Control of light source of pulse oximeter
By receiving sensor signals and adjusting light source control parameters and dynamically adjusting the light source current, the problem of high current consumption of pulse oximeter is solved, and the balance of current saving and measurement accuracy in portable applications is achieved.
Patent Information
- Application Number
- CN202510158652.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-02-13
- Filing Date
- 2025-02-13
- Publication Date
- 2025-08-15
AI Technical Summary
The existing pulse oximeters consume high current when the battery is running, especially in portable applications, with limited energy budget, and the current adjustment is not flexible enough when the sensor signal quality fluctuates, which affects the measurement accuracy.
By receiving the sensor signal, determining the scaling factor and adjusting the brightness and color control parameters of the light source, dynamically adjusting the light source current according to the amplitude change curve of the sensor signal to ensure measurement accuracy and reduce current consumption.
While maintaining measurement accuracy, the light source current is dynamically adjusted, which reduces current consumption, improves the stability of sensor signal quality, adapts to changes in different physiological conditions, and extends the use time of portable equipment.
Smart Images
Figure CN120477764A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for controlling a light source of a pulse oximeter. The invention also relates to a control unit, a computer program and a computer-readable medium for implementing the method, and a pulse oximeter. Background Art
[0002] A pulse oximeter is generally a device for determining the oxygen saturation of arterial blood in a non-invasive manner by measuring light absorption or light emission during fluoroscopy of blood-filled body tissue. Such a pulse oximeter can also be used for pulse rate monitoring.
[0003] Pulse oximeters are increasingly being used in battery-powered portable applications. For example, a pulse oximeter can be installed on a patient during emergency transport and remain with the patient during transfers between different hospital departments. Furthermore, pulse oximeters can be used as plug-in modules for multi-parameter patient monitors with limited energy budgets. Such applications are leading to a growing demand for pulse oximeters with lower current consumption. Summary of the Invention
[0004] The object of the present invention can be seen as providing a method by which the current consumption of a pulse oximeter, in particular a battery-operated pulse oximeter, can be reduced without significant loss of quality. A further object of the present invention can be seen as providing a control unit, a computer program, and a computer-readable medium for implementing such a method, as well as a corresponding pulse oximeter.
[0005] These objects are achieved by the subject matter of the independent claims. Advantageous embodiments of the invention are set forth in the dependent claims, the following description and the attached drawings.
[0006] A first aspect of the present invention relates to a method for controlling an (electrical) light source of a pulse oximeter. In addition to the light source, the pulse oximeter also includes a light sensor configured to convert light components transmitted and / or reflected by a body part when illuminated by light from the light source into an (electrical) sensor signal. The method comprises: receiving the sensor signal and a current value of at least one control parameter for controlling the brightness and / or color of the light source; determining a scaling factor from the time profile of the amplitude of the sensor signal while taking into account a setpoint value for the amplitude; determining a new value for the at least one control parameter by multiplying the current value by the scaling factor; and applying the new value to the at least one control parameter.
[0007] The method makes it possible to save current during operation of the pulse oximeter by, for example, firstly reducing the current flowing through the light source, referred to below as the light source current, as long as the quality of the photoplethysmograms (PPG) from the sensor signal is still sufficient and the required accuracy is still achieved, and secondly increasing this current if greater noise is present or the quality of the sensor signal generally deteriorates.
[0008] In order to ensure sufficient quality when determining the blood oxygen saturation, the amplitude of the pulsatile component of the sensor signal in the PPG (also referred to as the AC component) should not be less than a certain value.
[0009] In general, the amplitude of the sensor signal behaves approximately linearly with respect to the light source current in each patient, because physiological factors that influence light absorption by blood-supplied body tissue, such as finger thickness or skin color, do not change significantly during the measurement.
[0010] In order to ensure that the AC component lies within the desired range, the light source current can be adjusted accordingly during operation, for example, using the method. Excessively strong and / or excessively frequent adjustments should be avoided.
[0011] The method may be computer-implemented.
[0012] The steps of the method can be performed continuously, ie, repeated cyclically, during operation of the pulse oximeter. In other words, the value of at least one control parameter can be periodically updated by means of the method at specific time intervals, such as 0.01 s, 0.1 s, 1 s, or 10 s.
[0013] A “sensor signal” may be understood as an analog electrical signal or a digital electrical signal. An “amplitude” may be understood in particular as the amplitude of the AC component of the sensor signal.
[0014] For example, a "control parameter" may be understood to be one of the following parameters: the current flowing or intended to flow through the light source (e.g., between 3 mA and 50 mA); the voltage applied or intended to be applied to the light source; an adjustable series resistor connected upstream of the light source; the frequency at which the light source is switched on and off; and the time ratio between the on-phase, in which the light source is switched on, and the off-phase, in which the light source is switched off. For example, the frequency may be a clock frequency and / or the time ratio may be a duty cycle within the context of pulse width modulation of the light source. The current value of at least one control parameter may be an adjusted and / or measured and / or estimated value.
[0015] "Color" can be understood as a wavelength or a wavelength range of the electromagnetic spectrum. Different colors can differ from each other in terms of their wavelength or in terms of their wavelength range.
[0016] A "setpoint value" can be understood as a fixed, predetermined, or variable desired value for the amplitude of the sensor signal. For example, the variable setpoint value can be varied during operation based on changes in specific (measured or estimated) physiological factors of the respective patient. For example, the setpoint value can be between 2 nA and 3 nA, preferably 2.5 nA.
[0017] The new value may be equal to the product of the current value and the scaling factor or may be a value determined based on the product of the current value and the scaling factor. Application of the new value may result in adjusting the brightness and / or color of the light source according to the new value of the at least one control parameter (rather than the current value).
[0018] A second aspect of the present invention relates to a control unit comprising the following means: the means are configured to implement the method described above and below.
[0019] In general, the device may comprise hardware modules and / or software modules. In particular, the device may comprise a processor configured to implement a (computer-implemented) method. Additionally, the device may comprise a memory and / or a data communication interface for wireless and / or wired data communication with a peripheral device, such as a smartphone, a smartwatch, a tablet, a tablet, a PC or a ventilator. Alternatively, the control unit may be implemented solely as hardware, for example in the form of an ASIC structure group (ASIC=application-specific integrated circuit) or an FPGA structure group (FPGA=field-programmable gate array).
[0020] It should be pointed out that features of the method described above and below may also be features of the control unit (and vice versa).
[0021] A third aspect of the present invention relates to a pulse oximeter. The pulse oximeter includes a light source, a light sensor, and a control unit as described above and below. The light sensor is configured to convert light components transmitted and / or reflected from a body part when illuminated by light from the light source into (electrical) sensor signals.
[0022] The pulse oximeter, for example its control unit, can be designed to determine the blood oxygen saturation (sO 2 ) and / or the pulse from the sensor signal by means of absorption spectroscopy.
[0023] For example, a "light source" may be understood to mean a light emitting diode, a laser diode, an incandescent lamp, or a combination of at least two of these examples. In particular, the light source may be configured to emit light in at least two different predetermined wavelength ranges, such as red light, (near) infrared light, or green light. Examples of suitable wavelength ranges are 660 nm, 750 nm to 850 nm, and 905 nm to 940 nm.
[0024] For example, a “light sensor” may be understood as a photodiode, a photocell, a CMOS sensor (CMOS=complementary metal-oxide-semiconductor), a CCD sensor (CCD=charge-coupled device), or a combination of at least two of these examples.
[0025] "Pulse oximeter" can also be understood as a CO oximeter.
[0026] For example, the pulse oximeter may be configured as a clip for fastening to a body part, such as a finger, an earlobe, or a hand joint.
[0027] The pulse oximeter can be designed such that the light source and the light sensor can be arranged on the same side of the body part and / or on opposite sides of the body part.
[0028] Further aspects of the invention relate to a computer program and a computer-readable medium on which the computer program is stored.
[0029] The computer program comprises instructions which, when the computer program is executed by a processor, for example a processor of a control unit described above and below, cause the processor to carry out the method described above and below.
[0030] The computer-readable medium may be a volatile or non-volatile data storage device. For example, the computer-readable medium may be a hard disk, a USB (USB=universal serial bus) storage device, a RAM (random-access memory), a ROM (read-only memory), an EPROM (erasable programmable read-only memory), an EEPROM (electrically erasable programmable read-only memory), a flash memory, or a combination of at least two of these examples. The computer-readable medium may also be a data communication network or a cloud that enables the download of program code (e.g., via the Internet).
[0031] It should be pointed out that features of the method described above and below may also be features of the computer program and / or of the computer-readable medium (and vice versa).
[0032] Hereinafter, various embodiments of the present invention are described, which should not be construed as limiting the scope of the present invention.
[0033] According to one embodiment, an average value can be determined from the time profile of the amplitude. This average value can then be used to determine the scaling factor. The term "average value" can be understood, for example, as the arithmetic mean, geometric mean, square mean, or exponentially smoothed mean. The average value can be understood as a quality index ("QI") associated with the sensor signal.
[0034] According to one embodiment, a quotient can be formed from the average value and the setpoint value to determine the scaling factor. The scaling factor can be equal to the quotient or a value determined based on the quotient. The quotient can be formed by dividing the average value by the setpoint value or vice versa.
[0035] According to one embodiment, the average value can be a sliding average value. The sliding average value can be a simple or weighted sliding average value. This allows the sensor signal to be effectively smoothed before further processing. The sliding average value acts like a low-pass filter. In principle, the sliding average value can be determined by sampling the sensor signal segmentally within a window over a number of consecutive time steps. In each of these time steps, an average value can be calculated from the values of the sensor signal within the corresponding window. The window can then be shifted so that it partially overlaps the window of the previous time step. For example, the window can be shifted between (immediately following) consecutive time steps so that the last value in the last sampled segment of the sensor signal is removed from the window and the first value of the sensor signal in the currently sampled segment (i.e., the first value after the last sampled segment) is included in the window. The average value can then be recalculated from the values in the updated window. Additionally, the values in the window can be weighted in a suitable manner. The window can be fixedly predetermined in its width, i.e. constant, or can be variable, for example changing between time steps. In other words, the window can have a different width in one of the time steps than in at least one other of the time steps.
[0036] According to one embodiment, the sensor signal can be received in a plurality of consecutive time steps. In this case, the mean value in each of the time steps can be determined using the actual value of the amplitude of the sensor signal received in the respective time step and / or using (at least one) earlier mean value determined in an earlier time step (e.g., immediately preceding) the respective time step. In this way, the sensor signal can be effectively smoothed before further processing. In this case, the (sliding) mean value acts like a low-pass filter.
[0037] According to one embodiment, the method can be implemented in a plurality of consecutive time steps, wherein in each of the time steps, the sensor signal and the current value can be received, the average value, the scaling factor and the new value can be determined, and the new value can be applied.
[0038] According to one embodiment, the actual value and the earlier average value (or earlier average values) may be weighted differently, which enables the smoothing to be flexibly adjusted according to different operating conditions.
[0039] According to one embodiment, the average value in each of the time steps may be determined according to the following equation:
[0040] QI=α*A+(1-α)*QI alt .
[0041] Here, QI can represent the average value in the corresponding (current) time step, A can represent the actual value, and QI alt α may represent the earlier average value, and α may represent a weighting factor. The weighting factor may, for example, be a value between 0 and 1. In particular, the weighting factor may be an empirical value. The weighting factor may be the same, i.e., constant, in each of the time steps, or may be variable, e.g., change between time steps. In other words, the weighting factor in one of the time steps may deviate from the weighting factor in at least one other of the time steps.
[0042] According to one embodiment, applying the new value can include: determining a deviation value indicating the deviation of the new value from the current value; determining an adjustment value using the deviation value and an assignment rule, wherein the assignment rule assigns an adjustment value to each of the possible deviation values; determining an adjusted new value using the current value and the adjustment value, in particular by adding the current value and a (positive or negative) adjustment value; and applying the adjusted new value to the at least one control parameter. In other words, before the new value is applied to the at least one control parameter, its magnitude can be modified in a suitable manner. This can, for example, avoid excessively large and / or overly frequent jumps when adjusting the at least one control parameter. For example, an "assignment rule" can be understood to mean a mathematical function or a lookup table. For example, the assignment rule can be stored in a memory of the control unit described above and below.
[0043] According to one embodiment, the allocation rule can be a Sigmoid function or based on a Sigmoid function. Generally speaking, a "Sigmoid function" can be understood as a function with an S-shaped graph. Additionally, the Sigmoid function can include linear or almost linear segments. Such segments can be important for the stability of the method.
[0044] According to one embodiment, the allocation rule may be defined as follows:
[0045]
[0046] Here, f(Δ) can represent the adjustment value, Δ can represent the deviation value, and S can represent the maximum permissible magnitude of the adjustment value. During operation of the pulse oximeter, this magnitude can be constant or can be changed, for example, depending on the current operating conditions. For example, this magnitude can also be referred to as the (maximum) step size.
[0047] According to one embodiment, the equation for term 2 can be determined based on a series expansion, preferably based on a Taylor series, particularly preferably based on a Maclaurin series. -Δ In this case, the allocation rule can be defined as follows:
[0048]
[0049] Relative to calculation item 2 -Δ This can improve computational efficiency rather than the implementation of P. Thus, the current consumption of the pulse oximeter can be further reduced. Furthermore, this facilitates implementation of the method in hardware and / or software.
[0050] According to one embodiment, the approximation P can be defined as follows:
[0051] If -Δ≥0, then and / or
[0052] If -Δ<0, then
[0053] Here, N can represent a predetermined order of the series expansion, and k can represent a predetermined factor. For example, N can be a natural number between 1 and 10, preferably 5, and / or k can be a percentage value between 0 and 1, preferably between 0.5 and 1.0, particularly preferably 0.75. In particular, N and / or k can be one or more empirical values.
[0054] This allows for an approximation that is particularly computationally efficient and / or particularly simple to implement, without significantly impairing the accuracy of the method.
[0055] According to one embodiment, applying the new value can include: determining a rounded value from the new value; and applying the rounded value to the at least one control parameter. For example, the new value can be rounded to one or two decimal places according to rounding conventions. Thus, for example, the limits for the rounded value "1" can be between 0.5 and 1.4 or between 0.45 and 1.54. This can simplify further processing of the new value. In this context, "new value" can also be understood as an adjusted new value, as described above.
[0056] According to one embodiment, determining the rounded value may include: doubling the new value; rounding the doubled value; and halving the rounded, doubled value. This can achieve a relative reduction in the number of decimal places without significantly compromising accuracy.
[0057] According to one embodiment, the pulse oximeter can also include a battery for supplying electric or electronic components of the pulse oximeter, in particular the light source or the entire pulse oximeter, with electric power. This allows the pulse oximeter to be taken on the go.
[0058] According to one embodiment, the pulse oximeter can further comprise a display unit for displaying at least one value determined using the sensor signal, for example the blood oxygen saturation or the pulse. BRIEF DESCRIPTION OF THE DRAWINGS
[0059] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, which should not be construed as limiting the scope of the present invention.
[0060] Figure 1 A pulse oximeter according to one embodiment of the present invention is shown.
[0061] Figure 2 A graph is shown which illustrates an allocation rule for use in a method according to one specific embodiment of the present invention.
[0062] The drawings are only schematic and not to scale. If the same reference numerals are used in different figures, these reference numerals indicate the same or identically acting features. DETAILED DESCRIPTION
[0063] Figure 1 A pulse oximeter 1 is shown, which comprises an (electrical) light source 3, a light sensor 5, and a control unit 7. The light sensor 5 is designed to convert light components transmitted and / or reflected by a body part 9 (e.g., a finger, an earlobe, or a similar thin body part) when illuminated with light from the light source 3 into an (electrical) sensor signal 11.
[0064] In this example, the control unit 7 is designed to determine the blood oxygen saturation (sO 2 ) and / or the pulse from the sensor signal 11 .
[0065] Additionally, the pulse oximeter 1 may include a display unit 13 for displaying at least one value and / or at least one graph related to the sensor signal 11, in particular related to the blood oxygen saturation and / or pulse. The display unit 13 may be arranged, for example, in the form of a display in and / or on the housing of the pulse oximeter 1.
[0066] The pulse oximeter 1 preferably includes a battery 15 for supplying electric current to the pulse oximeter 1. Thus, the pulse oximeter 1 can also be carried on the go.
[0067] In general, the control unit 7 can be configured to change the intensity and / or color of the emitted light by correspondingly controlling the light source 3. In this example, the light source 3 includes a first light-emitting diode 3a for emitting light in a first wavelength range (e.g., 660 nm) and a second light-emitting diode 3b for emitting light in a second wavelength range (e.g., 880 nm to 940 nm), which is different from the first wavelength range. The control unit 7 can be configured to alternately switch the light-emitting diodes 3a, 3b on and off during operation of the pulse oximeter 1. Alternatively, the light source 3 can include only one light-emitting diode having a wavelength range that can be changed in a suitable manner. Other types of light sources, such as laser diodes or incandescent lamps, are also possible.
[0068] For example, the light sensor 5 may include a photodiode, a photocell, a CMOS sensor, a CCD sensor, or a combination of at least two of these examples.
[0069] For example, the pulse oximeter 1 can be designed as a clip for fastening to the body part 9 and / or as a CO-oximeter.
[0070] In this example, pulse oximeter 1 is configured such that light source 3 and light sensor 5 are arranged on opposite sides of body part 9 during operation of pulse oximeter 1. Therefore, when light source 3 illuminates body part 9, light sensor 5 primarily receives the light component transmitted from body part 9.
[0071] Alternatively, the pulse oximeter 1 can be designed such that the light source 3 and the light sensor 5 are arranged on the same side of the body part 9 during operation of the pulse oximeter 1 .
[0072] The control unit 7 includes the following components: the components are configured to implement a specific method for controlling the current supply of the light source 3, as described in more detail below. The components may include hardware modules and / or software modules. In particular, the components may include a memory and a processor. A computer program may be stored in the memory, and the processor may be configured to implement the method by executing the computer program. In addition, the components may include a data communication interface for wireless and / or wired data communication with peripheral devices, such as smartphones, smart watches, tablets, computer computers, or ventilators.
[0073] The control unit 7 can also be realized solely as hardware, for example in the form of an ASIC or FPGA architecture.
[0074] The computer-implemented method may include the following steps:
[0075] In a first step, the sensor signal 11 and the current value 17 of at least one control parameter for controlling the brightness and / or color of the light source 3 are received in the control unit 7, for example in a corresponding hardware module and / or software module of the control unit 7. In this example, the at least one control parameter is the current flowing through the light source 3. However, other control parameters are also possible, such as the voltage applied to the light source 3. For example, the current value 17 can be a set and / or measured and / or estimated value.
[0076] In a second step, a scaling factor is determined from the time profile of the amplitude of sensor signal 11 , taking into account the desired value for the amplitude.
[0077] In a third step, a new value for at least one control parameter is determined by multiplying the current value 17 by the scaling factor. For example, the new value may be equal to the product of the current value 17 and the scaling factor.
[0078] In a fourth step, the new value is applied to at least one control parameter. For example, a control signal 19 for controlling the light source 3 can be generated based on the new value.
[0079] This method makes it possible to save current during operation of the pulse oximeter 1 by, for example, firstly reducing the current flowing through the light source 3 as long as the quality of the photoplethysmogram (PPG for short) from the sensor signal 11 is still sufficient and the required accuracy is still achieved, and secondly increasing this current if greater noise is present or the quality of the sensor signal 11 generally deteriorates.
[0080] For example, in a second step, the mean value QI can be determined from the time profile of the amplitude. Using the mean value QI and the setpoint value, a scaling factor can then be determined, in particular as a quotient of the mean value QI and the setpoint value.
[0081] It is possible to receive sensor signal 11 in a plurality of consecutive time steps. In this case, the average value QI in each of the time steps can be determined from the actual value of the amplitude of sensor signal 11 received in the corresponding (current) time step and at least one earlier actual value of the amplitude of sensor signal 11 received in at least one earlier time step before the current time step.
[0082] Alternatively or additionally, it is also possible to use the actual value of the amplitude of the sensor signal 11 received in the respective time step and (at least one) earlier mean value QI determined in an earlier time step (immediately) before the respective time step. alt In the case of , the average value QI is determined in each of the time steps. Such a sliding average value can effectively smooth the sensor signal 11 before further processing. In this case, the sliding average value acts like a low-pass filter.
[0083] Such a low-pass filter can be implemented very easily if the mean value QI in each of the time steps is determined according to the following equation:
[0084] QI=α*A+(1-α)*QI alt .
[0085] Here, A represents the actual value of the amplitude in the current time step, and α represents the weighting factor.
[0086] For example, the weighting factor α can be any value between 0 and 1. The weighting factor α can be the same, i.e., constant, in each of the time steps, or it can be variable, for example, depending on the operating conditions that change between time steps. In other words, the weighting factor α in one of the time steps can deviate from the weighting factor α in at least one other of the time steps.
[0087] Additionally, before applying the new value to the at least one control parameter, the new value can be rounded in a suitable manner, for example by doubling the new value, rounding the doubled value, and finally halving the rounded, doubled value.
[0088] Advantageously, at least one control parameter is set to a new value only if it deviates significantly from its current value. In this case, it is possible to set the mean value QI for the next time step to be equal to the current actual value of the amplitude, while in other cases the mean value QI is calculated according to the aforementioned equation.
[0089] Alternatively, a deviation value Δ can be determined that shows the deviation of the new value from the current value, for example by subtracting the new value from the current value 17 (or vice versa). Then, using the deviation value Δ and a suitable assignment rule 21 (see Figure 2), a positive or negative adjustment value can be determined. The adjustment value can be used to calculate an adjusted new value, for example by adding the current value 17 and the adjustment value. The adjusted new value can then be applied—as a new value—to at least one control parameter.
[0090] The assignment rule 21 can be stored in a memory of the control unit 7 , for example, in the form of a mathematical function or a lookup table.
[0091] In particular, the allocation rule 21 can be a mathematical function based on the Sigmoid function. Such a function can be defined, for example, in the following way:
[0092]
[0093] Wherein, f(Δ) represents the adjustment value, S represents the maximum permissible value of the adjustment value (which can be changed or constant during the operation of the pulse oximeter 1) or the maximum step length. Undesirable fluctuations and / or jumps in the value of the at least one control parameter (and thus in the amplitude of the sensor signal 11 ) between consecutive time steps can thereby be avoided.
[0094] In order to reduce the computational effort, in particular when using a microcontroller in the control unit 7, as an option, the approximation P can be calculated instead of the term 2 in the function -Δ , so that the function is:
[0095]
[0096] This approximation can be performed, for example, according to the following equation:
[0097]
[0098] Here, N represents a predetermined order of the series expansion, and k represents a predetermined factor. For example, N can be a natural number between 1 and 10, preferably 5, and / or k can be a percentage value between 0 and 1, preferably between 0.5 and 1.0, particularly preferably 0.75. The number N influences the accuracy and computational effort of the approximation. For example, when N=5, a good compromise between accuracy and computational effort can be achieved.
[0099] Such a series expansion may also be referred to as a Maclaurin series. This allows for an approximation that is particularly computationally efficient and / or particularly simple to implement, without significantly impairing the accuracy of the method.
[0100] As in Figure 2As can be seen in FIG, the assignment rule 21 can include a relatively long (almost) linear section around the zero point, which is important for the stability of the calculation.
[0101] Finally, it should be pointed out that terms such as “having”, “comprising”, “including”, “containing” etc. do not exclude other elements or steps, and indefinite articles such as “a” or “an” do not exclude a plurality.
[0102] Furthermore, it should be pointed out that features or steps described with reference to one of the above embodiments may also be used in combination with features or steps described with reference to other embodiments of the above embodiments.
[0103] Reference signs in the claims should not be construed as limiting the scope of the subject matter defined by the claims.
[0104] Reference Signs List
[0105] 1 pulse oximeter
[0106] 3 light sources
[0107] 3a The first light emitting diode
[0108] 3b Second light-emitting diode
[0109] 5 light sensors
[0110] 7Control Unit
[0111] 9 body parts
[0112] 11Sensor signal
[0113] 13 Display unit
[0114] 15 Batteries
[0115] 17 Current value
[0116] 19 Control Signal
[0117] 21 Allocation Rules
[0118] S maximum allowable value
[0119] Δ Deviation
Claims
1. A method for controlling a light source (3) of a pulse oximeter (1), wherein: The pulse oximeter (1) comprises, in addition to the light source (3), a light sensor (5), which is designed to convert light components transmitted and / or reflected from a body part (9) when irradiated with light from the light source (3) into a sensor signal (11), wherein the method comprises: Receiving the sensor signal (11) and a current value (17) of at least one control parameter for controlling the brightness and / or color of the light source (3); determining a scaling factor from the time profile of the amplitude of the sensor signal (11) while taking into account a setpoint value for the amplitude; determining a new value for the at least one control parameter by multiplying the current value (17) by the scaling factor; The new value is applied to the at least one control parameter.
2. The method according to claim 1, in, A mean value is determined from the time profile of the amplitude, and the scaling factor is determined using the mean value.
3. The method according to claim 2, in, To determine the scaling factor, a quotient is formed from the mean value and the setpoint value.
4. The method according to claim 2 or 3, in, The average is a sliding average.
5. The method according to any one of claims 2 to 4, in, The sensor signal (11) is received in a plurality of consecutive time steps, and an average value is determined in each of the time steps using an actual value of the amplitude of the sensor signal (11) received in the respective time step and / or using an earlier average value determined in an earlier time step before the respective time step.
6. The method according to claim 5, When determining the average value, the actual value and the earlier average value are weighted differently.
7. The method according to claim 5 or 6, in, The mean value in each time step in that time step is determined according to the following equation: QI=α*A+(1-α)*QI alt ; Wherein, QI represents the average value in the corresponding time step, A represents the actual value, and QI alt represents the earlier average value, and α represents a weighting factor.
8. The method according to any one of the preceding claims, in, Applications of the new values include: determining a deviation value (Δ) indicating a deviation of the new value from the current value (17); determining a correction value using the deviation value (Δ) and an assignment rule (21), which assigns a correction value to each possible deviation value; determining an adjusted new value using the current value (17) and the adjusted value, in particular by adding the current value (17) and the adjusted value; The adjusted new value is applied to the at least one control parameter.
9. The method according to claim 8, in, The allocation rule (21) is a Sigmoid function or is based on a Sigmoid function; and / or The allocation rule (21) is defined as follows: Wherein, f(Δ) represents the adjustment value, Δ represents the deviation value (Δ), and S represents the maximum allowed magnitude of the adjustment value (S).
10. The method according to claim 9, in, Based on a series expansion, preferably based on a Taylor series, particularly preferably based on a Maclaurin series, the equation for the term 2 is determined. -Δ The approximation P of , and the allocation rule (21) is defined as follows 11. The method according to claim 10, in, The approximation P is defined as follows: If -Δ≥0, then and / or If -Δ<0, then wherein N represents a predetermined order of the series expansion, and k represents a predetermined factor.
12. A control unit (7) comprising means configured to carry out the method according to any one of the preceding claims.
13. A pulse oximeter (1), comprising: Light source (3), a light sensor (5) configured to convert light components transmitted and / or reflected from a body part (9) when irradiated with light from the light source (3) into a sensor signal (11); A control unit (7) according to claim 12. 14 . A computer program comprising instructions which, when executed by a processor, cause the processor to carry out the method according to claim 1 .
15. A computer-readable medium having stored thereon the computer program according to claim 14.