DE102006045192A1 - Method for measurement of absorption of light of two different spectral ranges by living tissue by invasive insertion of light emitter and photo sensor, involves arranging photo sensor relatively to light emitter - Google Patents

Abstract

The method involves arranging the photo sensor relatively to the light emitter (2) that the light incoming from the photo sensor goes through multiple tissues, particularly excluding arterially perforated tissue. The method is implemented that both modulation depths (pulsatile portion of alternating current to non-pulsatile portion of direct current) amounts to a 0.0005 and improves to 0.001. An independent claim is also included for a sensor device for the absorption of light of two different spectral ranges by living tissues has a sensor support, light emitter and a photo sensor carrier.

Description

I. Field of application

The The invention relates to a method and a measuring device in order to Absorption of light by living, light-radiated, tissue to measure in humans or animals, especially in human fetuses.

II. Definitions

For the purpose the present application is under "light" electromagnetic radiation in the field from 400 nm to 2000 nm, in particular in the range between 600 nm and 1000 nm, understood.

Further For the purposes of the present application, "absorption" is understood to mean the light intensity which is determined according to the Passage through the tissue at the sensor is measurable, regardless of whether the incident light intensity or the electric power is known or not and independent of whether the layer thickness of the irradiated tissue is known or not.

Under Net light path length Below is the minimum length understood the way the light from the exit from the light emitter until entering the light sensor, including scattered light and diffraction phenomena must go back. From the light emitter to the light sensor different light paths are different Length possible, depending on the multiple sites / scattering centers at which light rays on this Way can be distracted.

III. State of the art

at Tissue photometry is known to be the absorption of light, especially the temporally variable Absorption of light (modulation) in a certain frequency range (eg 0 to 0.5 Hz and 0.5 to 10 Hz), determined in the context with the smallest or largest to expected pulse rate or respiratory rate, and blood pressure blood pressure and other sizes of the is to be examined organism.

Of the Light flux in the tissue comes in particular through various optical Effects such as scattering, absorption, diffraction u. a. at interfaces between the different components of the living tissue, where "transmission" and "reflection" are simplistic terms are related to a behavior of light relative to transmitter and receiver Respectively.

So In optical plethysmography, the absorption of light, in particular the modulation of light in a certain frequency range namely the the arterial pulsation, ie from about 30 to 240 bpm, accordingly 0.5 to 4 Hz in relation to non-pulsatile absorption, So for absorption in the frequency range of less than 0.5 Hz. So let Pulse rate, respiratory rate, blood pressure and others determine.

eine Variable

die in weiten Bereichen unabhängig ist von Einflussfaktoren wie der Schichtdicke des durchstrahlten Gewebes oder der Intensität der Lichtemitter usw. und mit deren Hilfe sich die arterielle Sauerstoffsättigung ermitteln lässt, ggf. auch die venöse Sauerstoffsättigung, eventuell auch bei arteriell-venöser Sättigungsdifferenz.If an optical plethysmography in two or more spectral ranges (λ1, λ2 ... λn) is performed and the respective modulation depths (pulsatile component, AC, non-pulsatile component, DC) z. B. at 730 nm and 990 nm in relation to each other, it follows from the respective modulation depths

a variable

which is independent of influencing factors such as the layer thickness of the irradiated tissue or the intensity of the light emitter, etc., and with whose help the arterial oxygen saturation can be determined, possibly also the venous oxygen saturation, possibly also with arterial-venous saturation difference.

So comes human hemoglobin essentially in two states before, namely oxygenated and deoxygenated when modified from toxic or genetically aberrant hemoglobin fractions apart.

The oxygenated as well as the deoxygenated hemoglobin have different specific spectral absorption curves, of which in particular the area over 600 nm for Purposes of optical plethysmography, in which two different Spectral ranges the intensity or the absorption of light by the two hemoglobin fractions (oxygenated and deoxygenated) is measured.

Pulsoximetry is thus a tissue photometry in two or more spectral regions of the light and two frequency ranges of the circulation-induced modulation. With the help of this so-called pulse oximetry, heart rate and lung function can be monitored in a wide range of areas. In fetuses, pulmonary oximetry determines the pulmonary functions of the mother and the functionality of the placenta with respect to oxygen exchange supervised. Immediately after birth, ie during and after the switch from umbilical cord to pulmonary breathing, pulmonary respiration of the fetus as well as the shunt situation between right and left circulation can be assessed and monitored.

In the younger ones Pulse oximetry was especially the transmission pulse oximetry in the past Medicine very successful in living tissue up to a layer thickness of maximum 20 mm irradiated with light from 400 nm to 4000 nm wavelength and the amount of light absorbed by the tissue was measured.

By the limited thickness of the tissue to be irradiated and by the need to have opposing locations for light sensor and light emitters, the application sites were strong limited: in adult humans, for example, on single fingers or on earlobe in premature birth or newborn on a hand or foot.

Minimally invasive transmission pulse oximetry, for monitoring fetal oxygenation during birth, is also known ( DE 38 10 008 ).

Also Reflex Pulse Oximetry was used in an effort to limit the adverse effect in terms of layer thickness overcome, in contrast to the transmission pulse oximetry light emitter and light receiver not on each other lying sides of the tissue to be irradiated were arranged, but on the same side next to each other, usually in one Distance of only a few millimeters.

Of the However, there is a serious disadvantage of reflex pulse oximetry so-called shunt light, by which understood those lights be able to get from the emitter to the sensor, without affecting the arterial perfused tissues, especially those interspersed by arterioles Part of the fabric to have transpired.

To belong to this shunt light For example, those parts of light that are only superficial, little perfused skin layers are affected, and thus can not be modulated pulsatil and in this way by the light emitter get to the light sensor.

This Shunt light component affects the overall result so much negative, that a responsible applicability of this procedure today generally is called into question.

The Birth is a very special challenge for mother and child. With currently about one child death per 200 births the birth one of the biggest threats in the life of man.

A Oxygen deficiency situation during the birth can - if she does not and / or too late recognized and not optimally treated - to irreversible mental and physical Restrictions or lead to life-long disabilities in the child.

It therefore already has many Efforts given to determine the oxygenation of the fetus during childbirth, at least indirectly, e.g. above the pH, base excess, Lactate (discontinuous in microblood studies, MBU), off Heart rate (together with labor activity), CTG or analysis of the ECG, STAN.

To the direct methods of measuring oxygen saturation belongs the transcutaneously measured oxygen partial pressure. He does, however is only a local information and is therefore a screening method while not enough to give birth.

The reliable Method is finally the already mentioned above continuous measurement of arterial oxygen saturation by means of transmission pulse oximetry.

One The decisive advantage of pulse oximetry is that the parameter oxygen saturation is global, i. all over in the body correctly, the same arterial oxygen saturation prevails.

pulse oximetry Pulse oximetry on the fetus is under worst-case conditions - hence it requires more diverse and subtle optimization processes to get reliable pulse oximetry on the fetus at all To become reality.

So Already the application of the sensor is difficult: it usually takes place without vision, groping through vagina and cervix at the preceding Part of the fetus.

additional unfavorable optical factors are added: cheese grease, (Discolored) Amniotic fluid, body hair of the fetus etc. influence or hinder the coupling of the light from the emitter into the tissue or tissue into the recipient.

A particular problem is the disturbance of the measurement signals due to movement: Spontaneous movements of the fetus and, above all, uterine contractions lead to movement artifacts. The dominant mechanisms are movements of the pulse oximetry sensor relative to the site of application and the mirgation of blood in the vessels of the irradiated tissue.

In addition are especially in minimally invasive transmission pulse oximetry on Feten to comply with boundary conditions that partially contradict each other: On the one hand, the sensor should be as small and compact as possible be to him in early To introduce stages of childbirth through the vagina and cervix can and, if possible little attack surface for movement artifacts to provide for uterine contractions. On the other hand has become the length of the light path as an important influencing factor: The modulation depth grows with the light path length, if the light path in exclusively perfused Tissue runs. Thus, the AC light levels increase with increasing relative to the DC component path length in absolute terms, however, both fall with increasing path length of the Light off, so you have to make sure that both components do not fall below a reasonable signal-to-noise ratio.

Farther is a warming of the tissue of the fetus due to the power loss in the pulse oximetry sensor to below 43 ° C to keep at longer term Exposure no tissue damage to effect. This maximum allowed warming ultimately limits the permissible Power loss and thus the efficiency of the light emitter used.

IV. Presentation of the invention

• a) Die ermittelte Sauerstoffsättigung soll möglichst gut der realen Sauerstoffsättigung entsprechen. Die Genauigkeit der Sauerstoffsättigung wird jedoch meistens durch ungewolltes, häufig unvermeidbares Shuntlicht verfälscht. Shuntlicht meint zusätzliche zum modulierten Licht parallel geschaltete Lichtanteile, die durch arteriell nicht- oder minderdurchblutetes Gewebe oder durch parallel geschaltete nichtlebende Strukturen (Käseschmiere, nichtdurchblutete Hautanteile) verlaufen. Erfindungsgemäß verlaufen die Lichtwege in gut perfundierten Gewebsabschnitten, abseits nicht- oder minderdurchbluteter Gewebe bzw. abseites parallel geschalteter nichtlebender Strukturen.
• b) Die Streuung der Sauerstoffsättigung soll möglichst gering sein. Diese Forderung bedeutet, dass die Modulationstiefen selbst auch nur gering streuen dürfen. Dies wird erreicht, indem die Modulationstiefen in allen Spektralbereichen > 0.0005 liegen, bzw. besser > 0.001. Ferner steigen die Modulationstiefen mit zunehmendem Lichtweg im durchblutetem Gewebe. Es muss also der Lichtweg so lange gewählt werden, bis die Modulationstiefen jeweils einen ausreichenden Signal-Rauschabstand aufweisen. Sofern Lichtemitter und Lichtsensor beide in jeweils eine Richtung weisen, die von dem anderen Element weggerichtet ist, existieren mehrere solche Umlenkungen, was den Netto-Lichtweg gegenüber der Entfernung zwischen Lichtemitter und Sensor nochmals vergrößert und die Modulationstiefe verbessert.
• c) Ebenso wichtig für eine geringe Streuung der Sauerstoffsättigung ist die Begrenzung von Bewegungsartefakten. Konstruktiv kann dies durch einen guten Halt des Sensors am zu messenden Organismus erzielt werden – eine invasive Verankerung von Spiralsensoren trägt erheblich dazu bei. Dazu kommt auf der methodischen Seite, dass ein intrakutaner Lichtweg besonders wenig anfällig ist für bewegungsbedingte Änderungen der Lichtein- bzw. Lichtauskopplung.
• d) Die Lichtwege im Gewebe sollten möglichst ausschließlich in arteriell gut durchblutetem Gewebe verlaufen. Lichtwege in nicht arteriell durchbluteten Schichten bewirken einen Lichtverlust, der keinen positiven Beitrag zur Modulationstiefe leistet. Er ist damit schädlich für den nutzbaren Nettolichtweg. Daraus folgt, dass absorbierende Strukturen desto rigoroser zu vermeiden sind, je größer ihr Beitrag zur Gesamtabsorption ist. So ist z.B. beim Sensordesign darauf zu achten, dass die Melaninschicht aus dem Lichtweg herausgehalten wird, ebenso äußere Hautschichten, aber auch Haare und Käseschmiere usw. Auf der Basis dieser Überlegungen erweisen sich sämtliche Reflex-Pulsoximetriesensoren als ungünstig, ebenso wie invasive Lichtwege senkrecht zur Hautoberfläche. Die Lichtwege sind intrakutan in der optimalen Tiefe, also in einer Tiefe zu wählen, in der eine gute Gewebsperfusion herrscht, beim Feten also in einer Tiefe von etwa 2 mm bis 3 mm. Um diese Tiefe korrekt einzuhalten, sollte der Lichtweg intrakutan, parallel zu Hautoberfläche verlaufen – Lichtemitter und Lichtempfänger sollten also in der gleichen Tiefe unter Hautniveau liegen. Dies kann perfekt mit einer Doppelhelix erzielt werden, die zwei achsensymmetri sche Sensorträger besitzt. Die Singlehelix erlaubt nicht die gleiche Tiefe für Lichtemitter und Lichtempfänger. Will man dennoch bei der Singlehelix doch sehr weitgehend die selbe Tiefe muss dies durch entsprechende Senkung der Spiralensteigung in etwa einem Spiralengang erzwingen.
• e) Zur Optimierung der Modulationstiefe sollte bei möglichst geringen mechanischen Abmessungen des Sensors (zur Platzierung des Sensors in frühen Geburtsphasen) die Netto-Lichtweglänge maximiert werden. Es gilt also, den Lichtweg durch perfundiertes Gewebe möglichst lang zu wählen, und dies zu kombinieren mit möglichst kleinen mechanischen Abmessungen des Sensors. Diese gegensätzlichen Forderungen sind nur zu harmonisieren, wenn man gebogene Lichtwege einsetzt, die mittels der Lichtstreuung im Gewebe günstig zu realisieren sind. Es sind dann Lichtemitter und Lichtempfänger nicht direkt auf einander gerichtet. Günstig ist die Anordnung von Lichtemitter und Lichtsensor derart, dass wenigstens eines der beiden Elemente in eine Richtung weist, die von dem anderen Element weggerichtet ist; dadurch wird eine Vergrößerung der Netto-Lichtweglänge erreicht. Lichtwege mit solchen Umlenkungen sind im Gewebe aufgrund seiner optischen Streueigenschaften möglich. Bei Lichtsensor und Lichtemitter, die beide jeweils in die vom anderen Element wegweisende Richtung zeigen, ist der möglichst kürzeste Nettolichtweg somit um zweimal ein Viertel des Umfanges der Kanüle länger als der Abstand der Mittelpunkte der beiden Stellen in den Helix-Kanülen, in denen Sensor und Emitter angeordnet sind. Auf diese Art und Weise kann z. B. die Netto-Lichtweglänge auf mehr als 3 mm, insbesondere mehr als 4 mm vergrößert werden, obwohl der direkte Abstand zwischen Lichtemitter und Lichtsensor weniger als dieses Maß, also z. B. weniger als 4 mm beträgt.

The most important results of our research on fetal pulse oximetry include the identification of unresolved issues as well as the corresponding solutions, which are both methodological and constructive in nature.

• a) The determined oxygen saturation should correspond as well as possible to the real oxygen saturation. However, the accuracy of oxygen saturation is mostly corrupted by unwanted, often unavoidable shunt light. Shunt light means additional light components which are connected in parallel to the modulated light and which pass through tissue that is not perfused or perfused with blood or through parallel non-living structures (cheese smear, non-perfused skin components). According to the invention, the light paths run in well-perfused tissue sections, away from non-perfused or under-perfused tissue or abseites connected in parallel non-living structures.
• b) The scattering of oxygen saturation should be as low as possible. This requirement means that the modulation depths may also scatter only slightly. This is achieved by the modulation depths in all spectral ranges> 0.0005, or better> 0.001. Furthermore, the modulation depths increase with increasing light path in the perfused tissue. The light path must therefore be selected until the modulation depths each have a sufficient signal-to-noise ratio. If the light emitter and the light sensor both point in one direction, which is directed away from the other element, there are several such deflections, which further increases the net light path over the distance between light emitter and sensor and improves the modulation depth.
• c) Equally important for a low degree of oxygen saturation is the limitation of motion artifacts. Constructively, this can be achieved by a good hold of the sensor on the organism to be measured - an invasive anchoring of spiral sensors contributes significantly to this. In addition, on the methodological side, an intracutaneous light path is particularly vulnerable to movement-induced changes in the light input or light output.
• d) The light paths in the tissue should, if possible, run exclusively in tissue that is well supplied with blood. Light paths in non-arterially perfused layers cause a loss of light, which makes no positive contribution to the modulation depth. He is thus harmful to the usable net light path. It follows that absorbent structures are the more rigorously avoided the greater their contribution to total absorption. For example, in sensor design care should be taken that the melanin layer is kept out of the light path, as well as outer skin layers, but also hair and cheese grease, etc. On the basis of these considerations, all reflex pulse oximetry sensors prove to be unfavorable, as well as invasive light paths perpendicular to the skin surface , The light paths are to be selected intracutaneously at the optimal depth, that is to say at a depth in which there is good tissue perfusion, ie at a depth of about 2 mm to 3 mm in the fetus. To properly maintain this depth, the light path should be intracutaneous, parallel to the skin surface - light emitters and light receivers should be at the same depth below skin level. This can be achieved perfectly with a double helix having two axisymmetric sensor carriers. The single helix does not allow the same depth for light emitters and light receivers. If you still want to have the same depth for the single helix, you have to force it down by spiraling the spiral in the same direction.
• e) In order to optimize the depth of modulation, the net optical path length should be maximized with the least possible mechanical dimensions of the sensor (to place the sensor in early stages of birth). So the light path is valid To choose as long as possible by perfused tissue, and to combine this with the smallest possible mechanical dimensions of the sensor. These contradictory requirements can only be harmonized if one uses curved light paths that can be realized favorably by means of light scattering in the tissue. There are then light emitter and light receiver are not directed directly at each other. Conveniently, the arrangement of light emitter and light sensor is such that at least one of the two elements faces in a direction which is directed away from the other element; This achieves an increase in the net light path length. Light paths with such deflections are possible in the tissue due to its optical scattering properties. For light sensor and light emitter, both pointing in the direction pointing away from the other element, the shortest possible net light path is thus two times a quarter of the circumference of the cannula longer than the distance between the centers of the two points in the helix needles, in which sensor and Emitter are arranged. In this way, z. B. the net Lichtweglänge be increased to more than 3 mm, in particular more than 4 mm, although the direct distance between the light emitter and light sensor less than this level, ie z. B. is less than 4 mm.

It is therefore an essential part of the invention, these essential Research results in constructive and procedural embodiments and implement features to the measuring device and the method measuring the absorption of light by the blood of the fetus a vaginally insertable sensor support to optimize so that a measurement of the oxygen saturation of the arterial blood at all only possible becomes.

The Sensor device must therefore be designed in principle so that in the invasively inserted state of the sensor device, the light emitter and the light sensor in the same tissue depth and therefore in the same Tissue layer come to rest, especially when the sensor device Positioned on the tissue surface as far as the stop on the sensor base part or screwed. Light emitter and light sensor are then in terms of the axis of the single helix or double helix on which they are arranged are, on opposite, So centrally symmetric positions.

at a double helix, which is symmetrical, that is two same part spirals with the same slope and the same direction of rotation having offset by 180 ° are arranged, this is achieved simply by being emitter and sensor are located on the analogous positions on the two sub-spirals.

If Emitter and sensor are both arranged on a single helix, is an arrangement axially symmetric indeed possible, but usually connected to an axial offset from the emitter to the sensor. Too too in the single helix light emitter and light receiver in the same tissue depth to be able to position can you use the single helix z. B. so that they are not continuous even slope but in a central region over at least 180 ° at all has no slope and emitter and sensor at the beginning or End of this pitch-free section of the single helix are located.

Further is through the execution of the sensor carrier in the form of a single helix and in particular in the form of a double helix ensures that after the application of the sensor, i. of the minimally invasive application of the spiral (s) emitter and sensor mechanically stationary in the fabric of the preceding part (e.g. Head of the fetus) are arranged and thus optically constant Coupling conditions that are essential requirement for reliable Measurement results are.

At the In fetuses the light is absorbed or modulated differently than in adults People, so that the analysis of the signals preferably on the Frequency ranges 0 to 0.7 Hz and 0.7 to 3 Hz focused.

Around the absorption by the two (or more) hemoglobin fractions to be able to determine should the meter two (or more) different light emitters for light of different wavelengths or Have spectral ranges, in particular the wavelengths 730 nm and 880 nm.

When Light emitters are preferably either directly light-emitting Semiconductor elements, in particular light-emitting diodes used as a light receiver directly photosensitive semiconductors which are integrated into the sensor carrier or in a hollow sensor carrier be used. Alternatively you can as light emitter, or light receiver also serve the ends of light guides, to each other's other End the corresponding optical components are positioned.

Preferably, light emitter and light sensor are arranged at centrally symmetrical axial positions of the two sub-spirals of a double helix or at the radially opposite positions of a single helix. Light emitter and light sensor are located either at the free end of the two part spirals of the double helix, but preferably set back from the (ground) free end by at least 1 mm to 4 mm in the direction of rotation of the helix, the are 0.5 mm to 2 mm longer than the loop length corresponds.

The Both partial spirals of the double helix are at the common sensor device attached with one of its ends. Preferably, each extends the partial spirals of the double helix over 0.5 to 1.5 turns, or 1 to 3 revolutions in a single helix, with which the spiral (s) Completely, i.e. up to the stop on the end face of the sensor cup into the tissue be screwed; this corresponds to a total axial extent from about 2 mm to 4 mm, typically about 3 mm. The thickness (outer diameter) the spiral (s) of the helix is preferably between 0.7 mm and 1.2 mm selected, the inner diameter of the (steel) cannula is 60% to 70% of the outer diameter.

Of the outer diameter the turn of the helix is 4 mm to 10 mm, preferably 5 mm to 7 mm.

When Light emitters are usually used two separate light emitters, e.g. light-emitting semiconductor or the emitting end of Light guides, in each of which the light was fed, the light deliver in different spectral ranges, each one the desired (Center wavelengths the) spectral ranges (730 nm and 880 nm), ie the light emitters in the range from 400 nm to 2000 nm, in particular from 600 nm to 1000 nm, send out. It can take two separate light emitters as well a single, z. B. a white LED, be used, then from the filter by means of the two different desired spectral ranges must be extracted.

Around despite an upper limit of the energy input into the tissue a high To produce energy density, it has proven to be favorable to the light of Emitters in pulsed form, in particular with a pulse to break ratio of at least 1: 5, better of at least 1:30.

So it is advantageous if the sensor device is a temperature sensor which is preferably arranged in the vicinity of the light emitter is, since here the largest portion the power loss is incurred. It detects the temperature of the emitter or the emitting sensor carrier and Measures the temperature of the most thermally stressed Tissue. Furthermore can about this Temperature sensor not only those generated by the sensor device tissue warming be detected, but also a body temperature of the fetus, the his body core temperature comes pretty close when the electrical power loss of Pulsoximetriesensors via a certain amount of time is kept correspondingly low.

As a general rule it is difficult to apply a sensor to the unborn child. The best solution is the invasive anchoring of a short steel spiral proven in the tissue of the fetus, according to the anchoring principle of head skin electrodes.

These minimally invasive design of the sensor is extremely advantageous in two ways:

1. with regard to the application

The minimally invasive application ensures a secure fit and hold in the Tissue, which significantly lowers the motion artifacts.

2. in terms of Lichtwegführung

The minimally invasive light path guidance takes care of clean, trouble-free conditions and for a reliable one Light input and output, i. are the jumps of refractive indices small and thus trouble-free.

With minimally invasive anchoring (single helix or double helix) and / or with other measures is achieved that emitter and sensor under optically constant Coupling and decoupling conditions in the examined tissue of the preceding part are arranged, for example in the Kopfschwarte of the fetus, which in particular causes a fixed arrangement and a aqueous Surrounding the emitter and sensor (tissue water or plasma, Blood).

at a screwed single helix or double helix is an application rotation the helix of 0.5 turns basic requirement, more than 1.5 turns are no longer useful. Also, the entire axial extent limited to 2 mm to a maximum of 4 mm, to avoid damage other body parts to be able to effect. A complete screwing of the sensor on stop (end face of the sensor pot is in good contact with the tissue).

Yet can be due to the contractions of the cervix by the labor pains and especially by manual examination during childbirth etc. that over the scalp of the fetus projecting sensor base in the transverse direction be applied with force and moved or torn out.

To prevent this, a fixing device for fixing the sensor device is provided, which may in particular consist of a guard ring whose central bore fits exactly on the base part and are slipped over this can.

By a flat outward expiring edge of this fixing device, the possible gapless should rest on the skin, become radially approximated body parts or objects aslant distracted upward and over guided the base part, without a tilting or jamming of the sensor takes place, which contributes significantly to the reduction of motion artifacts.

The Sensor device contains either itself an evaluation unit or connection devices, to be connected to an evaluation unit.

at the procedure for using the sensor device is essential that during operation of the sensor device emitted by the emitter and the light arriving at the sensor as possible much, especially exclusively has undergone arterial perfused tissue, because only then is the highest possible modulates the light arriving at the sensor, and gives so a SaO2 with a small error width. It is essential in this Relation that sensor and emitter relative to each other in the tissue be arranged so that they are in the same tissue layer are located. It is also important that they relative to the skin (surface) in the same tissue depth.

By Maintaining a pulse to pause ratio of the light emitter from 1: 5, better of at least 1:30, will be the desired high Intensity of Signals reached without - at the unavoidable power losses - to critically warm the tissue, what controlled regularly or continuously close to the sensor device can be.

Around nevertheless a sufficient amount of light and thus a sufficient strong signal and in particular a good signal-to-noise ratio To achieve, it has to be favorable proven when the two individual LEDs have a current of at least 100 mA.

The Total power dissipation that the sensor device produces should be do not exceed 30 mW, wherein the electrical, that is converted into heat within the sensor device Energy is included as well like the percentage of tissue absorbed by the tissue Amount of light.

The aim is to achieve a photocurrent of 0.01 to 0.1 μA at the light sensor, which is possible with the aforementioned output values with correct optical coupling. Then, at the light sensor, a light output of about 60 nW is applied to the entire sensor surface, wherein the size of the sensor surface should be at least 0.5 mm ² , while an upper limit is predetermined by the design of the sensor device and the application site.

through the sensor unit and an evaluation unit cooperating therewith it is usually possible Oxygen saturation, Heart rate, respiratory rate and / or blood pressure in the examined To determine tissue.

If by one or more additional, nearer to the emitter receiver also the input light intensity at the radiation site in one or more spectral regions is known, open up further, interesting sizes, u. a. also absolute concentrations of components of the tissue or of the blood.

So It is quite possible that on the basis of the principles of the invention A sensor unit is created that has a number of important parameters can determine from blood pressure Heart rate up to body temperature and water balance.

Some embodiments according to the invention are shown by way of example with reference to the figures.

It demonstrate:

1 : Schematic diagrams of pulse oximetry,

2 : Representations of a double helix sensor, and

3 : Representations of a Single Helix Sensor.

1a shows the principle of operation in reflex pulse oximetry, in which at least two light emitters 2 and a photodiode as a light receiver 3 on the same side of the skin, ie side by side on the surface of the skin.

The light emitters (LEDs) emit light of certain spectral ranges through the skin into the tissue. Any number of different light courses are conceivable (some of which are shown by way of example), in particular light profiles 7 in near-surface skin layers that are not yet arterioles 5 happen, and deep light trails, in blood-bearing skin layers, moving from emitter to photodiode 3 arterioles 5 have happened. Simplified, one can say that the light is the light emitter 2 in the skin layer are quasi "reflected" 1A shows that in reflex pulse oximetry unfavorably the near-surface light paths 7 who have not passed arterioles and have not experienced absorption by hemoglobin, are shorter than those who have taken this information, and thus have a greater share of the total signal, which corresponds to a faulty contribution as a shunt light.

1b shows a schematic representation of the inventive form of transmission pulse oximetry, in which both the light emitter 2 as well as the light sensor 3 in such a depth and thickness of the skin 33 the shortest possible net light paths 8th forcibly by hemoglobin in the arterioles 5 run.

The 2 and 3 show practical embodiments of a corresponding sensor 1 ,

This consists of a sensor body 11 , from the front surface of a sensor carrier 11 protrudes and from the back of the cable 13 to the evaluation unit 4 extends. The sensor base body 11 serves both as a "housing" for electrical and mechanical additional components, as well as for applying a torque for introducing the sensor carrier with the light emitter 2 and the light sensor 3 into the skin, usually in the buttock of a fetus.

In the solution according to 2a the sensor carrier is a double helix 12 , their sub-spirals 12a , b offset for example by 180 ° from the front surface of the body 11 with an axial direction 10 the two sub-spirals 12 perpendicular to the front surface of the main body 11 stands, protrude. The two sub-spirals 12 have a common axial direction 10 ,

Each of the partial spirals extends over at least 180 °, more preferably at least 270 °, and is provided with a sharpened cannula cut obliquely to the direction of the partial spiral 16 equipped as a point to allow easy insertion and screwing of the double helix in the head rind.

Of the outer diameter the total double helix is between 4 mm and 10 mm, preferably between 6 mm and 8 mm and the axial extent is between 1.5 and 5 mm.

The main body 11 has a diameter which is preferably slightly larger than the diameter of the double helix and the devices provides to be able to effect a better gripping and turning.

The axial extent of the body 11 is at least 5 mm. The thickness of the individual helical cannulas is preferably between 0.7 mm and 1.2 mm, are at a minimum diameter of the total helix of 4 mm only a central, cylindrical space with a diameter of about 2 mm available.

emitter 2 and sensor 3 are each in one of the sub-spirals 12a , b arranged offset from the free tip ends by 1 to 4 mm in the direction of rotation, thereby ensuring that when screwing the double helix in the head scar to the stop on the body 11 Emitter 2 and sensor 3 are in a sufficient minimum depth of the head rind, in the already arterially perfused tissue is present.

Since a net optical path length of at least 3-4 mm is better aimed at 7 mm, emitters become 2 and light sensor 3 not on the inside of the helix facing each other, arranged on 180 ° with respect to the axial direction of the double helix opposing positions, but one of the two is arranged on the partial spiral pointing outward. This requires the light to go from the emitter 2 to the sensor 3 not only traverse the space inside the double helix, but also make a bow to reach the outside of the two elements (sensor or emitter).

The net light path length could be further increased by placing both elements facing outward. However, it must be ensured that the light intensity at the light sensor is not affected by the longer light path 3 is so low that an evaluation of the received light components is difficult or vice versa such a high amount of light from the emitter 2 must be discharged into the tissue that occur at the point of overheating problems.

Accordingly, in 2a and 2 B each exemplifies several possible light paths 8th shown, where the net optical path length of the shortest conceivable of these paths of emitters 2 to the sensor 3 is.

In the approximately axial supervision of 2c these light paths are omitted for reasons of clarity.

3 shows a second design, in which as a sensor carrier a single helix 14 is used, in turn, on the main body 11 is arranged and protrudes from this.

Again, these are emitters 2 and sensor 3 on opposite positions about 180 ° with respect to the axial direction 10 arranged as best in the approximate supervision of the 3c can be seen.

There are emitters 2 and sensor 3 however, usually in a different axi alen distance to the main body 11 and thus - screwed in the state until it rests against the body 11 - in a different tissue depth.

As long as this tissue depth is so great that both elements are in arterially perfused tissue, this is acceptable. In addition, this difference in axial distance can be minimized in which the single helix 14 in the area between emitters 2 and sensor 3 has a reduced slope or no slope at all, so only in the areas before and after has the helical pitch.

Also in this solution is of the two elements (emitter 2 and sensor 3 ) one of the two directed into the interior of the helix and the other to the outside.

1

Sensor, Part of the measuring device

2

Light emitter / LED

3

Light sensor / photodiode

4

evaluation

5

Arterioles / blood vessels

7

Shunt

8th

Net light path length

9

fixing

10

axial direction

11

Sensor main body

12

double helix

12a, b

partial helix

13

electric wire

14

Single-helix

16

cannula cut

17

Crinkle outer diameter

18

outer diameter Helix cannula

19

temperature sensor

20

Thickness measuring device

21

Plausibility control device

22

motion sensor

22 '

accelerometer

26

layer thickness

33

skin

33a

skin surface

34

Radiation direction

Claims (36)

Method for measuring the absorption of light from two different spectral regions by living tissue by means of an invasively introduced light emitter ( 2 ) and a light sensor ( 3 ), characterized in that the method is carried out such that both modulation depths (pulsatile component AC to the non-pulsatile component DC) are at least 0.0005, better than 0.001. Method for measuring the absorption of light from two different spectral regions by living tissue by means of an invasively introduced light emitter ( 2 ) and a light sensor ( 3 ), characterized in that the light sensor ( 3 ) relative to the light emitter ( 2 ) is arranged so that the light sensor ( 3 ) incoming light of the light sensor ( 3 ) has passed through as much as possible, in particular exclusively arterially perfused tissue. Method for measuring the absorption of light from two different spectral regions by living tissue by means of an invasively introduced light emitter ( 2 ) and a light sensor ( 3 ), characterized in that the sensor device is inserted so invasively that the light emitter ( 2 ) and the light sensor ( 3 ) come to rest in the same tissue depth, in particular the same tissue layer. Method according to one of the preceding method claims, characterized in that emitter ( 2 ) and sensor ( 3 ) are arranged under optically constant coupling and decoupling conditions, in particular stationary, in particular in the head of the fetus. Method according to one of the preceding method claims, characterized characterized in that the absorption in at least two different Spectral ranges is determined, of which in particular the one Spectral range the wavelength of 730 nm and the other the wavelength of 880 nm. Method according to one of the preceding method claims, characterized in that the light emitters each emit pulsed light with a pulse to break ratio at least 1: 5, better at least 1:30. Method according to one of the preceding method claims, characterized characterized in that the overheating of the on the sensor device adjacent tissue is prevented to over 43 ° C. Method according to one of the preceding method claims, characterized in that in the vicinity of the emitter ( 2 ) the temperature on the contact surface of the user's skin where the emitter ( 2 ), is measured. Method according to one of the preceding method claims, characterized characterized in that the evaluation unit is capable of monitoring the oxygen saturation, the heart rate, the respiratory rate and / or the blood pressure from the To determine determined by the sensor device data. Method according to one of the preceding Method claims, characterized in that the evaluation unit ( 4 ) is able to determine absolute concentrations of components of the tissue or blood by utilizing the measured input light intensity (I ₀ ) at the transmission site. Sensor device for the absorption of light of two different spectral ranges by living tissue with - at least one sensor carrier, - the at least one light emitter ( 2 ) and at least one light sensor ( 3 ), characterized in that the net effective optical path length is chosen such that both modulation depths (pulsatile fraction AC to non-pulsatile fraction DC) are at least 0.0005, better 0.001. Sensor device according to claim 11, characterized in that the light emitter ( 2 ) to the light sensor ( 3 ) at least to be covered net light path length at least 3 mm, in particular at least 4 mm. Sensor device according to one of the preceding device claims, characterized in that at least the light emitter ( 2 ) or the light sensor ( 3 ), in particular both, is oriented in a direction pointing away from the respective other element. Sensor device according to one of the preceding Device claims, characterized in that only the light emitter or only the light sensor aligned radially in the direction of the other element are. Sensor device for the absorption of light of two different spectral ranges by living tissue with - at least one sensor carrier, - the at least one light emitter ( 2 ) and at least one light sensor ( 3 ), characterized in that the sensor device is designed such that in the invasively inserted state of the sensor device the light emitter ( 2 ) and the light sensor ( 3 ) in the same tissue depth, in particular the same tissue layer, come to lie, and in particular light emitter ( 2 ) and light sensor ( 3 ) are arranged centrally symmetrically on a single helix or the two sub-spirals of a double helix as a sensor carrier. Sensor device according to one of the preceding Device claims, characterized in that the absorption of light, in particular the pulsatile due to the arterial circulation Modulation of light, in the frequency ranges from 0 to 0.7 Hz as well as 0.7 to 4.0 Hz (fetal) or 0-0.5 Hz and 0.5 to 3.0 Hz (adult) - the each second frequency range corresponding to the lowest or highest Heart rate - is performed. Sensor device according to one of the preceding device claims, characterized in that the light sensor ( 3 ) relative to the light emitter ( 2 ) is arranged so that the light sensor ( 3 ) incoming light has passed pulsately through tissue of the head of the fetus through which arterial blood flows. Sensor device according to one of the preceding device claims, characterized in that as light emitter ( 2 ) light-emitting semiconductors, in particular light-emitting diodes, directly or indirectly coupled by means of light guides can be used. Sensor device according to one of the preceding device claims, characterized in that the light sensor ( 3 ) detects the received light intensity. Sensor device according to one of the preceding Device claims, characterized in that the sensor carrier as a helix, in particular is designed as a single helix or symmetric double helix. Sensor device according to one of the preceding device claims, characterized in that the sensor carrier has the shape of a double helix and light emitter ( 2 ) and light sensor ( 3 ) are each arranged on a partial spiral of the double helix, in particular at the same axial positions of the two partial spirals. Sensor device according to one of the preceding device claims, characterized in that the sensor device connection means for connection to an evaluation unit ( 4 ) and in particular an evaluation unit ( 4 ) with. Sensor device according to one of the preceding Device claims, characterized in that the outer diameter of the helix cannula between 0.7 mm and 1.2 mm. Sensor device according to one of the preceding Device claims, characterized in that the coil outer diameter of the helix 4-10 mm, in particular 6-8 mm. Sensor device according to one of the preceding device claims, characterized in that in a double helix as the sensor carrier the partial spirals protrude axially over 0.5-2.5 turns from the sensor base part and in particular light emitter ( 2 ) and light sensor ( 3 ) are set back from the tip of the cannula cut of the part spirals by 1-4 mm in the direction of rotation. Sensor device according to one of the preceding device claims, characterized in that the measuring device ( 1 ) is designed so that the light sensor ( 3 ) a photocurrent of at least 0.01 μA to 0.1 μA by receiving the light emitter ( 2 ) emitted light is obtained. Sensor device according to one of the preceding device claims, characterized in that the measuring device ( 1 ) is designed so that the light sensor ( 3 ), a light output of 60 nW on the entire sensor surface occurs and in particular the sensor surface between 0.1 and 100 mm ² , in particular between 0.4 to 1.5 mm ² . Sensor device according to one of the preceding Device claims, characterized in that at least two light emitting diodes as a light emitter (LEDs) of different spectral ranges are used, of which In particular, the one spectral range is the wavelength of 730 nm and the other the wavelength of 880 nm. Sensor device according to one of the preceding Device claims, characterized in that at two individual LEDs as a light emitter this one amperage each of at least 10 mA. Sensor device according to one of the preceding device claims, characterized in that the two light emitters ( 2a , b) are arranged in fixed relation to one another, in particular on the same spiral. Sensor device according to one of the preceding Device claims, characterized in that the total power dissipation of the sensor device maximum 100 mW, in particular 30 mW, including the electrical, within the Sensorein direction converted into heat Energy and the amount of light absorbed by the tissue. Sensor device according to one of the preceding device claims, characterized in that a fixing device ( 9 ) for fixing emitter ( 2 ) and sensor ( 3 ) is present at a predetermined locations of the head of the fetus, in particular in the form of a protective ring ( 9a ) with a central bore ( 9b ) for slipping over the sensor base part, with outwardly decreasing, in particular to zero decreasing, thickness ( 9c ) of the ring. Sensor device according to one of the preceding device claims, characterized in that the light emitters ( 2a , b) emit light of wavelengths 400 nm to 2,000 nm, in particular 600-1,000 nm. Sensor device according to one of the preceding Device claims, characterized in that a white light emitting diode as a light emitter is used, from the means of optical elements, in particular Filter two different spectral regions of light extracted become. Sensor device according to one of the preceding device claims, characterized in that the sensor device comprises a temperature sensor ( 19 ), in particular in the vicinity of the light emitter ( 2 ). Sensor device according to one of the preceding Device claims, characterized in that the light emitters each pulsed light give up with a pulse to break ratio of at least 1: 5, better at least 1:30.