DEVICE, SYSTEM AND METHOD FOR GENERATING BIOFEEDBACK

Description

[0001] The invention relates to devices, systems, and methods for generating biofeedback. In particular, the invention relates to devices, systems, and methods that can provide information about changes in vital parameters during an exercise to make the effectiveness of the exercise discernible to a user.

[0002] High blood pressure represents a significant health risk that can have various causes. Chronic stress can play a significant role in the development of essential arterial hypertension, as it can lead to a shift in the autonomic balance between the sympathetic and parasympathetic nervous systems. Such a shift in the autonomic balance can affect various organs, such as the cardiovascular system, and can lead to an increase in heart rate, increased ventricular contraction, and constriction of peripheral vessels. Such a condition can initially lead to acute and temporary, but later also chronic, elevation of blood pressure, which increases the risk of consequences such as stroke, heart failure, and kidney failure.

[0003] Non-invasive techniques for lowering blood pressure are attractive. Breathing techniques such as mantra breathing are examples of relaxation techniques that can at least alleviate certain mild forms of arterial hypertension. Yoga or other relaxation techniques can also be used to influence blood pressure. It is desirable to provide the person performing a relaxation technique with feedback on its effectiveness. This allows correct execution to be verified and motivation to be increased. Traditionally, heart rate variability (HRV) derived from an electrocardiogram (ECG) signal is used and output as a surrogate parameter because it is easily detectable. However, such conventional systems do not currently offer a way to output the acute effects on blood pressure as biofeedback. However, changes in HRV do not necessarily have to accompany changes in blood pressure.The latter can, for example, only occur with a significant delay during a relaxation exercise compared to a change in heart or pulse rate.

[0004] Using a blood pressure cuff, blood pressure can be measured and output as biofeedback. An example system using a blood pressure cuff is described in DE 10 2010 014 761 A1. However, the use of a blood pressure cuff can be perceived as distracting by users and can be detrimental to the effectiveness of the relaxation exercise.

[0005] Changes in blood pressure lead to changes in the pulse transit time (PTT) and pulse wave velocity (PWV) of pressure or volume pulses in the bloodstream via a change in the transmural wall tension of the arteries. As blood pressure values ​​rise, the pulse wave velocity increases and the pulse wave transit time therefore decreases. Falling blood pressure values ​​lead to an increase in the pulse wave transit time. The pulse wave transit time can be used as a parameter indicating a change in blood pressure. Example systems that allow the measurement of the pulse wave transit time are described in DE 10 2005 003 678 A1 and DE 10 2010 014 761 A1. However, the biofeedback provided by such systems can only provide limited information about the effectiveness of a relaxation exercise, since, for example, it is not possible to determine the mechanism of action in the body that causes a detected change in blood pressure.

[0006] WO 2009 / 112000 A1 discloses a device for determining cardiovascular variability that uses noninvasively recorded blood pressure signals for analysis. This device is used for clinical analysis of recorded signals and is not configured to provide biofeedback.

[0007] WO 2006 / 100676 A2 discloses a system and method for continuous blood pressure monitoring, comprising a portable monitoring device with a display.

[0008] WO 00 / 51677 A2 discloses a method in which heart rate variability (HRV) information is received, power in the HRV is determined over a first frequency range, and a power peak in the first frequency range is selected.

[0009] The present invention is based on the object of providing devices, systems, and methods that offer improvements with regard to at least some of the aforementioned disadvantages of conventional systems. In particular, the present invention is based on the object of providing devices, systems, and methods that can derive additional information during the performance of a relaxation exercise that may be relevant to the effectiveness of the relaxation exercise.

[0010] According to the invention, a device, a system, and a method are provided having the features defined in the independent claims. The dependent claims define embodiments.

[0011] A device according to the invention for generating biofeedback has at least one interface for receiving a pulse wave signal, which represents a pressure or volume pulse of a pulse wave in a bloodstream as a function of time, and an ECG signal. The device has an evaluation unit configured to determine a pulse wave transit time based on the pulse wave signal and the ECG signal and / or to perform an evaluation of a pulse waveform of the pulse wave signal and to generate the biofeedback depending on the pulse wave transit time and / or the evaluation of the pulse waveform. The device has an output interface for providing the biofeedback.

[0012] The device can be designed in such a way that, during operation, it not only determines a pulse transit time, from which blood pressure changes can be detected, but can also evaluate the pulse waveform of the detected pressure or volume pulse. This can provide more meaningful biofeedback to the user. By analyzing the pulse waveform, typical hemodynamic changes can be detected. Based on changes in the peaks of the pulse waveform, the device can, for example, automatically determine whether only the cardiac pumping capacity and heart rate have changed, or whether the peripheral vascular resistance has also been reduced.

[0013] Pulse wave transit time is inversely proportional to pulse wave velocity. Accordingly, by measuring pulse wave transit time, information about pulse wave velocity is also determined. Biofeedback based on pulse wave transit time can be generated in various ways, including, in particular, determining pulse wave velocity from pulse wave transit time and further evaluating the pulse wave velocity.

[0014] Due to the relationship between the pulse wave transit time and the pulse wave velocity, reference will be made below only to the pulse wave transit time, it being understood that a dependence of biofeedback on the pulse wave transit time within the meaning of this application also implies a dependence of the biofeedback on the pulse wave velocity, and that a dependence of a physiological variable on the pulse wave transit time within the meaning of this application also implies a dependence of the physiological variable on the pulse wave velocity.

[0015] The evaluation device can be configured to determine, by evaluating the pulse waveform, an underlying mechanism of action for a blood pressure change, a magnitude of the blood pressure change, a change in cardiac pumping performance, and / or a change in pulse wave reflection. For this purpose, the evaluation device can, for example, use several recorded pressure or volume pulses to determine how the position and / or height of peaks in the pulse wave signal change with increasing duration of the relaxation exercise. Typical hemodynamic changes can be detected in this way, without, for example, the use of a blood pressure cuff being mandatory.

[0016] The evaluation device is configured to determine, by evaluating the pulse waveform, whether a blood pressure change is caused by a vagal activation or a sympathetic suppression. For example, it may be desirable to specifically induce a blood pressure change by activating the parasympathetic nervous system (vagal activation) to improve autonomic balance or by suppressing the sympathetic nervous system to reduce peripheral resistance. Accordingly, the device can detect the mechanism underlying the blood pressure change, for example, by automatically distinguishing between vagal activation and sympathetic suppression, and can provide appropriate biofeedback.

[0017] The evaluation device can be configured to indicate via the output interface whether a blood pressure change caused by a vagal increase or a sympathetic suppression is present. In this way, meaningful biofeedback can be provided to a user who, for example, is striving to reduce blood pressure by suppressing the sympathetic nervous system to reduce peripheral resistance.

[0018] The evaluation device can be configured to detect a change in at least one of the following variables in order to determine whether a blood pressure change caused by a vagal nerve increase or a sympathetic nerve depression is present: duration of an early systolic phase; pressure in the early systolic phase; and / or duration of a late systolic phase. Changes in these variables can be easily detected, for example, from heartbeat to heartbeat. By comparing these variables for several cardiac cycles, it can be determined whether the peripheral vascular resistance is reduced when the late systolic phase is prolonged. By comparing these variables for several cardiac cycles, a change in cardiac pumping performance can also be detected.

[0019] The evaluation device can be configured to determine the pulse transit time and / or evaluate the pulse waveform for each cardiac cycle of a plurality of consecutive cardiac cycles. This allows for time-resolved detection of changes in the transit time of the pressure or volume pulse from the heart until its detection by a sensor, as well as the transit time of the pressure or volume pulse reflected by the peripheral vessels, for each heartbeat.

[0020] The device can be configured to output the biofeedback for each of the plurality of consecutive cardiac cycles via the output interface. This allows time-resolved biofeedback to be provided to the user.

[0021] The biofeedback may include at least one piece of information selected from the group consisting of: a change in blood pressure, a blood pressure, cardiac pumping performance, a pulse wave reflection, and a mechanism of action underlying the change in blood pressure. This information allows the user to verify the effectiveness of the relaxation exercise for lowering blood pressure, for example, through vagal activation or sympathetic suppression.

[0022] The device can be configured to output both the biofeedback and instructions for performing the relaxation exercise, in particular breathing instructions, via the output interface. This allows the user to be guided through the relaxation exercise with just one device, which can be configured, for example, as a handheld device, and to assess its effectiveness based on the biofeedback.

[0023] The device can be configured to generate instructions for performing the relaxation exercise based on the pulse wave transit time and / or the evaluation of the pulse waveform. This allows the user's behavior during the relaxation exercise to be specifically influenced in a feedback loop.

[0024] The output interface may comprise an optical output unit. The device may be configured to output the instructions for performing the relaxation exercise and the biofeedback simultaneously via the optical output unit. The optical output unit may, for example, be a screen of a handheld device. This allows the user to receive a graphical impression of the effectiveness of the relaxation exercise. Alternatively or additionally, the output interface may comprise an acoustic output unit, for example, a loudspeaker.

[0025] The evaluation device can be configured to determine the pulse wave transit time and / or at least one characteristic of the pulse waveform determined by evaluating the pulse waveform as a function of a parameter of the relaxation exercise, in particular a breathing rate. This allows the execution of the relaxation exercise, for example, by gradually lowering the breathing rate during mantra breathing, to be correlated with the resulting change in vital parameters.

[0026] The device can be a mobile, particularly a portable device. The device can be designed as a handheld device. The device can be a portable communications device with a communications interface for communicating with a wide area network or a cellular communications network. The device can be a mobile phone, a tablet computer, or a portable computer for receiving signals from sensors and for determining the pulse transit time and for evaluating the pulse waveform.

[0027] A system according to the invention comprises the device for generating biofeedback according to one exemplary embodiment. The system comprises a sensor device that can be coupled to the at least one interface of the device and is configured to detect the pulse wave signal.

[0028] The sensor device can comprise a first sensor for detecting the pulse wave signal and a second sensor for detecting the ECG signal. The first sensor can be configured to detect the pulse wave signal by infrared light transmission or infrared light reflection. The first sensor can comprise a photoplethysmography device. The first sensor can be configured to be reversibly detachably attached, for example, to a finger, a wrist, or an arm.

[0029] The first sensor may be configured to transmit the pulse wave signal to the device in data packets or data frames. The first sensor may have an interface for wired or wireless packetized data transmission to transmit the pulse wave signal to the device. Similarly, the second sensor may be configured to transmit the ECG signal to the device in data packets or data frames. The second sensor may have an interface for wired or wireless packetized data transmission to transmit the ECG signal to the device.

[0030] The system may include a control unit for controlling the first sensor and the second sensor and for synchronizing the pulse wave signal detected by the first sensor and the ECG signal detected by the second sensor.

[0031] A method for generating biofeedback, particularly during a relaxation exercise to lower blood pressure, comprises the following steps: receiving a pulse wave signal representing a pressure or volume pulse of a pulse wave in a bloodstream as a function of time, and an ECG signal at an interface; determining a pulse wave transit time by evaluating the pulse wave signal and the ECG signal and / or evaluating a pulse waveform of the pulse wave signal; generating the biofeedback depending on the pulse wave transit time and / or the evaluation of the pulse waveform; and outputting the biofeedback.

[0032] The method not only determines the pulse transit time, which can be used to detect changes in blood pressure, but also evaluates the pulse waveform of the recorded pressure or volume pulse. This allows for more meaningful biofeedback to be provided to the user. By analyzing the pulse waveform, typical hemodynamic changes can be detected. Based on changes in the peaks of the pulse waveform, the device can, for example, automatically determine whether only cardiac pumping capacity and heart rate have changed, or whether peripheral vascular resistance has also decreased.

[0033] Biofeedback can be generated during a guided relaxation exercise to lower blood pressure, especially during a breathing exercise.

[0034] By analyzing the pulse waveform, it is determined whether a change in blood pressure is caused by an increase in vagal activity or a decrease in sympathetic activity. The resulting biofeedback can indicate whether the change in blood pressure is caused by an increase in vagal activity or a decrease in sympathetic activity.

[0035] The method can be performed by the device or system according to an embodiment.

[0036] Further optional features of the method and the effects achieved thereby correspond to the features and effects described with reference to embodiments of the device.

[0037] Preferred embodiments of the invention are described in detail below with reference to the figures. They show: Fig. 1 is a schematic representation of a system according to an embodiment; Fig. 2 is a schematic representation of a pulse wave signal and an ECG signal to explain the functioning of the device according to an embodiment; Fig. 3 is a schematic representation of a pulse waveform of a pulse wave signal to explain the functioning of the device according to an embodiment; Fig. 4 is a schematic representation of a pulse waveform of a pulse wave signal to explain the functioning of the device according to an embodiment; Fig. 5 is a schematic representation of a pulse waveform of a pulse wave signal to explain the functioning of the device according to an embodiment; Fig. 6 is a schematic representation of signal forms to explain the functioning of the device according to an embodiment; Fig. 7 is a flowchart of a method according to an embodiment; Fig.Fig. 8 is a schematic representation of an optical output unit for providing biofeedback in a device according to an embodiment; Fig. 9 is a change in a heart rate and a pulse wave transit time during a relaxation exercise; Fig. 10 is a block diagram of a system according to an embodiment; Fig. 11 is a schematic representation of an optical output unit for providing biofeedback in a device according to an embodiment; Fig. 12 is a further schematic representation of the optical output unit of . Fig. 11 ; Fig. 13 a further schematic representation of the optical output unit of Fig. 11 ; Fig. 14 is a diagram explaining techniques for generating biofeedback; and Fig. 15 is a flowchart of a method according to an embodiment.

[0038] Preferred and advantageous embodiments of the invention are described below with reference to the figures, in which identical reference numerals designate identical or similar elements. The features of the various embodiments may be combined with one another, unless expressly excluded in the following description.

[0039] Fig. 1 shows a schematic representation of a system 1 according to an exemplary embodiment. The system 1 comprises one or more sensors 21, 22 for detecting a pulse wave signal and an ECG signal. The system 1 comprises a device 10 for generating biofeedback. The device 10 can be configured to determine a pulse wave transit time of a pressure or volume pulse in the bloodstream from the pulse wave signal and the ECG signal and additionally evaluate a pulse waveform of the pulse wave signal in order to generate biofeedback. The device 10 can output the biofeedback via an optical output unit 30 that is structurally integrated into the device 10 or separate therefrom.

[0040] The sensors 21, 22 can be configured for non-destructive, reversibly detachable attachment to a human body. The sensors 21, 22 can use various measurement techniques to detect the pulse wave signal and the ECG signal. Such measurement techniques are known per se to those skilled in the art and are therefore not described in detail here. For example, the sensor 21 for detecting a pressure or volume pulse of a pulse wave in a bloodstream can comprise a photoplethysmography device. The sensor 21 for detecting the pressure or volume pulse can be designed for detachable attachment to a finger. The sensor 21 for detecting the pressure or volume pulse can be designed as a unit attachable to a wrist or integrated into such a unit together with other sensors.The sensor 21 for detecting the pressure or volume pulse can also be integrated into a unit that has additional functions, for example, a headset that can be attached in or to an ear. The sensor 22 for detecting the ECG signal can be integrated into a chest strap or other holding device, or can have an adhesive surface for attachment. The sensors 21, 22 can be coupled to a device 10 for generating biofeedback via a wired or wireless connection.

[0041] The device 10 has at least one interface 12, 13 for receiving the ECG signal and the pulse wave signal from the sensors 21, 22. The at least one interface 12, 13 can be configured for wired or wireless communication with the sensors 21, 22. The at least one interface 12, 13 can be a USB or Bluetooth interface. The at least one interface 12, 13 can be configured to receive the ECG signal and the pulse wave signal in data packets or data frames and to synchronize the data transmission and data acquisition between the sensors 21, 22.

[0042] The device 10 has an evaluation device 11 for evaluating the ECG signal and the pulse wave signal. The evaluation device 11 can have at least one integrated semiconductor circuit. The evaluation device 11 can have an application-specific special circuit, a controller, a microcontroller, a processor, a microprocessor, or any combination of these or other integrated semiconductor circuits. The evaluation device 11 is configured to evaluate the ECG signal and the pulse wave signal to generate biofeedback. The evaluation device 11 is configured to determine a pulse transit time of the pressure or volume pulse from the heart to the sensor 21 from the ECG signal and the pulse wave signal. The evaluation device 11 is configured to automatically determine further information in addition to the pulse wave transit time by evaluating a pulse waveform of the pulse wave signal.This additional information can, for example, include a change in cardiac pumping performance during a relaxation exercise, which can be determined from a change in the amplitude of pressure or volume pulses during the relaxation exercise. Alternatively or additionally, a change in peripheral circulatory resistance can be detected during the relaxation exercise, which can be determined from the relative position of two peaks of a pressure or volume pulse. Alternatively or additionally, it can be determined whether a change in blood pressure is caused by the sympathetic or parasympathetic nervous system (e.g., vagus nerve). Examples of other information that can be determined from the analysis of the pulse waveform include the change in the resistance of peripheral blood vessels or the change in pulse wave reflection in the circulatory system.

[0043] The evaluation device 11 is configured to generate biofeedback and output it via an output interface. The biofeedback can be transmitted, for example, via an interface 14 to an optical display unit 30 and output by the latter. The biofeedback can indicate the change in one or more vital parameters during a relaxation exercise as a function of time and / or as a function of a parameter characterizing the execution of the relaxation exercise, for example, a respiratory rate. The biofeedback can include, but is not limited to, information about a change in blood pressure, cardiac pumping capacity, pulse wave reflection, and / or an action mechanism underlying the change in blood pressure.

[0044] The device 10 can be used to output biofeedback during the performance of a relaxation exercise. In this case, the device 10 can generate not only the biofeedback for output via an output interface, but also instructions for performing the relaxation exercise. Breathing instructions are an example of such instructions. The instructions for performing the relaxation exercise can be generated depending on the time-dependent change in the pulse wave transit time and / or depending on the evaluation of the pulse waveform. For example, depending on the evaluation of the pulse waveform, the instructions can be generated in such a way that a change in blood pressure becomes more likely due to sympathetic suppression or vagal stimulation.

[0045] A non-limiting application of the device 10 is described below in the context of mantra breathing, although the device 10 is not limited to this application. Deep and slow mantra breathing represents a method for lowering blood pressure. Mantra breathing with breathing rates of six breaths per minute leads to acute and chronic sensitization of the baroreflex and thus to a reduction in blood pressure. Furthermore, it activates the parasympathetic nervous system (vagus nerve), thus improving autonomic balance. This can lower blood pressure and heart rate. As a directly, non-invasively, and continuously measurable parameter, the pulse transit time can be determined by the device 10 and output as acute feedback on blood pressure changes.The change in pulse transit time can vary depending on the user, so that the change in pulse transit time, viewed in isolation, can be influenced by several short-term factors of circulatory control. By analyzing the pulse waveform of the pulse wave signal, which represents a pressure or volume pulse in the bloodstream, the device 10 can generate additional and even more meaningful biofeedback. Recording and analyzing the pulse waveform and the pulse transit time from the heart to the periphery, for example, to a finger, allows the effects of various relaxation techniques on blood pressure to be recorded. Analyzing the pulse waveform enables a statement about the mechanism of action as well as conclusions about the magnitude of the blood pressure change.The recording and analysis of the pulse waveform and the pulse wave transit time can be done continuously or quasi-continuously during the relaxation exercise, so that the biofeedback can be updated with each heartbeat.

[0046] The determination of the pulse wave transit time and analysis of the pulse waveform carried out by the device 10 is described using exemplary signal shapes with reference to Fig. 2 bis Fig. 5 described in more detail.

[0047] Fig. 2 shows a schematic representation of a pulse wave signal 41 and an ECG signal 42. The device 10 can receive the pulse wave signal 41 and the ECG signal 42 from the at least one sensor 21, 22, for example in the form of data packets or data frames. To determine the pulse wave transit time, the device 10 can determine a time 44 of an R-wave of the ECG signal 42. The R-wave of the ECG signal 42 indicates the beginning of the propagation of the pressure or volume pulse in the bloodstream from the heart. To determine the arrival time of the pressure or volume pulse in a part of the bloodstream where the sensor 21 detects the pressure or volume pulse, the device 10 can determine a time at which the rising edge of the pulse wave signal 41 begins. This can be done, for example, by a threshold value comparison.In one embodiment, for more precise determination of the pulse wave transit time, an intersection point between a tangent 46 to the rising edge of the pulse wave signal 41 and a straight line 47 passing through the minimum of the J-curve of the pulse wave signal 41 can be determined. The time 45 to which this intersection point corresponds represents the arrival time of the pressure or volume pulse detected by the sensor 21. The pulse wave transit time 43 can be determined as the time difference between the R-wave of the ECG signal 42 and the arrival time of the pressure or volume pulse detected by the sensor 21.

[0048] The device 10 can determine the pulse transit time 43 for each of several pressure or volume pulses triggered by a plurality of sequential heartbeats. The device 10 can determine the pulse transit time 43 individually for each heartbeat during the performance of a relaxation exercise. The determined pulse transit time or the corresponding change in blood pressure, for example, relative to the start of the relaxation exercise, can be output as biofeedback from heartbeat to heartbeat. Optionally, further processing, for example, by calculating a moving average or by filtering out outliers, can be performed to generate the biofeedback.

[0049] Fig. 3, Fig. 4 und Fig. 5 each show a schematic representation of a pulse waveform of a pulse wave signal 41, 61, 65. The device 10 can receive the pulse wave signal 41, 61, 65 from the sensor 21, for example in the form of data packets or data frames. The pulse wave signal 41, 61, 65 represents the pressure or volume pulse detected by the sensor 21 as a function of time. In each case, only the pulse shape of the pulse wave signal is shown, which corresponds exactly to a pressure or volume pulse caused by a single heartbeat. The pulse waveform of the pulse wave signal 41, 61, 65 typically has a first peak 51 and a second peak 52. The second peak 52 is caused by the reflection of the pressure or volume pulse emanating from the heart in peripheral blood vessels. The pulse waveform depends, for example, on the cardiac pumping capacity and the resistance of peripheral vessels.For example, cardiac pumping performance influences an amplitude 53 of the first peak 51. The resistance of peripheral vessels influences an amplitude 54 of the second peak 52 as well as a time interval 55 between the peaks 51, 52. By changing the resistance of vessels, for example, the duration of an early systole 56 and / or the duration of the late systole 57 can be influenced.

[0050] The change in the pulse waveform during a relaxation exercise allows conclusions to be drawn that are suitable for use as biofeedback. For example, an increase in blood pressure triggered by the sympathetic nervous system leads to the following changes: increased peripheral resistance and increased afterload; increased cardiac pumping capacity; and increased heart rate. These hemodynamic changes are accordingly reflected in the pulse waveform and lead to the following changes: shortening of the early systolic phase 56; increased pressure in the early systolic phase 56; as well as earlier pulse wave reflection and shortening of the "late" systole 57, which is accompanied by a change in the pulse wave contour in this area. In contrast, an increase in blood pressure triggered by the vagus nerve (vagal damping) leads to the following changes: increased heart rate and increased cardiac pumping capacity.

[0051] The hemodynamic changes triggered by the vagus nerve thus alter the pulse waveform differently than those triggered by the sympathetic nervous system, since peripheral resistance and thus afterload are not influenced by the vagus nerve. Late systole is only marginally affected by vagal augmentation or vagal depressant activity.

[0052] A reduction in blood pressure induced by a relaxation technique such as mantra breathing can be non-specifically detected by an increase in pulse wave transit time. Furthermore, the underlying mechanism can be detected through additional analysis of the pulse wave contour. In particular, this allows a distinction to be made as to whether a change in blood pressure is caused by an increase in vagal activity or a decrease in sympathetic activity. The user can access information via an interface indicating whether a reduction in peripheral vascular resistance was achieved over several relaxation exercises. This information does not have to be displayed during the relaxation exercise but can, for example, be generated and displayed as part of a report for the subject or a professional supervising the subject, which is only created after several exercises.

[0053] Fig. 4 shows a pulse waveform 61 of a pulse wave signal recorded during a relaxation exercise in which sympathetic suppression is achieved. The pulse waveform of the pulse wave signal 41 recorded at the beginning of the relaxation exercise, which can serve as a reference for analyzing the changes in the pulse waveform, is also shown with a broken line. In the case of sympathetic suppression, the reduction in cardiac pumping power leads to the amplitude 53 of the first peak of the pulse wave signal 61 being reduced compared to the reference signal 41. The corresponding reduction 62 of the peak 51 can also be determined quantitatively by the device 10. In addition, the late systole 57 is prolonged because the second peak 52 of the pulse wave signal 61 has a shift 63 to a relatively later time compared to the reference signal 41 when the pulse wave signals are scaled to the same temporal duration.In the reduction in blood pressure caused by sympathetic suppression, the reduction in peripheral resistance and afterload thus leads to a shift 63 of the second peak in the pulse waveform of the pulse wave signal 61.

[0054] Fig. 5 shows a pulse waveform 65 of a pulse wave signal acquired during a relaxation exercise in which vagal stimulation is achieved. The pulse waveform of the pulse wave signal 41 acquired at the beginning of the relaxation exercise, which can serve as a reference for analyzing changes in the pulse waveform, is also shown with a broken line. In contrast to sympathetic suppression, the pulse waveform hardly changes in late systole, since peripheral resistance and afterload are not as significantly affected during vagal stimulation.

[0055] Both in the case of sympathetic suppression and vagal stimulation, the pulse waveform also changes, as does the heart rate and thus the duration of the pressure or volume pulse. To take this into account, the pulse waveforms are divided into Fig. 4 und Fig. 5 shown compressed along the time axis to the same time duration as the reference pulse waveform 41. The device 10 can also computationally take the change in heart rate into account by computationally determining the duration of each pressure or volume pulse and stretching or compressing the pulse waveform by a scaling factor along the time axis in order to facilitate comparability with a reference pulse waveform 41.

[0056] The device 10 can be configured to determine a time derivative of the pulse wave signal for analyzing the pulse waveform. The device 10 can be configured to determine both a first time derivative of the pulse wave signal and a second time derivative of the pulse wave signal. Optionally, the device 10 can be configured to determine at least a first time derivative of the ECG signal for determining the duration of the early systole and / or the duration of the late systole. Based on the time derivatives, the duration of the early systole 56 and the duration of the late systole 57, as well as optionally a curvature of the pulse wave signal in the late systole, can be reliably determined.

[0057] Fig. 6 shows an ECG signal 67, a pulse wave signal 68, a first time derivative 68' of the pulse wave signal 68, and a second time derivative 68" of the pulse wave signal 68 to further explain the functioning of the device 10. The device 10 can be configured to determine a time of an R-wave of the ECG signal 67. For this purpose, a maximum 111 of the ECG signal can be identified, wherein the device 10 optionally determines a first time derivative of the ECG signal for this purpose. Similarly, a maximum 112 of the pulse wave signal can be automatically identified by the device 10.

[0058] From the first time derivative 68' of the pulse wave signal and the second time derivative 68" of the pulse wave signal, the device 10 can determine the end of systole 113 and the curvature 114 of the pulse wave signal in the late systolic phase.

[0059] This additional information potentially allows for conclusions about afterload changes and / or sympathetic activity. A parameter quantifying afterload or sympathetic activity can be, for example, the ratio of the duration of late systole to the duration of early systole, the ratio of the duration of late systole to the total duration of early and late systole, and / or the ratio of the duration of late systole to the heart rate. Other ratios or other parameters derived from the duration of early systole, the duration of late systole, and / or the heart rate can also be used to obtain quantitative information about afterload changes and / or sympathetic activity.

[0060] The provisions of Fig. 1 bis Fig. 6 The evaluation steps described for determining the pulse transit time and obtaining additional information from the pulse waveform can be performed for each heartbeat of a sequence of heartbeats during a relaxation exercise. This can involve recording and evaluating the pulse waveform and the pulse transit time over a period of at least one minute, at least five minutes, at least ten minutes, or at least 15 minutes. Biofeedback, which depends on the pulse transit time and the evaluation of the pulse waveform, can be output during the relaxation exercise and updated from heartbeat to heartbeat.

[0061] To generate biofeedback, the pulse wave transit time and optionally the heart rate can be further processed. For example, a temporal averaging can be performed over a predetermined period, which can be at least one minute, in order to output the temporal mean values ​​of the pulse wave transit time and optionally the heart rate as biofeedback. Alternatively or additionally, the energy of the pulse wave signal, the ECG signal, or signals derived therefrom can be determined in different frequency ranges. For this purpose, the pulse wave signal and / or the ECG signal can be subjected to a Fourier transformation, and the spectral weight for at least two different frequency bands can be determined from the signal transformed into the Fourier space, as described with reference to Fig. 14 will be described in more detail below. The device 10 allows the blood pressure change to be individually output to the user via visual and / or acoustic signals, directly and during a relaxation exercise, through this evaluation of the pulse waveform and pulse transit time, which indirectly indicate changes in blood pressure. This offers improvements over conventional biofeedback methods, which, for example, are based solely on heart rate variability or conventional pulse transit time measurement.

[0062] Fig. 7 is a flowchart of a method 70 that can be carried out by the device 10 according to an embodiment. In the method, the pulse wave transit time can be determined for each heartbeat of a sequence of heartbeats from an ECG signal and a pulse wave signal, which represents a pressure or volume pulse in a bloodstream, and the pulse waveform of the pulse wave signal can be additionally evaluated. In the method, in step 71, it can be checked whether a new cardiac cycle is beginning. In steps 73 and 74, the ECG signal and the pulse wave signal can be received at at least one interface of sensors 21, 22. In step 75, the pulse wave transit time can be determined. For this purpose, the time interval between an R-wave of the ECG signal and the time at which the rising edge of the pulse wave signal begins can be determined. The determination of the pulse wave transit time can be carried out as described with reference to Fig. 2 described. In step 75, the pulse waveform can also be analyzed. For this purpose, it can be determined how the pulse waveform of the pulse wave signal that is recorded during the performance of a relaxation exercise changes in comparison to the pulse waveform of at least one previous pulse wave signal. To analyze the pulse waveform of the pulse wave signal that is recorded during the performance of a relaxation exercise, the pulse waveform can be compared with the pulse waveform of a reference pulse wave signal that is recorded, for example, at the beginning of the relaxation exercise. In order to be able to reliably and easily detect changes in the pulse waveform even with a changing heart rate, the pulse wave signal can be scaled along the time axis, which takes into account the different durations of the pulse wave signals recorded at different times.The analysis of the pulse waveform may include a comparison of the signal strength of the pulse wave signal, particularly at one or more local maxima. This may allow conclusions to be drawn about cardiac pumping performance. The analysis of the pulse waveform may include a comparison of a second peak in the pulse waveform, caused by a reflection of the pressure or volume pulse in the peripheral vessels, with a corresponding second peak in the pulse waveform of a reference pulse wave signal. Depending on whether the pulse waveform changes significantly in late systole, it may be determined whether a blood pressure change is induced via the sympathetic nervous system or the vagus nerve. Biofeedback may be output at step 76.The biofeedback may indicate the change in one or more vital parameters during a relaxation exercise as a function of time and / or as a function of a parameter characterizing the performance of the relaxation exercise, for example, respiratory rate. The biofeedback may include, but is not limited to, information about a change in blood pressure, cardiac pumping performance, pulse wave reflection, and / or a mechanism of action underlying the change in blood pressure. Optionally, instructions for performing the relaxation exercise may also be output. The instructions may be generated depending on the pulse wave transit time and / or the analysis of the pulse waveform. The biofeedback may be updated from heartbeat to heartbeat. For this purpose, the method may return to step 71.In parallel with steps 73-76 or until the start of a new cardiac cycle, various additional processing steps can be performed at step 72. For example, moving averages of the pulse wave transit time can be calculated and provided to the user as biofeedback.

[0063] Fig. 8 is a schematic representation of a graphic output via an optical output unit 30, which can be generated by the device 10. The device 10 can control the optical output unit 30 to output a graphic representation 81 of a change in blood pressure. The graphic representation 81 can include the change in pulse wave transit time during the relaxation exercise. The change in blood pressure can be represented via the pulse wave transit time as a function of time or as a function of a parameter of the relaxation exercise. The device 10 can control the optical output unit 30 to output additional or alternative information 82 as biofeedback, which depends on the analysis of the pulse waveform. The additional information can include information about cardiac pumping performance, pulse wave reflection, and / or a mechanism of action underlying the blood pressure change.The device 10 can optionally control the optical output unit 30 to output instructions for performing the breathing exercise. For example, a graphic symbol 83 can be output to prompt the user to breathe in rhythm with a movement 84 of the symbol 83. Alternatively or additionally, the device 10 can also output the instructions via an acoustic output interface, for example, a loudspeaker.

[0064] Fig. 9 shows the change in heart rate 91 and the change in pulse wave transit time 92 during a relaxation exercise, averaged over several subjects. Fig. 9 As illustrated, the heart rate 91 drops significantly to a lower value within a relatively short period of a few minutes after the start of the relaxation exercise and then maintains this value. However, the change in blood pressure, which is reflected in the determined change in pulse wave transit time 92, only subsides well after the heart rate has already settled to a lower value. Fig. 9 illustrates that the heart rate and pulse wave transit time have different time dependencies and therefore a determination of the pulse wave transit time and an analysis of the pulse waveform are useful for the user.

[0065] Fig. 10 is a schematic block diagram of a system 100 according to one embodiment. The system 100 includes an ECG device 101 for acquiring the ECG signal, a device 102 for acquiring the pulse wave signal, a control and signal analysis device 103, and an output interface 104. The control and signal analysis device 103 can be integrated into a handheld device, for example, a mobile phone, tablet computer, or portable computer.

[0066] The control and signal analysis device 103 can, on the one hand, control the interaction with the operator and, on the other hand, coordinate the signal and data flows within the system 100. The control and signal analysis device 103 can define the interfaces to the sensors as well as the process sequences for signal processing. The control and signal analysis device 103 performs the necessary calculations that allow statements to be made about central parameters based on peripherally measured data. The control and signal analysis device 103 can be configured to control and synchronize all internal processes as well as the various data interfaces.

[0067] Via an optical and / or acoustic output interface 104, the control and signal analysis device 103 can provide the user with individually set instructions for performing the relaxation exercise, for example, a breathing rate. With Matra breathing, this rate can begin at ten breaths per minute, for example, and can then be gradually adjusted down to six breaths per minute over the course of the next few weeks. A continuous recording of the pulse wave transit time, which depends on the blood pressure, as well as the change in the pulse wave transit time depending on the breathing rate can be output via the optical and / or acoustic output interface. A drop in blood pressure and thus an increase in the pulse wave transit time can be output to the user via color coding or with a corresponding acoustic signal.

[0068] The pulse transit time can be measured continuously via an (ECG) R-wave-triggered photoplethysmographic measurement, for example, at the fingertip. System and measurement control is advantageously performed online, as control is time-critical due to the transient nature of the cardiovascular system. The control and / or regulation processes executed by the control and signal analysis device 103 can be triggered by the ECG signal, since, on the one hand, it marks the recurring starting point of the cardiovascular circuit and, on the other hand, can be robustly acquired via one or more, for example, up to six, channels.

[0069] Since signal processing is time- and memory-critical, periodicity can be exploited and a recursive information window defined to synchronize all signals. This information window can depend on the existing natural frequency of the cardiovascular system, the information propagation, and the distances to be covered within the system. The natural frequencies of the human cardiovascular system typically lie between 0.5 Hz and 3.5 Hz, depending on the activation state. This is the starting point of the system's transient behavior. During the relaxation exercise, the natural frequency can change in a cascade-like manner. The wave propagation speed also changes in connection with the activation of the sympathetic or parasympathetic nervous system and typically ranges between 4 m / s and 30 m / s. The maximum wavelength is determined by the person's height.The observation window, over which changes are recorded and further processed computationally, thus depends on several parameters that can be user-defined or automatically estimated by the device according to the invention to define the observation window in such a way that extinction can be avoided and consistent information acquisition can be ensured. Cascading can result from the different recording locations and the different information propagation of the pulse wave, which can depend on the anatomy and circulatory state of the subject.

[0070] In addition to determining the pulse wave transit time, the ECG device 101 also allows the recording of the heart rate and / or the recording of heart rate variability as a parameter of vegetative balance.

[0071] Fig. 11, Fig. 12 and Fig. 13 show a schematic representation of a graphic output via an optical output unit 30, which can be generated by the device 10. The device 10 can control the optical output unit 30 to provide a plurality of activatable control panels 121-123.

[0072] In response to a user activity, for example, a selection of a control panel 121, the device can output a raw signal 124 from the first sensor and / or another raw signal 125 from the second sensor. The raw signal 124 can be the output signal of an ECG sensor. The further raw signal 125 can be the output signal of a PPG module or another sensor suitable for time-of-flight measurement. Based on the output of the raw signals 124, 125, the user can easily check whether the sensors are correctly attached to the body and / or whether the connection for transmitting the output signals is established. The device can also automatically perform a plausibility check based on the raw signals 124, 125 to determine whether the sensors are correctly attached and whether the connection between the sensors and the signal transmission device is correctly established.

[0073] The device can output instructions for performing the breathing exercise in response to a user activity, for example, a selection of another control panel 122. For example, a graphic symbol 83 can be output to prompt the user to breathe in rhythm with a movement 84 of the symbol 83. Alternatively or additionally, the device 10 can also output the instructions via an acoustic output interface, for example, a loudspeaker. At the same time, biofeedback can be provided. For example, a baseline pulse transit time value 126, which corresponds to the pulse transit time at the start of the exercise, and a current pulse transit time value 127 can be displayed.

[0074] In response to a user activity, for example, a selection of another control panel 123, the device can output a graphical representation 128 of a change in pulse transit time caused by a change in blood pressure. The graphical representation 128 can include the change in pulse transit time during the relaxation exercise and, optionally, the current value of the pulse transit time. The change in blood pressure can be represented via the pulse transit time as a function of time or as a function of a parameter of the relaxation exercise. The optical output unit 30 can be controlled to output additional information 129 as biofeedback, which depends on the analysis of the pulse waveform and / or the ECG signal. The additional information 129 can, for example, represent the heart rate as a function of time during the relaxation exercise.

[0075] In addition or alternatively to generating biofeedback during a relaxation exercise, the devices and systems according to embodiments can be configured to generate reports that depend on data collected and evaluated in multiple relaxation exercises. For example, the device can be configured to determine in each of multiple relaxation exercises whether an afterload change has been achieved. The afterload change or another variable quantifying the resistance of peripheral vessels can be stored non-volatilely for each of the multiple relaxation exercises. The corresponding variables can be determined by analyzing the pulse waveform, as described above.When generating a report after a large number of relaxation exercises performed over a period of several days or several weeks, the device 10 can generate information indicating whether the subject has succeeded in achieving a reduction in peripheral vascular resistance.

[0076] Fig. 14 shows exemplary information that can be output by the device 10 individually or in combination as biofeedback. The device 10 can determine a temporal average of the pulse transit time 131. In this case, the device 10 can temporally average the pulse transit time determined from heartbeat to heartbeat over a predetermined time interval, which can be at least one minute, for example. Fig. 14 In the graph for the temporal average of the pulse wave transit time 131, the mean values ​​of the pulse wave transit time determined for individual exercises are shown with dashed lines. The mean value determined by averaging across different exercises is shown with a solid line.

[0077] The device 10 can optionally also determine a time average of the heart rate 132. In this case, the device 10 can temporally average the heart rate determined from heartbeat to heartbeat over a predetermined time interval, which can be at least one minute, for example. Fig. 14 In the graph for the time-average heart rate 132, the mean heart rate values ​​determined for individual exercises are shown with dashed lines. The mean determined by averaging across different exercises is shown with a solid line.

[0078] The device 10 can also employ more complex processing techniques. For example, the device 10 can be configured to determine the energy of the pulse wave signal and / or the ECG signal in one, two, or more than two different frequency bands. To do this, the device 10 can, for example, subject the respective signal to a Fourier transformation. To determine the energy in a frequency band, the device 10 can numerically integrate the pulse wave signal and / or ECG signal Fourier-transformed into the frequency domain over the corresponding frequency band. Other techniques for determining the energy of the pulse wave signal, the ECG signal, or signals derived therefrom in one, two, or more than two different frequency bands can be employed.

[0079] As in Fig. 14 As shown, the device 10 can determine the energy 133 of the pulse wave signal and / or ECG signal in a first frequency band and the energy 134 of the pulse wave signal and / or ECG signal in a second frequency band. The first frequency band can be a frequency interval (f 11 , f 12 ), and the second frequency band can be a frequency interval (f 21 , f 22 ), where f 11 < f 12 < f 21 < f 22 . The device 10 can determine whether the energy 133 in the first frequency band, i.e., at lower frequencies, increases during the relaxation exercise, and / or whether the energy 134 in the second frequency band, i.e., at higher frequencies, decreases during the relaxation exercise. Accordingly, the energy 133, 134 in at least one frequency band can be used and output as biofeedback. Alternatively or additionally, a ratio 135 of the energy 133 in the first frequency band to the energy 134 in the second frequency band can be determined by the device 10.

[0080] The device 10 may also be configured to generate alternative or additional processing techniques for generating the biofeedback depending on the pulse wave transit time and / or the pulse waveform of pulse waves.

[0081] Fig. 15is a flowchart 140 of a method according to one embodiment. In step 141, biofeedback is generated during a relaxation exercise. The biofeedback generated during the relaxation exercise may depend on the pulse wave transit time and optionally on the heart rate and / or an analysis of the pulse waveform of the pulse wave signal. In step 142, data associated with the relaxation exercise may be stored non-volatilely. The non-volatilely stored data may be generated depending on the analysis of the pulse waveform during the relaxation exercise. The non-volatilely stored data may include quantitative information about a change in afterload or other quantitative information that depends on the resistance of peripheral blood vessels. In step 143, a check can be made to determine whether a detailed report should be generated for output to the subject and / or a professional caring for the subject.A detailed report may, for example, be generated when a predefined number of relaxation exercises have been performed using the device. Alternatively or additionally, a detailed report may be generated when relaxation exercises have been performed using the device over a predefined period of time. Alternatively or additionally, a detailed report may be generated when the subject or a professional caring for the subject requests it through a user input on the device. If a detailed report is to be generated, it is output via an interface at step 144. The output of the detailed report may include the output of information generated depending on the analysis of the pulse waveform, which information indicates whether the subject has succeeded in achieving a reduction in peripheral vascular resistance.For example, the change in afterload can be determined and evaluated over several relaxation exercises.

[0082] To use systems 1, 100, the user can attach both the ECG sensor, which can be configured as a single-channel ECG sensor, and the photoplethysmographic module, for example, to a finger. The ECG signal and the pulse wave signal are recorded. The pulse wave transit time is continuously determined from the offset.

[0083] At the beginning of a breathing exercise, the user may, for example, breathe at a normal breathing rhythm of 10-12 breaths per minute. The device 10 can guide the relaxation exercise by gradually shifting the timing to lower breathing rates until, for example, a rate of six breaths per minute is reached. The relaxation exercise lowers blood pressure, providing biofeedback to the user. The breathing rate and biofeedback can be transmitted via audio signals and / or visual signals.

[0084] The device can be used, for example, for home relaxation exercises lasting 10-20 minutes per day, cumulatively lasting at least 60 minutes per week. A reduction in blood pressure with effect sizes of approximately 5 mmHg can be achieved after one to two months.

[0085] While embodiments have been described with reference to the figures, variations can be realized in further embodiments. While the devices, systems, and methods can provide biofeedback without using a blood pressure cuff, the devices, systems, and methods can also be used with such a blood pressure cuff. For example, using the blood pressure cuff before starting a relaxation exercise or only at the start of a relaxation exercise, a calibration can be performed such that the pulse wave transit time can be related to an absolute value of the blood pressure. This enables the output not only of relative blood pressure changes during the relaxation exercise, but optionally also of absolute values ​​of the blood pressure.

[0086] While embodiments have been described with reference to generating biofeedback during guided breathing exercises, such as mantra breathing, the devices, systems, and methods for generating biofeedback may also be used in other relaxation exercises.

[0087] Devices, systems, and methods according to embodiments can use the ECG signal not only to determine the pulse transit time. Devices, systems, and methods according to embodiments can use the ECG signal both to determine the pulse transit time and to determine heart rate variability. Heart rate variability can be output as biofeedback, for example, in addition to the change in the pulse transit time. Devices, systems, and methods according to embodiments can be used to provide biofeedback, particularly during relaxation exercises to lower blood pressure in mild hypertension, but are not limited thereto.

Claims

1. Apparatus (10; 103, 104) for generating biofeedback, in particular during a relaxation exercise for lowering blood pressure, comprising: at least one interface (12, 13) for receiving a pulse wave signal (41; 61; 65), that represents a pressure pulse or volume pulse of a pulse wave in a blood circulation system as a function of time, and an ECG signal (42; 67), an evaluation device (11; 103) that is configured to determine, on the basis of the pulse wave signal (41; 61; 65; 68) and the ECG signal (42; 67), a pulse transit time (43), perform an evaluation of a pulse wave form of the pulse wave signal (41; 61; 65; 68), and generate the biofeedback depending on the pulse transit time (43) and / or the evaluation of the pulse wave form, wherein the evaluation device (11; 103) is configured to determine, by evaluating the pulse wave form, whether there is a change in blood pressure caused by vagus enhancement or sympathetic attenuation, and an output interface (14, 30; 104) for providing the biofeedback (31; 81, 82; 126, 127, 128, 129).

2. Apparatus according to claim 1, wherein the evaluation device (11; 103) is configured to determine a mode of action underlying a change in blood pressure, a magnitude of the change in blood pressure and / or a change in pulse wave reflection by evaluating the pulse wave form.

3. Apparatus according to claim 1 or claim 2, wherein the evaluation device (11; 103) is configured to determine a change in afterload by evaluating the pulse wave form, wherein the evaluation device (11; 103) is optionally configured to output the change in afterload via the output interface (14, 30; 104), and / or to indicate via the output interface (14, 30; 104) whether there is a change in blood pressure caused by vagus enhancement or sympathetic attenuation.

4. Apparatus according to any one of the preceding claims, wherein the evaluation device (11; 103) is configured to detect a change in at least one of the following variables in order to determine whether there is a change in blood pressure caused by vagus enhancement or sympathetic attenuation: duration of an early systolic phase (56); pressure in the early systolic phase (53); and / or duration of a late systolic phase (57), wherein the apparatus is optionally configured to determine a first time derivative and a second time derivative (68'; 68") of the pulse wave signal (41; 61; 65).

5. Apparatus according to any one of the preceding claims, wherein the evaluation device (11; 103) is configured to determine a change in cardiac pumping capacity by evaluating the pulse wave form.

6. Apparatus according to any one of the preceding claims, wherein the evaluation device (11; 103) is configured to perform the respective determination of the pulse transit time (43) and / or the respective evaluation of the pulse wave form for each cardiac cycle of a plurality of successive cardiac cycles, wherein the apparatus (10; 103, 104) is optionally configured to output the respective biofeedback (31; 81, 82; 126, 127, 128, 129) via the output interface (14, 30; 104) for each cardiac cycle of the plurality of successive cardiac cycles.

7. Apparatus according to any one of the preceding claims, wherein the biofeedback (31; 81, 82) comprises at least one piece of information selected from the group consisting of: a change in blood pressure, a blood pressure, a cardiac pumping capacity, a change in afterload, a pulse wave reflection, and a mode of action underlying the change in blood pressure.

8. Apparatus according to any one of the preceding claims, wherein the apparatus (10; 103, 104) is configured to output the biofeedback (31; 81, 82; 126, 127, 128, 129) and instructions for performing the relaxation exercise, in particular breathing instructions, via the output interface (14, 30; 104), wherein the apparatus (10; 103, 104) is optionally configured to generate the instructions for performing the relaxation exercise depending on the pulse transit time (43) and / or the evaluation of the pulse wave form, and / or optionally wherein the output interface (14, 30; 104) comprises an optical output unit (30), wherein the apparatus (10; 103, 104) is configured to output the instructions for performing the relaxation exercise (83) and the biofeedback (31; 81, 82; 126, 127, 128, 129) at the same time via the optical output unit (30).

9. Apparatus according to any one of the preceding claims, wherein the evaluation device (11; 103) is configured to determine the pulse transit time (43) and / or at least one core characteristic of the pulse wave form determined by the evaluation of the pulse wave form as a function of a parameter of the relaxation exercise, in particular a breathing rate.

10. Apparatus according to any one of the preceding claims, wherein the output interface (14, 30; 104) is configured to provide the biofeedback (31; 81, 82; 126, 127, 128, 129) as a graphic illustration which includes a change of the pulse transit time (43) during the relaxation exercise.

11. System (1; 100), comprising: the apparatus (10; 103, 104) for generating biofeedback according to any one of the preceding claims and a sensor device (21, 22; 101, 102) which is couplable to the at least one interface (12, 13) of the apparatus (10; 103, 104) and configured to detect the pulse wave signal (41; 61; 65; 68) and the ECG signal (42; 67).

12. System according to claim 11, wherein the sensor device (21, 22; 101, 102) comprises a first sensor (21; 102) for detecting the pulse wave signal (41; 61; 65; 68) and a second sensor (22; 101) for detecting the ECG signal (42; 67), optionally comprising a controller (11; 103) for controlling the first sensor (21; 102) and the second sensor (22; 101) and for synchronizing the pulse wave signal (41; 61; 65; 68) detected by the first sensor (21; 102) and the ECG signal (42; 67) detected by the second sensor (22; 101).

13. Method for generating biofeedback (31; 81, 82; 126, 127, 128, 129), in particular during a relaxation exercise for lowering blood pressure, comprising the steps of: receiving a pulse wave signal (41; 61; 65; 68), that represents a pressure pulse or volume pulse of a pulse wave in a blood circulation system as a function of time, and an ECG signal (42; 67) at at least one interface (12, 13), determining a pulse transit time (43) by evaluating the pulse wave signal (41; 61; 65; 68) and the ECG signal (42), evaluating a pulse wave form of the pulse wave signal (41; 61; 65; 68), wherein it is determined by the evaluation of the pulse wave form whether a change in blood pressure is caused by vagus enhancement or sympathetic attenuation, generating the biofeedback (31; 81, 82; 126, 127, 128, 129) depending on the pulse transit time (43) and / or the evaluation of the pulse wave form, and outputting the biofeedback (31; 81, 82; 126, 127, 128, 129).

14. Method according to claim 13, wherein the biofeedback (31; 81, 82; 126, 127, 128, 129) is generated during a guided relaxation exercise for lowering blood pressure, in particular during a breathing exercise, and / or wherein the output biofeedback (82) indicates whether the change in blood pressure is caused by vagus enhancement or sympathetic attenuation.

15. Method according to claim 13 or claim 14, wherein the ECG signal (42; 67) is used to determine the pulse transit time (43) and to determine a heart rate variability, and / or wherein the method is carried out by the apparatus (10; 103, 104) according to any one of claims 1 to 10 or by the system (1; 100) according to claim 11 or claim 12.