INTRACRANIAL PRESSURE ESTIMATING METHOD AND INTRACRANIAL PRESSURE ESTIMATING DEVICE

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First Claim
1. An intracranial pressure estimating method for estimating an intracranial pressure from timeseries data on external ear canal pressure pulse waves, the method comprising:
 an acquisition step of acquiring timeseries data on external ear canal pressure pulse waves of a subject;
an analysis step of analyzing external ear canal pressure pulse wave data obtained by digitalizing the timeseries data on the external ear canal pressure pulse waves to calculate a first formant frequency of the external ear canal pressure pulse wave data;
a correction step of correcting the first formant frequency based on personal information on the subject to calculate a corrected value; and
an estimation step of calculating an estimated value of an intracranial pressure based on the corrected value.
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Abstract
An intracranial pressure estimating method includes: an acquisition step (S10) of acquiring timeseries data on external ear canal pressure pulse waves of a subject; an analysis step (S12) of analyzing external ear canal pressure pulse wave data obtained by digitalizing the timeseries data on the external ear canal pressure pulse waves, to calculate a first formant frequency of the external ear canal pressure pulse wave data; a correction step (S13) of correcting the calculated first formant frequency based on personal information on the subject to calculate a corrected value; and an estimation step (S14) of calculating an estimated value of an intracranial pressure based on the calculated corrected value.
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5 Claims
 1. An intracranial pressure estimating method for estimating an intracranial pressure from timeseries data on external ear canal pressure pulse waves, the method comprising:
an acquisition step of acquiring timeseries data on external ear canal pressure pulse waves of a subject; an analysis step of analyzing external ear canal pressure pulse wave data obtained by digitalizing the timeseries data on the external ear canal pressure pulse waves to calculate a first formant frequency of the external ear canal pressure pulse wave data; a correction step of correcting the first formant frequency based on personal information on the subject to calculate a corrected value; and an estimation step of calculating an estimated value of an intracranial pressure based on the corrected value.  View Dependent Claims (2, 3, 4)
 5. An intracranial pressure estimating device comprising:
an external ear canal pressure pulse wave sensor that detects external ear canal pressure pulse waves of a subject; and an arithmetic unit that estimates an intracranial pressure from timeseries data on the external ear canal pressure pulse waves, wherein the arithmetic unit analyzes external ear canal pressure pulse wave data obtained by digitalizing the timeseries data on the external ear canal pressure pulse waves, calculates a first formant frequency of the external ear canal pressure pulse wave data, corrects the first formant frequency based on personal information on the subject to calculate a corrected value, and calculates an estimated value of the intracranial pressure based on the corrected value.
1 Specification
The present invention relates to an intracranial pressure estimating method and an intracranial pressure estimating device.
Many organs and nerves, including the brain, are concentrated in the head of a human, and measuring biological information in this site is very significant in terms of health control and disease prevention. In particular, intracranial pressure (ICP) is always maintained constant due to biological homeostasis, and it is known that the increased or decreased intracranial pressure may cause a fatal severe disease in some cases. Moreover, the intracranial pressure is used as an index for therapy and diagnosis of brain damage, stroke, and intracranial hemorrhage. Thus, it is particularly significant to find the establishment of an intracranial pressure measuring method.
As conventional intracranial pressure measuring methods, a method of placing a piezoelectric sensor directly under the cranium bones (PTL 1, NPL 1 and 2) and a method of directly inserting a tube into the lateral ventricle and measuring pressure of a water column rising therefrom (PTL 2, NPL 3) have been generally known. In each of the methods, however, a hole needs to be drilled in the cranium bone or a sensor or a tube needs to be placed inside the cranium bone, which is highly invasive for subjects and requires subjects to take a complete rest during measurement. It is difficult to measure and evaluate the intracranial pressure by only one momentary value, and it is a common practice to measure continuous values for a certain period of time. There is a risk that subjects may be infected with fungus during the measurement, and the countermeasures need to be taken into consideration. Thus, studies have been made on many intracranial pressure measuring technologies that put less burden on subjects, that is, lowinvasive.
Examples of the intracranial pressure measuring methods reported so far include a technology of injecting a contrast medium in the cranium bone of a subject and measuring the intracranial pressure by NMR measurement (PTL 3). Another report is a technology of injecting a contrast medium in the cranium bone of a subject, generating fine bubbles in this site, acquiring low frequency response, and analyzing resonant frequency (PTL 4). Another report is a technology of irradiating the eyeball of a subject with infrared rays and performing FTIR analysis of reflected light to measure the intracranial pressure (PTL 5 to 7). Another report as a technology of noninvasively detecting biological information from a site near the brain is a technology of measuring pulse waves in the ear canal (PTL 8 to 15). It has been reported to measure acoustic data on the artery blood pressure and the blood flow of middle cerebral artery and take a nonlinear correlation therebetween to calculate the intracranial pressure (PTL 16). In medical animal testing, it has been known from simultaneous recording of ear canal pressure waves, artery pressure waves, and intracranial pressure waves of cats, the amplitude of the ear canal pressure increases when the blood pressure rises, and the propagation time from the artery pressure waves to the ear canal pressure waves is shortened when the intracranial pressure rises (NPL 4), and it has been known from the measurement of artery pressure waves (which is main component of pressure waves in ear canal) and intracranial pressure waves of dogs that a notch appears on a transfer function and is affected by change in pressure in the brain (cerebrospinal pressure) (NPL 5).
To deal with the technical problems inherent to the abovementioned technologies, the inventors of the invention have proposed a method of measuring carotid pulse waves and external ear canal pressure pulse waves to estimate the intracranial pressure based on amplitude information and waveform information on both the pulse waves (PTL 17).
 PTL 1: JT2008539811
 PTL 2: JPA5300880
 PTL 3: JPA2001346767
 PTL 4: JPA2006230504
 PTL 5: JPT2002513310
 PTL 6: JPA2007301215
 PTL 7: JPT2008543352
 PTL 8: JPA884704
 PTL 9: JPA2000121467
 PTL 10: JPT2004528104
 PTL 11: JPA2006102163
 PTL 12: JPT2006505300
 PTL 13: JPA2008237847
 PTL 14: JPA201017317
 PTL 15: JPA2010187928
 PTL 16: JPT2006526487
 PTL 17: JPA2013102784
 NPL 1: Neurosurgery, 2003 March; 52(3): 61923; discussion 623
 NPL 2: Korean J Cerebrovasc Dis, 2002 March; 4(1): 5257. Korean
 NPL 3: Neurologia medicochirurgica, 29(6), 484489, 1989 Jun. 15
 NPL 4: Keio Medical Society, vol. 72(6), pp. 497509, 1995
 NPL 5: J. Neurosurg Pediatrics, vol. 2, pp. 8394, 2008
The importance of intracranial pressure measurement with a noninvasive and simple configuration is particularly recognized in emergency medical care and control of critically ill patients, such as patients with disturbance of consciousness due to brain disorder. For intracranial pressure measurement in such medical cares, a device used for the measurement needs to be able to measure the intracranial pressure noninvasively with as simple a configuration as possible.
The invention has been made in view of the abovementioned problems. The invention can provide an intracranial pressure estimating method and the like capable of estimating intracranial pressure in real time without putting burden on subjects by using a noninvasive and simple device.
According to this application example, there is provided an intracranial pressure estimating method for estimating an intracranial pressure from timeseries data on external ear canal pressure pulse waves, the method including:
an acquisition step of acquiring timeseries data on external ear canal pressure pulse waves of a subject;
an analysis step of analyzing external ear canal pressure pulse wave data obtained by digitalizing the timeseries data on the external ear canal pressure pulse waves to calculate a first formant frequency of the external ear canal pressure pulse wave data;
a correction step of correcting the first formant frequency based on personal information on the subject to calculate a corrected value; and
an estimation step of calculating an estimated value of the intracranial pressure based on the corrected value.
According to this application example, the intracranial pressure can be estimated based on external ear canal pressure pulse waves that can be measured by a noninvasive and simple device, and hence the intracranial pressure estimating method capable of estimating the intracranial pressure in real time without putting burden on subjects can be implemented. Further, the first formant frequency of the external ear canal pressure pulse wave data is corrected based on the personal information on the subject, and the obtained corrected value is used to calculate the estimated value of the intracranial pressure. Thus, an intracranial pressure estimating method capable of accurately estimating the intracranial pressure can be implemented.
In the abovementioned intracranial pressure estimating method, the analysis step may include analyzing data obtained by subjecting the external ear canal pressure pulse wave data to highpass filter processing to calculate the first formant frequency.
Consequently, influence of breathing and heartbeat of subjects can be reduced, and hence an intracranial pressure estimating method capable of accurately estimating the intracranial pressure can be implemented.
In the abovementioned intracranial pressure estimating method, the estimation step may include calculating an estimated value PICP of the intracranial pressure based on the following equation:
PICP=A·ln(Xf1)+B
where A and B are constants, and Xf1 is the corrected value.
Consequently, an intracranial pressure estimating method capable of accurately estimating the intracranial pressure can be implemented.
In the abovementioned intracranial pressure estimating method, the correction step may include calculating the corrected value Xf1 based on the following equation:
Xf1=f1+β1·ln(K/Age)+β2·FM
where f1 is the first formant frequency, β1, K, and β2 are constants, Age is the age of the subject, and FM is the sex of the subject (0 for male and 1 for female).
Consequently, an intracranial pressure estimating method capable of accurately estimating the intracranial pressure can be implemented.
According to this application example, there is provided an intracranial pressure estimating device including:
an external ear canal pressure pulse wave sensor that detects external ear canal pressure pulse waves of a subject; and
an arithmetic unit that estimates an intracranial pressure from timeseries data on the external ear canal pressure pulse waves,
wherein the arithmetic unit analyzes external ear canal pressure pulse wave data obtained by digitalizing the timeseries data on the external ear canal pressure pulse waves, calculates a first formant frequency of the external ear canal pressure pulse wave data, corrects the first formant frequency based on personal information on the subject to calculate a corrected value, and calculates an estimated value of the intracranial pressure based on the corrected value.
According to this application example, the intracranial pressure can be estimated based on external ear canal pressure pulse waves that can be measured by a noninvasive and simple device, and hence the intracranial pressure estimating device capable of estimating the intracranial pressure in real time without putting burden on subjects can be implemented. Further, the first formant frequency of the external ear canal pressure pulse wave data is corrected based on the personal information on the subject, and the obtained corrected value is used to calculate the estimated value of the intracranial pressure. Thus, an intracranial pressure estimating device capable of accurately estimating the intracranial pressure can be implemented.
Preferred embodiments of the invention are described in detail below with reference to the drawings. The drawings to be referred to are illustrative. Note that the following embodiments do not unduly limit the scope of the invention as stated in the claims. In addition, all of the elements described in connection with the following embodiments should not necessarily be taken as essential requirements of the invention.
The external ear canal pressure pulse wave sensor 10 detects external ear canal pressure pulse waves. The external ear canal pressure pulse waves (ear canal pulse wave sound pressure) detected by the external ear canal pressure pulse wave sensor 10 are amplified by the amplifier 20, converted into digital data by the AD converter 30, and output to the arithmetic unit 40. As the external ear canal pressure pulse wave sensor 10, a sound sensor or a pressure sensor can be used.
Referring back to
The display unit 50 (display) displays the external ear canal pressure pulse wave data and arithmetic results of the arithmetic unit 40 (estimated value of intracranial pressure). As the display unit 50, for example, a liquid crystal display or a CRT display can be employed.
When it is supposed from the equivalent circuit model illustrated in
When the natural resonant frequency fo is supposed to be a single resonant system as illustrated in
2π·fo=1/(L1·Cx)^{1/2} (1)
From Equation (1), the compliance Cx in the cranium is expressed by the following Equation (2).
Cx=1/{L1·(2π·fo)^{2}} (2)
The intracranial pressure ICP is given by the following Equation (3) based on the known relational expression between the intracranial pressure ICP and the compliance Cx inside the cranium.
ICP=α1·ln(1/Cx)=α1·ln(4π^{2}·L1·fo^{2}) (3)
where α1 is a proportionality constant.
The first formant frequency f1 illustrated in
Thus, in the intracranial pressure estimating method in an embodiment of the invention, the first formant frequency f1 is corrected based on the age and the sex of the subject. Specifically, the first formant frequency f1 is corrected by the following Equation (4) to calculate a corrected value Xf1.
Xf1=f1+β1·ln(K/Age)+β2·FM (4)
where β1, K, and β2 are constants, and Age is the age. FM is the sex, which is 0 for male and 1 for female.
The corrected value Xf1 in Equation (4) is used to rewrite Equation (3), and the estimated value PICP of the intracranial pressure is given by the following Equation (5).
PICP=A·ln(Xf1)+B (5)
where A and B are constants. For example, the constants in Equation (4) are set such that β1=1.5,β2=−0.4, and K=50, and the data (first formant frequency f1, age, and sex) illustrated in
The optimal values of the constants and the corrected value Xf1 obtained from the data illustrated in
First, the arithmetic unit 40 acquires external ear canal pressure pulse wave data obtained by digitalizing timeseries data on external ear canal pressure pulse waves detected by the external ear canal pressure pulse wave sensor 10 (Step S10). Further, the arithmetic unit 40 acquires age Age and sex FM of a subject input from an input unit (not shown).
Next, the arithmetic unit 40 executes highpass filter processing on the acquired external ear canal pressure pulse wave data (Step S11). For example, a highpass filter for cutting frequencies of 3 Hz or lower can be applied to remove disturbance elements, such as breathing and heartbeat of the subject. Next, the arithmetic unit 40 analyzes the external ear canal pressure pulse wave data subjected to the highpass filter processing (such as LPC analysis) to calculate a first formant frequency f1 (Step S12).
Next, the arithmetic unit 40 corrects the calculated first formant frequency f1 by Equation (4) based on the age Age and the sex FM of the subject to calculate a corrected value Xf1 (Step S13). Next, the arithmetic unit 40 calculates an estimated value PICP of the intracranial pressure by Equation (5) based on the calculated corrected value Xf1 (Step S14).
According to an embodiment of the invention, the intracranial pressure can be estimated based on external ear canal pressure pulse waves that can be measured by a noninvasive and simple device, and hence the intracranial pressure can be estimated in real time without purring burden on subjects. Further, the first formant frequency f1 of the external ear canal pressure pulse wave data is corrected based on the age and the sex of the subject, and the obtained corrected value Xf1 is used to calculate the estimated value PICP of the intracranial pressure. Thus, the intracranial pressure can be accurately estimated in consideration of the difference in inertial mass L1 in the cranium depending on the age and the sex of subjects.
While the embodiment or the modification has been described above, the invention is not limited to the embodiment or the modification, and can be carried out in various modes within the range not departing from the invention.
The invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, a configuration having the same function, method and result or a configuration having the same objective and effect). The invention also includes configurations in which nonessential elements described in the embodiments have been replaced by other elements. The invention further includes configurations having the same effects as those of the configurations described in the embodiments, or configurations capable of achieving the same objectives as those of the configurations described in the embodiments. Moreover, the invention includes configurations in which known art is added to the configurations described in the embodiments.
 1 Intracranial pressure estimating device
 10 External ear canal pressure pulse wave sensor
 11 Sealed portion
 12 Microphone
 13 Sound hole
 14 Sound hole
 20 Amplifier
 30 AD converter
 40 Arithmetic unit
 50 Display unit