Device and method for measuring a pressure of a fluid in an elastic medical tube which is transparent at least to light of a particular optical wavelength

Abstract

The invention relates to a device (1) for measuring a pressure (P) of a fluid in an elastic medical tube (L) which is transparent at least to light of a particular optical wavelength, having - a light source (Q) which is suitable for emitting at least partially coherent light of the particular optical wavelength to which the elastic medical tube (L) is transparent, and - an at least one-dimensional light-sensitive sensor (S), - wherein the optical axes (AQ, AS) of the light source (Q) and of the at least one-dimensional light-sensitive senor (S) are aligned on spatially adjacent points on the elastic medical tube (L) such that at least partially coherent light from the light source (Q) which reaches the at least one-dimensional light-sensitive sensor (S) from the inner boundary surface of the elastic medical tube (L) and at least partially coherent light from the light source (Q) which reaches the at least one-dimensional light-sensitive sensor (S) from the outer boundary surface of the elastic medical tube (L) interfere with each other on the path to the at least one-dimensional light-sensitive sensor (S), - wherein the at least one-dimensional light-sensitive sensor (S), when in operation, detects an interference pattern of the light towards the at least one-dimensional light-sensitive sensor (S), said interference pattern having a dependence on the pressure (P) of the fluid in the elastic medical tube (S).

Description

[0001] Device and method for measuring the pressure of a fluid in an elastic medical tube that is transparent at least to light of a certain optical wavelength.

[0002] The invention relates to a device and a method for measuring the pressure of a fluid in an elastic medical tube that is transparent at least to light of a certain optical wavelength.

[0003] background

[0004] In many areas of technology, it is desirable to be able to retrofit measuring systems into an existing system. Various considerations can underlie this.

[0005] Patient safety is of paramount importance, especially in medicine. This includes ensuring that all equipment can be kept sterile. However, the effort required to achieve this must always be considered so that medical advancements become cost-effectively available to a large number of patients.

[0006] The disinfection of measuring instruments, in particular, places high demands on the system, as on the one hand, cleanliness must be ensured when the measuring instruments come into contact with the patient or when materials are carried to or from the patient, and on the other hand, the measuring instruments themselves must not be subjected to excessive stress during the disinfection process, as this could negatively affect their lifespan.

[0007] One example is pressure measurement, which is frequently required in medical lumens. Measuring devices inserted into the lumen pose a potential risk of contamination. Furthermore, this results in direct contact with fluids flowing to or from the patient.

[0008] Therefore, it would be desirable to be able to provide external measurements in simple and cost-effective tubing systems, i.e., without insertion into the lumen, since lumens can generally be sterilized easily and cost-effectively and are also often safe as disposable products.

[0009] There are already several approaches in the state of the art to provide pressure measurements.

[0010] The applicant's prior art is known from DE 10 2019 123 527 A. This patent attempts to determine hose pressure using laser interferometry, i.e., the change in transit time differences with respect to the outer surface. This requires fixing the hose in a specific position using a guide.

[0011] Furthermore, DE 38 38 689 CI of the applicant is known from the prior art. This document describes a device for monitoring the pressure in a fluid line by means of an actuating element on the lumen.

[0012] The prior art also includes US patent application US 2005 / 012935 Al and international patent application WO 2009 / 062162 Al. The US patent application describes a Fabry-Perrot arrangement attached to the outside of the lumen, while international patent application WO 2009 / 062162 Al directly measures back-emissivity from the outer wall.

[0013] However, it is known that elastic tubing used in medical applications exhibits a phenomenon called "creep" over time, due to temperature changes or other environmental conditions—a slow, slight expansion. The elasticity and wall thickness hardly change during this process. In other words, directly observing a change in the length of the outer surface would introduce a measurement error that could be so significant as to render the sensitivity for pressure measurements unusable.

[0014] Task

[0015] Starting from this situation, the object of the invention is to offer a device or a method for measuring the pressure of a fluid in an elastic medical tube, which makes it possible to provide meaningful pressure values ​​in a cost-effective manner.

[0016] Brief description of the invention

[0017] The problem is solved by a device according to claim 1 or a method according to claim 12. Further advantageous embodiments are the subject of the dependent claims, the description as well as the figures.

[0018] Brief description of the characters

[0019] The invention is explained in more detail below with reference to the figures. These show:

[0020] Fig. 1 shows a schematic representation in a side-view crackle view according to embodiments of the invention,

[0021] Fig. 2 is a schematic representation corresponding to Figure 1 in a top-down crack view according to embodiments of the invention, and

[0022] Fig. 3 shows a schematic representation of possible process steps according to embodiments of the invention.

[0023] Detailed Description of the Invention The invention will be described in more detail below with reference to the figures. It should be noted that different aspects are described, each of which can be used individually or in combination. That is, each aspect can be used with different embodiments of the invention unless explicitly presented as a pure alternative.

[0024] Furthermore, for the sake of simplicity, reference will generally be made to only one entity at a time. Unless explicitly stated otherwise, the invention may also include several of the entities concerned. Therefore, the use of the words "a", "an", and "one" should only be understood as an indication that at least one entity is used in a simple embodiment.

[0025] Unless explicitly stated otherwise, the following descriptions of procedures stipulate that the individual steps of a procedure can be arranged and / or combined in any order. Furthermore, unless expressly indicated otherwise, the procedures can be combined with one another.

[0026] Information with numerical values ​​should generally not be understood as exact values, but also include a tolerance of + / - 1% to + / - 10%.

[0027] References to standards or specifications are to be understood as references to standards or specifications that are valid or were valid at the time of filing and / or – insofar as priority is claimed – at the time of the priority filing. However, this does not imply a general exclusion of applicability to subsequent or superseding standards or specifications.

[0028] Figures 1 and 2 show a device 1 according to embodiments of the invention from different directions. Figure 1 shows a sectional view allowing a view into the tube L, while Figure 2 shows a top view of the situation shown in Figure 1. In Figure 2, only the outer side walls of the tube S are shown. In the embodiments of the invention, the device 1 is designed to measure the pressure P of a fluid in an elastic medical tube L, which is transparent at least to light of a certain optical wavelength. Although only a specific optical wavelength will be referred to below, this does not preclude the possibility that the elastic medical tube L is transparent to light of different (adjacent) wavelengths.In the following, one wavelength from the multitude of wavelengths for which the elastic medical tube L is at least partially transparent will be referred to as the specific wavelength. Partial transparency means that at least 50% of the light of the specific wavelength can propagate through a side wall of the elastic medical tube L.

[0029] The device 1 has a light source Q that is suitable for emitting at least partially coherent light of the specific optical wavelength for which the elastic medical tube L is transparent. For example, green (laser) light can be used for blood as the fluid in the elastic medical tube L.

[0030] The device 1 further comprises at least a one-dimensional light-sensitive sensor S.

[0031] For example, but not necessarily, the light source Q and the at least one-dimensional light-sensitive sensor S can be arranged relative to each other and to the elastic medical tube L in such a way that their respective optical axes – optical axis of the source to the tube L in the direction of irradiation A or optical axis from the tube S to the at least one-dimensional sensor S As – do not intersect on the directly irradiated surface of the elastic medical tube L, nor on the inner surface Oi of the elastic medical tube L located in the immediate line with the optical axis of the light source Q, nor in the interior of the elastic medical tube L.

[0032] The optical axes AQ,AS of the light source Q and the at least one-dimensional light-sensitive sensor S are aligned to spatially adjacent points on the elastic medical tube L, such that at least partially coherent light from the light source Q, traveling from the inner interface of the elastic medical tube L to the at least one-dimensional sensor S, and at least partially coherent light from the light source Q, traveling from the outer interface of the elastic medical tube L to the at least one-dimensional sensor S, interfere with each other on their way to the at least one-dimensional light-sensitive sensor S. In general, if coherent rays are scattered coherently, the scattered rays can interfere with each other.

[0033] Without limiting the generality, it may be sufficient if essentially only light from one side of the tube, i.e., light from the outer interface O, is present. aand interfere with the immediately adjacent inner interface Oi. It should be noted in this context that returning light – unlike incident light – does not propagate solely along the optical axis.

[0034] In operation, the at least one-dimensional light-sensitive sensor S can then detect an interference pattern of the light towards the at least one-dimensional light-sensitive sensor S, which has a dependence on the pressure P of the fluid in the elastic medical tube L.

[0035] Without limiting generality, the fluid in the elastic medical tubing L can be any fluid that needs to be monitored in medicine or during medical treatment. A medical tube is suitable for transporting a fluid to or from a patient. In particular, the fluid can be blood or a dialysate, as required for various forms of dialysis or apheresis. Typical elastic medical tubing S has inner diameters ranging from 2 mm to 15 mm. Particularly in dialysis, an inner diameter of 5 mm is common, with an outer diameter typically being 6.8 mm or 8 mm.

[0036] The invention thus allows the measurement of the pressure inside a flexible medical tube L or the hydrostatic pressure of the medium inside the tube L. The measurement is non-invasive.

[0037] The invention takes advantage of the fact that coherent light experiences an interference effect as it travels through the tube L. Light from the inner interface of the tube and light from the outer interface of the tube cause an interference pattern to appear. The tube L thus becomes a path component of a laser interferometer. The interference pattern is very sensitive to changes in length or distance between the two interfaces of the tube, which are related to the thickness of the tube wall.

[0038] If the pressure of the medium inside the hose changes relative to the external pressure, the wall thickness of the elastic hose changes. Thus, a pressure change leads to a change in the interference pattern. This change in the interference pattern can be recorded over time, and a pressure change or pressure itself can be determined from it.

[0039] It should be noted that this does not refer to short-term fluctuations or disturbances, but rather to the currently prevailing general hydrostatic equilibrium pressure of the

[0040] Mediums in hose L go.

[0041] The invention utilizes the interference of light from the outside and inside of the tube to determine the pressure. Unlike the prior art, this approach does not have the same disadvantages, as the slow changes in length on the outside and inside of the tube S compensate each other. The wall thickness is used instead to determine the pressure. For the compensation of a measurement error due to creep, it is not crucial whether the interference of light, which is provided by the outside of the tube on the one hand and by the inside of the tube S on the other, both on the side of the tube facing the light source, is generated by speckle or by other effects at the interface and from there reaches the light detector.

[0042] Regardless, providing light at the interfaces using laser speckle offers the additional advantage that the speckle effect ensures this light actually originates at the media interface – for example, at the transition from ambient air to the transparent tube or from the transparent tube to the fluid within it. However, providing the light for interference via speckle is optional.

[0043] In one embodiment of the invention, the optical axes AQ,AS are essentially parallel to each other.

[0044] According to a further embodiment of the invention, one of the optical axes AQ,AS corresponds to the

[0045] Surface normals of the elastic medical tube L. In yet another embodiment of the invention, the at least one-dimensional light-sensitive

[0046] Sensor S is a CCD sensor.

[0047] According to yet another embodiment of the invention, the at least one-dimensional light-sensitive sensor S has a focusing optic.

[0048] In another embodiment of the invention, the light-sensitive sensor S is two-dimensional.

[0049] According to a further embodiment of the invention, the light source Q comprises a laser, in particular a diode laser, or a high-pressure gas discharge lamp.

[0050] In another embodiment of the invention, the distance between the light source Q and / or the at least one-dimensional light-sensitive sensor S and the elastic medical tube L is 2 m and less, particularly in the range of 20 cm and less, but preferably more than 1 mm.

[0051] According to another embodiment of the invention, the optical axis Aq of the light source Q to the elastic medical tube L and the optical axis As from the elastic medical tube L to the at least one-dimensional light-sensitive sensor S are separated from the outside of the elastic medical tube L by a distance d. L offset in relation to the circumference of the elastic medical tube L.

[0052] Furthermore, in one embodiment of the invention, the optical axis Aq of the light source Q to the elastic medical tube L and the optical axis As from the elastic medical tube L to the at least one-dimensional light-sensitive sensor S may be separated from the outside of the elastic medical tube L by a distance d. T in relation to the flow direction of a fluid - exemplified by an arrow in Figure 2 - in the elastic medical tube L are offset.

[0053] Without limiting the generality, a device 1 according to the invention can be used in medicine, in particular in dialysis.

[0054] In a further embodiment of the invention, a method for measuring the pressure P of a fluid in an elastic medical tube L is provided, using a light source Q suitable for emitting at least partially coherent light of a specific optical wavelength, for which the elastic medical tube L is transparent, and an at least one-dimensional light-sensitive sensor S. The method is further explained with reference to Figure 3 in conjunction with Figures 1 and 2 and the preceding description.

[0055] The method comprises a step of illuminating 100 an elastic medical tube S to be measured with a light source Q, wherein the light source Q is suitable to emit at least partially coherent light of the specific optical wavelength for which the elastic medical tube L is transparent.

[0056] Furthermore, the method includes the step of receiving a time series of at least one-dimensional light intensity distributions using the at least one-dimensional light-sensitive sensor S, where, for example, but not necessarily, the light source Q.and the one-dimensional light-sensitive sensor S can be arranged relative to each other and to the elastic medical tube L such that their respective optical axes AQ,AS do not intersect on the directly irradiated surface of the elastic medical tube L, nor on the nearest inner surface of the elastic medical tube L located in the immediate line with the optical axis of the laser light source Q, nor in the interior of the elastic medical tube L, wherein the optical axes Aq,As of the light source Q and of the at least one-dimensional light-sensitive sensor S are aligned to spatially adjacent points on the elastic medical tube L, such that light from the inner interface of the elastic medical tube L and light from the outer interface of the elastic medical tube L interfere with the at least one-dimensional light-sensitive sensor S.

[0057] Furthermore, the procedure includes the step of determining 300 interference-related image elements of the received time series of at least one-dimensional light intensity distributions.

[0058] Finally, in one step of determining 400, the pressure P is determined based on temporal changes between light intensity distributions.

[0059] According to one embodiment of the method according to the invention, the determination of pressure P includes a determination of autocorrelation between at least two temporally separated light intensity distributions.

[0060] In one embodiment of the method according to the invention, the determination 400 of the pressure P comprises the steps of determining 400a interference-related image elements from the received time series of at least one-dimensional light intensity distributions, determining 400b a displacement of the interference-related image elements, and the step of determining 400c the pressure based on the determined displacement.

[0061] According to a further embodiment of the method according to the invention, the method includes the step of filtering out motion artifacts 350 that are based on a movement of the elastic medical tube L relative to the device 1. Such movement can occur, for example, through a translation of the elastic medical tube S, e.g., during movement of the patient, or through vibrations.

[0062] In a further embodiment of the method according to the invention, the step of determining a displacement 400b is based on at least two temporally successive two-dimensional light intensity distributions.

[0063] It should also be noted that an evaluation of image data may, for example, involve tracking of light and dark stripes of the interference pattern or be based on autocorrelation.

[0064] The setup described in the invention aims to arrange the optical elements in such a way that the high light intensity of a direct reflection on the outside of the hose does not reach the receiver, since this light does not contain the pressure information but has a higher intensity than the relevant light. Depending on the sensor, this can lead to a deterioration of the signal-to-noise ratio.

[0065] Without limitation of generality, a method according to the invention can be used in medicine, in particular in dialysis.

[0066] It should be noted that alternative arrangements, in which, for example, the light source Q shines through the sensor S onto the elastic medical tube S, so that light is also reflected directly from the outer surface onto the at least one-dimensional sensor, can also be used to determine the pressure.

[0067] It can also be advantageous to continue providing a temperature sensor.

[0068] Furthermore, it can also be advantageous to provide an ambient pressure sensor.

[0069] Both a fluid temperature sensor and an ambient pressure sensor can provide data that allows for a more precise and / or faster measurement of the fluid pressure within the flexible medical tube L. For example, the temperature can be measured on the outside of the tube L. Alternatively, the fluid temperature can be measured using an IR temperature sensor. Furthermore, the fluid temperature can also be provided by an external sensor located nearby, such as in a blood treatment machine. Finally, the ambient temperature can also be measured.

[0070] The invention relates to a device and a method for measuring the pressure of a fluid, for example blood or dialysate, in an elastic tube L for medical applications, wherein the tube L is illuminated, for example, with laser light from a source Q, and light emanating from the tube L is received by an optical sensor S. Light emanating from the source Q is at least partially coherent and can therefore exhibit interference effects. Since the tube L is elastic, pressure changes in the medium lead to deformations of the tube L. The shape of the tube L is thus pressure-dependent. To determine the pressure P in the tube L, the fact that the light emanating from the tube L exhibits interference patterns is exploited. The interference patterns change when the tube L is deformed, for example, by a pressure change. Through this relationship, the properties of the received light intensity distribution are also influenced by the pressure P of the fluid in the tube L.Thus, by receiving and analyzing the light intensity distribution emanating from tube L, it is possible to deduce the pressure P inside tube L. Both the interference patterns and speckle exhibit components that do not result from reflection.

[0071] For the indirect measurement of the fluid pressure P in the tube L, the invention utilizes the fact that the tube L expands when the pressure increases, and that larger pressure increases lead to greater expansion. As a consequence of the pressure-induced deformation of the tube L, the path of the light beam in the tube wall changes. This change in the tube wall and the beam path is comparatively small. To achieve the desired sensitivity to pressure changes, the invention therefore employs an arrangement for measuring light interference in the tube wall.

[0072] A camera, as an example of a sensor S, and a laser, as an example of an at least quasi-coherent source Q, can be arranged such that their optical axes do not intersect on or within the surface of the tube L, but are aligned to adjacent points on the tube L to be measured. For example, the optical axes are aligned parallel or nearly parallel (angle approximately 0.1–5°) to the elastic tube L to be measured for medical applications. In the preferred example of a possible arrangement shown, the optical axis of the camera is aligned perpendicular to the cylindrical surface of a substantially straight tube segment, such that the surface normal of the tube points to the camera lens and is parallel to the optical axis of the camera. Thus, the optical axis of the camera is perpendicular to the longitudinal axis (axis of rotational symmetry) of the observed tube segment.The laser is positioned slightly parallel and offset to the side of the camera, so that it is not just perpendicular to the circumference of the hose at the same hose segment and approximately the same longitudinal position of the hose as the camera is aimed at. This prevents the camera from directly reflecting light back from the hose onto the sensor. The optical axis of the laser is not parallel and congruent with the surface normals of the hose's outer surface in the illuminated area. This setup offers the advantage that no laser light is reflected from the outer hose surface into the optical receiver in the conventional way.

[0073] However, this does not exclude other setups that are less sensitive to direct reflection.

[0074] Without restriction of generality, the device can also be part of a blood treatment device, or the method can also be used in a blood treatment device. Blood treatment device refers in particular to devices for dialysis in their various forms, devices for apheresis in their various forms, devices for the

[0075] Blood oxygenation in its various forms.

Claims

Claims 1. Device (1) for measuring a pressure (P) of a fluid in an elastic medical tube (L) which is transparent at least to light of a certain optical wavelength, comprising • A light source (Q) suitable for emitting at least partially coherent light of the specific optical wavelength for which the elastic medical tube (L) is transparent, and • An at least one-dimensional light-sensitive sensor (S), • Where the optical axes (AQ,AS) of the light source (Q) and the at least one-dimensional light-sensitive sensor (S) are aligned to spatially adjacent points on the elastic medical tube (L), such that at least partially coherent light from the light source (Q), which travels from the inner interface of the elastic medical tube (L) to the at least one-dimensional light-sensitive sensor (S), and at least partially coherent light from the light source (Q), which travels from the outer interface of the elastic medical tube (L) to the at least one-dimensional light-sensitive sensor (S), interferes with each other on the way to the at least one-dimensional light-sensitive sensor (S), • Whereas the at least one-dimensional light-sensitive sensor (S) in operation detects an interference pattern of the light towards the at least one-dimensional light-sensitive sensor (S) which has a dependence on the pressure (P) of the fluid in the elastic medical tube (S).

2. Device according to claim 1, characterized in that the optical axes (AQ,AS) are essentially parallel to each other.

3. Device according to claim 1 or 2, characterized in that one of the optical axes (Aq,As) corresponds to the surface normal of the elastic medical tube (L).

4. Device according to one of the preceding claims, characterized in that the at least one-dimensional light-sensitive sensor (S) comprises a CCD sensor.

5. Device according to one of the preceding claims, characterized in that the at least one-dimensional light-sensitive sensor (S) has a focusing optic.

6. Device according to one of the preceding claims, characterized in that the light-sensitive sensor (S) is two-dimensional.

7. Device according to one of the preceding claims, characterized in that the light source (Q) comprises a laser, in particular a diode laser, or a high-pressure gas discharge lamp.

8. Device according to one of the preceding claims, characterized in that the distance from light source (Q) and / or at least one-dimensional light-sensitive sensor (S) to the elastic medical tube (L) is 2 m and less, in particular in the range of 20 cm and less, but preferably more than 1 mm.

9. Device according to one of the preceding claims, characterized in that the light source (Q) and the at least one-dimensional light-sensitive sensor (S) are arranged relative to each other and to the elastic medical tube (L) such that their respective optical axes (Aq,As) do not intersect either on the directly irradiated surface of the elastic medical tube (L), nor on the inner surface (Oi) of the elastic medical tube (L) located in the immediate line with the optical axis of the light source (Q), nor in the interior of the elastic medical tube (L).

10. Device according to claim 9, characterized in that the optical axis (Aq) of the light source (Q) to the elastic medical tube (L) and the optical axis (As) from the elastic medical tube (L) to the at least one-dimensional light-sensitive sensor (S) are separated from the outside of the elastic medical tube (L) by a distance (d). L ) are offset (L) with respect to the circumference of the elastic medical tube.

11. Device according to claim 9 or 10, characterized in that the optical axis (Aq) of the light source (Q) to the elastic medical tube (L) and the optical axis (As) from the elastic medical tube (L) to the at least one-dimensional light-sensitive sensor (S) with respect to the outside of the elastic medical tube (L) by a distance (d T ) are offset with respect to the flow direction of a fluid in the elastic medical tube (L).

12. Use of a device (1) according to one of the preceding claims in medicine, in particular in dialysis.

13. Method for measuring a pressure (P) of a fluid in an elastic medical tube (L), using a light source (Q) suitable for emitting at least partially coherent light of a certain optical wavelength for which the elastic medical tube (L) is transparent, and an at least one-dimensional light-sensitive sensor (S), comprising the steps: • Illuminating (100) an elastic medical tube (S) to be measured with a light source (Q), wherein the light source (Q) is suitable to emit at least partially coherent light of the specified optical wavelength for which the elastic medical tube (L) is transparent, • Receiving (200) a time series of at least one-dimensional light intensity distributions using the at least one-dimensional light-sensitive sensor (S), • Where the optical axes (AQ,AS) of the light source (Q) and the at least one-dimensional light-sensitive sensor (S) are aligned to spatially adjacent points on the elastic medical tube (L), such that at least partially coherent light from the light source (Q), which travels from the inner interface of the elastic medical tube (L) to the at least one-dimensional light-sensitive sensor (S), and at least partially coherent light from the outer interface of the elastic medical tube (L) to the at least one-dimensional light-sensitive sensor (S), interferes with each other on the way to the at least one-dimensional light-sensitive sensor (S), • Determining (300) interference-induced image elements from the received time series of at least one-dimensional light intensity distributions, • Determination (400) of the pressure (P) based on temporal changes between light intensity distributions.

14. Method according to claim 12, characterized in that the determination (400) of the pressure (P) includes a determination of autocorrelation between at least two temporally separated light intensity distributions.

15. Method according to claim 12, characterized in that the determination (400) of the pressure (P) comprises the following steps: • Determining (400a) interference-induced image elements from the received time series of at least one-dimensional light intensity distributions, • Determine (400b) a shift of the interference-induced image elements • Determination (400c) of the pressure based on the determined displacement.

16. Method according to any one of the preceding claims 12 to 14, further comprising the step of filtering out (350) motion artifacts which are based on a movement of the elastic medical tube (L) relative to the device (1).

17. Method according to any one of the preceding claims 14 to 15, wherein the step of determining a displacement (400b) is based on at least two temporally successive two-dimensional light intensity distributions.

18. Use of a method according to any of the preceding claims 12 to 16 in medicine, in particular in dialysis.

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