en s in the first embodiment in the vicinity the mask and in the alternative embodiment in the vicinity of a blower. Because of these differences, the alternative embodiment is the more relevant one. The blower is driven by a blower motor driven by a motor servo controlled by a microprocessor to which the flow signal from a differential pressure transducer and the pressure signal from a pressure transducer are fed. The mask has an outlet. According to an expedient extension of the first embodiment, the air flow and the pressure at the outlet of the turbine is measured and the pressure in the mask is calculated taking into account the pressure drop at the air supply hose. Among other things, according to the second embodiment, the following operations are executed every 20 milliseconds: measuring a flow at a flow sensor and a pressure at a pressure detection port; Calculating a mask pressure and a flow of the sensor pressure and the flow; Calculating a conductivity of the mask leak; Adding a loss of tube pressure to the EPAP pressure. The hose pressure loss is calculated as tube resistance * flow ² . The conductivity of the leak is calculated from a low-pass filtered mask air flow and the low-pass filtered square roots of the mask pressure.

DE 691 32 030 T2 discloses a respiratory tract pressure system that does not operate at constant pressure (bi- or multi-PAP). Nevertheless, the term "CPAP" is mentioned. A blower unit, in one embodiment, generates an overall constant volume of respirable gas per unit of time, which is selectively vented through a vent end or supplied to the patient. The vent end can be closed by a valve element of different widths. The valve element is rotated by a stepper motor. To control the fan motor, a microprocessor controller generates a pulse width modulated signal. This is converted to an analog voltage by a low pass filter formed of a resistor and a capacitor which is fed to the motor driver. The blower motor is equipped with a Hall effect converter, whose output pulses are fed to a frequency-voltage converter, which consists of several capacitors and resistors and a diode, so that the motor driver, a second voltage signal is supplied.

DE 690 24 063 T2 seeks to avoid the disadvantages of the CPAP method in that when an apnea occurs an air pulse of about 1.5 liters opens the airways.

DE 199 28 003 A1 discloses a respiratory assistance device for the treatment of obstructive sleep apnea. A gas humid CPAP system delivers humidified and compressed gases to a patient through a nasal mask connected to a humidified gaseous transport line or to a breathing tube. A controller receives input signals from a set screw with which a user of the device e.g. sets a required value of the humidity or temperature of the gases. The controller may also receive input signals from other sources, e.g. obtained from flow velocity sensors.

The subsequently published DE 101 03 973 A1 discloses a method and a device for sleep monitoring, which takes place, for example, by the direct or indirect measurement of the respiratory flow or the heart activity. A respiration device comprises a CPAP device with a pressure generator and possibly an additional control circuit and an actuating device.

DE 199 40 070 A1 discloses a system for monitoring patients with sleep disorders. Here, therapy-relevant parameters are determined by means of sensors and can be transmitted via a communication network to a spatially separated monitoring, analysis and control device. The therapy devices may be a CPAP device. It is an object of the invention to provide a method for a less expensive CPAP device, in which the pressure in the respiratory mask is regulated to a target pressure set in the CPAP device.

This object is achieved by the teaching of the independent claims. Preferred embodiments of the invention are subject of the dependent claims.

An advantage of the invention is that the manufacturing costs of the CPAP device decrease, because no special ventilation hoses must be used.

An advantage of measuring the pressure in the CPAP device at a point in time when the air flow is zero is that no pressure drops on the breathing tube and therefore the pressure in the mask is measured in the CPAP device.

An advantage of measuring the pressure at a time when the air flow is just equal to the average air flow, is that at this time of the breathing air flow from or to the patient is equal to zero.

An advantage of the determination of the air flow over an integer number of respiratory cycles is that the mean value is not falsified by inhalation or exhalation and thus the average value of the air flow even with a short averaging time is independent of the averaging time.

An advantage of using the negative spikes of the airflow dissipation to divide the airflow into respiratory cycles is that these peaks are particularly pronounced, allowing accurate separation of the respiratory cycles. The advantage of determining the air flow from two of the measurements, motor voltage, motor current, fan speed, and the pressure supplied by the fan is that no additional flow sensor is required in an auto-CPAP device. This leads to a significant reduction in manufacturing costs, since unlike competing products, an expensive flow sensor in the device can be dispensed with. An advantage of the evaluation of both the motor voltage and the motor current in addition to a pressure measurement is that thereby further fault conditions, such as wear, can be determined in a CPAP device.

In principle, the pressure in the CPAP device and the air flow can be determined from two of the measured quantities of motor voltage, current through the motor and engine speed using a characteristic field. An advantage of such a procedure is that neither a pressure nor a flow sensor is required.

Advantageous in the recording of the air flow as a function of two of the measured quantities of motor voltage, current through the motor, the pressure generated by the fan and the Blower speed, for example, at a final inspection, is that the use of this family of characteristics compensated for manufacturing tolerances.

An advantage of the calculation of a characteristic field by the test apparatus, from which the air flow can be calculated at a given pressure and given motor voltage, is that the computing power required for this computation-intensive method does not have to be integrated in a CPAP device.

An advantage of a combination of the calculation of the air flow from the blower voltage and the measured pressure and the consideration of the falling pressure on the breathing tube is that without additional hardware, such as flow sensor, connection cable or hoses to the face mask, a target pressure in the mask can be maintained with high accuracy.

In the following, a preferred embodiment of the invention will be explained in more detail with reference to the accompanying drawings. Showing:

1 shows a CPAP device in therapy use; Fig. 2 is a schematic diagram of a CPAP device;

3 shows the block diagram of a test apparatus according to the invention;

4 shows the block diagram of a test apparatus according to the invention with two turbines; and

5 shows the block diagram of a test apparatus according to the invention with a lung simulator. Fig. 1 shows a CPAP device 1 in therapy use. The CPAP device 1 contains a blower 2. In the vicinity of the breathing tube connection 8 within the CPAP device, a differential pressure sensor 3 is provided for measuring the overpressure generated by the blower relative to the ambient pressure. The air conveyed by the fan is supplied via a breathing tube 4 to a face mask 5, which the patient 6 carries himself. The face mask 5 can cover either mouth and nose or only nose. In or near the face mask 5, an exhalation opening 7 is provided through which a continuous flow of air from the breathing tube takes place in the environment. This air flow ensures that the air exhaled by the patient is vented to the environment and prevents the accumulation of 4 C0 ₂ in the breathing tube. The pressure drop across a hose such as the breathing tube 4 can be calculated from the following formula (Technical Fluid Mechanics 1, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig).

Here Δp is the pressure falling on the hose, ξ is a pressure loss coefficient of the hose, λ is a pipe friction value of the hose, I is the length of the hose, p is the density of the flowing medium, ie approx. 1.2 kg / m ³ for air for CPAP devices and v is the averaged cross-sectional flow velocity from the CPAP device toward the mask, a is 2 for turbulent flows and 1 for laminar flows. In practice, a can also assume intermediate values because there is seldom an ideal-typical flow form. in the

The following is based on turbulent flows. Where d is the diameter of the hose. Equation (1) is also known from Fluid Dynamics, J.H. Spurk, 4th edition, Springerverlag, Berlin, 1996, where λ is referred to as a resistance number. The

• averaged flow velocity is related to the air flow V in the following

Context:

V = v - π - (d / 2) ² (2)

V itself stands for an air volume. The dot denotes the derivative after time d / dt.

V can be detected by a flow sensor 9 or, as will be explained below, calculated from the pressure measured by the differential pressure sensor 3 and the motor voltage.

Substituting (2) in (1) gives the following quadratic dependence of the pressure drop Δp

from the air flow V. The dependencies of λ, I, d and p have been summarized by the constant C, where C is a parameter for the hose used:

, 2

Δp = C - V - sign (V) (3)

The factor sign (V) either assumes the value 1 with air flow to the patient or -1 with air flow from the patient in order to take the flow direction into consideration. If the patient puts the device into operation, first of all a value for the pressure to be generated by the fan is calculated from the therapy pressure p _s programmed by the physician, ie the setpoint pressure in the mask, and the stored pressure loss coefficient ξ ₀ or a stored characteristic value C ₀ for a standard tube p from equation (4): p = p _s + Δp (4) The pressure p determined from equation (4) varies depending on the respiratory activity of the patient. This is particularly important because the pressure p and thus the pressure Δp must be calculated repeatedly within a breathing cycle, ie within about 4 seconds, from equations (3) and (4) in order to constantly increase the pressure p _M in the mask So, p should be determined so that p = p _s .

In order to keep the computational effort low, in one embodiment the constant C in equation (3) is first determined from the pressure loss coefficient ξ of the breathing tube. In this way, only equations (3) and (4), but not equation (1), need to be calculated frequently. In one embodiment, the CPAP device is equipped with a non-volatile memory in which the constant C or the pressure loss coefficient ξ are stored after their calculation. In addition, the constant C ₀ and / or the pressure loss coefficient ξ ₀ for a standard breathing tube are stored in a read-only memory (ROM) in the event that the pressure loss at value ξ or the constant C are nevertheless deleted. As the patient exhales, there is a backflow of air in the air

Breathing tube. The volume flow V assumes negative values for a short time.

Immediately upon the reversal of flow directions from CPAP device to patient in patient

• to CPAP device and vice versa, the volumetric flow V = 0. At this moment, P = P, i. The pressure measured in the ventilator is exactly equal to the pressure in the respiratory mask.

The supplied by fan 2 airflow V is divided into a patient going

• • •

Breathing air flow V A and a leakage Vι_. on. While the respiratory air flow V A varies over time and can assume both positive and negative values during inhalation and exhalation,

is the leakage current V | _ a direct function of the mask pressure p _M. It flows out of a fixed opening 7 in the mask or in the vicinity of the mask and serves to dispose of the carbon dioxide exhaled by the patient.

The respiratory air flow VA is zero on average over time, as the patient inhales the same amount of air as exhales:

| V _A dt = 0 (5) The integration or averaging of the air flow V over suitable time intervals therefore provides

• • • • an exact value for the leakage current Vι_. From V | _ and V, V _A can be calculated.

^• 1 ^{t +} _f ^{τ •}

VL = ^ V- dτ (6)

T J

A suitable time interval T is in particular an integer number of breathing cycles. By averaging over whole respiratory cycles, the influence of the inhalation or exhalation is kept as low as possible, even at short time intervals.

As described in the German patent application with the official file reference 101 18 968.0, the first derivative of the respiratory flow curve is estimated for the detection of individual breathing cycles. Due to noise in the measured airflow, the airflow curve is not only derived according to time, but additionally 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 and is called the derivative of the derivative. The negative peaks in the estimated derivative of the airflow have proven to be a robust demarcation criterion between the various breathing cycles. The mask pressure p is just the pressure drop across the exhalation port. With the through

Averaging determined leakage current V | _ the pressure loss coefficient ξ _L can the leakage aperture by means of equation (1) or a corresponding value of C _L in equation (3) can be determined.

As a result of the pressure control in the CPAP device, the mask pressure becomes constant and equal to

Therapy pressure p _s held. Thus, the pressure loss coefficient ξ or the constant C for the breathing tube can be determined from the total volume flow V and the pressures p and p _M

become. For this purpose it is expedient to use the values measured at V = V | _, because

while just the breathing air flow VA = 0 and thus sources of error can be reduced. Of the

• Leakage current VL can be used to check for leaks that may vary with time, such as a misplaced face mask or leaking or damaged connections. By carefully evaluating the pressure loss coefficients ξ and ξ _L , it is possible to determine the location of a leak in the hose or to find out whether the leak in the hose is a problem

Face mask is located. This is essential for prescribing better fitting masks, replacing defective parts, and correcting therapy pressure. Through a Leak increases the calculated from equation 6 leakage current V | _ and a by means of equation

(1) determined pressure loss ξ _L decreases. From the change in the leakage current VL. or the Druckverlustbeiwerks ξι_ you can close the size of the leak. The change in the pressure loss coefficient ξ of the breathing tube gives an indication of the position of the leak. The pressure loss coefficient ξ changes greatly when the leak is close to the CPAP device and almost does not change when the leak is near the face mask.

By calculating the pressure loss coefficients ξ and ξ _L or the values C and C _u , one obtains a constantly verified model of the airways.

The airflow V can be measured by a flow sensor in the CPAP device. In another embodiment, the air flow is determined by evaluating the supply voltage U for the motor for the device-internal fan 2, and measured in the device in the vicinity of the air outlet by the differential pressure sensor 3 pressure p.

From a continuous detection of the value pairs p, U, a function of the volume flow over time is determined by means of the stored characteristic field. During the final inspection of the CPAP devices, a characteristic field can be recorded by the manufacturer by means of a test apparatus, which determines the relationship between motor voltage

U, pressure p and the air flow V generated thereby indicates:

V = f (p, U) (6)

The characteristic field also covers a certain range of negative volume flows. The

preferred form of the characteristic field stores air flows Vjj, pressures Pi and voltages U _j ,

where i runs from 1 to n and j from 1 to m. We have Vy = f ( _pj , Uj). If the characteristic field is stored in this way, intermediate values can be calculated according to the following formula by bilinear interpolation:

Pi + 1 - Pi ^U j + 1 ^{~ U} j

where Pj <p <P _{j + 1} and Uj <U <Uj ₊₁ FIG. 2 shows a block diagram of a preferred CPAP device. The block diagram shows a central processing unit 23, to which the output signal of the differential pressure sensor 3 is supplied, which is digitized in the analog-to-digital converter 24. The central processing unit 23 outputs a value proportional to the motor voltage 25 to the digital analog converter 22. The analog voltage output from the digital-to-analog converter 22 is amplified by the motor driver 21 and supplied to the motor 11. The motor 11 then drives the blower 2. Mostly the rotor of the motor and the impeller or propeller of the fan are mounted on a shaft so that the engine speed is equal to the fan speed. In modern CPAP devices computing units with clock frequencies of 80 MHz are used. These are able to generate a digital pulse width modulated signal with a frequency of more than 20 kHz with a sufficient accuracy of the duty cycle for driving the motor 11. In this embodiment, therefore, no digital / analog converter 22 is required. Between the motor driver 21 and motor 11, a low-pass filter for radio interference suppression can still be switched.

15 In the central processing unit 23 is constantly running a program that compares the pressure measured by the pressure sensor 3 with a determined from equation (4) setpoint pressure and readjusted the motor voltage. The program preferably implements a PID controller. Furthermore, an electrical connection 26 may be provided, which is preferably designed as an RS-232 interface.

Finally, the CPAP device may include a resistor 27 for measuring the electrical current flowing through the motor 11. At the resistor 27 drops a current through the motor 11 proportional voltage. This is digitized in this embodiment by the digital-to-analog converter 28 and the central processing unit 23 is supplied. As will be explained in more detail below, from two of the measured quantities of motor voltage, by the motor

25 flow and fan speed determine both the pressure in the CPAP device and the airflow generated by the CPAP device. A calculation of the pressure due to two of the measured quantities may make the pressure sensor 3 and the analog-to-digital converter 24 superfluous. Capture of two of the above metrics along with the pressure allows for a high degree of functional control of the CPAP device. So, for example

30 are determined whether an impeller or a propeller of the blower rubs or the bearings of the fan motor are worn.

Since the central processing unit 23 in cooperation with the digital-to-analog converter 22 and the motor driver 21 generates the motor voltage, it is not necessary to measure the motor voltage itself. Rather, the motor voltage can be calculated from the value output to the digital-to-analog converter 35 22 by the central processing unit.

If instead of the digital / analog converter 22 from the central processing unit 23, a pulse width modulated signal is output, instead of the digital / analog converter Transducer output value, the duty cycle of the pulse width modulated signal can be used as a motor voltage proportional signal.

In order to keep the computational effort low, the characteristic field can be stored so that instead of the measured pressure and the measured motor voltage read out by the analog-to-digital converter 24 pressure value and the output to the digital-to-analog converter 22

• Voltage or duty cycle used to determine airflow V.

Fig. 3 shows a schematic diagram of a test apparatus according to the invention. The test apparatus comprises an air connection 31, with which the test apparatus can be connected via a breathing tube 4 with a CPAP device. Furthermore, the test apparatus has a flow sensor 36 and an electrically controllable valve 32. The valve 32 can be controlled via a digital-to-analog converter 33 by a central processing unit 34. The flow sensor 36 forms with the resistors 37 to 39, a measuring bridge whose detuning amplified by the differential amplifier 40, digitized in the analog-to-digital converter 41 and the central processing unit 34 is supplied. In addition, a keyboard 43 for input and a display 42 for displaying the operating state of the test apparatus are provided. Finally, an electrical interface 35 is provided for data exchange with the CPAP device to be tested.

For example, a test method may be as follows. In an outer loop, different resistance values W | _<set one after the other. In an inner loop, different target pressures pi are successively transmitted to a connected, tested CPAP device and set there. After reaching

• a stationary state of the air flow Vkl is measured by the flow sensor 36 and read the motor voltage U «or a value proportional to her from the CPAP device. After setting all the test pressures pi, the next resistance value W _{k +} 1 is set at the valve 32.

After receiving this characteristic field by the test apparatus is from this

Characteristic field preferably a characteristic curve described above field Vy for the pressures pi and the voltages U _j in the test apparatus by the central processing unit 34 calculated. For this purpose, the bilinear interpolation explained above with reference to equation (7) can be used if the measurement points W _k and pi are close enough. Since sufficient computing power is generally available in the test apparatus, more sophisticated higher-order interpolation methods than bilinear interpolation can also be implemented. In another embodiment, in a field resistance values W _w in the

Test apparatus are stored, which are already chosen so that the resistance value W _k | at all pressures p _k results in an approximately equal voltages U _w . In this embodiment

• the measured characteristic Vkl is already pretty much a preferred one

Characteristic field Vy for the CPAP device. Due to the manufacturing tolerances in the manufacture of the CPAP devices, the resistance values W _w can not be selected so that the voltages U _w for all the corresponding pressures p _{k are the} same for all CPAP devices. That's why

on a conversion of the measured characteristic field Vkl in the preferred characteristic field

Vy can not be waived.

By a suitable choice of the resistance values W _k ι an optimal accuracy of the calculated characteristic field can be achieved at an optimally small number of measuring points of a test program of the test apparatus. In another embodiment, after testing one or more CPAP devices, the field of resistance values W _k | is recalculated based on the old resistance values W _k |, and / or the characteristic field newly measured during testing, so that the voltages U _w for the corresponding pressures p _{k are} as equal as possible.

At the end of the test program, the calculated characteristic field is preferably stored in the CPAP device.

In another embodiment, instead of the motor voltage U, the electric current I can also be used by the motor 11. Equations 6 and 7 remain valid, but the voltage U is to be replaced by the current I. Also in the characteristic curves, the motor voltage U _{w is to be} replaced by the current l _w and U _j by l _j .

As stated above, the air flow V and the pressure p can be calculated from the motor voltage U and the electric current through the motor I. This functional relationship can be described by Equations 8 and 9, where g and h are functions of the motor voltage U and the current I:

V = g (l, U) (8)

P = h (l, U) (9)

In a test method, similar to that described above, which can be carried out, for example, in the context of a final inspection, can at the valve of the test apparatus different resistance W _k and in the CPAP device different motor voltages U |

be specified. In this case, depending on a characteristic field for the air flow Vkl the pressure p _k ι and the current through the motor l _k | added. As explained above in connection with the test method, a resistance value field W | are given, so that the characteristic field for the current flowing through the motor l _k | for fixed k contains approximately equal currents.

For this is a characteristic field for the calculation of the air flow V and another

Characteristic field required for the calculation of the pressure p. If only the pressure

• is to be calculated, of course, the characteristic field for the air flow V can be omitted and vice versa. This also applies mutatis mutandis to equation pairs (10), (11) and (12), (13).

For the calculation of intermediate values the bilinear interpolation can be used.

• In order to calculate the airflow V in Equation 7, the pressure p must be replaced by the current I and the function f by the function g. For calculating intermediate values for the

Pressure in equation (7) is to replace the flow V by the pressure p, the pressure p by the current I and the function f by the function h.

Another size that is easy to measure with some CPAP devices is the speed of the fan and the motor driving the fan. These CPAP devices are often equipped with a contactless 3-phase DC motor. The motor has Hall sensors that provide output signals to drive the motor windings in phase. To determine the speed of the motor either the signals supplied by the Hall sensors or the voltage applied to the motor windings voltages can be used. The engine speed can replace the current I in equations 8 and 9 to give equations 10 and 11:

V = g (n, U) (10)

p = h (n, U) (11)

The pressure p is, in a good approximation, proportional to the working range of CPAP devices

Square of the speed n. For this purpose, resistance values W _k and voltages U | at the

Test equipment or on the CPAP device can be set one after the other. Here are each one

• Characteristic field for the air flows Vkl, the pressures p _w and the speeds n _w measured. As stated above, a resistance field W _w can also be specified so that the rotational speed n _k | for fixed k are about the same size and this resistance field W _M from time to time due to the characteristic fields of several CPAP devices as described above.

As described above, the characteristics Vkl, p _k ι, n _M and U | in fields V, py, nj, and

U _{j can be} calculated so that air flow V and pressure p can be calculated quickly by means of bilinear interpolates (see equation (7)). The latter fields are then stored in the CPAP device.

In another embodiment, the speed may be used in conjunction with the current I.

to calculate the airflow V and the pressure p, so that equations (12) and (13) result:

V = g (n, l) (12)

p = h (n, l) (13)

Advantageous in the use of speed n in conjunction with the motor voltage U over the use of motor speed n in conjunction with current through the motor I is that no additional means, such as resistor 27 and analog / digital converter 28 for measuring the current I necessary are. To determine the frequency n only a counter with a digital input and no analog / digital converter is required. The counter can be implemented by software in the central processing unit 23 without requiring additional hardware. The statements made above in connection with equations 8 and 9 also apply mutatis mutandis to equations 10 and 11 as well as 12 and 13.

To determine the characteristic curves, resistance values W _k and voltage values U | be set one after the other on the test apparatus or on the CPAP device. Here are four

Characteristic fields, namely one each for the air flow Vkl, for the pressure p _Ml for the current through the motor l _M and the engine speed n _w measured. As stated above, can also be a

Field for resistance values W _w and for voltage values U _{w are} given so that the measured currents l _k | for fixed k and the speeds n _k | for solid I are about the same size. In another embodiment, resistance values W _w and voltage value U _M can also be specified so that the currents I _k for fixed I and the speeds n _M for fixed k are approximately the same. The resistance field W _w and the voltage field U _w can be like

• updated above. As described above, the characteristic curves Vkl, p _k ι,

n _w and U | in fields Vy, p ^, nj and U _j are converted so that target flow V and the pressure p can be calculated quickly by means of bilinear interpolation (see Equation (7)). As described above, the latter fields are then stored in the CPAP device.

Of the four measured quantities pressure p, motor voltage U, current through the motor I and motor speed n, at least two must be measured in order to calculate the pressure p and

to calculate the airflow V. If more than two measured variables are measured, redundant information is obtained. If, for example, the pressure p and two of the measured quantities motor voltage U, current through the motor I and motor speed n are measured, then the pressure p can be calculated from motor voltage U, current through the motor I and / or motor rotational speed n according to one of the above methods be measured. The CPAP device typically provides an air inlet filter and silencer with soundproofing foam in the air inlet area. The air inlet filter may become clogged with dust in the ambient air over time, such that it has a slowly increasing air resistance over time. The soundproofing foams can also change, for example due to water retention, and thus change the air resistance of the air inlet. By slowly increasing the air resistance of the air inlet filter, the engine power increases with time, which is required to produce a constant overpressure. After recording the characteristic field, measured and calculated pressure are in good agreement. By increasing the air resistance in the air intake area, the calculated pressure versus the measured pressure decreases over time. This allows cleaning and / or maintenance intervals to be defined.

When the three measured quantities of motor voltage U, current through motor I and motor speed n are measured, information about the wear on motor and motor can be obtained

Win fan bearings. If the current increases with time for the same motor voltage and motor speed, this is an indication that the friction in the bearings of the motor and the fan is increasing and thus these bearings are becoming increasingly worn. As stated above,

• For example, the pressure p and the air flow V can be calculated from the engine speed n and the

Calculate motor voltage U. When recording the characteristics fields can also be a

Characteristic field l _k | and a current characteristic field I ,, be calculated and stored so that an (original) current value in dependence on the engine speed n and the motor voltage U from the field l, _j can be calculated. This can then be compared with the measured current value I. When using the three measured quantities

Motor voltage U, current through the motor I and motor speed n, however, can not be excluded that an increase in the measured current I compared to a calculated current value due to aging in the air inlet area. In another embodiment, the four variables pressure p, motor voltage U, current be measured by the engine I and engine speed n, so information about the Aging of the air intake, in particular the air inlet filter and the engine and fan bearings, are obtained.

To record the characteristic curves for calculating air flow and / or pressure from the engine voltage and the current flowing through the motor, it is necessary that the test apparatus is equipped with a differential pressure sensor that measures the differential pressure between the pressure generated by the CPAP device and the ambient pressure , Such a pressure sensor may be arranged, for example, in the vicinity of the flow sensor 36. The electrical output signal of the pressure sensor is digitized by a further analog-to-digital converter and fed to the central processing unit 34. If the characteristic curves are recorded with the breathing tube, which is also used during the therapy use of the CPAP device, the pressure sensor of the testing device essentially measures the pressure which is established in the mask during the therapy. Thus, a correction for the decreasing pressure on the breathing tube, as explained above with reference to equations (1) to (4) omitted. The characteristics fields stored in the CPAP device are calculated in such a way that the characteristic fields result in mask pressure.

If, on the other hand, a different breathing tube is used when recording the characteristic fields than during therapy, the pressure in the CPAP device is first determined from equations (1) to (4) and the constant C or the pressure loss coefficient ξ for the respiratory flow used in the recording of the characteristic curves calculated. The pressure map, which is finally stored in the CPAP device, is calculated to give the pressure in the CPAP device. During therapy, the pressure calculated from the characteristic field is then corrected by the pressure drop across the breathing tube, as explained above. If the pressure loss coefficient of the respiration tube used in the therapy is known when recording the characteristic fields, a characteristic field can be calculated and stored in the CPAP device during or immediately after the recording of the characteristic curves from which the mask pressure results directly.

A further preferred embodiment of the test apparatus is shown in FIG. 4. This embodiment has, in addition to a test apparatus according to FIG. 3, the fans 51 and 53. The speed of the fans can be controlled by the central processing unit 34. By way of example, the digital-to-analogue converters 52 and 54 are shown in FIG. 34 for this purpose. Via the three / two-way valve 50, the air connection 31 can be connected either to the blower 51 or to the blower 53. The control of the two-way valve 50 via the digital control lines 55 and 56 by the central processing unit 34. The inhalation of the patient is simulated by the blower 53, which can generate a negative pressure relative to the ambient pressure. The exhalation of the patient is simulated by the blower 51. This fan creates an overpressure against the Ambient pressure and provides a negative flow when the pressure generated by the blower 51 is higher than the overpressure generated by the blower of the CPAP device. By using the additional fans 51 and 53, a further pressure and flow range for the characteristic field or fields can be measured. 5 shows a further embodiment of a testing apparatus according to the invention. Instead of the fans 51 and 53, this test apparatus contains a lung simulator 60. The lung simulator consists essentially of a cylinder in which a piston can be moved up and down in a controlled manner. This can be done for example by the wheel 63 eccentrically mounted connecting rod. The wheel 63 may be driven, for example, by a DC or stepper motor. In Fig. 5, the digital-to-analog converter 61 for controlling a DC motor is shown as an example. In addition, the throttle valve 32 is shown in Fig. 5, which can be controlled via the digital-to-analog converter 62. The throttle valve 32 simulates different sized exhalation openings 7 in or at the mask 5 of the patient. By using the lung simulator 60, both inspiratory and expiratory events can be simulated. Thus, with an inspection apparatus according to FIG. 5, an equally large pressure and flow range can be traversed for calculating the characteristic field (s). A particular advantage of the embodiment according to FIG. 5 is that few breathing cycles simulated by the lung simulator 60 are sufficient to determine a sufficiently dense characteristic field for a CPAP device.

In order to increase the accuracy of the measurement results in a measuring apparatus according to FIG. 5, the piston in the lung simulator can be moved up or down at a constant speed

so that during such operation the airflow V remains constant.

Due to the known piston speed of the lung simulator can at

closed valve 32 of the air flow V can be calculated, so that the flow sensor 36, the resistors 36 to 39, the differential amplifier 40 and the analog-to-digital converter 41 can be omitted.

4 and 5, an additional pressure sensor may preferably be provided in the vicinity of the flow sensor 36. Such a pressure sensor makes it possible to calibrate the pressure sensor used in the CPAP device, that is to record a characteristic for the pressure sensor in the CPAP device, for example. This allows the use of less accurate and thus cheaper pressure sensors in the CPAP devices. In addition, this additional pressure sensor also allows a functional check of the pressure sensor in the CPAP device to be tested. 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 33 Digital-to-analog converter

2 blower 34 central processing unit

3 differential pressure sensor 35 electrical CPAP connection

10 4 Ventilation tube 30 36 Flow sensor

5 face mask 37, 38, 39 resistors

6 patient 40 differential amplifier

7 Exhalation port 41 Analog-to-digital converter

8 Ventilation hose connection 42 Display

15 9 Flow sensor 35 43 Keyboard

11 Motor 50 Three / two-way valve

21 motor drivers 51 blowers

22 Digital-to-analog converter 52 Digital-to-analog converter

23 central rake unit 53 blower

20 24 Analog-to-digital converter 40 54 Digital-to-analog converter

25 motor voltage 55 digital control line

26 electrical connection 56 digital control line

27 resistance 60 lung simulator

28 Analog-to-digital converter 61 Digital-to-analog converter

25 31 Air connection 45 62 Digital-to-analog converter

32 electrically controllable valve 63 wheel

Claims

claims:

A method of determining a mask pressure for pressure control in a CPAP apparatus, comprising the step of:

Calculating a target pressure for the location where a pressure sensor (3) is housed in the housing of the CPAP apparatus by adding a correction pressure to a constant pressure; characterized by the steps:

Calculating the correction pressure in response to the current airflow generated by the CPAP device; Repeating the two calculation steps;

Determining a first time when the airflow is 0; and measuring a first pressure by the pressure sensor (3);

Measuring a second pressure by the pressure sensor at a second time when the airflow is not equal to zero; Measuring the airflow at the second time; and

Calculating the pressure loss coefficient of the breathing tube (4) from the first and second pressure and the measured air flow at the second time.

2. The method according to claim 1, characterized by the steps:

Calculating the mean airflow from repeatedly measured values of the airflow; Determining a second time at which the airflow equals the middle one

Airflow is; and

Measuring the pressure at this second time.

3. The method according to claim 2, characterized by the steps: determining breathing cycles from the time course of the air flow; and calculating the average airflow as an average over an integer number of breathing cycles.

4. The method according to claim 3, characterized in that the derivative of the air flow is estimated and the negative peaks in the derivative, which occur in the transition from inhalation to exhalation, are used as the beginning and end of the breathing cycles.

5. The method according to any one of claims 2 to 4, characterized in that the temporal change of a moving average value of the air flow is evaluated.

A method of determining airflow in a CPAP apparatus, characterized by the steps of: determining first and second values, wherein the first value is proportional to one and the second value is proportional to another of the following quantities. a motor voltage; a current through the motor (11); an overpressure relative to the ambient pressure; a speed of the fan; and

Determine the airflow from the two values.

7. Method for determining the air pressure in a CPAP device. characterized by the steps:

Determining a first and a second value, wherein the first value is proportional to one of the following quantities and the second value is proportional to another of the following quantities: a motor voltage; a current through the motor (11); a speed of the fan; and determining the air pressure from the two values.

8. The method according to claim 6, characterized by:

Measuring the differential pressure between the pressure supplied by the blower (2) and the ambient pressure;

Measuring the electric current through the motor (11); and calculating the airflow from the differential pressure and the flow through the engine (11).

9. The method according to claim 6, characterized by:

Measuring the differential pressure between the pressure supplied by the blower (2) and the ambient pressure; Reading out a value proportional to the motor voltage (14); and

Calculating the air flow from the differential pressure and the value proportional to the motor voltage.

10. The method according to claim 8 or 9, characterized by the steps: 5 adjusting an air resistance by a test apparatus;

Setting a target pressure on the CPAP device;

Measuring an air flow through the test apparatus; and

Repeating the steps of adjusting an air resistance, adjusting the target pressure, and reading the motor voltage at different air currents and 10 target pressures.

11. The method according to any one of claims 8 to 10, characterized in that further calculates a characteristic field and stored in the CPAP device, wherein the characteristic field is constructed so that calculated at a predetermined pressure and predetermined motor voltage or current through the motor, the air flow can be.

15 12. The method according to any one of claims 1 to 6, characterized in that the air flow is measured by one of the methods according to claims 8 to 11.

13. CPAP device comprising: a fan (2); a central processing unit (23); 20, characterized in that the arithmetic unit (23) carries out a method according to one of claims 1 to 14.

14. Test apparatus comprising: an air connection (31) via which the test apparatus can be connected to a CPAP device;

25 a controllable valve (32) connected to the air port (31); a central processing unit (34) controlling the valve (32); and a CPAP electrical connection (35), via which the test apparatus can be connected to the CPAP device, wherein the central processing unit (34) via the Electrical CPAP port (35) can output a signal that causes a connected CPAP device to set a certain target pressure.

15. Test apparatus according to claim 14, characterized in that via the electrical CPAP connection (35) a characteristic measured by the tester to a connected CPAP device can be output.

16. Test apparatus according to claim 14, characterized in that the test apparatus via the electrical CPAP connection (35) from a connected CPAP device by the pressure sensor (3) of the CPAP device measured pressure and the motor (11) of the CPAP Device can read from the CPAP device voltage applied (14), and can transmit to the CPAP device a characteristic field, which represents a function when entering the measured by the pressure sensor (3) and the pressure applied to the motor (11) Voltage supplies the airflow.

17. Test apparatus according to one of claims 14 to 16, characterized in that the test apparatus is equipped with a flow sensor (36).