Device for measuring a person's respiratory activities

Abstract

Respiration measuring device for measuring the respiration of a person who is resting with his head on a headrest, with at least one flow measuring sensor, which is arranged in a position-maintaining manner relative to the head-resting surface and opposite the head-resting surface and which measures an exhalation by a flow change at the flow measuring sensor due to the breath flowing past it, and with at least one bridge circuit (1) with two voltage dividers, which has the at least one flow measuring sensor as a resistor of one of the two voltage dividers and which has two measuring poles between the voltage dividers, and with an evaluation device which is electrically connected to the two measuring poles of the at least one bridge circuit (1) and measures the breathing pauses of the person, characterized in that the flow measuring sensor comprises an exposed measuring element which is designed as a wire coil and an identical measuring element is provided which is introduced into a glass bulb and a plurality of flow measuring sensors are provided, each of which is arranged in a fixed position relative to the headrest surface.

Description

[0001] The invention relates to a respiration measuring device for measuring a person's breathing.

[0002] Respiration measuring devices are known in the prior art. WO 2016 / 027086 A1 describes a handheld monitoring device for a patient's breathing pattern. A mask is placed on the patient's face, which is designed to have little or no influence on respiratory activity. A disadvantage of this is that the mask remains permanently fixed on the patient's face during sleep, minimizing the influence of the airflow on the sensor located in the mask.

[0003] WO 02 / 062282 A1 discloses an infant incubator with contactless sensor and monitor monitoring. The sensors include an infrared sensor, a camera, microphones, and a speaker. The infrared sensor and camera are connected to video processing software for detecting respiration rate, heart rate, and skin perfusion.

[0004] US 2010 / 0145211 A1 describes a system for measuring a patient's respiratory activity, which includes a mask that is placed on the patient.

[0005] DE 10133120 C2 describes a hot-wire anemometer with two bridge circuits and US 2015 / 0309067 A1 also discloses a hot-wire anemometer with a downstream amplification element and a downstream signal processing unit.

[0006] US 2010 / 0145211 A1 discloses a flowmeter that also includes a mask placed over the patient's mouth and nose. The flowmeter includes a filament that serves as the resistance of a bridge circuit. A voltage signal from the bridge circuit is evaluated by an extraction circuit and a detection circuit.

[0007] DE 10 2005 000 964 B3 discloses a method for measuring a volume flow difference, which is particularly suitable for use in a ventilator with a first resistive flow sensor and a second resistive flow sensor, wherein the first resistive flow sensor is arranged in the inflow and the second resistive flow sensor is arranged in the outflow. Unfortunately, the apparatus is relatively complex.

[0008] US Pat. No. 4,036,217 discloses a measuring device using a hot-wire anemometer. Electrodes are applied to the patient's chest. Unfortunately, this also brings the patient into direct contact with the measuring device.

[0009] US 7,533,670 B1 discloses a respiration measuring device, in which sensors are also placed on the chest or in the nose and throat area of ​​the patient.

[0010] US 8,434,479 B2 concerns a hot wire anemometer in which a mask is also placed over the patient's mouth / nose area.

[0011] US 2011 / 0201956 A1 concerns a measuring device for diagnosing physiological parameters of the lungs, whereby a bronchoscope is inserted into the lungs via the trachea.

[0012] In addition, ventilators are known, such as the EvitaXL from Dräger Medical AG & Co. KGaA, but they are not suitable for monitoring respiratory pauses.

[0013] Another disadvantage of these respiration monitors is the fact that they feature a mask that must be tightly tightened over the patient's mouth and nose and must remain in place during respiration recording, especially while sleeping. Another disadvantage of these respiration monitors is that the tightened mask disrupts the patient's sleep rhythm.

[0014] It is therefore an object of the invention to provide a respiration measuring device as mentioned above which does not have the disadvantages mentioned.

[0015] This task is solved by a respiration measuring device for measuring the respiratory activity of a person resting with their head on a headrest. The person can be a patient, an adult, a child, or an infant, but the device can also be used on animals.

[0016] A person's respiratory activities can be measured in medical, industrial, military, or domestic settings, while awake, but preferably while asleep. For this purpose, the person is conveniently lying on a substantially horizontal surface with the person's head resting on a portion of the surface, the headrest.

[0017] The respiration measuring device according to the invention has at least one flow measuring sensor, which according to the invention maintains its position relative to the head support and is arranged opposite the head support. The at least one flow measuring sensor is arranged in a position-maintaining manner relative to the head support during the measurement of the person's respiration, even while the person is sleeping, and preferably throughout the entire measurement process, so that the person can move their head without the at least one flow measuring sensor moving with it. The at least one flow measuring sensor remains in a position-maintaining manner relative to the head support during the measurement and preferably remains stationary in the room. According to the invention, no mask is required. A mask is not part of the respiration measuring device according to the invention. The respiration measuring device is maskless.During the measurement of respiration, the person's head is arranged between the headrest and the at least one flow measuring sensor; usually, the at least one flow measuring sensor is arranged vertically above the headrest.

[0018] The at least one flow measuring sensor is preferably attached to a holder which can run at a distance from and above the headrest surface. The holder can be a preferably horizontally arranged rod. The rod is advantageously attached to a stand on the floor or directly to a bed frame in which the person is lying. Other types of attachment are also conceivable. Position-maintaining is to be understood broadly. The relative arrangement does not have to be permanently fixed, such as attachment to the bed frame, but can also be changeable, such as the stand next to the bed frame. During operation, in particular during measurement, the flow measuring sensor is immobile in relation to the headrest surface despite possible head movements of the person, in particular during sleep.

[0019] The respiratory measuring device according to the invention is designed to be contactless. Breath measurements are taken without the need to touch the person through the device, for example, in the form of a mask. Contact independent of pure respiratory measurements, such as pulse measurements, is still possible.

[0020] The at least one flow sensor according to the invention is preferably designed as at least one temperature sensor. It measures temperature changes due to the airflow flowing past it during exhalation. The breath flowing past the temperature sensor causes a temperature change, preferably at the temperature sensor or in areas of the outer surface of the temperature sensor. Preferably, the existence of respiratory pulses is measured, i.e., the fact of whether inspiration or expiration has occurred is indicated by a sudden temperature change at the temperature sensor. If no inspiration or expiration occurs, no pulses are measured. The respiration measuring device according to the invention is therefore used in particular for measuring apnea or preventing sudden infant death syndrome.

[0021] The respiration measuring device according to the invention comprises at least one bridge circuit with two voltage dividers, which has the at least one flow measuring sensor as a resistor of one of the two voltage dividers and which has two measuring poles between the voltage dividers.

[0022] Each of the at least one flow sensor is assigned a separate bridge circuit with two voltage dividers, and each flow sensor is provided as a resistor for one of the two voltage dividers. If the respiration measuring device has two or more flow sensors and two or more bridge circuits, according to the invention, each flow sensor is assigned exactly one separate bridge circuit, wherein the bridge circuits and the flow sensors assigned to them are essentially identical to one another, preferably of identical construction.

[0023] According to the invention, an evaluation device is also provided which is electrically connected to the two measuring poles of the at least one bridge circuit and which measures and preferably signals the pauses in the breathing of the person.

[0024] According to the invention, the flow sensor, in particular the temperature sensor, has a measuring element that is completely exposed to the ambient air. Essential to the invention is that the measuring element of the temperature sensor is completely exposed to the ambient air, whereby "completely exposed" is understood here to mean that the person's breath flow, at least when the person's mouth is positioned in front of the temperature sensor in the direction of the breath flow, impinges on the measuring element without interference.

[0025] During operation of the respiration measuring device, the measuring element preferably has an operating temperature of over 100°C, preferably between 100°C and 300°C. Other operating temperatures are also possible. The measuring element is preferably heated to an operating temperature significantly above ambient temperature or room temperature, so that the person's breathing impulses during exhalation, even if the airflow only or only partially passes the measuring element, lead to a temperature change, preferably a temperature decrease, of the measuring element, preferably of a region of the measuring element.

[0026] The temperature change of even just one area of ​​the measuring element generates an ohmic resistance change of the measuring element, which can be detected at the temperature sensor as a change in a voltage difference by means of the bridge circuit.

[0027] The measuring element can be the filaments of a standard incandescent lamp. The filaments are made of tungsten wire with a diameter of 10 to 30 µm. The tungsten wire is typically 99% ±1% tungsten.

[0028] However, it is also conceivable to use conductively coated carriers as measuring elements, which are brought to an operating temperature above room temperature.

[0029] However, it has proven particularly advantageous to use the wire filaments of incandescent lamps as temperature sensors. This involves removing a glass bulb from the lamp. The remaining bulb is screwed into a conventional socket with its thread, forming the temperature sensor.

[0030] The bridge circuit of at least one temperature sensor is balanced when the person is not breathing, i.e. no air flow passes the temperature sensor, i.e. no voltage can be measured between the two measuring poles of the bridge circuit.

[0031] In the balanced state, a sufficiently strong current still flows through the at least one temperature sensor to bring the temperature sensor, in particular the measuring element, preferably the wire coil, to the aforementioned operating temperature and maintain it there. In the operating state, the temperature sensor has a hot resistance that differs sufficiently from the cold resistance.

[0032] Although the energy stored in the wire coil is very low, for safety reasons, the wire coil may be surrounded by a wire mesh permeable to ambient air to prevent accidental contact.

[0033] Preferably, the at least one flow sensor is positioned at a distance of between 10 and 30 cm from the patient's mouth. Any distance between these values ​​is disclosed. However, larger distances are also possible. Of course, the distance varies depending on the patient's head movements.

[0034] According to the invention, a resistor of the bridge circuit, preferably connected in parallel with the flow sensor, in particular the temperature sensor, comprises a measuring element of the same construction as the measuring element of the temperature sensor, but which is shielded from the ambient air in a way that prevents the flow of breathing air from entering. The identical measuring element, which, unlike the measuring element of the temperature sensor, is shielded from the breathing air flow, balances out longer-term temperature changes in the bridge circuit, for example, changes in room temperature.Thus, long-term temperature changes are recorded in the same way by both the at least one temperature sensor and the at least one identical measuring element, leading to an equal change in resistance and balancing the bridge circuit, while the short-term temperature changes caused by the breathing impulses are only recorded by the at least one temperature sensor, while the identical measuring element is shielded in a breathing air flow-tight manner.

[0035] Particularly preferably, the identical measuring element is also designed as a wire coil, preferably as an identical wire coil, wherein the identical wire coil is arranged in a glass bulb, and the glass bulb advantageously has a hole with a diameter of 1 to 3 mm, through which the identical wire coil is in air-conducting contact with the ambient air, but is also shielded to prevent breathing air flow. In practice, the temperature sensor is therefore formed by a light bulb from which the glass bulb is removed, while the identical wire coil is arranged in an identical light bulb, in whose glass bulb the above-mentioned hole is introduced to prevent breathing air flow.

[0036] To adjust the operating current of at least one temperature sensor, an adjustable resistor is advantageously connected in series with the bridge circuit. This resistor can be used to adjust the temperature sensor's hot resistance. The temperature sensor's hot resistance is advantageously set to one of the aforementioned temperatures.

[0037] According to the invention, a plurality of flow measuring sensors, in particular temperature sensors, are provided, each of which is arranged in a fixed position relative to the head surface.

[0038] It has been shown that when using a single temperature sensor, measurements of the breath pulses during a person's exhalation vary in strength depending on the position of the person's mouth relative to the temperature sensor. When the breath is directed directly toward the temperature sensor, a greater temperature change is observed than when the head is tilted to the side, where the breath only results in a smaller airflow at the temperature sensor.

[0039] Therefore, according to a further development of the invention, the above-described structure of a temperature sensor is preferably provided in multiple locations. A plurality of temperature sensors is provided, each of which is fixedly positioned at different locations relative to the headrest. It has been shown that, for measuring respiratory pulses, it is sufficient to arrange a plurality of temperature sensors transversely to the longitudinal direction of the person's body, i.e., along the direction of rotation of the person's head or mouth, since, depending on the rotational position of the head, at least one of the temperature sensors receives a sufficiently strong exhalation pulse.

[0040] It has been shown that just four temperature sensors are sufficient to reliably detect a person's exhalation pulse, regardless of head rotation. However, it is also conceivable that any higher or lower number of temperature sensors could be used.

[0041] The evaluation device preferably comprises a summation circuit that sums the measured values ​​of the plurality of temperature sensors at different and multiple points in time, preferably continuously. This can be used, in particular, to determine whether a respiratory impulse is present or not.

[0042] In a further development of the respiration measuring device according to the invention, weighting factors that can be assigned to the temperature sensors can be determined by the evaluation device, and higher weighting factors are assigned to the temperature sensors that are more strongly affected by the air flow during exhalation than to the temperature sensors that are less strongly affected by the air flow during exhalation.

[0043] This allows information to be obtained, for example, about the rotation of the person's head, the frequency of head rotation, etc. Background noise can also be reduced. Ideally, a decision processor is installed in the evaluation device that only considers the measurement pulses when, for example, a minimum value is exceeded. This means that only the measured values ​​from the temperature sensors located directly in front of the person's mouth are taken into account, allowing a head movement profile to be detected. The decision processor can also order the size of the measurement pulses and determine the weightings accordingly.

[0044] Particularly preferably, the evaluation device comprises at least one analog filter and at least one analog amplifier, which are electrically connected to the two measuring poles of the bridge circuit.

[0045] Preferably, when a plurality of temperature sensors are present, a plurality of bridge circuits, preferably also a plurality of amplifiers and filters, are provided, each of which is assigned to one of the bridge circuits.

[0046] To evaluate the voltage signals between the measuring terminals of the bridge circuit, the evaluation device according to the invention is provided, which preferably comprises two operational amplifiers connected as low-pass filters. The operational amplifiers can be coupled to each other via a high-pass filter. A bandpass filter formed from a high-pass and low-pass filter is advantageously asymmetrical and permeable to signals with frequencies between 0.15 Hz and 20 Hz. The average and usual respiratory rate is one breath every four seconds, so the aforementioned bandpass filter has proven to be useful. Of course, the bandwidths of the bandpass filter are adjustable and can be adapted to the individual.

[0047] Conveniently, an A / D converter is connected downstream of the analog amplifier and filter, which converts the analog measurement signals into digital measurement signals. Digitization has proven advantageous for comparing the digital measurement values ​​with a threshold value after digitization or for performing digital filtering. The threshold value is set so that the ever-present background noise does not distort the evaluation results. This noise typically produces significantly smaller voltage measurements than an exhalation pulse. The exceedance of the threshold value, caused solely by the exhalation pulse, is recorded.For this purpose, a microcontroller or digital signal processor (DSP) is connected downstream of the A / D converter. This compares the digitized measured values ​​with the threshold value. If the threshold value is exceeded, it measures a measurement signal regardless of the extent of the excess. It determines a time interval between consecutive measurement signals and generates a warning signal if the time interval is greater than a predefined maximum time. For apnea detection, the maximum time is ideally set to 12 seconds ± 2 seconds.

[0048] The invention is described using an exemplary embodiment in twelve figures. These show: Fig. 1 a block diagram of a signal processing system according to the invention, Fig. 2 a bridge circuit without adjustable resistance, Fig. 3a, Fig. 3b, Fig. 3c Voltage measurements of different wire coils at different distances, Fig. 4 a graphical representation of the measured values ​​in Fig. 3a against 1 / r 2 , Fig. 5a, Fig. 5b an analog voltage curve at the bridge circuit according to Fig. 2 when simulating exhalation by operating an air pump, Fig. 6 a digitized voltage measurement curve over time for a person lying on his back and breathing towards the temperature sensor 17 cm away, Fig. 7 a digitalized voltage measurement curve over time for a person in front of whose mouth the temperature sensor is placed at a distance of 20 cm, Fig. 8 a digitized voltage curve over time when the person is lying on his back and the temperature sensor is at a distance of 11 cm from the nose through which he breathes, Fig. 9 a schematic diagram of a respiration measuring device with a plurality of temperature sensors.

[0049] A problem today is the sleep-robbing breathing disorder apnea. Approximately five percent of the population is affected. The consequences of apnea are fatigue, lack of concentration, and headaches, which can lead to increased cortisol levels, persistent stress, and, in the case of breathing pauses, life-threatening situations. The breathing monitor according to the invention is proposed to diagnose such situations early and without the need for complex equipment.

[0050] The respiration monitor has at least one flow sensor for measuring the smallest respiratory airflows. Apnea is recorded as the person's lack of respiratory airflow.

[0051] The flow sensor for measuring the finest respiratory air flows is designed as a temperature sensor. In this embodiment, the temperature sensor according to the invention consists of a wire coil arranged inside conventional light bulbs. The ohmic resistance of the wire coil changes due to the temperature change of the wire coil in the respiratory air flow. The basic signal processing is shown in a block diagram in Fig. 1. The change in resistance causes small changes in the measured voltage in a bridge circuit 1, into which the temperature sensor is inserted. These changes are then amplified and filtered with high sensitivity in an amplifier and bandpass filter. These changes are digitized with the aid of an A / D converter 3, stored in a data logger 4, and evaluated in a diagnostic unit 6. A warning signal is also emitted from there if necessary.

[0052] A significant improvement over conventional respiration monitors is that the temperature sensor detects respiratory airflow without contact, even at a distance of a few centimeters from the sleeper's mouth and / or nose. This means that the sleeper is not touched by the respiration monitor, even through a conventional mask, and their sleep is not disturbed.

[0053] The respiratory rate is typically 0.2 to 0.25 Hz, but in newborns it can be as low as 0.6 to 0.7 Hz. The tidal volume of one exhalation is typically 0.5 liters, and the respiratory pressure is 50 to 100 mbar. The respiratory flow velocity is approximately V=0.8 m / sec.

[0054] The design of the temperature sensor is crucial to the invention of the respiration measuring device. The temperature sensor comprises a wire coil. A glass bulb of the light bulb is removed, leaving the wire coil completely exposed. It has full contact with the ambient air. The wire coil can remain in the lamp thread. The lamp thread is screwed into a conventional lamp socket, and the resulting assembly is used as a temperature sensor.

[0055] It has proven beneficial to heat the wire coil to an operating temperature higher than room temperature. However, the wire coil should not yet glow, as this would cause it to burn out. The breathing air flow passing by the wire coil cools the heated wire coil and thereby changes its ohmic resistance. The equation for the temperature dependence of the ohmic resistance of wires for small temperature changes ΔR=R0αΔT, where ΔR = R T - R0 is the temperature-dependent resistance change, and R0 is the resistance at a specific reference temperature. This equation is also used approximately here. The resistance is given at a temperature of 20 °C, ΔT denotes the temperature difference from this reference temperature, and α is the linear, positive temperature coefficient of the wire coil. The exhaled air passing the temperature sensor is likely to have a temperature of approximately 20-30 °C. The exhaled air therefore leads to a reduction in the temperature of the wire coil, at least on its surface, and thus also to a reduction in the ohmic resistance of the wire coil.

[0056] The temperature sensor is supplied with power in a bridge circuit described below.

[0057] The wire coil of the temperature sensor has a cold resistance R0, approximately the warm resistance R T= R0 (1 + αΔT + βΔT 2 ), where β is significantly smaller than α. α is the linear temperature coefficient of tungsten or the material from which the wire coil is constructed. The relationship between temperature change and resistance change is thus: ΔT=RT−R0αR0 For tungsten, α = 4.5 10 -3 / °C and β = 9.62 10 7 / °C.

[0058] The temperature sensor is integrated in a bridge circuit according to Fig. 2 is installed as one of the resistors R1. The bridge circuit is balanced at operating temperature. The current operating temperature is approximately 300 °C, significantly higher than room temperature. This allows air currents at room temperature to cool the filament and be detected as a change in resistance. Furthermore, the filament can quickly warm up again after cooling. The remaining resistors R2, R3, and R4 are dimensioned so that the basic circuit is balanced in operating condition, i.e., the measuring voltage U Mess = 0. To more easily determine the current through the temperature sensor branch of the bridge circuit, and thus through the heat resistance of the wire coil, large resistors are chosen for R3 and R4, preferably in the kΩ range. Favorable currents are approximately one-quarter to one-third of the normal operating current of the incandescent lamp.

[0059] The measuring voltage is obtained in the bridge circuit according to Fig. 2 to: UMess=UB(R3R3+R4−R1R1+R2), if the ratio of the resistors R1 / R2 of one voltage divider corresponds to the ratio of the resistors R3 / R4 of the other voltage divider.

[0060] Three series of tests were carried out using different wire coils as temperature sensors. In each case, the Fig. The bridge circuit shown in Figure 2 is used to measure voltage.

[0061] In the first test setup, a large wire coil of a 60W / 220V incandescent lamp with a hot resistance of 71 Ω and an operating temperature of 420 °C was used; the measurement results are shown in Fig. 3a. The wire coil is a tungsten wire coil. Exhalation was simulated by an air pump. A pump head was installed parallel to the wire coil with the air outlet directed toward it. The distance between the wire coil and the pump head was gradually changed by a few centimeters, and the voltage measurements U Mess measured as a function of the increasing distance. The first measurement was taken at a distance of 30 cm, and the distance was then increased in 5 cm steps. Fig. Figure 3a shows that the measured voltage decreases depending on the distance between the pump head and the wire coil, which is due to the decreasing intensity of the air flow with increasing distance from the wire coil. Measurement errors caused by external factors, such as drafts or similar, can occur, as was the case with the measurement at a distance of 40 cm.

[0062] The measurement curve shows that, starting at a distance of approximately 55 cm and with a measurement sensitivity of 20 mV / cm, the voltage measurements of the airflows are no longer clearly distinguishable from background noise. It should be noted that the air pump presumably delivers stronger and more regular airflows than normal breathing.

[0063] In a second experiment, a medium-sized wire coil of a light bulb with 3.8V / 0.07A and a cold resistance of 3.6Ω was used, the measurement results are shown in Fig. 3b. The measured voltages are significantly lower; the sensitivity in the second test is 0.5 mV / cm. The wire coil has a hot resistance of 1.97 Ω and an operating temperature of approximately 250 °C. Here, too, the second value is an outlier, presumably due to other air movements. The decrease in the measured voltage with distance is also clearly visible.

[0064] In a third experiment, a small filament lamp coil with 6.7 Ω was used. The coil has a hot resistance of 6.61 Ω at an operating temperature of approximately 230 °C. The measurement results are shown in Fig. 3c. Again, an outlier is likely to be present at a distance of 55 cm, the measured curve should be approximately proportional to 1 / r 2 The voltage measurements are in the microvolt range.

[0065] In Fig. 4 are the measured values ​​that correspond to the Fig. 2 shown bridge circuit, against the reciprocal square of the distance (1 / r 2 ) between sensor and air flow source, the linearity of the curve confirms the relationship.

[0066] The bridge circuit also features an adjustable resistor R5, which allows the current I1 through the temperature sensor R1 to be adjusted. The current I1 is adjusted so that the wire coil of the temperature sensor R1 reaches the operating temperatures described above, at which the bridge circuit is preferably balanced.

[0067] The Fig. 5a, Fig. 5b shows the analog voltage curve at the bridge circuit when simulating regular breathing by periodically operating an air pump. Fig. 5a the large wire coil is used. In the Fig. Figure 5b shows the voltage curve using the small wire coil.

[0068] After the analogue tests described above, the measurement results were digitally evaluated. Since exhalation produces a much weaker signal than the air pump used above, an amplifier circuit was used according to Fig. 5. This or a corresponding amplifier circuit is also used in the respiration measuring device according to the invention.

[0069] In the respiration measuring device, the measurement pulses generated by temperature changes are amplified between the two measuring terminals P1 and P2 using a two-stage amplifier circuit. Each amplifier stage has an operational amplifier Op1 and Op2, each configured as a low-pass filter. The two amplifier stages can be coupled via a high-pass filter. The high-pass filter can also be omitted if necessary.

[0070] The amplified and filtered signal is fed to an A / D converter 3, and the converted digital signals are fed to a microcontroller or a digital signal processor (DSP) and evaluated there.

[0071] Fig. Figure 6 shows the measurement curve for a person lying supine and breathing toward the temperature sensor. The temperature sensor is positioned 17 cm from the person's mouth, suspended freely in the air.

[0072] Fig. Figure 7 shows the measurement results of a test that simulates a sleeping situation as realistically as possible. For this test, a person sleeps beneath the temperature sensor. The temperature sensor is positioned approximately 20 cm from the mouth. The temperature sensor is not suspended vertically above the head, but is positioned slightly offset toward the feet, so that the exhaled airflow hits the temperature sensor as centrally as possible. Fig. The measured voltage signals shown in Figure 7 clearly show the breaths, with each peak representing a single breath. Since the measurement was performed with only one temperature sensor, there are periods in which the measurement signal becomes smaller; this can be seen particularly in the rectangular, enlarged and marked area in the graph in Fig. 7. At the beginning of the marked area, the peaks are clearly visible until the person has presumably turned. After that, the peaks are no longer visible. Before the person turns, the respiratory impulses are clearly visible against the background noise. Fig. The measurement curve shown in Figure 7 is used as the basis for further evaluation to generate a signal tone. A threshold value U schThis ensures that the measured values ​​are easily processed. This prevents the results from being distorted, as noise amplitudes are normally smaller than the respiratory peaks. The respiratory peaks are always recorded with the same amplitude, the exceeded threshold U sch , registered; as soon as the threshold is reached, the microcontroller or the digital signal processor (DSP) receives a breathing signal.

[0073] Fig. Figure 8 shows the digitized measured values ​​over time in a test setup in which the person lies on their back and the temperature sensor is 11 cm away from the nose through which they breathe. The threshold value U sch which is suitable for distinguishing apnea from normal breaths, whereby the threshold value U sch above a constant background noise. In this case, a threshold of U sch =1,500 mV. If the threshold value Usch This excess is registered as exhalation and a time counter is reset to zero. If longer than a maximum time value t h of for example t h =10 s no further exceedance of the threshold value U sch occurs, after the maximum value t h A warning tone is emitted. This is indicated by a horizontal bar in the Fig. 8. The warning tone remains until the threshold U sch is exceeded again.

[0074] In Fig. 9 is the respiration measuring device with a plurality of temperature sensors with associated signals s1, ..., s Mwhere M indicates the number of temperature sensors. The individual measurement signals are measured in a bridge circuit 1 as in the case of the single temperature sensor described above and amplified and filtered in an amplifier and a bandpass filter 2, then converted into digital signals in the A / D converter 3 and subsequently filtered in a digital filter 5. The individual signals s1, ..., s m The temperature sensors can then be summed in a summation circuit 10.

[0075] The individual signals s1, ..., s M can be weighted with w1 to w M weighted, which are determined, for example, as follows: wi=si∑j=1Msj, i=1,…,M The weightings w iare determined using a comparator 11. For example, if the temperature sensor with the signal s1 is breathed, i.e. the mouth or nose is positioned directly in front of the temperature sensor with the signal s1, s1 > s2, s3, ... s M . The temperature sensor with signal s1 provides the largest signal. The other temperature sensors with signals s2, ..., s M record either the weakened respiratory signal or only the ambient noise. To minimize the noise components, the signals are i not evaluated equally, but the signals s i are determined by the different weighting factors w1,...,w M weighted. The strongest signal, in this example s1, is given the most weight. By dividing the individual signals s i by the sum of all signals ∑j=1Msj or the sum of the other signals ∑j=1Msjj≠i the factor wi of the temperature sensor with the largest signal s i This means that the noise can compare the strongest respiratory signal of the affected temperature sensor with the signal s i no longer have such a significant impact. In addition to providing information about whether breathing is present or not (12), it can also determine whether the person has turned their head (13). List of reference symbols 1 bridge circuit 2 bandpass filters 3 A / D converters 4 data loggers 5 digital filters 6 Diagnostic unit 10 Summation circuit 11 Comparator 12 Information 13 Information

Claims

[1] Respiration measuring device for measuring the respiration of a person who rests with his head on a headrest, with at least one flow measuring sensor, which is arranged in a position-maintaining manner relative to the head-resting surface and opposite the head-resting surface and which measures an exhalation by a flow change at the flow measuring sensor due to the breath flowing past it, and with at least one bridge circuit (1) with two voltage dividers, which has the at least one flow measuring sensor as a resistor of one of the two voltage dividers and which has two measuring poles between the voltage dividers, and with an evaluation device which is electrically connected to the two measuring poles of the at least one bridge circuit (1) and measures the breathing pauses of the person, characterized bythat the flow measuring sensor comprises an exposed measuring element which is designed as a wire coil and an identical measuring element is provided which is introduced into a glass bulb and a plurality of flow measuring sensors are provided, each of which is arranged in a fixed position relative to the headrest surface. [2] Respiration measuring device according to claim 1, characterized by that the flow measuring sensor includes a temperature sensor. [3] Respiration measuring device according to claim 2, characterized by that the temperature sensor includes the measuring element which is completely exposed to the ambient air. [4] Respiration measuring device according to claim 1, 2 or 3, characterized by that the measuring element is heated to over 100 °C during operation, preferably between 100 °C and 300 °C. [5] Respiration measuring device according to claims 1 to 4, characterized bythat a resistor of the bridge circuit (1) connected in series with the flow measuring sensor comprises the measuring element which is identical in construction to the flow measuring sensor and which is shielded from the ambient air in a breathing air flow-tight manner. [6] Respiration measuring device according to claim 1, characterized by that the glass bulb has a hole through which the identical wire coil is in air-conducting contact with the ambient air. [7] Respiration measuring device according to claim 2, characterized by that the bridge circuit (1) is connected in series with an adjustable resistor with which a warm resistance of the temperature sensor can be adjusted. [8] Respiration measuring device according to claim 1, characterized by that the flow measuring sensors are arranged next to each other across the headrest surface and opposite the headrest surface. [9] Respiration measuring device according to claim 1 or 8, characterized bythat the evaluation device comprises a summation circuit (10) which sums up the measured values ​​of the plurality of flow measuring sensors at different times. [10] Respiration measuring device according to claim 9, characterized by that weighting factors can be determined in the evaluation device which can be assigned to the flow measuring sensors, and temperature sensors which are more strongly affected by the air flow during exhalation are assigned higher weighting factors than flow measuring sensors which are less strongly affected by the air flow during exhalation. [11] Respiration measuring device according to claim 10, characterized by that each of the flow measuring sensors is a resistor of one of the bridge circuits (1). [12] Respiration measuring device according to one of claims 1 to 11, characterized bythat the evaluation device comprises at least one analog filter (2) and at least one analog amplifier, which are electrically connected to the two measuring poles of the bridge circuit (1). [13] Respiration measuring device according to claim 12, characterized by that the at least one analog amplifier is followed by an A / D converter (3) which converts the analog measurement signals into digital measurement signals and which is followed by a digital filter (5). [14] Respiration measuring device according to claim 13, characterized by that the digital filter (5) is designed as a low-pass filter whose cut-off frequency is below 50 Hz. [15] Respiration measuring device according to claim 14, characterized bythat the evaluation device comprises a microcontroller (7) which compares the digitized measured values ​​with a threshold value and registers a measurement signal when the threshold value is exceeded, and determines a time interval between successive measurement signals and generates a warning signal when the time interval is greater than a predetermined maximum time value.

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