Attaching a sensor to a body part for measuring a body parameter - Patents.com

Abstract

An apparatus for measuring a body parameter of a subject, the apparatus comprising a sensor for measuring said body parameter, a housing element for positioning said sensor on a body part of the subject, and an actuator system within said housing element for applying a pressure to said body part, the actuator system having two states, a first state based on the actuator system applying a first pressure to a first region of the body part, and a second state based on the actuator system applying a second pressure to a second region of the body part, the apparatus also comprising a controller configured to apply the first and second states at different times.

Description

[Technical field]

[0001] The present invention relates to a device for fastening to a body part of a subject, in particular to a device for measuring a body parameter of a subject whilst the device itself is fastened to the body part of the subject. [Background technology]

[0002] Pulse oximetry is a well-known method for measuring the saturation of hemoglobin with oxygen. A related sensor is the SpO2 sensor. Hemoglobin is a component of red blood cells, which are present in the blood flowing through arteries, capillaries and veins. The method uses two light-emitting diodes (LEDs) of different wavelengths, the light transmission of which is measured by a photodetector. From the pulsatile portion of the transmitted light, the heart rate and the ratio of hemoglobin with bound oxygen to hemoglobin without bound oxygen can be determined. Ideally, the measured oxygen saturation is indicative of arterial oxygen saturation.

[0003] Two LEDs and a photodetector are assembled into a housing. The LEDs and photodetector are wired and the wires are collected into a cable. This cable may be a shielded cable, for example consisting of an additional shield surrounding the wires to the detectors and surrounding the wires to the LEDs. The other end of the cable is terminated by a connector that is coupled to a patient monitoring device (patient monitor). The patient monitor provides voltage to both LEDs and reads the signal from the photodetector.

[0004] The SpO2 sensor can be placed on different body positions of a human, such as a finger, nostril, forehead, or ear. Fixation is achieved by applying pressure to this body position. There are reusable sensors with a hollow elastic housing that applies continuous pressure to a body position, such as a finger. Others use a more rigid housing with hinges and springs, again applying continuous pressure to the body position. Furthermore, disposable SpO2 sensors are composed of a flexible material to which the LED and detector are attached. This flexible material can be wrapped around a finger to fixate the sensor to the finger, and pressure can also be applied to the finger. In addition to providing fixation, pressure on the SpO2 sensor can also be used to suppress or reduce the contribution of pulsating venous blood and tissue fluid in the SpO2 signal. Summary of the Invention [Problem to be solved by the invention]

[0005] SpO2 sensors for fingers have been available for many years. However, there is a compliance issue with users removing the SpO2 sensor from the finger. The SpO2 sensor applies continuous pressure to the finger, which results in some users experiencing discomfort. In addition, other sensors in other body locations (with sufficient blood perfusion for reliable measurements) that are secured by applying continuous pressure may cause discomfort.

[0006] The effect of continuous pressure is to constantly stimulate the nerves in the skin, which are translated by the brain into discomfort. Blood flow is also partially restricted, causing further discomfort. Complete blood flow restriction can even lead to local necrosis. This has been observed in forehead SpO2 sensors, which are fixed with a stretched elastic band. The challenge is often to find the right balance between sufficient pressure for an accurate measurement and low enough pressure to be comfortable and ensure sufficient blood flow even for users with blood perfusion problems.

[0007] Therefore, for devices that require (or benefit from) being attached to a body part for measurement of a physical parameter (e.g., heart rate, blood pressure, blood oxygen saturation, etc.), there is a need to improve comfort and therefore subject compliance. [Means for solving the problem]

[0008] The invention is defined by the claims.

[0009] According to an example embodiment of the present invention, there is provided an apparatus for measuring a physical parameter of a subject, the apparatus comprising: a sensor for measuring said body parameter; a housing element for positioning the sensor on a body part of the subject; an actuator system within said housing element for applying pressure to said body part, said actuator system having two states, namely: a first state based on the actuator system applying a first pressure to a first region of the body part; and A second state based on the actuator system applying a second pressure to a second region of the body part. The actuator system, a controller configured to apply the first and second states at different times; has.

[0010] For example, devices used to measure the saturation percentage of blood oxygen (SpO2 devices) typically have compliance issues with subjects finding these devices uncomfortable and moving or removing them. This is because SpO2 devices must be secured to the body part being measured (e.g., finger, nose, forehead, etc.), which constantly irritates nerves and causes blood flow restriction in the area where the device is secured. Over time, this constant irritation and continuous restriction of blood flow causes discomfort to the subject.

[0011] The present invention provides a device with an actuator system that allows the device to be fixed to a body part (one resting position) while varying the area to which pressure is applied to the body part. The actuator system has two states, a first state where pressure is applied to an area of ​​the body part, and a second state where pressure is applied to a different area of ​​the body part, thus limiting the time each area is stimulated and blood flow is restricted. The actuator system is also capable of varying the amount of pressure between the first and second states. A controller is used to change the state of the actuator system based on a predefined time period (e.g. change state every 5 minutes, change state every 30 seconds, etc.).

[0012] The device also has a sensor for measuring body parameters (e.g. pulse rate, respiratory rate, photoplethysogram, etc.) from the body part to which the device is fixed, and a housing element that houses the sensor and the actuator system. The actuator system then fixes the device to the body part by creating a pressure between the housing element (and / or the sensor) and the body part, which pressure increases the friction between the device and the body part.

[0013] The actuator system has at least two actuator elements, each configured to change volume or shape when the actuator element is stimulated, and a controller is further configured to stimulate the actuator elements and define a state of the actuator system.

[0014] One way that actuator systems secure a device to a body part is by using actuator elements that increase in volume or change shape when they are stimulated, thus increasing the pressure between the device and the body part.

[0015] For example, the device is designed for measuring on a finger: the device can be placed around the finger (completely surrounding the finger) and then the first actuator element can be stimulated.

[0016] For example, the actuator element completely surrounds the finger. Activation causes the actuator element to increase in volume or change shape, thus creating pressure between the housing element and the finger that secures the device to the finger. After, for example, 5 minutes, the first actuator element is deactivated and the second actuator element is stimulated.

[0017] When encircling a finger, the actuator elements are spaced apart by only a few millimeters. The actuator system can have an even number of actuator elements that encircle the finger as a whole. The actuator system can have a first n number of actuator elements in the top half of the system and an equal n number of actuator elements in the bottom half. Assuming there are four actuator elements in the top and bottom halves, in a first state of the actuator system, two of the actuator elements in the top half are activated (i.e., stimulated) and two of the actuator elements in the bottom half are also activated (i.e., the first set of actuators). This essentially creates four pressures applied from four directions that clamp the device to the finger. When the actuator system changes to a second state, the actuator elements change to actuator elements that were not activated in the first state (i.e., the second set of actuators). In both states, the actuator system provides a clamping pressure between the finger and the device while changing the area of ​​the finger to which pressure is applied.

[0018] However, the actuator elements may instead be spaced along a straight line, for example a second actuator element being 10-50mm away from the first actuator element along the length of the finger, thus applying pressure to different areas of the finger whilst maintaining the device fixed to the finger.

[0019] The actuator elements may be electroactive polymers configured to expand in volume when a voltage is applied thereto, the controller being further configured to apply a voltage to the electroactive polymers.

[0020] Electroactive polymers are convenient because they expand with an applied voltage, and because the sensor also requires a voltage to power it, a shared power supply and cabling arrangement may be used for both the sensor and the electroactive polymer.

[0021] The actuator element may alternatively be an expandable element that is configured to expand when the actuator element expands.

[0022] The inflatable element may be inflated by an external pressure pump, for example a pressure pump typically used to inflate blood pressure cuffs, with the controller being configured to operate the pump.

[0023] The controller may be further configured to vary the pressure applied to the subject's body part by the actuator system.

[0024] For example, different subjects may require different pressures depending on the subject's health, fat content, size of body parts, etc. A particular pressure (in one or both states of the actuator system) may increase comfort with the device and may also ensure more accurate measurements by the device.

[0025] The apparatus further includes an accelerometer for determining a posture of the subject, and the controller is further configured to vary the pressure applied to the body part of the subject by the actuator system based on the posture of the subject.

[0026] Subject posture also affects the optimal pressure for any given subject, and therefore an accelerometer (e.g., a 3D accelerometer) provides an indication of subject posture that is used to modify the pressure in one or both of the states of the actuator system.

[0027] The sensor may be a pulse oximeter having an LED unit and a photodetector, the photodetector configured to obtain a signal related to the saturation percentage of blood oxygen.

[0028] A pulse oximeter indirectly monitors the oxygen saturation of a patient's blood (as opposed to measuring oxygen saturation directly using a blood sample). More specifically, a pulse oximeter measures the percentage load of hemoglobin, the protein in the blood that carries oxygen. The acceptable normal range for subjects without pulmonary pathology is 95% to 99%.

[0029] An LED unit typically contains two LEDs that alternately emit light of different wavelengths, and a photodetector then detects the light from both LEDs after it has been transmitted through or reflected from the medium.

[0030] The LED unit may be disposed at an end of a first actuator element and the photodetector may be disposed at an end of a second actuator element.

[0031] The accuracy of a pulse oximeter typically depends on the pressure applied between the components (the LED unit and the photodetector) and the body part. Thus, for example, an additional actuator system can provide pressure between the sensor components and the body part, thereby increasing the accuracy. Furthermore, by having the sensor components at the tip of the actuator elements of this additional actuator system, the controller can control the pressure between the components (i.e., the LED unit and the photodetector) and the body part.

[0032] The controller may be further configured to control the actuator system to apply a predetermined pressure to the body part, where applying the predetermined pressure to the body part reduces the venous contribution to the signal acquired by the optical detector.

[0033] The device may further comprise an adhesive layer at an interface between the housing element and the body part of the subject, the actuator system being configured to apply pressure between the sensor and the body part.

[0034] In some cases, it may be impossible / impractical for the housing element of the device to surround and remain on a body part (e.g., forehead, torso, etc.). In these cases, the housing element benefits from an adhesive layer that allows the housing element to be fixed to the body part. An actuator system is then used to apply pressure to the body part to the sensor (e.g., a reflective SpO2 sensor).

[0035] For example, a first state of the actuator system may ensure that a sensor has pressure on a body part. To reduce discomfort from this pressure, the actuator system may change to a second state after a predetermined period of time (e.g., 30 seconds to 5 minutes). At this time, the second state may reduce the pressure applied to an area of ​​the body part or change the area to which the pressure is applied.

[0036] The actuator system may include a rotating element having two or more protrusions and an elastic layer between the rotating element and a body part of the subject, and the controller is configured to rotate the rotating element when changing states.

[0037] The protrusions of the rotating element cause the elastic layer to expand, thus exerting pressure from the elastic layer on the body part, whereupon the rotating element can be rotated (e.g., 22.5 degrees, 45 degrees, etc.) when the state of the actuator system is changed to change the area of ​​the body part to which pressure is applied, thus reducing discomfort to the subject.

[0038] If the elastic layer rotates with the rotating element, the elastic layer needs to be fairly smooth (in the direction of rotation) so that the elastic layer does not injure the subject's body part. Instead, the elastic layer does not move, but the rotating element can change the position where it bulges on the elastic layer.

[0039] The device may further include a friction enhancing layer at the interface between the device and the subject's body part.

[0040] A friction enhancing layer, ie a rough layer, at the interface of the device to the subject increases the friction on the body part and therefore enhances the fixation of the device to the body part.

[0041] The device further includes a moisture trapping element at an interface between the device and the subject's body part to reduce moisture accumulation at the interface. The moisture trapping element may also be disposably connected to the device such that the moisture trapping element may be replaced (e.g., for a different subject).

[0042] The present invention also provides a method for measuring a physical parameter of a subject, the method comprising: applying a first pressure to a first region of a body part with an actuator system, the actuator system being within a housing element, the housing element being secured to the body part; applying a second pressure to a second region of the body part with the actuator system at a different time than the first pressure is applied to the first region of the body part; and Measuring the body parameter with a sensor positioned on the body part by the housing element. has.

[0043] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. [Brief description of the drawings]

[0044] For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Figure 1] FIG. 1 shows an actuator device comprising an electroactive polymer as the actuator element. [Diagram 2] FIG. 2 shows a cross section along the length of the housing. [Diagram 3] FIG. 3 shows an EAP actuator element with electrodes indicated. [Figure 4] FIG. 4 shows an actuator device with an LED unit and a photodetector at the tip of the actuator element. [Diagram 5] FIG. 5 shows a cross section of a device with three actuator devices. [Figure 6] FIG. 6 shows a cross section of a device comprising two actuator devices with expandable actuator elements. [Figure 7] FIG. 7 shows an actuator device with eight expandable elements. [Figure 8] FIG. 8 shows a schematic diagram of a microfluidic circuit comprising two actuator devices, each containing two sets of expandable elements, and a valve. [Figure 9] FIG. 9 shows a cross section of a rotary actuator device. [Figure 10] FIG. 10 shows a cross section along the length of a device comprising two rotary actuator devices. [Figure 11] FIG. 11 shows a cross section of a device with a reflective SpO2 sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] The present invention will now be described with reference to the drawings.

[0046] It should be understood that while the detailed description and specific examples set forth exemplary embodiments of the devices, systems and methods, they are for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects and advantages of the devices, systems and methods of the present invention will become better understood from the following description, appended claims and accompanying drawings. It should be understood that the drawings are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to denote the same or similar parts.

[0047] The present invention provides an apparatus for measuring a body parameter of a subject. The apparatus comprises a sensor for measuring the body parameter, a housing element for positioning the sensor on a body part of a subject, and an actuator system within the housing element for applying a pressure to the body part. The actuator system has two states, a first state based on the actuator system applying a first pressure to a first region of the body part, and a second state based on the actuator system applying a second pressure to a second region of the body part. The apparatus comprises a controller configured to apply the first and second states at different times.

[0048] Continuous pressure on a body position by the actuator system is avoided by periodically changing the body position used to fix the housing element, thereby locally and temporarily relieving the skin contact sensors, arteries and capillaries from pressure.

[0049] 1 shows an actuator device 114 comprising an actuator system having an electroactive polymer as the actuator element 106. The electroactive polymer (EAP) actuator element 106 converts an applied voltage directly into a volume expansion to exert pressure to fix the housing 102 to the body position 104. The grip of the actuator element 106 may be enhanced by a friction-enhancing layer 110 with sufficient roughness.

[0050] The actuator device 114 applies alternating position fixation using multiple EAP actuator elements 106, thereby minimizing obstruction of blood flow. Local electronic circuitry can be used to convert a low supply voltage to the higher voltage required to drive the various EAP actuator elements 106, control the intermittent and alternating movement of the EAP actuator elements 106, and, if necessary, suspend sensor measurements while switching the fixation positions on the body part 104. Switching fixation positions changes the area of ​​the body part to which pressure is applied from a first area to a second area of ​​the body part 104, such that for a period of time, the first area is free of pressure while pressure is applied to the second area, and vice versa.

[0051] The device can function on a variety of body parts 104. However, for the purposes of the following example, we will assume that the body part 104 is a finger.

[0052] In Fig. 1a, a cross section of the housing 102 and eight EAP actuator elements 106 are shown. Other components such as sensors and controllers (i.e. electronic circuitry) are positioned elsewhere in / on the housing 102 (and therefore are not visible in the cross section shown). In the cross section shown, two sets of four actuator elements 106 are shown. Both the cross section of the housing 102 and the cross section of the finger 104 are shown diagrammatically. The cross section of the finger 104 is shown very diagrammatically as a circular cross section. However, the cross section of the housing 102 can be adapted to a shape that better fits the cross section of the finger 104, although this is not necessary for the functionality of the actuator device 114.

[0053] FIG. 1b shows a cross-section of the device with the first set of actuator elements 106 activated (i.e., the actuator system is in a first state). FIG. 1c shows a cross-section of the device with the second set of actuator elements 106 activated (i.e., the actuator system is in a second state). After placing the housing 102 over the finger 104 and then powering the controller (e.g., by connecting the device to a patient monitor), the first set of actuator elements 106 are activated, which results in the electroactive polymer (of the first set of activated actuator elements 106) expanding. The EAP actuator elements 106 are bounded by the rigid housing 102 and the rigid isolation element 108. As such, the EAP actuator elements 106 expand towards the finger 104, and in the process, press a friction-enhancing layer (i.e., a roughened layer) 110 with a defined roughness against the finger 104. The rough layer 110 separates the actuator elements 106 from the fingers 104 and also provides a roughness that aids in gripping the fingers 104. The rough layer 110 also insulates the fingers from the voltage applied to the actuator elements 106.

[0054] It should be noted that the use of EAP actuator elements 106 is safe since they operate based on an electric field, and the current applied to charge the electrodes of the EAP actuator elements 106 is small and completely safe if damaged. The controller can be designed such that it only supplies a small current (e.g., less than 5 mA) to the EAP actuator elements 106.

[0055] For example, after 30 seconds to 5 minutes, the second set of actuator elements 106 is activated and then the first set is deactivated. After another 30 seconds to 5 minutes, a similar process is initiated by activating the first set and then deactivating the second set. By repeating these operations, pressure is alternately positioned on different areas of the finger, as shown by the expanded portion 112 in Figures 1b and 1c. In this case, the actuator elements 106 are segmented so that the finger 104 is not pressurized around the entire circumference of the finger, thereby minimizing blockage of blood flow in the finger.

[0056] Alternatively, each set of actuator elements 106 can consist of fewer or more actuator elements 106 than the four shown. For example, each set can include only two actuator elements 106. This is appropriate for different sized fingers (e.g., infants and children have smaller fingers and can therefore benefit from fewer actuator elements 106). Furthermore, each set of actuator elements 106 can be located at different positions (i.e., different cross-sections) along the length of the housing. These variations can further optimize design and comfort based on the same principles of localized and temporary pressure relief.

[0057] Additionally, multiple actuator devices 114 can be provided along the length of the housing 102, which has the advantage of increasing the fixation area on the finger 104 while at the same time reducing pressure on the finger 104 by reducing the activation level of the actuator elements 106.

[0058] Fig. 2 shows a cross section along the length of the housing 102. In Fig. 2, the sensor is a pulse oximeter with an LED unit 204 (two LEDs 208) and a photodetector 206 for measuring the oxygen saturation in the blood of a subject (i.e., SpO2 measurement). For example, the first LED 208 emits light at a wavelength of 660 nm and the second LED 208 emits light at a wavelength of 940 nm. Also shown are the housing 102, the controller 202 (electronic circuitry), the cable 212 and the connector 214. Two actuator devices 114 are shown, which may be, for example, equivalent to the actuator device 114 described above.

[0059] The connector 214 (in this case a male connector) has two pins that are used for sensor identification. Identification can be accomplished by measuring resistance or by reading data from a single wired device. The patient monitor can use this to identify the type of sensor that is connected. These pins also serve two functions as explained below.

[0060] These pins are connected to the electronic circuit 202 via cable 212. The advantage of using these two pins is that the sensitive signals from the pulse oximeter are not coupled to the power to activate the actuator device. The signals from the pulse oximeter are controlled by a first set of pins that provide a pulse signal to the LED 208 and a second set of pins that receive said signal from the photodetector 206, and the first and second sets of pins are not connected to the electronic circuit 202.

[0061] The electronic circuit 202 has two main functions. The first is to return a resistance value (or a reading of one wire) to the patient monitor in order to identify the type of sensor. The second is to provide control of the actuator elements 106. In this case, the patient monitor supplies a voltage, for example 5 volts, through these pins, thereby powering the electronic circuit 202 and performing said identification. The electronic circuit 202 then increases said voltage up to the voltage desired to drive the actuator elements 106, by using a voltage boost circuit, for example several voltage doublers. For EAP actuator elements 106, this voltage is typically 200 volts. However, for other actuator elements 106, 5 volts is already sufficient. Furthermore, the electronic circuit 202 has a logic circuit for alternately driving the two sets of actuator elements 106 in each actuator device 114.

[0062] The EAP actuator elements 106 are actuated by an electric field, so that they act like capacitors with a low capacitance requiring only a small amount of current.

[0063] A connection (point 210) between the electronic circuitry 202 and the EAP actuator element 106 can provide power to the electrodes of the EAP actuator element 106. These electrodes then provide a voltage to the expanding electroactive polymer material.

[0064] FIG. 3 shows an EAP actuator element 106 with electrodes 302 shown. In the most basic configuration, there is simply a layer of EAP material sandwiched between electrodes. However, the EAP actuator element 106 may have a stack of multiple electroactive polymer layers sandwiched between electrodes 302. These electrodes 302 are then alternately connected to a voltage supply line and a voltage of 200 volts is applied to actuate the electroactive polymer layers. FIG. 3 is a representation of the basic structure and therefore does not show the layers of electrodes 302 and the stack of electroactive polymer layers. Only the outer electrodes 302 connected to the electronic circuitry 202 are shown, although other electrodes 302 may be used.

[0065] Some sensors (e.g., blood pressure sensors) benefit from pressure applied between the sensor and finger 104. Additionally, for pulse oximetry, it is advantageous to apply pressure to finger 104 along the same axis as the optical path from LED unit 204 to photodetector 206, particularly to improve the signal accuracy of photodetector 206.

[0066] 4 shows an actuator arrangement with an LED unit 204 and a photodetector 206 at the tip of selected ones of the actuator elements 106. Preferably, a separate LED unit 204 and photodetector 206 (e.g. a photodiode) is implemented for each "pressure direction". The various LED units 204 are activated in synchronism with the activation of their respective EAP actuator elements 106. In this case, the LED units 204 and photodetectors 206 are each located at the top of the actuator elements 106.

[0067] Figure 4a shows the actuator arrangement 114 when none of the actuator elements 106 are activated, and Figure 4b shows the actuator arrangement 114 when a first (exemplary) set of actuator elements 106 are activated such that one-dimensionally opposed LED and photodetector pairs are pressed against a body part.

[0068] In applications where an intermittent signal from the photodetector 206 is sufficient, a sensor comprising one LED unit 204 and one photodetector 206 is combined with the EAP actuator element 106. During SpO2 measurements, the LED unit 204 and respective EAP actuator element 106 are activated, while between SpO2 measurements, the LED unit 204 is deactivated when the (one of) the other EAP actuator elements is activated. As mentioned above, additional actuator devices 114 may be provided along the length of the housing 102.

[0069] 5 shows a cross-section of a device with three actuator devices 114. Only one of these actuator devices 114 is used to press the LED unit 204 and the photodetector 206 against the finger 104.

[0070] If intermittent measurements are insufficient, two LED units 204 and two photodetectors 206 may be used, mounted on the associated actuator element 106. In Figure 5, one LED unit 204 and one photodetector 206 are out of plane.

[0071] An arrangement of two (or more) circular actuator devices is also possible. For example, if the pressure required for fixation is relatively low and blood flow is only slightly restricted, all actuator elements 106 in one actuator device 114 can be activated simultaneously. When these actuator elements 106 are deactivated, the other actuator device 114 is activated, so that the finger is always fixed. In this case, the actuator elements 106 may be replaced by one circular actuator element 106.

[0072] Other actuator elements 106 that are not based on electroactive polymers can also be used, for example, expandable elements may be used.

[0073] 6 shows a cross-section of a device having two actuator devices 114 with an expandable actuator element 106. Also shown for this context are the LED 208, the photodetector 206, the housing 102, the cable 212 and the connector 214. Two actuator devices 114 are shown. In this example, the actuator element 106 is an expandable element (e.g., a balloon) that is expanded by a mini-pump 602 disposed adjacent to the housing 102, which applies pressure, reinforced by the roughened layer 110, to secure the housing 102 to the finger 104.

[0074] The electronic circuitry 202 drives the pump 602. In addition, a microfluidic circuitry 604 with valves regulates which expandable element 106 is expanded, and if necessary, pauses the SpO2 measurement while switching between fixation positions.

[0075] FIG. 7 shows an actuator device 114 with eight expandable elements 106. In FIG. 7a, a cross section of the actuator device 114 and the housing 104 is shown when the expandable elements 106 are not activated. Other components such as, for example, the LED 208, the photodetector 206, the electronic circuit 202, the microfluidic circuit 604 and the pump 602 are positioned on different cross sections along the housing 102. In the cross sections shown, two sets of four expandable elements 106 are shown. FIG. 7b shows a first set of expandable elements 106 activated (i.e. the actuator system is in a first state) and FIG. 7c shows a second set of expandable elements 106 activated (i.e. the actuator system is in a second state). Both the cross sections of the housing 102 and the fingers 104 are again displayed in a schematic manner.

[0076] After placing the housing over the finger and then powering the electronic circuitry 202, for example by connecting to a patient monitor, one set of expandable elements 106 begins to expand by activating the pump 602 and valves of the microfluidic circuitry 604. Because each expandable element 106 is bounded by the rigid housing 102 and rigid separation element 108, the expandable elements have no choice but to expand towards the finger 104, and in the process, press the roughened layer 110 against the finger 104. Portions 112 in Figures 7b and 7c show the expanding portions of the expandable elements 106 of the first set of expandable elements 106 and the second set of expandable elements 106, respectively.

[0077] The rough layer 110 also has a roughness that separates the expandable elements 106 from the finger 104 and helps grip the finger 104. Thirty seconds to five minutes after the first set of expandable elements 106 is expanded (as shown in FIG. 7b), the second set of expandable elements 106 is expanded and the first set is immediately deflated (as shown in FIG. 7c). Thirty seconds to five minutes later, a similar process is initiated by expanding the first set and immediately deflating the second set. By repeating these operations, pressure is alternately positioned at different locations on the finger 104. In effect, the expandable elements 106 are segmented so that the finger 104 is not pressurized over the entire circumference of the finger, thereby minimizing blockage of blood flow in the finger. If desired, such actuator devices 114 can be repeated along the length of the housing 102, which has the advantage of increasing the fixation area on the finger 104 while at the same time reducing the expansion of the expandable element 106, thereby reducing pressure on the finger 104.

[0078] As mentioned above, there are various mini-pumps 602 that can be deployed and driven by the electronic circuitry 202. If a higher voltage is beneficial to drive the pumps 602, as mentioned above, a voltage boost circuit, such as, for example, a voltage doubler circuit, can be used in the electronic circuitry 202. The electronic circuitry 202 drives the pumps 602 and valves in the microfluidic circuitry 604 such that the two sets of expandable elements 604 are alternately expanded.

[0079] The pump 602 can use air to inflate the expandable element 106. However, since air is compressible and hydropneumatic fluid is substantially incompressible, a hydropneumatic fluid can also be used. However, since the expandable element 106 is a collapsible container, inflation with either air or hydropneumatic fluid is possible.

[0080] FIG. 8 shows a schematic diagram of two actuator devices 114a and 114b, each of which includes two sets of inflatable elements 106 and a microfluidic circuit 604 with a valve 806. The microfluidic circuit 604 allows the expansion and contraction of the inflatable elements 106 triggered by a mini-pump 602 made of a motor that moves a plunger 804 into a housing 802 of a syringe, thus changing the state of the actuator system. When the device is connected to a patient monitor, the electronic circuit 202 is activated. The first valve 806 (valve 1) is then opened and the motor moves the plunger 804 into the housing 802 of the syringe. As a result, the left inflatable element 106 (i.e. the first set of inflatable elements 106 of the first actuator device 114a and the first set of inflatable elements 106 of the second actuator device 114b) expands, thereby gripping the finger 104.

[0081] After a certain time, typically 30 seconds to 5 minutes, the second valve 806 (Valve 2) opens and the plunger 804 is moved further into the syringe housing 802, thereby expanding the right-side expandable element 106 as well (i.e., the second set of expandable elements 106 of the first actuator device 114a and the second set of expandable elements 106 of the second actuator device 114b). Shortly after, Valve 2 closes and the plunger 804 is moved outward, causing the left-side expandable element 106 to contract. The finger 104 continues to be held stationary by the right-side expandable element 106. After 30 seconds to 5 minutes, the plunger 804 is again moved inward, causing the left-side expandable element 106 to expand. Shortly after, Valve 1 closes and Valve 2 opens. The plunger 804 is then moved outward, causing the right-side expandable element 106 to contract. This is repeated periodically. The microfluidic circuitry 604, mini-pumps 602, and / or valves 806 are, for example, disposed on a PCB (not shown) of the electronic circuitry 202. There are a variety of state of the art mini-pumps 602 (e.g., motors and syringes) that may be used.

[0082] For SpO2 measurements, it is advantageous to apply pressure to the finger 104 along the same axis as the light path from the LED 208 to the photodetector 206. Preferably, a separate LED unit 204 is implemented for each "pressure direction." Different LED units 204 are activated according to the activation of the respective expandable element 106. In this case, the LED 208 may be located on top of the expandable element 106. Furthermore, the photodetector 206 may also be located on top of the expandable element 106.

[0083] As mentioned above, in applications where intermittent SpO2 measurements are sufficient, a sensor comprising one LED unit 204 and photodetector 206 can be combined along one direction with an expandable element 106. During SpO2 measurements, the LED unit and the respective expandable element 106 are activated, while between SpO2 measurements the LED unit is inactive and the (one of) the other expandable elements 106 of the actuator system is activated.

[0084] Any other pump 602 that uses pressure on the inflatable element 106 (including pumps that use hydraulic pressure) may be used in place of the plunger 804 and syringe housing 802 shown. These may be miniaturized MEMS pumps. Alternatively, a pressure pump typically used to inflate a cuff (e.g., a pressure pump found on a patient monitor) may be used. This would require an additional pressure line in the cable 212 and connector 214 to the patient monitor.

[0085] 9 shows a cross section of a rotary actuator device 114. In this example, a rotary mechanical element 902 with protrusions 904 that apply pressure at a series of positions is used to periodically deform an elastic layer 906, thereby fixing the housing 102 (not shown) to the finger 104. The rotary actuator device 114 includes a rotary mechanical element 902, a motor (not shown) that induces this rotation, and an elastic layer 906 that contacts the skin of the finger 104. An electronic circuit 202 is used to drive the motor and the sensor to induce the rotation. To prevent the housing 102 from rotating relative to the finger 104, two counter-rotating mechanical elements 902 can be driven by the same motor.

[0086] The cross section shown is of one position of the rotating mechanical element 902. A rotating mechanical element 902 is illustrated with four protrusions 904 that locally indent the elastic layer 906, thereby exerting a localized pressure on the finger 104. The four protrusions 904 provide a continuous fixation of the finger 104.

[0087] The motor controls the rotation speed via a gearbox, typically in the order of 1 revolution per minute. Figure 9a shows the actuator device 114 before any rotation (i.e. the actuator system is in a first state), Figure 9b shows the actuator device 114 after rotation of 22.5 degrees (i.e. the actuator system is in a second state) and Figure 9c shows the actuator device 114 after rotation of 45 degrees (i.e. the actuator system is in a third state).

[0088] Both a cross-section of the actuator device 114 and a cross-section of the finger 104 are shown diagrammatically.

[0089] After placing the housing 102 over the finger 104 and then powering the electronic circuitry 202, for example by connecting the device to a patient monitor, rotation is initiated. The elastic layer 906 can have some roughness on the side of the finger 104 that helps immobilize the finger 104. Successive rotations alternately position pressure at different locations on the finger 104. Due to the protrusions 904, the finger 104 is not pressurized all around the finger, thereby minimizing blockage of blood flow in the finger. Such a rotating element 902 works in conjunction with a second rotating element that rotates in a counter-direction relative to the first rotating element, thereby minimizing the net rotational force on the finger 104.

[0090] The elastic layer 906 between the rotating element 902 and the finger 104 may be fixed to the housing 102 (and therefore not fixed onto the rotating element 902). In this case, friction exists between the rotating element 902 and the elastic layer 906. However, there is no friction between the elastic layer 906 and the finger 104 due to rotation (only friction exists due to pressure from the protrusions 904 to the finger 104).

[0091] Alternatively, the elastic layer 906 can be fixed to the rotating element 902 (i.e., not fixed to the housing 102). With this alternative, there is no friction between the rotating element 902 and the elastic layer 906. However, there is friction between the elastic layer 906 and the finger 104. In this case, the elastic layer 906 is preferably smooth to reduce rotational friction while maintaining sufficient fixation of the finger 104.

[0092] The number of protrusions 906 may also be less than or greater than the four shown.

[0093] 10 shows a cross section along the length of the device with two rotary actuator devices 114. The rotary elements 902 can rotate counter to each other. For reference, the LED 208, the photodetector 206, the housing 102, the cable 212 and the connector 214 are shown. There are bearings (not shown) between the rotary elements 902 and the housing 102. The motors and gearboxes 1002 are positioned on the PCB of the electronic circuit 202. One of the gearboxes 1002 provides counter rotation to one of the rotary elements 902. A motor can be used that generates a circular linear motion that is utilized to apply pressure.

[0094] An alternative actuator device 114 includes the use of an electric coil to apply a force to a magnet which then generates pressure. Shape memory material can also be used to generate pressure by changing its shape using an electric heater.

[0095] The layer of material directly in contact with the skin of the finger 104 can be replaced by a ring-shaped pouch containing an absorbent (i.e. moisture trapping element). This pouch is made of a face sheet with certain holes that act as fluid diodes. For the parts that are not pressed against the skin (i.e. there is no pressure between the skin and the pouch), holes are open, which allow the pouch to absorb sweat, thereby keeping the skin dry. This contributes to the comfort of the subject wearing the device. For the parts that are pressed against the skin, the holes are closed, preventing sweat from being pushed back onto the skin.

[0096] The above examples are used for a finger 104. However, these examples can be used for any body part 104 that can be grasped by applying an opposing force, such as the ear. However, there are body parts 104 for which this is highly impractical. For example, a reflective SpO2 sensor may be positioned on the forehead or torso. Pressure may be applied using a band around the head or torso, but this does not contribute to a comfortable feeling, and on the torso this results in a pressure that is dependent on the respiratory cycle.

[0097] For such body locations (eg, forehead and torso), alternative pressure devices are needed for localized and temporary pressure relief.

[0098] 11 shows a cross-section of a device with a reflective SpO2 sensor. For reliable SpO2 measurements, good contact is required between the LED unit 204 and photodetector 206 of the SpO2 sensor and the finger. Proper contact can be provided by pressure from the actuator element 106.

[0099] In FIG. 11, a cross section of the device is shown with a rigid housing 102 containing an SpO2 sensor (consisting of two LEDs of the LED unit 204 and one photodetector 206 in the sub-housing). At the top of the sub-housing is an actuator element 106 (for example an electroactive polymer or an inflatable balloon). In this case, pressure is applied only when a measurement is made by inflating the actuator element 106 (i.e. when the actuator system is in a first state). Release of pressure is obtained by deactivating the actuator element 106 (i.e. when the actuator system is in a second state). Measurements can only be performed when pressure is applied (usually for tens of seconds to minutes), followed by a pressure release period of tens of seconds to minutes. The area to which the housing 102 is attached by the adhesive layer 1102 is larger than the area of ​​the actuator element, thus minimizing the force per surface area exerted on the body part 104 under the adhesive layer 1102.

[0100] The example actuator system shown in Figure 11 includes only one actuator element 106, so that pressure relief is obtained by cyclically activating and deactivating that actuator element 106. However, the actuator system may have two or more actuator elements 106 that are activated simultaneously, or one (or more) is activated while the other is deactivated. The actuator system may also have two or more actuator devices with two or more sets of actuator elements 106, as described above.

[0101] For accurate SpO2 measurement, an appropriate pressure is needed between the body part 104 and the sensor (LED unit 204 and photodetector 206). This "optimal" pressure depends on many parameters and varies from person to person. Active pressure optimization can significantly improve the accuracy of SpO2 measurement. For example, for measurements on the torso, different postures (supine or lateral) require different pressures to suppress artifacts in the PPG (photoplethysmography) signal acquired by the photodetector 206. A 3D accelerometer can be used to determine the posture and adjust the pressure of the actuator element 106 accordingly.

[0102] The PPG signal features can also be used to optimize the pressure. If the pressure is too low, there are artifacts due to venous and skin tissue pulsation in addition to arterial pulsation. If the pressure is increased, the artifacts become smaller and the accuracy of the SpO2 measurement (from the PPG signal) increases. However, at higher pressures, the accuracy of the SpO2 measurement decreases as arterial pulsation and perfusion start to decrease again. The accelerometer measurements and / or the PPG signal features can be used as input parameters for an algorithm that derives the optimal pressure and generates a feedback signal to adjust the pressure.

[0103] A feedback loop is also created that controls the applied pressure so that the amplitude of the cardiac component in the PPG signal is maximized, which may result in uncomfortably high pressures, so the feedback loop has a maximum pressure limit that should not be exceeded to ensure comfort.

[0104] Furthermore, when the feedback loop identifies the external pressure at which the cardiac component in the PPG signal has the maximum amplitude, this external pressure is indicative of the mean arterial pressure in the body part 104. Thus, the feedback loop is able to simultaneously optimize the contact pressure and provide an estimate of the mean arterial pressure.

[0105] An estimate of venous oxygen saturation can also be obtained. For example, when changing the set of actuator elements 106 to which the SpO2 sensor is fixed, an estimate of venous oxygen saturation is obtained. During this fixing process, at a certain point, both sets of actuator elements 106 are activated. At this point, the externally applied pressure is full circumference and maximum, which reduces the venous return if the sensor fixing is performed proximal to the LED and photodiode, and thus leads to a decrease in the baseline of the PPG signal. The ratio between the relative decrease in the baseline of the red and infrared PPG signals can provide an estimate of venous oxygen saturation.

[0106] Furthermore, when one set of actuator elements 106 is deactivated again, this leads to a subsequent increase in venous return, resulting in an increase in the baseline of the PPG signal. The ratio between the relative increases in the baseline of the red and infrared PPG signals can provide a second estimate of venous oxygen saturation. Both estimates can be combined into a single estimate of venous oxygen saturation, or either one of the two estimates can be used to provide an estimate of venous oxygen saturation. Both sets of actuator elements 106 need to be activated long enough to achieve a sufficient decrease in the baseline of the PPG signal. Based on the decrease in the baseline measured in the PPG signal, the duration of the simultaneous activation of both sets of actuator elements 106 can be adapted.

[0107] The set of actuator elements 106 is also used to induce low amplitude fluctuations of the pressure of the fixation of the SpO2 sensor with a known frequency. The mean pressure and pressure fluctuations must be small enough to only induce fluctuations in the venous blood volume and not affect the arterial system. By extracting the fluctuations of the red and infrared PPG signals occurring at this known frequency, it is possible to estimate the venous oxygen saturation, similar to how the arterial oxygen saturation is estimated. The contact pressure fluctuations to obtain an estimate of the venous oxygen saturation are intermittently induced, for example, after the moment when the fixation position is changed.

[0108] The controller 202 is configured to perform processing of the PPG signal, the 3D accelerometer signal, etc., as described in the examples above. Alternatively, a separate processor may be used to perform processing as described in the examples above. This processor is connected (wired or wirelessly) to the controller 202, for example to provide instructions to the controller 202 regarding pressure values, switching times, etc. The controller 202 and / or the processor may also be connected to a display for displaying any of the information described above.

[0109] The above examples are described using an SpO2 sensor. However, the device may be designed with any other sensor that requires fixation to the body part 104. For example, some heart rate sensors require at least some fixation to the body part 104 to measure heart rate. Measuring blood pressure also typically requires pressure to be applied to a body part. Alternatively, the sensor may be a sensor for measuring the amount of carboxyhemoglobin and / or methemoglobin in addition to or instead of measuring oxyhemoglobin (i.e., hemoglobin with bound oxygen).

[0110] The time between switching actuator elements 106 (or sets of actuator elements 106) depends on the subject, the body part 104, the amount of pressure applied, the number of actuator elements 106 activated, etc. In general, the time between switching should not be less than 1 second and not longer than 20 minutes. In particular, the time between switching between the first and second states should ensure that the sensor can properly take measurements and that the subject does not experience unnecessary levels of discomfort.

[0111] The above examples have only two (or three) states for the actuator system. The actuator system has at least two states for releasing pressure. However, the actuator system can have any other number of states (greater than two) for releasing pressure even more locally (e.g., along the length of the housing 102).

[0112] The actuator system may have an annular band, provided that the blood flow is less restricted. If the blood flow is restricted by encircling the circumference of a body part, the blood flow will still be restricted even if the fixation is intermittently changed to another position. For example, a circular elastic band encircling a finger will restrict the blood flow. If two such bands in different positions are used alternately, the blood flow will still be restricted. Therefore, the housing is preferably fixed to the finger or other body position with an actuator system that applies pressure only to a part of the circumference of the finger or other body position, as described above.

[0113] Preferably, the electrical connection port used by the device is the same or similar to the port used by the current sensor (e.g., a 4-pin connection port). Thus, the present invention can be used with existing patient monitors. The sensor can then operate with the same functionality provided by the current port of the patient monitor to provide alternating fixation using two pins. The internal software of the patient monitor can be updated to allow the use of new devices while remaining compatible with existing sensor types.

[0114] As discussed above, the embodiments utilize a controller 202. The controller 202 can be implemented in many ways using software and / or hardware to perform the various functions required. A processor is one example of a controller using one or more microprocessors that are programmed using software (e.g., microcode) to perform the required functions. However, the controller 202 can be implemented with or without a processor, and may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions.

[0115] Examples of controller components used in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).

[0116] In various implementations, the processor or controller 202 is associated with one or more storage media, e.g., volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that, when executed on the one or more processors and / or controllers, perform the required functions. The various storage media may be mounted within the processor or controller 202 or may be transportable such that one or more programs stored on the media can be read into the processor or controller.

[0117] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, nor does it exclude a plurality of elements or steps even if the plurality is not stated.

[0118] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0119] When the term "suitable for" appears in the claims or specification, it is intended to be equivalent to the term "configured to."

[0120] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. 1. An apparatus for measuring a physical parameter of a subject, the apparatus comprising: a sensor for measuring said body parameter; a housing element for positioning the sensor on a body part of the subject; an actuator system within said housing element for applying pressure to said body part, said actuator system being capable of being in two states: a first state based on the actuator system applying a first pressure to a first region of the body part; and a second state based on the actuator system applying a second pressure to a second region of the body part different from the first region. The actuator system, a controller configured to apply the first and second states at different times such that an applied pressure is alternately positioned at the first region and the second region. An apparatus having the above configuration.

2. the actuator system having at least two actuator elements, each of the actuator elements configured to change volume or shape when the actuator element is stimulated; The apparatus of claim 1 , wherein the controller is further configured to stimulate the actuator elements to define the states of the actuator system.

3. the actuator element being based on an electroactive polymer configured to expand in volume when a voltage is applied; The apparatus of claim 2 , wherein the controller is further configured to apply a voltage to the electroactive polymer.

4. The device of claim 2 , wherein the actuator element is an expandable element configured to expand when the actuator element expands.

5. further comprising a pump for inflating the inflatable element; The apparatus of claim 4 , wherein the controller is further configured to operate the pump.

6. 6. The apparatus of claim 1, wherein the controller is further configured to vary the pressure applied to the body part of the subject by the actuator system.

7. and further comprising an accelerometer for determining a posture of the subject; The apparatus of claim 6 , wherein the controller is further configured to vary the pressure applied by the actuator system to the body part of the subject based on the posture of the subject.

8. the sensor is a pulse oximeter having an LED unit and a photodetector; 8. Apparatus according to any one of the preceding claims, wherein the optical detector is arranged to obtain a signal related to the saturation of oxygen in the blood.

9. 9. The apparatus of claim 8, wherein the LED unit is disposed at a tip of a first actuator element and the photodetector is disposed at a tip of a second actuator element.

10. the controller is further configured to control the actuator system to apply a predetermined pressure to the body part; The apparatus of claim 8 , wherein applying a predetermined pressure to the body part reduces venous contribution to the signal acquired by the optical detector.

11. and further comprising an adhesive layer at an interface between the housing element and the body part of the subject; 11. The apparatus of claim 1, wherein the actuator system is configured to apply pressure between the sensor and the body part.

12. The actuator system comprises: A rotating element comprising two or more lobes; and an elastic layer between the rotating element and the body part of the subject 2. The apparatus of claim 1, wherein the controller is configured to rotate the rotating element when changing states.

13. 12. The device of claim 1, further comprising a friction enhancing layer at an interface between the device and the body part of the subject.

14. 14. A device according to any preceding claim, further comprising a moisture capture element at an interface between the device and the body part of the subject for reducing moisture accumulation at the interface.

15. 1. A method for measuring a physical parameter of a subject, the method comprising: applying a first pressure to a first region of a body part with an actuator system, the actuator system being within a housing element, the housing element being secured to the body part; applying a second pressure to a second region of the body part at a different time than the first pressure is applied to the first region of the body part using the actuator system such that the applied pressure is alternately positioned on the first region and a second region of the body part different from the first region; and measuring said body parameter with a sensor positioned on said body part by said housing element. The method comprising:

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