DEVICE FOR DETERMINING A KEY METHODOLOGICAL REGULATION FOR THE DIAGNOSTIC OF HYDROCEPHALUS AND OTHER DISORDERS OF INTERNAL PRESSURE

Description

[0001] The present invention relates to a device for determining a parameter for diagnosing hydrocephalus and other disorders of intracranial pressure, and to a method for determining a parameter of the head contents of humans and other mammals.

[0002] For the diagnosis of patients with an imbalance between the production and reabsorption of cerebrospinal fluid (CSF), so-called hydrocephalus patients, and also in other patients with disturbed pressure conditions in the head or brain, devices are used, among other things, to determine the pressure or volume elasticity of the space within the skull. In many of these patients, the mean pressure in the CSF is not pathologically elevated. However, the volume elasticity of the skull's contents is restricted, and even the slightest pressure changes trigger wave-like increases in pressure, especially during sleep and when lying down. In other patients, the reduction in volume elasticity is accompanied by an increase in pressure.

[0003] Volume elasticity is a measure of the brain's ability to compensate for changes in volume. The brain is enclosed within the rigid bony skull. In addition to the brain tissue, this cavity contains arteries that supply blood to the brain, veins that carry blood away from the brain, and cerebrospinal fluid spaces containing cerebrospinal fluid. If the volume of one of these compartments increases, the volume of one or more of the other compartments must be displaced, since the total volume of the rigid cavity remains constant. In a healthy state, volume elasticity is so high that changes in the volume of one of the compartments, such as swelling of the brain tissue due to injury, can be compensated for without a significant increase in pressure.

[0004] Volume elasticity (compliance) can be determined using an invasive procedure in which a catheter is inserted into the cerebrospinal fluid space via a burr hole in the skull, a specific volume ΔV of fluid is injected, and the resulting pressure increase Δp is measured. The resulting compliance C is calculated using the equation C = ΔV / Δp. In healthy individuals, volume elasticity is greater than 1 ml / mmHg.

[0005] Naturally, with each heartbeat, a certain volume of blood is supplied through the arteries, causing a pressure increase. This pressure increase can be measured with an invasive pressure probe. However, the volume of blood supplied by the heartbeat is unknown, so compliance cannot be calculated numerically. An experienced physician, however, can obtain an indication of compliance from the pulse amplitude of the intracranial pressure (ICP).

[0006] For direct measurement of intracranial pressure, miniaturized pressure transducers are used, which are invasively inserted into the skull. Such pressure transducers are designed as semiconductor sensors (e.g., according to DE000002206624) or as fiber optic sensors (e.g., according to US4787396). Direct measurement of intracranial pressure is also a highly invasive procedure that poses a significant burden and risk to the patient.

[0007] Due to the disadvantages of direct measurements, various attempts have been made to determine intracranial pressure and / or compliance non-invasively "from the outside".

[0008] Paulat (DE000019606687A1) describes the measurement of the electrical impedance of the skull using two or more electrodes attached to the scalp. The impedance curve is periodically influenced by the ratio of the compartments blood, brain tissue, and cerebrospinal fluid with each heartbeat, resulting in a curve with periodic components. Characteristic points (landmarks) are identifiable in this curve, the amplitude of which is described as characteristic of intracranial pressure (ICP). However, this relationship varies from patient to patient due to such diverse influences that a reliable diagnostic procedure could not be developed from it.

[0009] Yost (US 673773407) describes a method in which the transit time of an ultrasound signal through the skull is determined. The speed at which the pulse travels through the skull's contents is influenced by the varying speed of sound in the compartments and their composition. However, because the calibration of this method is unreliable and the relationship between the measurement results and the quantity being measured varies from patient to patient due to numerous factors, a reliable diagnostic procedure could not be developed from it.

[0010] Ben-Ari (WO 20141167418) proposes deriving a parameter for possible edema (fluid retention in the tissue) inside the head from the electrical capacitance and / or impedance of the head. However, this method has not gained widespread acceptance due to the difficulty of calibration and the large interindividual variability.

[0011] Furthermore, US 2014 / 0371545 A1 describes a cerebro-hemodynamic measuring device with at least one processor.

[0012] Furthermore, US 2005 / 0015009 A1 describes a method for determining a subject's ICP based on at least two variable inputs. Additionally, S. Jetzki, M. Kiefer, R. Eymann, M. Walter, and S. Leonhardt [1] mention the consideration of the so-called PA-PM slope in connection with the dynamic course of intracranial pressure (ICP).

[0013] Similar procedures are also known from documents US 6387051 B1, US 2006 / 079773 A1 and US 2013 / 109979 A1.

[0014] In fact, such parameters have been considered for some time, which are calculated from the ratio of all spontaneous changes in pulse amplitude to all spontaneous changes in mean intracranial pressure, see e.g. the parameter RAP in [2], or the parameter AMP / P in [3] or the parameter RPPC in [4].

[0015] However, the state of the art [1] - [4] has in common that all changes in pulse amplitude are correlated with all changes in mean pressure. The causes of the changes in pulse amplitude can be: Changes in the pulse amplitude of the arterial pressure pulse, changes in compliance (the elasticity of the head contents) due to changes in cerebrospinal fluid volume, and changes in compliance due to changes in intracranial blood volume via changes in arterial diameter. (The brain regulates its blood flow by constricting or dilating the arteries in response to blood pressure. This mechanism is called autoregulation. Furthermore, the brain regulates its blood flow by constricting or dilating the arteries in response to demand. This mechanism is called metabolic coupling.) Changes in pulse amplitude due to changes in pressure and thus compliance through respiration.

[0016] The causes of changes in mean pressure are also diverse: Changes in pressure due to hydrostatic effects during changes in position (lying, sitting, standing), changes in pressure due to changes in cerebrospinal fluid volume, changes in pressure due to changes in intracranial blood volume through changes in arterial diameter (autoregulation, metabolic coupling), and changes in pressure due to respiration.

[0017] Since all these changes in pulse amplitude and pressure are correlated in the methods cited above, the correlation coefficients are low in clinical practice and the parameter has little significance. None of the described systems for the non-invasive diagnosis of hydrocephalus has yet proven effective in practice.

[0018] The object of the present invention is therefore to provide a device for diagnosing hydrocephalus and other disorders of intracranial pressure, or a method in which information about volume elasticity is obtained from a pressure signal or another signal containing information about the pressure or volume composition in the skull.

[0019] The invention utilizes the fact that periodic pressure fluctuations occur in the intracranial pressure (ICP) due to heartbeat, respiration, and other naturally occurring periodic events. Surprisingly, it was found that dimensionless parameters characteristic of compliance can be calculated from the ratios of these pressure fluctuations to one another. One parameter determined according to the invention, RAQ, is, for example, the ratio of the amplitude Arp of the respiration-related waves in the pressure signal to the amplitude AAvp of the respiration-related waves during the course of the heartbeat-related pulse amplitude Avp.

[0020] According to the invention, alternative parameters or output variables can also be calculated from the values ​​mentioned above, in particular dimensionless parameters, especially in the form of quotients or parameters that exhibit such quotients. The calculation of a parameter or output variable according to the invention is preferably carried out using at least one or more of the following quantities: Avp, Arp, AAvp. Optionally, further quantities can be used to determine the parameter (such as heart rate and / or respiratory rate). A parameter according to the invention can, of course, be suitably scaled or shifted by adding or subtracting, for example, constant values. In particular, the parameter can be made dimensionless by means of a suitable proportionality constant.

[0021] The evaluated signal can be, as described below, the directly measured pressure signal. However, it can also be an impedance, capacitance, or ultrasound signal. For example, the amplitude of the pulse is determined, which is caused by the natural flow of a certain volume of blood through the arteries with each heartbeat. Furthermore, the lower-frequency pressure wave is determined, which is caused by the periodic obstruction of blood outflow with each breath, also corresponding to a volume change that is expressed as a pressure change. Since compliance also periodically decreases and increases with the periodic pressure change caused by respiration, respiration is also reflected in a modulation of the amplitude of the heartbeat-induced pulse. The pulsations caused by the heartbeat and respiration are recognizable and measurable in the ICP pressure curve. Figure 1schematically shows the course of intracranial pressure with a cardiac cycle 1 and a respiratory cycle 2.

[0022] While respiration modulates the heartbeat-related—higher-frequency—pulse amplitude in the range of the respiratory rate (10 to 20 per minute), other periodic influences modulate the amplitude of the heartbeat-related pulse wave (and other, higher-frequency periodic waves) in other frequency ranges: A-waves in the range of less than 1 per 3 minutes; B-waves (natural oscillations of blood flow regulation, the so-called autoregulation) in the range of 3 to 1 per 3 minutes; and C-waves in the range of 3 to 9 per minute. Each of the amplitudes of the aforementioned periodic waves is modulated by the corresponding lower-frequency waves. The terms "modulated wave" and "modulating wave" will be used in the following discussion.Therefore, if the amplitude of heartbeat-related pulses is modulated by respiratory waves, the heartbeat-related pulses are the modulated wave, and the respiratory waves are the modulating wave. For clarity, the following illustrations refer to the modulation of the heartbeat-related pulse wave amplitude by the respiratory wave. However, they are also applicable to any other combination of modulating and modulated waves by appropriately modifying the frequency-determining components.

[0023] The ratio RAQ, derived from the amplitude Arp of the respiratory waves in the evaluated signal to the amplitude AAvp of the respiratory waves during the heartbeat-related pulse amplitude Avp of the evaluated signal, is a ratio calculated according to the equation RAQ = Arp / AAvp. It is independent of calibration. Therefore, the device according to the invention is particularly suitable for evaluating non-invasively acquired signals that contain information about pressure, volume composition, or volume elasticity in the skull. In this way, it is possible for the first time to obtain reliable information about intracranial compliance from uncalibrated signals in a non-invasive manner. Furthermore, it is possible for the first time to obtain reliable information about intracranial compliance from the invasively measured pressure signal without having to inject any substance.

[0024] According to the invention, a device for determining a characteristic parameter of the head contents of humans and other mammals is provided, which is designed to acquire and evaluate a signal characteristic of the head contents as an input parameter, wherein the device is configured to a. to calculate the pulse amplitude Avp of each individual period (or half-period) of a modulated wave of the characteristic signal and to generate a signal Avp or a time series Avp, b. to calculate the mean value MICP for each individual period (or half-period) of the modulated wave of the characteristic signal and to generate a signal MICP or a time series MICP, c. to calculate the amplitude Arp of a modulating wave in the time series MICP or in the signal MICP, d. to calculate the amplitude AAvp of the modulating wave in the time series Avp or in the signal Avp, e. to calculate the characteristic parameter as an output parameter using at least one or more of the following quantities: Avp, Arp, AAvp, wherein the characteristic parameter is a quotient comprising the quantities Arp and Avp.

[0025] The characteristic signal is one of the following: the electrical impedance of the skull, the directly measured pressure inside the head, the electrical capacitance of the skull, the transit time of an ultrasound signal passed through the skull.

[0026] According to one embodiment of the invention, the characteristic parameter is a dimensionless parameter.

[0027] The solution according to the invention thus eliminates, in particular, the weakness of the approaches cited above [1] to [4] by considering only one influence (e.g., respiration) for both the change in pulse amplitude and the change in mean pressure (MICP). Specifically, only changes in the amplitude of a modulated wave in a narrow frequency band and changes in the amplitude of a modulating wave in the same narrow frequency band are considered. For example, highly selectively, only periodic changes in the same narrow frequency range are considered in both the numerator and denominator of the quotient RAQ.

[0028] In the application of the invention to the respiratory wave as a modulating wave and the pulse wave as a modulated wave, for example, only the changes in pulse amplitude in the respiratory frequency range are considered as a modulated wave and the changes in mean pressure in the respiratory frequency range as a modulating wave. By narrowly limiting the parameter to, for example, the respiratory frequency range, only one influence is considered in the parameter, particularly in both the numerator and the denominator, while all fluctuations caused by changes in position, autoregulation, etc., are filtered out.

[0029] The above-mentioned step a) is therefore to be understood in particular as meaning that the pulse amplitude A vp of each individual period (or half-period) of exactly one or only one modulated wave of the characteristic signal is calculated and a signal A vp or a time series A vp is generated,

[0030] Furthermore, in accordance with step c) mentioned above, it is to be understood in particular that the amplitude A rp of exactly one, or only one, modulating wave in the MICP time series or in the MICP signal is calculated. Furthermore, according to one embodiment of the invention, the characteristic value is a quotient or comprises a quotient.

[0031] Furthermore, according to one embodiment of the invention, the characteristic value is a quotient comprising the quantities A rp and AA vp.

[0032] Furthermore, according to one embodiment of the invention, the characteristic parameter is a quotient that includes the quantity HF and / or AF, where HF is the heart rate and AF is the respiratory rate.

[0033] Furthermore, according to one embodiment of the invention, the quotient RAQ is proportional to or equal to one of the following expressions: A rp / AA vp , A rp / (AAvp / AF), A rp / (AA vp *HF), A rp / (AA vp *(HF / AF)).

[0034] Furthermore, according to one embodiment of the invention, the characteristic signal is the directly measured pressure inside the head (ICP).

[0035] Furthermore, according to one embodiment of the invention, the characteristic signal is the electrical impedance of the skull, which can be recorded by means of electrodes that can be attached to the outside of the skull.

[0036] Furthermore, according to one embodiment of the invention, the characteristic signal is the electrical capacitance of the skull, which can be recorded by means of electrodes that can be attached to the outside of the skull.

[0037] The device according to the invention can have said electrodes, wherein these may optionally be connected to the unit(s) of the device according to the invention, so that said impedance or capacitance can be processed by means of the device.

[0038] Furthermore, according to one embodiment of the invention, the characteristic signal is the transit time of an ultrasound signal that is passed through the skull.

[0039] Furthermore, according to one embodiment of the invention, the characteristic signal is the transit time of an ultrasound signal that is reflected from inside the skull.

[0040] Furthermore, according to one embodiment of the invention, the device comprises one or more units configured for this purpose. a. to calculate the pulse amplitude Avp of each individual period (or half-period) of the modulated wave of the characteristic signal and to generate a signal Avp or a time series Avp (3), b. to calculate the mean value MICP for each individual period (or half-period) of the modulated wave of the characteristic signal and to generate a signal MICP or a time series MICP (4), c. to calculate the amplitude Arp of a modulating wave in the time series MICP or in the signal MICP (5), d. to calculate the amplitude AAvp of the modulating wave in the time series Avp or in the signal Avp (6), e. to calculate the characteristic parameter as an output parameter using at least one or more of the following quantities: Avp, Arp, AAvp.

[0041] In particular, a separate unit can be provided for each of the aforementioned calculations or steps a to e. However, it is also conceivable that the individual calculations / steps are performed by one unit or by several units, among which the calculations are appropriately distributed. The unit that performs the calculation of the characteristic value can, of course, also perform all other variants of the characteristic value calculation disclosed herein.

[0042] Furthermore, according to one embodiment of the invention, the respective unit is an analog computing circuit, a digital computing circuit or a program-controlled microprocessor circuit.

[0043] According to one embodiment, the modulated wave can be one of the periodic signals from the group of B-waves (1 / 3 period per min to 3 periods per min), C-waves (3 periods per min to 9 periods per min), respiratory waves (10 periods per min to 20 periods per min), heartbeat waves (20 periods per min to 240 periods per min).

[0044] Furthermore, according to one embodiment, the modulating wave can be one of the periodic signals from the group of A-waves (< 1 per 4 min), B-waves (1 / 3 per min to 3 per min), C-waves (3 per min to 9 per min), breathing waves (10 per min to 20 per min), which is lower frequency than the modulated wave.

[0045] According to a further embodiment, a device is disclosed which is configured to calculate said characteristic value as the first output value, and which is additionally configured to calculate another characteristic value as the second output value, wherein, in particular, a combination of modulated and modulating wave is used to calculate the further output value, which differs from the combination of modulated and modulating wave used to calculate the characteristic value or first output value, wherein the device is configured here to form the quotient of the first output value and the second output value as the characteristic value of the head content.

[0046] In this embodiment, the device can, for example, comprise two devices according to the invention, one device calculating the first output variable and the other device calculating the second output variable. The device then calculates the aforementioned quotient of the first and second output variables.

[0047] Furthermore, according to one embodiment, the device is configured to form the time series Avp by using the difference between the local maximum and the local minimum as the value for the time series Avp for the time interval between a local minimum and the subsequent local maximum of the modulated wave of the characteristic signal, and by using the difference between the local maximum and the subsequent local minimum as the value for the time series Avp for the subsequent time interval between the local maximum and the subsequent local minimum of the modulated wave of the characteristic signal.

[0048] Furthermore, according to one embodiment, the device is configured to form the MICP time series by using the mean value between the local maximum and the local minimum as the value for the MICP time series for the time interval between a local minimum and the subsequent local maximum of the modulated wave of the characteristic signal, and by using the mean value between the local maximum and the subsequent local minimum as the value for the MICP time series for the subsequent time interval between the local maximum and the subsequent local minimum of the modulated wave of the characteristic signal.

[0049] Another aspect of the present invention relates to a method for determining a characteristic parameter of the head contents of humans and other mammals, using a device according to the invention, comprising the steps of: a. Calculation of the pulse amplitude Avp of each individual period (or half-period) of a modulated wave of the characteristic signal and generation of a signal Avp or a time series Avp (3), b. Calculation of the mean value MICP for each individual period (or half-period) of the modulated wave of the characteristic signal and generation of a signal MICP or a time series MICP (4), c. Calculation of the amplitude Arp of a modulating wave in the time series MICP or in the signal MICP (5), d. Calculation of the amplitude AAvp of the modulating wave in the time series Avp (6), e. Calculation of the characteristic value using at least one or more of the quantities: Avp, Arp, AAvp.

[0050] According to one embodiment of the method according to the invention, the characteristic parameter is a dimensionless parameter.

[0051] Furthermore, according to one embodiment of the method according to the invention, the characteristic parameter is a quotient or has a quotient.

[0052] Furthermore, according to one embodiment of the method according to the invention, the characteristic value is a quotient comprising the quantities A rp and AA vp.

[0053] Furthermore, according to one embodiment of the method according to the invention, the characteristic parameter is a quotient that includes the quantity HF and / or AF, where HF is the heart rate and AF is the respiratory rate.

[0054] Furthermore, according to one embodiment of the method according to the invention, the quotient RAQ is proportional to or equal to one of the following expressions: A rp / AA vp , A rp / (AAvp / AF), A rp / (AA vp *HF), A rp / (AA vp *(HF / AF)).

[0055] Furthermore, according to one embodiment of the method according to the invention, the characteristic signal is the directly measured pressure inside the head.

[0056] Furthermore, according to one embodiment of the method according to the invention, the characteristic signal is the electrical impedance of the skull, which is recorded by means of electrodes attached to the outside of the skull.

[0057] Furthermore, according to one embodiment of the method according to the invention, the characteristic signal is the electrical capacitance of the skull, which is recorded by means of electrodes attached to the outside of the skull.

[0058] Furthermore, according to one embodiment of the method according to the invention, the characteristic signal is the transit time of an ultrasound signal that is passed through the skull.

[0059] Furthermore, according to one embodiment of the method according to the invention, the characteristic signal is the transit time of an ultrasound signal that is reflected from inside the skull.

[0060] Furthermore, according to one embodiment of the method according to the invention, the time series Avp is formed by using the difference between the local maximum and the local minimum as the value for the time series Avp for the time period between a local minimum and the following local maximum of the modulated wave of the characteristic signal, and by using the difference between the local maximum and the following local minimum as the value for the time series Avp for the following time period between the local maximum and the following local minimum of the modulated wave of the characteristic signal.

[0061] Furthermore, in the inventive method, two devices according to the invention can also be used (see above) or two output variables can be calculated, wherein the first device or output variable is characterized by a specific combination of modulated and modulating wave, and wherein the second device or output variable is characterized by a different combination of modulated and modulating wave, and wherein the characteristic value of the head content is formed by the quotient of the first output variable and the second output variable. For the aforementioned combinations of modulated and modulating wave, all combinations or examples described herein can be used in particular.

[0062] Further features, embodiments and advantages of the present invention will be explained below with reference to the figures. They show Fig. 1 shows a representation of the course of intracranial pressure with a cardiac cycle 1 and a respiratory cycle 2; Fig. 2 shows a block diagram of a device or method according to the invention; and Figs. 3A-3J show by way of example the evaluation of the pressure signal ICP within the scope of the present invention.

[0063] A device or method according to the invention is described in the Fig. 2 schematically represented.

[0064] According to one embodiment of the invention, the device consists, as shown in Fig. 2 An example of ICP evaluation shown as a block diagram, from an evaluation unit for an invasively or non-invasively obtained characteristic signal, which contains units for the following evaluations: a. Calculation of the pulse amplitude Avp of each individual heartbeat in the characteristic signal and generation of a signal Avp or a time series Avp (3). b. Calculation of the mean value MICP of the characteristic signal for each individual heartbeat and generation of a signal MICP or a time series MICP (4). c. Calculation of the amplitude Arp of the respiratory wave in the generated signal MICP or in the time series MICP (5). d. Calculation of the amplitude AAvp of the respiratory wave in the generated signal Avp or in the time series Avp (6). e. Calculation of the quotient of the characteristic parameter as a quantity RAQ that is proportional to RAQ = Arp / AAvp (7), or calculation of the characteristic parameter in the form of the quotient RAQ, where RAQ = Arp / AAvp (7).

[0065] In this embodiment of the invention, the heartbeat-induced wave is the modulated wave and the breathing-induced wave is the modulating wave. Similarly, any combination of a higher-frequency modulated wave and a lower-frequency modulating wave is possible.

[0066] Surprisingly, it was found that calculating the pulse amplitude Avp as the mean of the difference between two local maxima of the modulated wave of the characteristic signal and the local minimum of the modulated wave of the characteristic signal lying between these two maxima leads to amplitude values ​​that are systematically distorted by the modulating wave.

[0067] Therefore, to calculate the pulse amplitude Avp within the scope of the present invention, the difference between the local maximum and the local minimum is preferably chosen for the time interval between a local minimum and the subsequent local maximum of the modulated wave of the characteristic signal, and correspondingly, the difference between the local maximum and the subsequent local minimum is chosen for the subsequent time interval between the local maximum and the subsequent local minimum. This will be explained further below using the Figure 3C Explained using an example.

[0068] Since stroke volume decreases with increasing heart rate and constant blood flow, one embodiment of the invention provides that the characteristic value or quotient RAQ is multiplied by the amplitude AAvp with the heart rate or with a quantity derived from it, so that the characteristic value RAQ is proportional to Arp / AA vp * HF , or such that the parameter RAQ is given by RAQ = A rp / AA vp * HF , where HR refers to heart rate. This makes RAQ independent of stroke volume.

[0069] Furthermore, according to one embodiment of the invention, it is provided that the respiratory rate RR can also be taken into account (because the rate of change per unit time is higher at high respiratory rates). Accordingly, it is possible to correct the parameter or the aforementioned quotient RAQ by the respiratory rate by dividing the amplitude AA vp by the respiratory rate RR or by a quantity derived from the respiratory rate RR when calculating the parameter or the quotient RAQ.

[0070] Accordingly, the parameter RAQ is then proportional to A rp / AA vp / AF or results as a quotient RAQ = A rp / AA vp / AF

[0071] This makes the parameter or quotient RAQ independent of the respiratory rate.

[0072] The two correction methods mentioned above can, of course, also be combined according to another embodiment. The aforementioned parameter (here the RAQ ratio) is then calculated as follows: RAQ = A rp / AA vp * HF / AF , or is proportional to A rp / (AA vp *(HF / AF)).

[0073] The formulas mentioned above for calculating RAQ may contain a proportionality factor on the right-hand side, meaning that the calculated parameter or quotient RAQ may be dimensionless. This is particularly the case when correction is made solely using the quantities HF or AF, which each have the dimension of a frequency.

[0074] If the respiratory rate (RR) and / or the heart rate is used to determine the parameter, the device according to the invention may include a unit for measuring the heart rate and / or a unit for measuring the respiratory rate.

[0075] When calculating the RAQ quotient according to the example of the Figure 2 The AAvp value can be multiplied by the heart rate (HR) and / or divided by the respiratory rate after step 6, i.e., after the determination of AAvp.

[0076] Figs. 3A to 3J They show, also as an example for the evaluation of the ICP, how the individual values ​​are determined from the pressure signal.

[0077] Fig. 3A It initially shows one period of the ICP pressure signal. In the Fig. 3B It is evident how the mean MICP of the shown period of ICP is calculated from this. Furthermore, the Fig. 3CThe pulse amplitude Avp can be calculated, for example, by determining the difference between the local maximum MAX of ICP and the first local minimum MIN1 of ICP for the time interval T1 between the first local minimum MIN1 and the first local maximum MAX of ICP (Avp(T1) = MAX - MIN1). For the second time interval T2 between the local maximum MAX of ICP and the second local minimum MIN2 of ICP, Avp can be calculated as the difference between the local maximum MAX of ICP and the second local minimum MIN2 of ICP (i.e., Avp(T2) = MAX - MIN2). Similarly, MICP is then also determined separately for the half-periods T1 and T2 as the mean pressure between MIN1 and MAX and between MAX and MIN2. This can be done for the subsequent periods of ICP, which are in the 3D to 3I figuresAs shown, the following can be continued. In essence, Avp and MICP can each be determined for "half-periods" between a local minimum and a local maximum as the first half-period and between a local maximum and the next local minimum as the second half-period, or they can each be determined for whole periods.

[0078] Fig. 3J The calculation of the amplitude AAvp from the time series Avp and the calculation of the amplitude Arp from the time series MICP are then shown as examples. AAvp is the difference between the maximum and minimum of the time series Avp. Arp is the difference between the maximum and minimum of the time series MICP.

[0079] The resulting RAQ value is dimensionless and independent of the calibration and transfer factor of the acquired signal. Therefore, it is particularly suitable for use with non-invasively acquired signals whose calibration and transfer factors are unknown.

[0080] In a preferred embodiment of the invention, the evaluation described above is performed by one or more analog computing circuits.

[0081] In a further preferred embodiment of the invention, the evaluation is carried out by one or more digitally operating computing circuits.

[0082] In a particularly preferred embodiment of the invention, the evaluation is performed by one or more microprocessor circuits controlled by one or more programs. Furthermore, the calculation of the pulse amplitude described in a) and the signals or time series described in a) and b) is carried out by an algorithm in the time domain. Preferably, the calculation of the amplitudes described in c) and d) is performed by determining the maxima and minima in the time series Avp and AArp and calculating the differences between successive maxima and minima.

[0083] The calculation of the amplitudes described under c) and d) is particularly preferred if it is carried out by calculating the amplitude spectra of the time series A vp and AA rp and determining the maxima in the range of the respiratory rate.

[0084] In a further particular embodiment of the invention, two devices according to the invention are provided for different combinations of modulated and modulating waves, and the characteristic value is formed by calculating the quotient of the output value or output signal of the first device and the output value or output signal of the second device. Preferably, in the first device, the signal RAQ1 is generated with the respiratory wave as the modulating wave and the heartbeat-induced pulse wave as the modulated wave; in the second device, the signal RAQ2 is generated with the B-wave as the modulating wave and the heartbeat-induced pulse wave as the modulated wave, wherein the characteristic value is calculated as the quotient RAQ1 / RAQ2 or its reciprocal. literature

[0085] [1] S. Jetzki, M. Kiefer, R. Eymann, M. Walter, und S. Leonhardt, "Analysis of pulse waves in intracranial pressure" in Conference proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, 2006, vol. 2007, pp. 2863-2866. [2] D. J. Price, M. Czosnyka, and M. Williamson, "Attempts to continuously monitor autoregulation and compensatory reserve in severe head injuries," in Intracranial Pressure VIII, Springer, 1993, pp. 61-66, [3] M. Czosnyka, Z. Czosnyka, N. Keong, A. Lavinio, P. Smielewski, S. Momjian, E. A. Schmidt, G. Petrella, B. Owler, and J. D. Pickard, "Pulse pressure waveform in hydrocephalus: what it is and what it isn't," Neurosurg. Focus, vol. 22, no. 4, pp. 1-7, 2007. [4] N. Lenfeldt, N. Andersson, A. Ågren-Wilsson, A. T. Bergenheim, L.-O. D. Koskinen, A. Eklund, and J.Malm, "Cerebrospinal fluid pulse pressure method: a possible substitute for the examination of B waves," J. Neurosurg., vol. 101, no. 6, pp. 944-950, 2004.

Claims

1. A device for determining a characteristic parameter of the head content of humans and other mammals with obtaining and processing of a signal characteristic of the head content as an input, wherein the characteristic signal is one of: the electrical impedance of the skull, the directly measured pressure inside the head, the electrical capacitance of the skull, the transit time of an ultrasonic signal passed through the skull, and wherein the device is configured to a. calculate the pulse amplitude Avp of each individual period or half period of a modulated wave of the characteristic signal and to generate a signal Avp or a time series Avp (3), b. calculate the mean value MICP for each single period or half period of the modulated wave of the characteristic signal and generate a signal MICP or a time series MICP (4), c. calculate the amplitude Arp of a modulating wave in the time series MICP or in the signal MICP (5), d. calculate the amplitude AAvp of the modulating wave in the time series Avp or in the signal Avp (6), e. calculate the characteristic parameter as an output value using at least one or more of the quantities: Avp, Arp, AAvp, wherein the characteristic parameter is a quotient comprising the quantities Arp and AAvp.

2. Device according to claim 1, characterized in that the characteristic parameter is a dimensionless parameter.

3. Device according to one of the preceding claims, characterized in that the characteristic parameter is a quotient comprising the quantities HF and / or AF, where HF is the heart rate and AF is the respiratory rate.

4. Device according to one of the preceding claims, characterized in that the quotient (RAQ) is proportional to or equal to one of the following expressions: A rp / AA vp , A rp / AA vp / AF , A rp / AA vp * HF , A rp / AA vp * HF / AF .

5. Device according to one of the preceding claims, characterized in that the characteristic signal is the transit time of an ultrasonic signal which is reflected from the interior of the skull.

6. Device according to one or more of the preceding claims, characterized in that the device comprises one or more units that is / are configured to a. calculate the pulse amplitude Avp of each individual period of the modulated wave of the characteristic signal and to generate a signal Avp or a time series Avp (3), b. calculate the mean value MICP for each individual period of the modulated wave of the characteristic signal and generate a signal MICP or a time series MICP (4), c. calculate the amplitude Arp of a modulating wave in the time series MICP or in the signal MICP (5), d. calculate the amplitude AAvp of the modulating wave in the time series Avp or in the signal Avp (6), e. calculate the characteristic parameter as an output value using at least one or more of the quantities: Avp, Arp, AAvp.

7. Device according to claim 6, characterized in that the respective unit is an analog computing circuit, a digital arithmetic circuit or a program-controlled microprocessor circuit.

8. Device according to one of the preceding claims, characterized in that the modulated wave is one of the periodic waves from the group of B-waves, C-waves, respiratory waves, heartbeat-induced waves.

9. Device according to one or more of the preceding claims, characterized in that the modulating wave is one of the periodic waves from the group of A-waves, B-waves, C-waves, respiratory waves, which has a lower frequency than the modulated wave.

10. Device for determining a characteristic parameter of the head content of humans and other mammals characterized by the extraction and evaluation of a head content characteristic signal, comprising a first device according to one of the preceding claims and a second device according to one of the preceding claims, wherein the first device is configured to use a particular combination of a modulated and a modulating wave, and wherein the second device is configured to use another combination of a modulated and a modulating wave, and wherein the device is configured to form the characteristic parameter of the head content as the quotient of the output value of the first device and the output value of the second device.

11. Device according to one of the preceding claims, characterized in that the device is configured to form the time series Avp by using for the time period from a local minimum to a subsequent local maximum of the modulated wave of the characteristic signal the difference between the local maximum and the local minimum as the value for the time series Avp, and by using for the ensuing time period between the local maximum and the subsequent local minimum of the modulated wave of the characteristic signal the difference between the local maximum and the subsequent local minimum as the value of the time series Avp, and / or to form the time series MICP by using for the time period between a local minimum and the subsequent local maximum of the modulated wave of the characteristic signal the average value between the local maximum and the local minimum as the value for the time series MICP, and by using for the subsequent time period between the local maximum and the subsequent local minimum of the modulated wave of the characteristic signal the average value between the local maximum and the subsequent local minimum as the value of time series MICP.

12. A method for determining a characteristic parameter of the head content of humans and other mammals using a device according to one of the preceding claims, comprising the steps: a. calculating the pulse amplitude Avp of each individual period or half period of a modulated wave of the characteristic signal and generating a signal Avp or a time series Avp (3), b. calculating the average value MICP for each individual period or half period of the modulated wave of the characteristic signal and generating a signal MICP or a time series MICP (4), c. calculating the amplitude Arp of a modulating wave in the time series MICP or in the signal MICP (5), d. calculating the amplitude AAvp of the modulating wave in the time series Avp or in the signal Avp (6), e. calculating the characteristic parameter using at least one or more of the following variables: Avp, Arp, AAvp, wherein the characteristic parameter is a quotient comprising the quantities Arp and AAvp.