JPS6351022B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel intracranial pressure measuring device.

Control of intracranial pressure is essential in the management and treatment of patients with severe brain diseases. but,
Conventionally, in order to continuously measure intracranial pressure, it was necessary to perform surgery and place a pressure sensor epidurally, or to perform ventricular puncture to measure intraventricular pressure. This method is highly invasive to the patient, and considering the possibility of bacterial infection of the brain, it is not something that anyone can easily perform, and even if pressure can be measured temporarily, there are limits and limitations to long-term intracranial pressure measurement.

The object of the present invention is to provide an intracranial pressure system that can continuously measure intracranial pressure and the reactions of the cerebrovascular system associated with changes in intracranial pressure, without any surgical intervention or other intervention on the patient, and as easily as testing electroencephalograms on the scalp. To provide measuring equipment.

A feature of the present invention is that electrodes similar to those used to measure brain waves are placed on the scalp and the electrical impedance of the head is measured.
This is the point at which intracranial pressure can be measured.

The brain is suspended in the cerebrospinal fluid of the intracranial cavity, which has a fixed volume, by cranial nerves and the vascular system, and dynamic energy from breathing and heart pulsations aids intracerebral microcirculation via the vascular system. Maintains cerebral blood circulation under constant perfusion pressure. The brain's volume changes in sync with the heartbeat due to fluctuations in blood volume associated with the heartbeat.
Due to changes in blood volume associated with breathing, the volume changes in synchrony with breathing. Now, let ΔPA be the rapid brain movement (volume change) caused by heartbeat, and ΔR be the slow brain movement caused by breathing. We found that when intracranial pressure increases, respiratory brain movement ΔR decreases;
On the contrary, they found that heartbeat brain movement ΔPA increased, and that this correlation increased as intracranial pressure rose. As a result, as the intracranial pressure increases, the value of ΔPA/ΔR gradually increases while showing a certain correlation function in the closed intracranial cavity. From this, it can be seen that intracranial pressure can be expressed as a function of ΔR/ΔPA or ΔPA/ΔR.

Therefore, if we can capture the brain's respiratory and heartbeat movements, which show ΔR and ΔPA, from above the scalp, we can detect them without drilling a hole in the skull like in the past.
Whether the patient is a child or an adult, intracranial pressure can be measured completely non-invasively. The present inventors focused on the fact that both brain movements ΔR and ΔPA are caused by changes in cerebral blood volume, and predicted that changes in brain blood volume naturally change the electrical impedance of the brain. As a result of conducting experiments, we confirmed that intracranial pressure can be measured by measuring the electrical impedance of the head.

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining its operation.
In the figure, 1, 2 and 3, 4 are two pairs of electrodes attached to the head, and 5 is an amplifier for measuring head impedance. The measurement amplifier 5 is for example 50kHz
oscillator, several 10s to several 100μA than this oscillator
50kHz alternating current is applied to the outer electrode pair 1 and 2. The voltage corresponding to the current passed through the head is measured using another pair of electrodes 3 and 4, and the electrical impedance Z of the head is measured. The example in the figure is a four-electrode method, but
Impedance can also be measured by a two-electrode method. Since the information necessary for this device is the impedance fluctuation part due to heartbeat and respiratory movements ΔPA and ΔR in the head impedance Z, the DC part of the impedance Z is cut in the measurement amplifier 5, and the fluctuation part ΔZ Amplify only. Figure 2 shows the waveform. The impedance variation ΔZ includes a cardiac impedance variation ΔZ _PA and a respiratory impedance variation ΔZ _R. Since the difference between the minimum value A and the maximum value B for each heartbeat in the ΔZ _PA fluctuation waveform corresponds to the impedance change due to the brain movement ΔPA, this is referred to as ΔPA′ for convenience. Similarly,
The difference between the minimum value C and maximum value D for each breath in the ΔZ _R fluctuation waveform corresponds to the impedance change due to the brain movement ΔR, and for convenience, this is referred to as ΔR'. These impedance change signals ΔPA′ and ΔR′ are
Find it as follows.

6 is an amplifier for measuring arterial pressure, which measures arterial pressure by either an invasive method or a non-invasive method;
Average to obtain the mean arterial pressure signal AOP _M. 7 is 1
An electrocardiogram as shown in Figure 2 from the paired electrodes 8 and 9.
It is an amplifier that measures ECG and respiration curve RESP. The respiration curve RESP can also be measured by attaching a thermistor to the nostrils and detecting changes in the temperature of exhaled and inhaled air, or by detecting changes in chest circumference. In order to
We will show how to obtain a respiration curve RESP by measuring ECG and detecting changes in thoracic impedance. The electrocardiogram ECG is converted by the QRS detection circuit 12 into a heartbeat signal QRS synchronized with the heartbeat, that is, the R pulse, and is supplied to the A and B detection circuits 10. Similarly,
The respiration curve RESP is determined by the exhalation/inhalation detection circuit 13.
Detecting the point that intersects the baseline, the (+) side is taken as inhalation (-) side is taken as inhalation, a synchronized breathing signal RS is obtained for each breath, and this is sent to the C and D detection circuits 11 and 1.
It is supplied to the breath-to-breath averaging circuit 14. The A and B detection circuit 10 receives the heartbeat signal QRS, detects the minimum value A and maximum value B for each heartbeat, and outputs the difference ΔPA'. Further, in order to improve the measurement accuracy of ΔPA', ΔPA' is input to the one-breath averaging circuit 14, and the average value ΔPA' _M of ΔPA' during one breath is obtained from the respiratory signal RS. C and D detection circuit 1
1, the respiratory signal RS is received, the minimum value C and the maximum value D for each breath are detected, and the difference ΔR' is output. Since the A and B detection circuit 10 and the C and D detection circuit 11 can be easily designed by those skilled in the art, a detailed description of their configuration will be omitted.

The cardiac average impedance change signal ΔPA′ _M , the respiratory impedance change signal ΔR′ and the average arterial pressure signal AOP _M obtained in this way are applied to the calculation circuit 15, and the following calculations are performed to calculate the Obtain internal pressure ICP.

ICP=K ₁ (1+logΔPA′ _M /ΔR′)×10 (1) However, K ₁ is a constant that varies among individuals.

Furthermore, when the arterial pressure fluctuates greatly, the intracranial pressure is affected in proportion to the arterial pressure, so the following calculation is performed to obtain the intracranial pressure ICP.

ICP=K ₂ AOP _M /10 (1+logΔPA' _M /ΔR')...(2) However, K ₂ is a constant that varies between individuals.

These equations are experimental equations determined from the correlation observed between the intracranial pressure, ΔPA/ΔR, and blood pressure mentioned at the beginning, and ΔPA′ _M /ΔR′ in the equations corresponds to ΔPA/ΔR. In addition, in equation (2),
Since AOP _M is almost 100, divide this by 10 and get K ₂
The order of is adjusted to K ₁ in equation (1). These constants K ₁ and K ₂ are normally values close to 1 and can be arbitrarily set by the key switch 16.
The obtained intracranial pressure ICP can be continuously recorded as an analog waveform or digitally displayed as numbers.

FIG. 3 is a diagram comparing the values measured using an epidural pressure measurement sensor in an animal experiment (with constant arterial pressure) and the values measured according to the present invention. The vertical axis of the figure shows the intracranial pressure measured using the epidural pressure measurement sensor, and the horizontal axis shows the actual value measured by this device (1 + log
ΔPA′ _M /ΔR′)×10. C is a plot point representing the average value of the measured values, and B is the positive direction of variation.
A is a straight line drawn to connect plot points C, and Y
It can be expressed as =1.25X. Therefore, by setting K ₁ =1.25, the measured value according to the present invention will almost match the actual measured value. This shows that intracranial pressure can be measured by the present invention. Therefore, intracranial pressure can be measured even in humans by determining the values of K ₁ and K ₂ .

As explained above, according to the present invention, it is possible to continuously and easily measure intracranial pressure and the reaction of the cerebrovascular system associated with its changes from the scalp without any invasiveness such as surgery on the patient. can.

In the above embodiment, each circuit is described as being independent, but in reality, a computer can be used to perform the same function. Furthermore, a filter can be used to separate the cardiac and respiratory impedance change signals.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram for explaining its operation, and Fig. 3 is a comparison diagram of measured values according to the present invention and actual measured values using the conventional method. be. 1-5... Impedance measuring device, 7-13...
... Impedance change detection means, 15, 16...
calculation means.

Claims (1)

[Claims] 1. An impedance measuring device that measures the electrical impedance of the head using electrodes on the scalp, and each impedance change signal based on heartbeat and respiratory brain movements included in the impedance signal. The device includes an impedance change detection means that outputs the impedance change signals separately, and a calculation means that receives the heart rate and respiratory impedance change signals and performs a certain calculation to give an intracranial pressure signal. 1. An intracranial pressure measuring device comprising the step of calculating a ratio of a respiratory impedance change signal to a respiratory impedance change signal. 2. The intracranial pressure measuring device according to claim 1, wherein each of the impedance change signals is an average value signal within a certain period of time.