WO2023113671A1

WO2023113671A1 - A system and method for assessment of a blood flow

Info

Publication number: WO2023113671A1
Application number: PCT/SE2022/051111
Authority: WO
Inventors: Johannes WALFRIDSSON; Tova PERSSON; Viktor VIBERG
Original assignee: Pu Sensor Ab
Priority date: 2021-12-14
Filing date: 2022-11-28
Publication date: 2023-06-22
Also published as: SE2151527A1

Abstract

The present disclosure relates to a method and system for assessment of a blood flow in an assessment area of the skin and underlying tissue of a patient. The system comprises a sensor plate (115) having a blood flow sensor obtained by means of photoplethysmography, wherein the assessment area of the skin is arranged to be provided with such sensor plate, and an expandable mattress (105) comprising at least one expandable element (115) having a controllable expansion state. The system comprises further an expansion control system (130) arranged to control expansion of the at least one expandable element to two different expansion states. The system comprises further a computer (150) arranged to perform data processing of said blood flow data, wherein the at least one blood flow sensor is arranged to obtain blood flow data while subjecting each assessment area to two different pressure states, and wherein the computer (150) is arranged to, for each assessment area, assess the obtained blood flow data for the two different pressure states to determine a suitable expansion of the expandable mattress (105) in a use mode.

Description

A system and method for assessment of a blood flow

TECHNICAL FIELD

The present disclosure relates to a system and method for assessment a blood flow in at least one assessment area of the skin and underlying tissue of a patient.

BACKGROUND

Pressure ulcers are injuries to skin and underlying tissue resulting from prolonged pressure on the skin. Those are most often developed on skin that covers bony areas of the body, such as the heels, ankles, hips and sacrum.

People most at risk of developing pressure ulcers are those with a medical condition that limits their ability to change positions or those who spend most of their time in a bed or chair. Immobile individuals frequently develop painful pressure ulcers. Moreover, pressure ulcers cause high costs for the health care system.

US 2021068743 discloses a method and system for assessment of a blood flow in an area of the skin and underlying tissue of a patient. The method includes subjecting the assessed area to at least two different pressure states. The method further includes obtaining blood flow data related to the assessed area while subjecting the assessed area to the at least two different pressure states, wherein the blood flow data is obtained by means of photoplethysmography, and assessing the risk of pressure ulcers on the patient based on assessment of the blood flow data obtained for the at least two different pressure states. The different pressure states are obtained by the patient's weight pressuring against a support on which the patient is placed and an expandable element at least partly circumventing the assessed area and expandable a direction from the support against the patient to substantially eliminate pressure on a patient's body from the support in the area at least partly circumventing the assessed area

SUMMARY

The present disclosure relates to an improved system for assessment of blood flow data. The system is used for prevention or at least reduction of pressure ulcers. This has been achieved by means of a system for assessment of a blood flow in at least one assessment area of the skin and underlying tissue of a patient. The system comprises at least one sensor plate having at least one blood flow sensor obtained by means of photoplethysmography, wherein each assessment area of the skin of the patient is arranged to be provided with such sensor plate. The system comprises further an expandable mattress comprising at least one expandable element having a controllable expansion state. The system comprises further an expansion control system arranged to, in a measurement mode, control expansion of the at least one expandable element to at least two different expansion states. Thereby, each assessment area is subjected to at least two different pressure states obtained by the patient's weight pressuring against the expandable mattress and by the at least two expansion states of the mattress. The system comprises further a computer arranged to perform data processing of said blood flow data, wherein the at least one blood flow sensor is arranged to obtain blood flow data while subjecting each assessment area to the at least two different pressure states, and wherein the computer is arranged to, for each assessment area, assess the obtained blood flow data for the at least two different pressure states to determine a suitable expansion of the expandable mattress in a use mode

The system is easy to use and give rise to a decreased discomfort for the patient.

The patient may lie down in the same position during the entire measurement. Further, measurements can be made during normal use of the mattress.

Further, the mattress can adapt to a suitable expansion state adapted to the individual. The suitable expansion state may include a static expansion state or a dynamic expansion state changing with time.

Thus, the support on which the patient is resting, i.e. the mattress, is used for making the measurements. Where the support on which the patient is resting is used for the measurements (in a measurement mode), an individualized expansion (static or dynamically changing) in a use mode can be determined for the expandable mattress based on the assessment of the obtained blood flow data for the at least two different pressure states.

The expansion state of the at least one expandable element of the expandable mattress may be controlled by the computer. By this automatization, the requirements on education etc. of personnel using the method may be decreased. Preferred embodiments may have one or more of the features as defined in the dependent claims.

For example, in an option, the expandable mattress comprises a plurality of expandable elements. The expandable elements may be individually controllable. Alternatively, the expandable elements may comprise at least two subsets, wherein the subsets are differently controllable or controlled.

In an option, a plurality of assessment areas are assessed, and wherein the computer is arranged to determine the suitable expansion of the expandable mattress in the use mode based on a comparison of the result of the assessment of the obtained blood flow data for the different assessed areas.

This means that, in the measurement mode, one or a plurality of assessment areas may be investigated, and the results of using different timings, pressures and expansion patterns of the individually/group wise controllable expandable elements may be investigated. In the measurement mode, testing may be performed according to a predetermined or adaptable test scheme. The measurement mode may be active in for example an hour. The suitable expansions are then determined accordingly.

The present disclosure further relates to a control element for assessment of a blood flow in an area of the skin and underlying tissue of a patient. The control element comprises an interface arranged to receive blood flow sensor data obtained by means of photoplethysmography, said blood flow sensor data being obtained from at least one assessment area subjected to at least two different pressure states obtained by the patient's weight pressuring against a support on which the patient is placed and an expansion state of an expandable element in a direction from the support against the patient. The control element comprises further a processor arranged to assess said blood flow data for the at least two different pressure states, based on assessment of the blood flow data for the at least two different pressure states, and to determine a suitable expansion of the expandable mattress in a use mode based the assessment of the obtained blood flow data for the t least two different pressure states. The present disclosure relates further to a computer-implemented method for assessment of a blood flow in an area of the skin and underlying tissue of a patient. The method comprises the steps of:

• control expansion of the at least one expandable element of an expandable mattress to at least two different expansion states; whereby the at least one expandable element secures that each assessment area is subjected to at least two different pressure states obtained by the patient's weight pressuring against the expandable mattress and by the at least two expansion states of the mattress,

• obtain, using at least one blood flow sensor, blood flow data while subjecting each assessment area to the at least two different pressure states, and

• for each assessment area, assess (S5) the obtained blood flow data for the at least two different pressure states to determine a suitable expansion of the expandable mattress in a use mode.

In an option, the method further comprises a step of obtaining pressure data and identifying the respective pressure states based on the obtained pressure data, wherein the step of assessing the assessment of blood flow data obtained for the identified at least two different pressure states is made based on the identified at least two different pressure states.

In an option, the method further comprises controlling the expandable element(s) according to the determined suitable expansion in the use mode.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures la and lb is a schematic sketch illustrating an example of a set-up according to the present disclosure.

Figures 2a-c illustrate an expandable mattress in accordance with first embodiments of the invention.

Figures 3a-d illustrate an expandable mattress in accordance with second embodiments of the invention. Figures 4 illustrate an expandable mattress in accordance with third embodiments of the invention.

Figure 5 is block scheme illustrating an example of a system for assessment of a tissue under pressure.

Figure 6 illustrates schematically an example of a design of a sensor plate.

Figure 7 is a flow chart illustrating an example of a method for assessment of a blood flow.

Figure 8 is flow chart illustrating a step of obtaining blood flow data in a method for assessment of a blood flow for example according to figure 7.

DETAILED DESCRIPTION

Figures la and lb disclose an example of a set-up for assessment of a blood flow in at least one assessment area of the skin and underlying tissue of a patient. The assessment is used for prevention or at least reduction of pressure ulcers.

As is seen in figure la, at least one blood flow sensor obtained by means of photoplethysmography is provided at one or more assessment areas 120 of the skin of a patient 110. In the illustrated example, the at least one blood flow sensor of each assessment area 120 is formed at a sensor plate 115. The sensor plate(s) may be flexible and arranged to follow the curvature of the skin. The sensor plate (s) may be provided with an adhesive for attachment to the patient.

The assessment area(s) 120 are intended to face an expandable mattress 105 during measurements with the at least one blood flow sensor, as illustrated in figure lb.

The expandable mattress 105 comprising at least one expandable element subjects the assessment areas 120 of the patient 110 lying on the expandable mattress 105 to at least two different pressure states caused by the patient's weight pressuring against the expandable mattress 105 and by at least two different expansion states of the at least one expandable element. The at least one blood flow sensor obtains blood flow data while the assessment area(s) 120 is subjected to the at least two pressure states. The obtained blood flow data relating to the at least two different pressure states is assessed. The assessment may be made for assessing a risk of developing pressure ulcers on the patient. The assessment is used to determine a suitable expansion or expansion scheme for the expandable mattress to decrease the risk of developing pressure ulcers. The expansion scheme of the mattress is accordingly individualized based on the assessment of the blood flow in the respective assessment area of the patient. The determined suitable expansion or expansion scheme can be determined as a suitable static pressure and/or a suitable pressure cycle of the at least one expandable element

Characteristically, this set-up is used in a measurement mode and in a use mode. In the measurement mode, the suitable expansion or expansion scheme is determined. In the use mode, the determined suitable expansion or expansion scheme is used for controlling the at least one expandable element of the expandable mattress. The patient may lie down in the same position during the entire measurement, and also in the subsequent use mode. This means that measurements can be made during normal use of the mattress. Thus, it can be switched between measurement mode and use mode during normal use of the mattress.

Thus, the support on which the patient is resting, i.e. the mattress, is used when making the measurements. When the support on which the patient is resting is used for the measurements (in the measurement mode), an individualized expansion (static or dynamically changing) in the use mode can be determined for the expandable mattress based on the assessment of the obtained blood flow data for the at least two different pressure states.

Further, the mattress can adapt to a suitable expansion adapted to the individual. The suitable expansion may include a static expansion or a dynamic expansion changing with time.

Further, as it can be switched between measurement mode and use mode during normal use of the mattress, the suitable expansion state adapted to the individual may be changing with time. After some time in the use mode, the patient's weight pressuring against the expandable mattress 105 may cause need for a changed and a new suitable expansion state adapted to the individual can then be determined in the measurement mode or applied based on previously made measurements. The system is easy to use and give rise to a decreased discomfort for the patient.

The exemplified set-up for assessment of a blood flow in a skin area is easy to use and gives rise to a decreased discomfort for the patient.

The assessment is, as described above, based on the concept that the assessed skin area is subjected to at least two different pressure states, wherein the different pressure states are obtained by the patient's weight pressuring against the expandable mattress on which the patient is placed.

Blood flow data related to the assessed area is obtained while subjecting the assessed area to the at least two different pressure states. The blood flow data is obtained by means of photoplethysmography. The blood flow data may be obtained only by means of photoplethysmography, PPG. In detail, a PPG is an optically obtained volumetric measurement of an organ. A PPG may be obtained by illuminating the skin and underlying tissue, and measuring changes in light absorption.

In systole in each cardiac cycle the heart pumps blood to the tissue. Even though this pressure pulse is somewhat damped by the time it reaches the skin, it is enough to distend the arteries and arterioles in the subcutaneous tissue. The change in volume caused by the pressure pulse is detected by illuminating the skin and underlying tissue with the light from a light-emitting diode (LED) and then measuring the amount of light reflected to a photodiode. Each systole cycle appears as a peak. Thus, these pressure pulses are in the present disclosure compared while the skin is subjected to different external pressures caused by the patient's weight, as discussed above.

In fig 2a-2c, an expandable mattress 105 is exemplified having one expandable element 125. In the illustrated example, the expandable element 125 substantially coincides with the extension of the mattress. However, in a not disclosed example, the expandable element 125 only covers a part of the mattress 105. The expandable element 125 is then characteristically designed to be positioned at a part of the mattress where a patient's body normally pressure against the underlying mattress.

Figure 2a is a perspective view seen from above of the expandable mattress 105 having one expandable element 125.

Figure 2b is a side view of the expandable mattress 105 wherein the expandable element is controlled to a first, lower expansion state.

Figure 2c is a side view of the expandable mattress 105 wherein the expandable element is controlled to a second, higher expansion state.

The pressures subjected to the body of a patient (the patient not disclosed in figures 2a-c) in the assessment areas 120 are characteristically different in the first and second expansion states of the expandable elements. The blood flow characteristics are characteristically different in the first and the second expansion states. The blood flow characteristics are probably different in the different assessment areas 120. Note that the expansion state of the expandable mattress affects the body pressure applied to the assessed skin area of the patient.

The assessment of blood flow data obtained for the at least two pressure states comprises determining a suitable expansion state for the expansion element in normal use of the mattress. Thus, the determined suitable expansion state is designed for the individual patient. If a new patient is to use the expandable mattress, a new assessment of blood flow data should be made for that patient. As stated above, when the expandable element is in the determined suitable expansion state, the set-up is in a use mode. When the measurements and assessment is made, we define that the set-up is in the measurement mode.

Further, when the patient lies on the expandable mattress in use mode, blood flow measurements and assessment may continuously be performed during use. Thus, the measurement mode and use mode are simultaneously active. Thus, in the use mode, blood flow measurements may for example be compared with previous measurements and when a deviation above a threshold deviation value is detected, this may be observed. For example, an alarm may be activated. Instead, or in addition thereto, the measurement mode may be activated. Then, it may in the measurement mode be determined, by again obtaining data for at least two different pressure states, that another expansion state of the mattress is suitable for use in the use mode. Alternatively, or in addition thereto, when a deviation above a threshold deviation value is detected, an alternative use mode may be activated. For example, in the alternative use mode the expansion state of the mattress is not constant and instead is varied in accordance with a predetermined scheme. Thus, a plurality of suitable expansions of the expandable mattress (105) may be determined, either during a single measurement period or during a measurement period after each deviation detection.

Thus, there is a link between the examination of the status of the patient (measurement mode) and the treatment of the patient (use mode). The effect of the treatment in the use mode can thereby be secured. As discussed above, in the use mode, measurements can be made continuously to detect any deviation above the threshold deviation value and the suitable expansions of the expandable mattress can be updated in response this detection.

When a plurality of assessment areas are assessed, a suitable expansion of the expandable mattress in a use mode is determined based on a comparison of the result of the assessment of the obtained blood flow data for the different assessed areas.

At least when there are a plurality of assessment areas 120, the suitable expansion state may be controlled according to a scheme so the pressure against the patient in the assessment areas is changing with time according to the scheme.

This means that, in the measurement mode, one or a plurality of assessment areas may be investigated, and the results of using different timings, pressures and expansion patterns of individually/group wise controllable expandable elements may be investigated. In the measurement mode, testing may be performed according to a predetermined or adaptable test scheme. The measurement mode may be active in for example an hour. The suitable expansions are then determined accordingly.

In fig 3a-3d, an example of an expandable mattress 105 is illustrated, said expandable mattress having a plurality of expandable elements 125a, 125b. In the illustrated example, the expandable elements 125a, 125b are extending substantially over the whole mattress. However, in a not disclosed example, the expandable elements 125a, 125b only cover a part of the mattress 105. The expandable elements 125a, 125b are then characteristically designed to be positioned at a part or parts of the mattress where a patient's body normally pressure against the underlying mattress.

Figure 3a is a perspective view seen from above of the expandable mattress 105 having a plurality of expandable element 125a, 125b. In the illustrated example, the expandable elements each extend along the extension of the expandable mattress. In an alternative example (not disclosed), the expandable elements extend in another direction, such as across the extension of the expandable mattress.

In the illustrated example, the expandable elements comprise a first subset 125a and a second subset 125, wherein the first and second sets have different expansion states.

Figure 3b is a side view of an expandable element 125a in a first, lower expansion state.

Figure 3c is a side view of an expandable element 125b in a second, higher expansion state.

In the perspective view of figure 3d, assessment areas 120 of a patient (not shown) are indicated.

The pressures subjected to the body of a patient (the patient is not disclosed in figures 3a-d) in the assessment areas 120 are characteristically different in the first and second expansion states of the expandable elements. The blood flow characteristics are characteristically different in the first and the second expansion states. The blood flow characteristics are probably different in the different assessment areas 120.

As stated above, the expandable elements comprise at least two subsets, wherein each subset comprises one or a plurality of expansion elements. Each subset is differently controlled. For example, the expandable elements may be alternatingly controlled so that the first subset 125a is in the first expansion state while the second subset 125b is in the second expansion state and vice versa.

In accordance with this configuration, the first and second expansion states may be selected such that when the patient is lying on the expandable mattress, the first subset of expandable element(s) 125a in the first, lower state are not in contact with the body of the patient (at least not in assessment a rea(s) ) while the body of the patient pressure against the second subset of expandable elements 125b in the second, higher state. Then, body weight of the patient exercises pressure against assessment area(s) 120 at the second subset of expandable elements but not on the assessment area(s) at the first subset of expandable element. Thus, the second subset of expandable elements protects the sensor element at least partly circumvented by the second subset of expansion element from the body weight of the patient. Accordingly, substantially no pressure is applied to the assessed area at the first subset of expansion elements.

Thus, the at least two different pressure states applied to the assessed skin area may comprise a first pressure state where the assessed skin area is subjected to substantially no pressure. In this first pressure state, the assessed skin area is lifted from the support on which the patient is placed by means of the second subset of expandable elements. The assessed skin area is in an example lifted from the support no more than enough to substantially eliminate a pressure on the assessed skin area of the patient's body from the support. If lifting the assessed skin area more than necessary above the support, this requires providing a higher pressure than necessary to parts of the skin and underlying tissue around the assessed skin area by means of the expandable element. This may lead to a risk that the blood flow within the assessed area is affected by the pressure subjected to the skin and underlying tissue parts around the assessed area.

When no pressure is provided in the assessed area, a measurement of the basal blood flow is obtained and any blood flow measured under pressure can be related to the basal blood flow.

Comparing the basal blood flow to the blood flow reflecting the daily situation for the patient can be used to provide a risk assessment with an increased reliability.

Thus, the assessment of blood flow data obtained for the at least two different pressure states may in this example comprise determination of a risk of pressure ulcers on the patient

In this example, where the subsets of expansion elements are alternating between expansion states a dividing between a measurement mode and user mode may be superfluous, measurements may continuously be made during use.

In another example, where the subsets of expansion elements are alternating between expansion states, the expansion states are selected such that a certain pressure is always experienced by the patient's body in the assessment areas. Different types of assessment of blood flow can be made.

The assessment of blood flow data obtained for the at least two pressure states may comprise determining suitable first and/or second expansion states for the first and second expansion element, respectively, in normal use of the mattress. Accordingly, the determined suitable first and second expansion states are designed for the individual patient. If a new patient is to use the expandable mattress, a new assessment of blood flow data should be made forthat patient.

Further, when the patient lies on the expandable mattress in use mode, blood flow assessment may continuously be performed during use. Thus, blood flow measurements may be compared with previous measurements and when a deviation above a threshold deviation value is observed, this may be detected. For example, an alarm may be activated. Instead, or in addition thereto, the measurement mode may be activated. Then, it may in the measurement mode be determined, by again obtaining data for at least two different predetermined pressure states, that other expansion states of the mattress are suitable for use in the use mode.

At least when there are a plurality of assessment areas 120, the suitable expansion state may be controlled according to a cycle so the pressure against the patient in the assessment areas is changing with time according to the scheme.

Figure 4 is a perspective view seen from above of the expandable mattress 105 having a plurality of expandable elements 125. In the illustrated example, the expandable elements 125 are extending substantially over the whole mattress. However, in a not disclosed example, the expandable elements 125 only cover a part of the mattress 105. The expandable elements 125 are then characteristically designed to be positioned at a part or parts of the mattress where a patient's body normally pressure against the underlying mattress.

In the illustrated example, the controllable elements form a matrix. Thus, the expansion of the expandable mattress 105 can be differently controlled both along the extension of the expandable mattress and across the extension of the expandable mattress. The expandable elements are for example individually controllable. The expandable elements are in an example group-wise controllable. The expandable element may for example comprise at least two subsets, wherein the subsets are differently controlled or controllable.

Control of the expansion elements in a measurement and use mode may be performed in line with was described in relation to the setups discussed in relation to figures 2a-c and 3a-d.

In figure 5, a system 500 for assessment of a blood flow in at least one assessment area of the skin and underlying tissue of a patient is illustrated. The system 500 may be arranged to operate in according to any of the set-ups as discussed in relation to figures 1-4.

The system 500 comprises at least one sensor plate 115 having at least one blood flow sensor obtained by means of photoplethysmography, wherein each assessment area of the skin of the patient is arranged to be provided with such sensor plate. In an example, the at least one sensor plate 115 is flexible and arranged to follow the curvature of the skin. In an example, the at least one sensor plate is provided with an adhesive for attachment to the patient. Further details of an example of a sensor plate is discussed more in detail in relation to figure 6.

The system 500 comprises further an expandable mattress 105 comprising at least one expandable element having a controllable expansion state. The expandable mattress may comprise one expandable element. The expandable mattress may comprise a plurality of expandable elements.

The expansion elements may be designed in many different ways. The expansion element may for example be expandable by means of a gas, such as air, or liquid. The expandable element may be expandable by means of a mechanical solution.

The system 500 comprises further an expansion control system 130 arranged to control expansion of the at least one expandable element to at least two different expansion states at least in a measurement mode

For example, expandable element(s) are inflatable element(s). The inflatable element(s) comprises an inflatable chamber, wherein an amount of air or another gas or the like is controllable. Accordingly, in the illustrated example, the system comprises a compressor 135 in communication with the inflatable element(s) via at least one pressure regulator 140and a valve 145. In different examples, the inflatable element comprises an inflatable chamber, wherein the amount of air in the inflatable chamber is controlled to provide the controllable inflation. The inflatable element may be controlled to at least a first inflation state and a second inflation state by controlling the amount of air in the inflatable chamber.

At least one pressure sensor (see below) may instead or in addition to measuring the body pressure applied by the patient's bodyweight in the assessed skin area be arranged to sense a pressure in the interior of the inflation element and/or a pressure applied over a pressure line (not disclosed). These pressures may be used to determine the body pressure applied by the patient's bodyweight in the assessed skin area.

However, this is only an example of a design of an expansion control system 130. The design of the expansion control system is not part of the invention and person skilled in the art may consider other deigns that this exemplified design.

The expansion control system 130 may be arranged to individually control the expansion of each expandable element. The expansion control system 130 may be arranged to control the expansion elements group-wise, i.e. different subsets. Further, the expansion control system 130 may be arranged to provide the same expansion state to all expansion elements.

The expansion control system 130 may be controlled to provide at least two expansion states of the mattress. Thereby, each assessment area is subjected to at least two different pressure states obtained by the patient's weight pressuring against the expandable mattress. The at least one blood flow sensor is arranged to obtain blood flow data while subjecting each assessment area to the at least two different pressure states.

The system 500 further comprises a computer 150 arranged to perform data processing of said blood flow data, wherein the computing system 150 is arranged to, for each assessment area, assess the obtained blood flow data for the at least two different pressure states. The computer may be arranged to, for each assessment area assess a risk of pressure ulcers on the patient based on the obtained blood flow data for the at least two different pressure states.

The computer may be arranged to operate in a measurement mode and a use mode.

A suitable expansion of the expandable mattress in a use mode may be determined based on the assessment of the obtained blood flow data for the at least two different pressure states. When a plurality of assessment areas are assessed, a suitable expansion of the expandable mattress in a use mode may be determined based on a comparison of the result of the assessment of the obtained blood flow data for the different assessed areas. The determined suitable expansion may comprise a suitable expansion and/or a suitable expansion cycle of the at least one expandable element.

In an example, the system 500 further comprises at least one pressure sensor (not shown) obtaining pressure data, wherein the computer 150 is arranged to identify the respective pressure states based on the obtained pressure data and to assess the blood flow data based on the identified at least two different pressure states. The at least one pressure sensor may for example be formed at the sensor plate 115.

The system 500 may comprise a memory (not shown) for storage of the measured data used by the computer 150. The memory may further be arranged to store assessments made.

The system 500 may further comprise a user interface 155. The user interface is operatively connected to the computer 150. The user interface 155 may be arranged to display information related to the blood flow assessments. For example, the result of the assessment may be presented by means of the user interface.

The user interface may further be arranged to present information related to the performance of the assessment. For example, if an individual LED or photodiode has been determined to be defected, this may be presented by means of the user interface. If evaluation of the data obtained by the photo detectors reveals that the results obtained from measurements at different parts of the sensor plate differs, a warning may be presented. For example, this may indicate that at least some part of the sensor plate is not in abutment to the skin.

In figure 6, an example of a sensor plate is illustrated. The sensor plate may be flexible and arranged to follow the curvature of the skin. Many other designs of the sensor plate may be considered enabling the sensor plate to follow the curvature of the body. Measurements may be improved if it can be secured that the sensor plate rest against the skin while making the measurements.

The sensor plate comprises a blood flow sensor element. In an example, the blood flow sensor comprising a plurality of LEDs arranged to emit light at at least two different wavelengths. In one example, the LEDs may be arranged to emit red and green light. The blood sensor element further comprises at least one photodetector such as a photodiode. In the illustrated example, the blood flow sensor element further comprises a plurality of photodiodes arranged to receive the light emitted from the LEDs and reflected from the skin and underlying tissue. In the illustrated example, the blood flow sensor element comprises a plurality of LEDs emitting light which may be of at least two different wavelengths. Further, in the illustrated example, the blood flow sensor element comprises six photodiodes.

Each at least one photodetector may be arranged to receive data from a plurality of LEDs and to measure the data from each LED individually.

The sensor plate may further comprise at least one pressure sensor (not illustrated) arranged to measure the pressure caused by the body weight of a patient in the assessed skin area.

The sensor plate is intended to be attached to the skin for example by means of an adhesive. The attachment may for example be provided by means of a double sided tape. The adhesive preferably is substantially transparent to the rays emitted by and reflected to a blood flow sensor element of the sensor plate in order not to disturb the measurements.

Figure 7 illustrates a method 700 for assessment of a blood flow in an area of the skin and underlying tissue of a patient.

The method 700 comprises a step of controlling SI expansion of the at least one expandable element of an expandable mattress to at least two different expansion states, whereby the at least one expandable element secures that each of at least one assessment area is subjected to at least two different pressure states obtained by the patient's weight pressuring against the expandable mattress and by the at least two expansion states of the mattress.

The method 700 may further comprise a step of obtaining S2 pressure data related to the body pressure applied to the assessed skin area. The pressure data may be provided by measuring the body pressure applied to the assessed skin area. The pressure may for example be measured by means of at least one pressure sensor. The at least one pressure sensor may be formed at the sensor plate which also comprises the blood flow sensor element.

The respective pressure states may be identified S3 based on the obtained pressure data. The identification of the respective pressure state may then be used for initializing obtaining of blood flow data. Alternatively, the identification of the respective pressure state may then be used for selection of blood flow data for analysis. In accordance with this example, blood flow data corresponding to pre-set pressure intervals may be selected for analysis.

The method 700 further comprises obtaining S4, using at least one blood flow sensor, blood flow data while subjecting each assessment area to the at least two different pressure states.

The obtaining of blood flow data may be provided upon determination that the expandable element is in the respective state. In accordance therewith, when it has been determined that the respective expansion state has been reached, the obtaining of blood flow data may be initiated for that expansion state. The obtaining of blood flow data may be performed during a pre-set amount of time. Alternatively, blood flow data may be continuously obtained during the entire procedure.

The method further comprises, for each assessment area, assess S5 the obtained blood flow data for the at least two different pressure states to determine a suitable expansion of the expandable mattress (105) in a use mode. The assessment has been described in detail herein.

There is generally less risk for pressure ulcers when a blood flow increases with the increased body pressure applied by the patient's weight. On the other hand, there is an increased risk for pressure ulcers when a blood flow decreases with increased body pressure applied by the patient's weight. Thus, the assessment of the risk of pressure ulcers on the patient involves determining whether the blood flow increases or decreases with increased body pressure applied to the assessed skin area by the patient's weight. Preferably, the increase or decrease of the blood flow is related to a basal blood flow, i.e. a blood flow measured unloaded.

The assessment may for example be made based on obtained blood flow data obtained at discrete, predetermined pressure states, such as the first pressure state where no pressure is provided in the assessed skin area and the second pressure state where the body weight pressures against the assessed area, or based on continuously obtained blood flow data. In the first case, the obtained pressure data may be used for identifying S3 the discrete, predetermined pressure states. This identification may in turn be used for initiating blood flow measurements. The obtained pressure data may in the latter case be continuously associated to corresponding continuously obtained blood flow data. The obtained pressure data may then be used for selecting intervals of the blood flow data for the assessment of the risk of pressure ulcers.

In the illustrated method, a measurement mode and a use mode is illustrated. As disclosed herein, these modes may be operating simultaneously, i.e. measurements and assessment is mode during normal use, or alternating. In figure 7, a separate step S6 for control of the expandable element(s) according to a predetermined scheme in a use mode is illustrated.

Figure 8 discloses examples of details of the step of obtaining S4 blood flow data related to an assessed skin area. The blood flow data is as discussed in relation to figure 7 obtained by means of photoplethysmography. The obtaining of blood flow data may comprise illuminating S41 the skin with the light from a LED, and measuring S42 the amount of light reflected to a photodiode. The LED and the photodiode form a blood flow sensor element. The blood flow sensor element may be arranged at a sensor plate. The LEDs may emit light having one wavelength. Alternatively, the LEDs may emit light having at least two different wavelengths. In accordance with the latter example, a first set of LEDs emitting at a first wavelength and a second set of LEDs emitting at a second wavelength may be illuminating the skin. The one or a plurality of photodiodes measuring the amount of light reflected thereto may each measure light originating from a plurality of LEDs.

In detail, the strength of the pulse of the body is measured by means of the blood flow data in at least two different expansion states.

Claims

1. A system (300) for assessment of a blood flow in at least one assessment area of the skin and underlying tissue of a patient, said system comprising: at least one sensor plate (115) having at least one blood flow sensor obtained by means of photoplethysmography, wherein each assessment area of the skin of the patient is arranged to be provided with such sensor plate; an expandable mattress (105) comprising at least one expandable element (115) having a controllable expansion state; an expansion control system (130) arranged to, in a measurement mode, control expansion of the at least one expandable element to at least two different expansion states; whereby each assessment area is subjected to at least two different pressure states obtained by the patient's weight pressuring against the expandable mattress and by the at least two expansion states of the mattress, and a computer (150) arranged to perform data processing of said blood flow data, wherein the at least one blood flow sensor is arranged to obtain blood flow data while subjecting each assessment area to the at least two different pressure states, and wherein the computer (150) is arranged to, for each assessment area, assess the obtained blood flow data for the at least two different pressure states to determine a suitable expansion of the expandable mattress (105) in a use mode.

2. The system according to claim 1, wherein the expandable mattress (105) comprises a plurality of expandable elements (125).

3. The system according to claim 2, wherein the expandable elements (125) are individually controllable.

4. The system according to claim 2, wherein the expandable elements (125) comprises at least two subsets, wherein the subsets are differently controlled.

5. The system according to any of the preceding claims, wherein a plurality of assessment areas are assessed, and wherein the computer is arranged to determine the suitable expansion of the expandable mattress (105) in the use mode based on a comparison of the result of the assessment of the obtained blood flow data for the different assessed areas.

6. The system according to any of the preceding claims, wherein the determined suitable expansion comprises a suitable pressure and/or cycle of the at least one expandable element.

7. The system according to any of the preceding claims, wherein the computer (150) is arranged to operate in the measurement mode and the use mode.

8. The system according to any of the preceding claims, wherein the at least one sensor plate (115) is flexible and arranged to follow the curvature of the skin.

9. The system according to any of the preceding claims, wherein the at least one sensor plate (115) is provided with an adhesive for attachment to the patient.

10. The system according to any of the preceding claims, further comprising at least one pressure sensor obtaining pressure data, wherein the computer (150) is arranged to identify the respective pressure states based on the obtained pressure data and to assess the blood flow data based on the identified at least two different pressure states.

11. The system according to any of the preceding claims, wherein the computer (150) is further arranged to, for each assessment area assess a risk of pressure ulcers on the patient based on the obtained blood flow data for the at least two different pressure states.

12. A control element (150) for assessment of a blood flow in an area of the skin and underlying tissue of a patient, said control element comprising: an interface arranged to receive blood flow sensor data obtained by means of photoplethysmography, said blood flow sensor data being obtained from at least one assessment area subjected to at least two different pressure states obtained by the patient's weight pressuring against a support on which the patient is placed and an expansion state of an expandable element in a direction from the support against the patient ; and a processor arranged to assess said blood flow data for the at least two different pressure states , , to determine a suitable expansion of the expandable mattress in a use mode based the assessment of the obtained blood flow data for the at least two different pressure states. A computer-implemented method (700) for assessment of a blood flow in an area of the skin and underlying tissue of a patient, said computer-implemented method comprising the steps of: control (SI) expansion of the at least one expandable element of an expandable mattress to at least two different expansion states; whereby the at least one expandable element secures that each assessment area is subjected to at least two different pressure states obtained by the patient's weight pressuring against the expandable mattress and by the at least two expansion states of the mattress, obtain (S4), using at least one blood flow sensor, blood flow data while subjecting each assessment area to the at least two different pressure states, and for each assessment area, assess (S5) the obtained blood flow data for the at least two different pressure states to determine a suitable expansion of the expandable mattress in a use mode. The computer-implemented method according to claim 13, further comprising a step of obtaining (S2) pressure data and identifying (S3) the respective pressure states based on the obtained pressure data, wherein the step of assessing (S5) the assessment of blood 22 flow data obtained for the identified at least two different pressure states is made based on the identified at least two different pressure states. The computer-implemented method according to any of the preceding claims, further comprising controlling (S6) the expandable element(s) according to the determined suitable expansion in the use mode. Software for performing the computer-implemented method as defined in any of the claims 13- 15.