FI79456B - FOERFARANDE FOER MAETNING AV NERVSYSTEMETS STIMULUSRESPONS. - Google Patents

Description

1 79456

The present invention relates to an apparatus for examining the nervous system, comprising a sensor connected to a pulse source for stimulating her-5 mon and a second sensor for receiving a nerve response and means for recording and processing the response of the device. An interesting field of application of this invention is in the fields of medicine, clinical neurophysiology, intensive care and anesthesia.

10 A method for studying nervous system excitatory responses is already known (Duodecim 101: 2374-2377, 1985). Evoked potentials (EP) refers to a change in the electrical functions of the nervous system caused by an external stimulus. Stimulus response here also means a change in nervous system function caused by an external stimulus over a period of more than 15 minutes, corresponding mainly to electron neurography (ENG) and electron neurosculography (ENMG).

In practice, three stimulus response studies are used: somatosensory evoked potentials (SEP), brainstem auditory evo-. Ked potentials (BAEP) and visual evoked potentials (VEP). These studies have expanded the research possibilities of the nervous system and provide information on the course of sensory impulses from the extreme edge of the nervous system. · 25 to the cortex.

Somatosensory arousal responses (SEPs) are elicited by electrically stimulating the peripheral nervous system. The measured responses describe the impulse flow in the nerve plexus, root, pelvic and cervical spinal cord in the thalamus, and in the cerebral cortex.

- Visual stimulus responses (VEP) determine the function of the visual pathways by measuring the passage of the visual impulse from the retina to the visual center to the dorsal segment of the cerebral cortex. A chessboard pattern is used as the stimulus, in which the dark and light squares change and the overall brightness remains unchanged.

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Another stimulus is the diffuse flash of light, the so-called Flash VEP.

Auditory cerebral arousal responses (BAEP) measure, on the one hand, the functioning of the auditory system and, on the other hand, the passage of impulses in the area of the brainstem. The stimulus uses 5 audible clicks through the headphones. The responses describe the passage of the impulse in the auditory nerve, the cerebral bridge, and the midbrain.

Technically, stimulus response studies are based on averaging. Repeat stimuli ta-10 at intervals of several, even thousands of times, and average the measured responses. The method improves the poor signal-to-noise ratio of a weak response.

The above-mentioned research methods take advantage of the measurement of the electrical activity of the nervous system. However, 15 studies are also performed by measuring the magnetic fields of the nervous system with a SQUID magnetometer (Mikko Sams: Magnetic and electrical responses in the human brain caused by frequency changes in the heart rate. Psychology 1/86, pp. 22-25). The nervous system is also studied by measuring the nuclear magnetic resonance of the atoms (so-called NMR devices).

It is an object of the present invention to provide; an apparatus for examining the nervous system, by means of which any of the above-mentioned basic research methods, modified in accordance with the invention, can be utilized, whereby it is possible to obtain essential additional information in comparison with previously known research methods. The device according to the invention implementing this is characterized in that the pulse source is a sequence generator transmitting a predetermined code, and that the means for registering and processing the response comprises a correlator for correlating the response with the code transmitted by the sequence generator to determine the nerve impulse response.

The purpose is therefore to study the impulse transmission properties of the nervous system. The nerve impulse can be described by the function g (t), where t represents time. The Fourier transform of this 79956 is G (f), where f represents the frequency. The transfer property of the nervous system is described by H (f), and its inverse Fourier transform is h (t). The measured response is described by a function i (t) with a Fourier transform of 1 (f). The response thus measured is i (f) = g (t) x 5 h (t), and its Fourier transform is 1 (f) = G (f). H (f).

The present invention is not based on averaging but the signal-to-noise ratio is improved by transmitting the stimulus as a specific code-compliant pulse train (sequence) and mathematically analyzing in both analog, digital and analog-to-digital (hybrid) ways. The device according to the invention further prints a normal time-response curve, a frequency spectrum and parameters describing the state of the brain derived from the above. It is therefore preferred that the impulse response is subjected to a Fou-15 rier transform to obtain a complex frequency response and that the frequency response is statistically processed to obtain parameters related to different disease states. The obtained frequency response is subjected to statistical processing on the one hand to obtain parameters related to different disease states and on the other hand to find out the signal-to-noise ratio. . sex. The signal-to-noise ratio reflects the quality of the measurement.

The following statistical treatments are possible: regression analysis yielding regression points, factor analysis yielding factor scores, difference analysis yielding separation points, and grouping analysis.

The device according to the invention can be applied in such a way that:. : that in order to examine the optic nerve, the visual stimulus is produced according to a certain code, that the vibrational sensation is examined by stimulation according to a certain code, that the auditory sensation is stimulated according to a certain code, or that the nervous system is stimulated by a stimulus. Li. In addition, the device can be used to study the taste buds and * · hot-cold sensations of the tongue.

The invention comprises a nervous system response measuring device which has in principle almost the same function as a prior art nervous system response measuring device. A novelty of the invention is that the device transmits a pulse train according to a certain sequence and is not based on averaging techniques. In addition, the device produces real and 5 complex Fourier transforms of the responses, as well as the parameters describing the state of the brain calculated on the basis of these. New types of sensors make it possible to study other types of neural pathways.

The function of the nervous system has so far been described by 10 i (t). However, there are difficulties of interpretation. The elucidation of transfer properties and their functions h (t) and especially H (f) better describe the function of the nervous system. By introducing these parameters, the effects of various diseases on the nervous system can be elucidated.

The present invention is based on communication theory, correlation technology and radar technology. The device can be implemented using the latest analog and digital microcircuit electronics.

This device allows the research method, which previously required a specialist-20 doctors, can now be performed quickly, reliably and simply. Thus it is possible; continuously monitor central nervous system status in patients during and after surgery. For newborns, this study is also valuable because it can be used as a method of monitoring 25 fetuses or newborns by measuring and monitoring the response to a sound stimulus in the nervous system.

The details and advantages of the invention will become apparent from the following detailed description, which is in no way limiting, with reference to the accompanying drawings, in which Figure 1 shows a method of measuring stimulus responses as a device, Figure 2 shows a Barker code, Figure 3 shows an example of a correlator structure 5 79456 ta, Fig. 4 shows the Frank code and Fig. 5 shows a complex correlator.

The present device consists of two parts: 5 The stimulus development part and the response analysis part. The stimulus development part consists of the sequence generator SEK, the amplifier VAH and the stimulus-forming sensor ANTI.

The purpose of the sequence generator SEK is to produce im-10 pulse sequences. These consist of successive pulses that are not continuous and uniform as in conventional excitation potential equipment, but are amplitude, phase or frequency modulated with a given code. The structure of the code is known in radar technology and is referred to in more detail in the 15 literature (Hovannessian: "Radar Detection and Tracking Systems"). Examples of codes are the Barker code (Figure 2) and the Frank code. The 13-element Barker code is shown in Figure 2. Its decoder consists of a tapped analog delay (TAD) line, where after each delay line 20 the signal is summed or subtracted according to the above code (Figure 3).

The pulses generated by the sequence generator SEK are applied to an amplifier VAH, which raises the level of the signals to suit the sensor.

: 25 ANTI acts as a sensor if the nerve is electrically stimulated, a standard electrode. Other sensor alternatives are: a device for generating a visual stimulus, which may be a lamp, an LED or a video monitor, a device for stimulating a sense of vibration, for example a piezoelectric element,. - a device for generating a auditory stimulus, - a device for stimulating a hot-cold sensation, for example a Peltier element.

‘35 The analysis apparatus comprises a sensor ANT2, an amplifier 6 79456 men VAH2, a correlator KORR and a printing apparatus. It can be connected to a Fourier converter F.

If the electrical functions of the nervous system are measured, the sensor ANT2 is a standard electrode. When measuring the magnetic events of the her-5 bridge, the sensor is a SQUID-: magnetometer. When measuring nuclear magnetic resonance, the corresponding NMR equipment acts as a sensor.

Amplifier VAH2 raises the obtained potential to suit the correlator KORR. In the EP study, the amplifier is a 10 standard EEG amplifier.

The correlator KORR can be implemented analogously or digitally. A correlator implemented with analog circuits is shown in the book: RETICON, "Analog Signal

Processing Integrated Circuits ". The correlator process-15 processes the obtained signal i (t) into the binary transmitted signal g (t). Thus, the result is h (t). The correlator is thus a binary analog correlator. Its output can be real or complex 3, 5).

Claims (4)

7 79456 A device for examining a nervous system, comprising a sensor (ANTI) connected to a pulse source (SEK) for stimulating a nerve and a second sensor (ANT2) for receiving a nerve response and means and recording and processing a response (KORR, F), characterized in that the pulse source is a sequence generator (SEK) transmitting a predetermined code, and that the means for recording and processing the response comprises a correlator (KORR) for correlating the response with the code transmitted by the sequence generator (SEK) to determine a nerve impulse response. Device according to Claim 1, characterized in that a correlator (KORR) is connected 15 Fourier transducer (F) to determine the complex frequency response of the nerve.