NL2023481B1

NL2023481B1 - Blood pressure instrument

Info

Publication number: NL2023481B1
Application number: NL2023481A
Authority: NL
Inventors: Lakka Sami
Original assignee: Vivae Ip B V
Priority date: 2019-07-11
Filing date: 2019-07-11
Publication date: 2021-02-03
Also published as: WO2021006740A1

Abstract

The present disclosure concerns a blood pressure measurement cuff formed on a carrier comprising a cavity for receiving a body extremity. The body extremity is received between a contact area of a slider element and an inner contact bounding the cavity opposite the slider element. The slider element is reversibly movable relative to the carrier from an initial position away from the inner contact area toward a contactingposition for contacting the received the body extremity. The slider element is coupled to an actuating mechanism mounted on the carrier, to, when triggered, impose a contact force at a first level to the body extremity by the contact area of the slider element corresponding to a first pressure, higher than a systolic pressure of an artery in the body extremity.

Description

P124061NL00 Title: BLOOD PRESSURE INSTRUMENT

TECHNICAL FIELD AND BACKGROUND The present disclosure relates to blood pressure measurement devices and cuffs for use in a blood pressure measurement method or device. Blood pressure may be defined as the pressure of blood on the walls of blood vessels of animals and humans. Blood pressure is one of the vital signs. Accordingly, there exists an ongoing need for devices and/or methods to determine blood pressure in an accurate and non-invasive way. For humans two non-invasive invasive blood pressure measurement methods can be discerned: auscultatory and oscillometric. In the auscultatory method, sounds relating to arterial blood flow, also known as Korotkoff sounds, are monitored. Auscultatory blood pressure measurements typically require a trained operator to monitor and/or assess the sounds. The oscillometric method monitors small fluctuations in the pressure level of the cuff, due to arterial motion. Commercial automated blood pressure instruments (e.g. Omron) relying on the oscillometric method typically comprise an inflatable cuff and device, e.g. pump, which, upon initiating the measurement, automatically inflates to about 180 mm Hg. Connected to the cuff is a pressure sensor, e.g. manometer, which is used to monitor the pressure in the cuff and the amplitude of small pressure fluctuations due to movements in a subject’s artery as the pressure in the cuff is gradually reduced. The maximum amplitude of these fluctuations may be interpreted as a mean arterial pressure (MAP) and may be empirically correlated to the systolic and diastolic pressure using heuristically derived correction factors. There is wide uncertainty in the factors and as such, there is also a wide uncertainty in the derived estimates of the subject’s systolic and diastolic blood pressure values. Since the inflatable cuff filters out low-frequency sounds, direct measurement of Korotkoff sounds, e.g. at the location of the cuff is hampered. The use of an inflatable cuff is further disadvantageous for a wearer. Already in view of the dimension of the cuff, but also in view of an associated pump and/or further in view of noise associated to inflating and deflating of the cuff. These disadvantages become particularly pronounced in cases in which a wearer is subjected to prolonged measurements and/or subjected to a series of measurements over a prolonged period of time. The present disclosure aims to mitigate one or more of the above or further disadvantages by providing a blood pressure measurement cuff and/or instrument which, by the features as disclosed herein, may benefit from one or more of an improved comfort, e.g. fit, to the wearer, a smaller form-factor, while providing accurate determination of blood pressure values.

SUMMARY Aspects of the present disclosure relate to a blood pressure measurement cuff, e.g. an instrument for measuring blood pressure and particularly arterial blood pressure, 1.e. a sphygmomanometer, the device comprising a carrier having a cavity for receiving a body extremity between a contact area of a slider element and an inner contact area bounding the cavity opposite the slider element. The slider element is reversibly movable relative to the carrier from an initial position away from the inner contact area in a direction towards a contacting position for contacting the received the body extremity, to start a blood pressure measurement. The slider element is coupled to an actuating mechanism. The actuating mechanism is preferably mounted on the carrier. When triggered, the actuating mechanism may impose a contact force by the contact area of the slider element to the body extremity. In an occlusion stage, the force is provided at a first level corresponding to a first pressure, higher than a systolic pressure of an artery in the body extremity, to occlude by the contact area of the slider element the artery for an occlusion period. The blood pressure measurement cuff is further provided with a sensing means for measuring a response signal. The response signal includes a signal pertaining to the contact force imposed by the contact area of the slider element to the body extremity. In an embodiment, the sensing means is further arranged for measuring a response signal formed by a blood pressure variation signal resulting from a blood flow in the artery. Preferably, e.g. in a preferred operating mode, the response signal ofthe sensing means, during a measurement period, includes time traces of the contact force imposed by the contact area. In another or further preferred embodiment, the response signal further includes time traces of the blood pressure variation signal over a measurement period. The measurement period, i.e. time traces, preferably include at least a portion of the inclusion period. After the occlusion period, during the measurement period, the imposed force is gradually reduced from the first level to a second level, lower than the first, over a trajectory including the systolic and a diastolic pressure of the artery.

BRIEF DESCRIPTION OF DRAWINGS These and other features, aspects, and advantages of the apparatus, systems and methods of the present diselosurs will become better understond Hom the nllowing desoniption, appended claims, and aceompanving drawing wherein: FIG 1 shows recorded signals for a comparative blood pressure measurement using an inflatable arm cuff; FIG 2A schematically depicts a cross-section side-view of an embodiment of a blood pressure measurement cuff;

FIG 2B schematically depicts a cross-section side-view of a further embodiment of a blood pressure measurement cuff; FIG 3 schematically depicts partial cross-section side-views of embodiments of blood pressure measurement cuffs; FIG 4A schematically depicts a cross-section side-view of a further embodiment of a blood pressure measurement cuff; FIG 4B schematically depicts a cross-section front-view of a further embodiment of a blood pressure measurement cuff; FIG 5 schematically depicts a cross-section front-view of yet a further embodiment of a blood pressure measurement cuff; FIG 6 provides a perspective view drawing detailing the interior of an exemplary embodiment of a blood pressure measurement cuff in a ring format; and FIG 7 depicts a cross-section detail side-view drawing of a further exemplary embodiment of a blood pressure measurement cuff .

DETAILED DESCRIPTION Terminology used for describing particular embodiments is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and/or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and/or "comprising" specify the presence of stated features but do not preclude the presence or addition of one or more other features. It will be further understood that when a particular step of a method is referred to as subsequent to another step, it can directly follow said other step or one or more intermediate steps may be carried out before carrying out the particular step, unless specified otherwise. Likewise it will be understood that when a connection between structures or components is described, this connection may be established directly or through intermediate structures or components unless specified otherwise.

5 As used herein, the blood pressure may be understood as the pressure that circulating blood exerts the walls of blood vessels. Blood pressure is usually expressed in terms of the systolic pressure (As) and diastolic pressure (Ap). The systolic pressure is defined as the maximum pressure in an artery during a heartbeat. The diastolic pressure is defined as the minimum pressure in an artery during a heartbeat. Both values may be of importance in assessing a subject’s vital parameters, e.g. in determining an acute and/or long-term condition, e.g. risk to a certain long- term adverse effects. Some methods, incapable of directly determining the systolic and/or diastolic blood pressure may report a mean arterial pressure (Am) during a heart beat. It will be appreciated that this differs form a mean systemic pressure measured after cessation of the heart beat.

As used herein, the term body extremity refers to the anatomy of humans and animals and as such includes all body parts from which a blood pressure measurement can be obtained using a device as disclosed herein.

Included in particular are limbs, e.g. legs and arms, including an upper arm, forearm, and wrist, but also digits.

At the moment, two clinically validated, non-invasive blood pressure measurement methods are available. As introduced above these can be separated into auscultatory and oscillometric methods. In a typical auscultatory measurement, an inflatable cuff around a subjects arm, e.g. upper arm, is pressurized (around 180 mm Hg) to occlude a blood vessel in the arm. A stethoscope is placed on down-stream position along the vessel, e.g. in the antecubical fossa. Using the stethoscope sounds are monitored while slowly decreasing the pressure in the cuff. As the pressure drops to a level equal to that of the subject’s systolic blood pressure, an amount of blood will be able to flow past the cuff and the first Korotkoff sounds can be observed. As pressure is further reduced more blood is able to pass the cuff and flow through the artery. This may be followed with distinct changes in the Korotkoff sounds up to a pressure level corresponding to the subjects diastolic pressure, at which all sounds finally disappear completely. The Korotkoff method is considered as the most accurate type of blood pressure measurement. It is used as a golden standard against which blood pressure instruments are validated.

Oscillometric methods typically also comprise an inflatable cuff to occlude a blood vessel. Rather than relying on the detection of faint audible signals the oscillometric devices comprise a pressure sensor, e.g. a thin film pressure sensor, connected to the cuff. Alternatively this response signal may be measured by another sensor outside the cuff, e.g. a conventional stethoscope. This sensor is used to monitor the amplitude of small pressure fluctuations due to artery movements, e.g. by a returning blood flow, as the pressure exerted to the artery by the cuff is gradually reduced, e.g. to zero, over a period of time.

FIG 1 depicts signal exemplary time traces of auscultatory and oscillometric blood pressure signals as the exerted pressure by the cuff is gradually decreased from about 190 mmHg (at the start of the measurement period) to about 0 mm Hg at the end of the measurement period. The trace marked “A” depicts sound volume (in arbitrary units). The trace marked “C” depicts pressure variation amplitude (in arbitrary units). The trace marked “B” depicts the corresponding cuff pressure in mm Hg. All traces are aligned in time such that events in auscultatory and oscillatory traces may be correlated to a cuff pressure. Starting from the upper trace “A” one can see that at a pressure corresponding to about 157 mm Hg the so-called Korotkoff sounds suddenly start to appear as the first quantities of blood, at atop of a heart beat, are able to pass the cuff. It is believed that this pressure corresponds to the systolic blood pressure Aq in the artery. Upon further decreasing the pressure more blood passes the cuff and the volume of corresponding sounds initially increases to completely disappear at a pressure of about 92 mm Hg, which is believed to correspond to the diastolic blood pressure A4. Now with reference to trace “C” one can observe that the initial pressure variation signals start to appear at pressured well before the Korotkoff sounds appear, i.e. before reaching the systolic blood pressure A,. Further it can be observed that the signal continues to be detectable well after crossing the diastolic blood pressure A4. An exact determination the As and Aa based, solely on the pressure oscillometric signal is not feasible, already due to the non-ideal base-line and/or the gradually increasing magnitude of the pressure variation signal.

In the oscillometric method a mean arterial pressure point Am, (i.e. where pressure variation is maximum) can be detected reliably. The systolic and diastolic pressure points may be calculated using heuristic formulas from the mean arterial pressure point. These formulas are empirically derived using patient tests. One common algorithm is: As = Am + 0.55 * An (1) Aa= 0.85 * Am (2) Due to the heuristic nature of the algorithm, there is wide uncertainty in the factors. In literature one may find a broad ranges for the systolic pressure factor (0.45 — 0.57) and for the diastolic pressure factor (0.69 — 0.89). Accordingly, the oscillometric method of measuring blood pressure with an automated cuff yields comparatively accurate readings of a mean pressure but questionable estimates of systolic and diastolic pressures. Further, as explained in an article by C. F. Babbs in Biomed Eng Online. 2012; 11: 56 existing algorithms are sensitive to differences in pulse pressure and artery stiffness. As such, oscillometric method can never be as accurate as Korotkoff method where the systolic and diastolic points are accurately detected from the signal. The invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. In the drawings, the absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments may be described with reference to schematic and/or cross- section illustrations of possibly idealized embodiments and intermediate structures of the invention. In the description and drawings, like numbers refer to like elements throughout. Relative terms as well as derivatives thereof should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the system be constructed or operated in a particular orientation unless stated otherwise.

FIG 2A schematically depicts a cross-section side-view of an embodiment of a blood pressure measurement cuff 1. The device is formed on a carrier 2 defining a cavity 3. The cavity is dimensioned, e.g. has a dimension, suitable for comfortably receiving a body extremity 4, e.g. a lower arm, or a finger, between a contact area 5 of a slider element 6 and an inner contact area bounding the cavity 7opposite the slider element across the cavity. The slider element is reversibly movable relative to the carrier from an initial position away from the inner contact area bounding the cavity opposite the slider element to a contacting position closer towards a contacting position closer to the inner contact area. The slider element is coupled to an actuating mechanism 8 that is preferably connected, e.g. mounted on the carrier. In some embodiments, e.g. as shown, a portion of the slider, e.g. a rod or piston-shaped part protrudes through an opening 2a in the carrier 2. In such arrangement, e.g. as shown, part of the slider element 6 with the contact area 5 may be moved, e.g. slid, with respect to the cavity in inward and/or outward directions by an actuation element positioned outside the carrier 2, e.g. affixed to an outward surface of the carrier.

By providing a slider element that is reversibly movable, a body extremity in the cavity may be contacted by the contact area of the slide element and an opposed contact area of the carrier, i.e. an inner contact area bounding the cavity.

Upon contacting the body extremity 4 a blood pressure measurement may be started.

When the actuating mechanism 8 is triggered a contact force F may be imposed to the body extremity by the contact area of the slider element.

Since the area of the slider element is known the applied contact force may be correlated to a contact pressure.

It will be appreciated that the slider element at a location of the contact area and/or the inner contact area of the carrier bounding the cavity 7 are preferably shaped with a curvature similar to a curvature of the body extremity to be received.

By providing the device with contact areas having a similar curvature as the body extremity to be received the contact area between device and body extremity during a blood pressure measurement may be less dependent, preferably independent, of the applied contact force.

The contact force is provided at a first level F1 that corresponds to a first pressure, that is preferably al least higher than a systolic pressure of an artery 9 in the body extremity 4. By providing a force, corresponding to pressure higher than a systolic pressure of the artery in the body extremity 4, the artery may be occluded, i.e. reducing, preferably stopping, blood flowing past the occlusion.

In other words the carrier and actuating mechanism 8 may cooperatively be used to cause a constriction in an artery, e.g. similar to a inflatable cuff in a commercial blood pressure measurement instrument.

By reducing the contact force the pressure on the extremity and/or artery may be reduced allowing blood to resume flowing.

It will be appreciated that the applied contact force “F” preferably does not exceed levels at which the resulting contact pressure would results in severe user discomfort, e.g. pain and or damage to the body part. Typically, for adult human subjects, the maximum applied contact force corresponds to a contact pressure in a range around 160 to 240 mm Hg, e.g. 180, 200, or 220 mm Hg. It will be appreciated that the maximum applied contact force may be suitably adjusted, depending on the age and/or nature of the subject, and/or according to the type of body extremity the instrument is to be used on.

In a preferred embodiment, e.g. as shown in FIGs 2A-B, the blood pressure measurement cuff is further provided with a sensing means for measuring a response signal. The sensing means may include a force sensor 10 that outputs at least a signal related to the contact force imposed by the contact area of the slider element to the body extremity. Preferably, the response signal also includes a blood pressure variation signal resulting from a blood flow in the artery, e.g. a blood pressure variation signal.

Alternatively this response signal may be measured by another sensor outside the cuff, e.g. a conventional stethoscope. The blood pressure variation results from a resuming blood flow in the artery upon a gradual decrease in contact pressure after an occlusion period, e.g. upon a reduction of the imposed force F (and corresponding first contact pressure) from the first level F1 to a second level F2, lower than the first over a trajectory including the systolic and a diastolic pressure of the artery. Inventors find that the exact location and/or type of force sensor may be varied. In some embodiments, the force sensor may be arranged to measure a position and/or a displacement of the sliding element and/or of the actuating mechanism 8. As such the sensing means may be provided at a positon on or near, e.g. adjacent, to the actuating mechanism and/or the slider element 6, e.g. as shown in FIG 2A. In other or further embodiments, the force sensor 10 may be provided at a position along the cavity, e.g. as shown in FIG 2B. It will be appreciated that the sensing means may include a plurality of sensors and/or sensors operating on fundamentally differing principles as will explained in more detail herein below.

In a preferred embodiment the carrier is non-inflatable.

In other words, preferably the cuff does not comprise an inflatable carrier.

By not including an inflatable carrier, e.g. an inflatable blather, noises relating to the inflating and/or deflating of the blather and/or noise relating to inflation/deflation mechanisms may be avoided and a measurement may be performed with a comparatively lower base level of sounds.

In another or further preferred embodiment, the carrier is a rigid carrier, 1.e. a carrier with a stiffness sufficient to retain its general shape during normal operation of the device.

It will be appreciated that the device and/or carrier may be provided with means to adjust the size and/or shape of the cavity to match a dimension of the body extremity.

FIG 3 schematically depicts partial cross-section side-views of embodiments of blood pressure measurement cuffs.

In order to clarify the relation between the actuation only part of the carrier 2, part of slider element 6 and part of the actuating mechanism 8 are depicted.

Note that (although not depicted) the actuating mechanism 8 is connected to the carrier and that the slider element 6 is provided with contact area 5 for contacting a body extremity 4. In some embodiments, e.g. as shown in FIG 3A and 3B, the blood pressure measurement cuff comprises a first spring 11. The first spring 11, when exposed to a force from the actuating mechanism 8, provides a bias force acting on the slider element and/or the actuating mechanism in a direction opposite the actuation force and, in use, opposite the contact force.

By providing a bias force acting onto the slider element and/or the actuating mechanism in a direction opposite the contact force, the actuating mechanism 8 may, e.g. in the absence of the trigger, be restored the towards an initial state, preferably to an initial (untriggered) state.

Alternatively or additionally, the first spring 11, may upon absence of the trigger, e.g. upon release of the contact force, move the sliding element away from the inner contact area bounding the cavity 7, e.g. out of contact of a received body extremity 4. In a preferred embodiment, the first spring 11 is a compression spring, preferably provided between the actuating mechanism 8 and the carrier. Preferably, the actuation range of the spring,

1.e. displacement length, is long enough to return the actuator to an initial state. The range, i.e. displacement length may vary with an indented application, e.g. type of body extremity 4. Typically, the spring 11 has a displacement length, e.g. a compression length in case of a compression spring, in a range between 1 and 10 mm. In some embodiments, e.g.

intended for use on a finger an actuation range between 1 and 5 mm may be sufficient. As will be explained below with reference to FIG 3B and 3C, the displacement length may further determine a range over which the device can accommodate, adapt a dimension of the cavity, to receive differently dimensioned body extremities 4. The displacement length may further determine to what extent the device can compensate dimensional changes of a given body extremity, e.g. a finger swelling or contracting under influence of temperature changes. Long displacement ranges increase overall dimension of the device making the device more bulky and/or reducing visual appeal and/or comfort for a user, e.g. a wearer.

Alternatively, or in addition, the spring 11 can be used to measure the force, i.e. the contact force, that is experienced by a body extremity, e.g. finger or arm. When the actuation distance of the spring, e.g. spring length, is measured, the contact force can be derived in an effective and reliable way using Hook’s law (F = k-Ax, where k is the known spring constant and Ax is the measured actuation distance, i.e. length difference). The spring length can be measured in several ways, including but not limited to: with a magnetic angle sensor, with a linear variable differential transformer (LVDT), with an inductive sensor, with a capacitive sensor, and with a strain gauge. Reference is made to FIG 3B schematically depicting a blood pressure measurement cuff 1 in which the sensing means 10 includes a sensing means 10a to measure the contact force by measuring a deformation of the first spring. In some embodiments, e.g. as shown in FIG 3C and 3D the blood pressure measurement cuff is further provided with a second spring 12 in addition to the first. FIG 3C depicts the actuating mechanism 8 in an initial state, e.g. an untriggered state. Accordingly, the slider element 6 and the first and second springs are in an initial state as well. FIG 3D depicts the actuating mechanism in a triggered state 8’, represented by an increased dimension. Accordingly, the slider element and first and second springs are depicted in a displaced position 6’, 12’ and/or in compressed state 11°. The second spring 12 acts in a direction against the first spring. The second spring has a spring constant k2 which is larger than the spring constant k1 of the first spring. In a preferred embodiment, the second spring is a compression spring. In other or further embodiments, e.g. as shown in FIG 3C-D, the second spring 12 is provided between the actuating mechanism 8 and the slider element 6. By placing the second spring 12 between the actuating mechanisms and the slider, forces from the actuator may be passed on to the slider and, in use, consequently onto the body extremity 4. Preferably, the stiffness of the first spring 11 (acting against the second spring and against the actuating force) is much smaller than the stiffness of the second spring such that k1 is practically negligible compared to k2. By selecting the stiffness of the second spring to be much larger than the stiffness of the first spring, the contribution of bias force to the contact force, in use, may be negligible, i.e. preferably smaller than 5%. Thusly one of the springs may be used to derive the applied contact force whereas the other may provide a desired bias force. Accordingly, k1 is preferably maximum

0.05 times k2, preferably up to 0.01 times k2. Further, the stiffness of the first spring is less than the stiffness of the body extremity 4 by a factor of at least 5 times, preferably more, e.g. 10 times or 20 times. By providing the devices with first and second springs as specified, a force from the actuating mechanism 8 acting onto a body extremity 4 via the slider element may result in a deformation of the first spring before the artery in the body extremity is occluded. Accordingly, spring 12, e.g. an actuation distance of spring 12, can be used to measure the force, i.e. the contact force, that is experienced by a body extremity, e.g. finger.

During operation of a device provided with first and second springs as described above the following sequence of events/steps may typically be discerned. In a first step a body extremity is received in the cavity between the contact area of the slider element and the inner contact area bounding the cavity . At this point there need not yet necessarily be contact between the body extremity 4 and the contact areas. Upon triggering the actuating mechanism 8 a force is provided onto the slider element 6 (and both springs) which results in a translation (sliding) of the slider element towards the body extremity 4. Upon contacting the body extremity 4 between the opposing contact areas further translation, e.g. sliding, of the slider element 6 is opposed by a force from the body extremity 4 resisting compression. Continued application of force from the actuating mechanism 8 results in a deformation of the spring with lowest stiffness, e.g. the first spring. At this stage the pressure asserted to the body extremity remains below the force required to occlude the artery, e.g. below the systolic pressure. Since the second spring has a much higher stiffness, deformation of the second spring is, at this stage, comparatively small, preferably negligible. Upon reaching a maximum deformation of the first spring, e.g. upon complete compression of a compression spring, the second spring starts to deform. The stiffness of the second spring is much larger than the stiffness of the first spring. During deformation of the second spring a comparatively larger force is passed onto the body extremity and as a result the artery therein is compressed along with the deformation of the second spring. The contact forces may be determined by measuring an actuation distance of the second spring. Since the contact area is known the force may be translated to a contact pressure.

Upon reaching a pre set maximum contact force, corresponding to a given contact pressure at which the artery is occluded actuation of the actuating mechanism is stopped.

As explained above the response signal of the sensing means includes a contact force imposed by the contact area of the slider element to the body extremity.

In some preferred embodiments, the sensing means 10 may include a means to measure a sliding distance of the slider element 6. Inventors find that translation of the sliding element 6 may correlate to an imposed contact force.

By measuring a sliding distance of the slider element 6 the applied contact force and correspondingly the applied contact pressure may be followed.

In other or further preferred embodiments, e.g. as explained in relation to FIGs 3A-D the sensing means 10 includes a means 10a arranged to measure an actuation distance (e.g. compression distance) of the first and/or second spring.

Accordingly, in a preferred embodiment, the sensing means 10 includes a sensor 10a arranged to measure an actuation distance of the first spring.

In another or further preferred embodiment, the sensing means includes a sensor arranged to measure an actuation distance of the second spring.

As explained above the response signal of the sensing means further includes a blood pressure variation signal resulting from a blood flow in the artery.

Accordingly, in other or further preferred embodiments, the sensing means 10 may include a plurality of sensors in which a first part of the plurality is arranged to obtain a contact force imposed by the contact area of the slider element to the body extremity and wherein a second part of the plurality is arranged to obtain a blood pressure variation signal resulting from a blood flow in the artery.

Sensors suitable to obtain a blood pressure variation signal include pressure sensors such as thin film pressure sensors for measuring pressure variations in the artery.

Said pressure sensor, e.g. pressure variation sensor may be positioned onto the blood pressure measurement cuff suitable for measuring a blood pressure variation, for example, at a location on the carrier along the cavity. Preferably the pressure sensor is provided at a position opposite the contact area of the slider element such that, in use the artery is sandwiched between the sensor and the contact area. Optionally the pressure sensors may be provided onto the slider element 6, e.g. at a location along its contact area 5 or even on the actuating mechanism 8 or between the actuating mechanism and the slider element.

Alternatively, or in addition, the sensing means may include a sensor for detecting Korotkoff sounds, e.g. an acoustic sensor.

Advantageously, the blood pressure measurement cuff, may be actuated, e.g. occlude the artery and/or release pressure to the artery with a low base level of (acoustic) noise as will be explained in detail below. Accordingly, in some embodiments, the blood pressure measurement cuff 1 comprises a pressure sensor for measuring pressure variations in the artery and a sensor for detecting Korotkoff sounds. Reference is made to FIG 4A, depicting an embodiment provided with a acoustic sensor 13 and a pressure sensor 14. By providing the device with such types of sensors the blood pressure of a subject wearing the device may be determined with improved accuracy. For example, output from the acoustic sensor may be used to provide input for the (heuristic) model used by interpretation of the output of the pressure variation sensor. Further, input from the acoustic sensor may provide independently obtained systolic and diastolic pressure values in addition to values derived from the reading with the pressure sensor. Accordingly, in a preferred embodiment, the blood pressure measurement includes an acoustic sensor for measuring Korotkoff sounds; and a pressure sensor for measuring pressure variations in the artery. Optionally, the sensor for measuring pressure variations in the artery and/or the sensor for detecting Korotkoff sounds may be provided on one or more separate devices. When used in combination the blood pressure measurement cuff 1 and/or a cuff as described herein below the combination may be used with similar advantages. It will be appreciated that the pressure sensor may be the same as the sensing means arranged to measure a sliding distance and/or actuation distance of the sliding element and/or second spring respectively. In other words, in some embodiments, the sensing means arranged to measure a sliding distance and/or actuation distance of the sliding element may advantageously also be used to obtain a pressure variation signal from the artery pressure as, in use, during gradual reduction of the contact force, pressure variations in the artery due to a resuming blood flow may be observed by variations in a position, e.g. sliding distance, of the slider element 6 contacting the body extremity 4.

FIG 4A schematically depicts a cross-section side-view of a embodiment of a blood pressure measurement cuff 1. In the embodiment, an acoustic sensor 13 as well as a thin film pressure sensor 14 are provided at positions adjacent to the cavity at positons along the contact area 7 of the carrier 2 opposite the contact area 5 of the slider element 6. A portion of the slider element 6 outside the carrier connected to a actuating mechanism 8 comprising a thermal actuator element 8a. Accordingly, in another or further preferred embodiment, the blood pressure measurement cuff 1 is formed with an actuating mechanism comprising a thermal actuator element 8a fixed to the carrier and acting on the sliding element such that a volumetric or geometric change in the thermal actuator element 8a results in a translation of the sliding element 6. The element formed of or comprising a composition that may be thermally actuated to change shape and/or volume. A sensing means 10a, e.g. as shown, may be provided to measure an expansion/compression of the thermal actuator element 8a and accordingly report a translation e.g. sliding distance, of the slider element 6 along a direction and distance towards the cavity to, in use, occlude an artery in a received body extremity 4 (not shown). In some preferred embodiments, the device comprises a means to control a temperature of the thermal actuator to at least a temperature above a trigger temperature

(transition temperature) of the thermal actuator element 8a. Cooling may proceed naturally, e.g. by dissipation and/or convection to ambient. Alternatively, or in addition, the blood pressure measurement cuff 1 may comprise a means, e.g. a fan or Peltier cooler, to actively cool the thermal actuator element 8a. Below the trigger temperature the thermal actuator element 8a preferably does not undergo considerable changes in shape and/or volume, e.g. beyond normal volumetric changes due to thermal expansion. In some embodiments, the trigger temperature may be phase transition temperature. Preferably, the means to control the temperature is arranged to provide a temperature, i.e. bring the thermal actuator element 8a to a temperature above a temperature at which the phase transition of the thermal actuator is complete (>95%). Phase transitions may be understood to include transitions such as gas/liquid or solid/gas transitions. Phase transitions may further be understood to include transitions between crystal structures of materials. Accordingly, in some preferred embodiments, wherein the thermal actuator element 8a is formed of a composition comprising a shape memory material. Shape memory materials include materials known as shape memory polymer (SMP) and shape memory alloy (SMA). Advantages of SMP include ease of processing and easy of forming a desired shape. Advantages of SMA typically include a comparatively fast response and comparably higher attainable forces.

In a preferred embodiment, the thermal actuator element 8a is formed or comprises a composition comprising a shape memory alloy (SMA). Shape-memory alloys include alloys that can be deformed when cold but than return to a pre-deformed shape when heated above a phase transition temperature (trigger temperature). A broad number of differently shaped and dimensioned SMAs are commercially available. In a preferred embodiment, e.g. as shown in FIG 4B, the thermal actuator element 8a is a shape memory alloy wire 8b. FIG 4B schematically depicts a cross-section front-view of an embodiment of a blood pressure measurement cuff 1 with an actuating mechanism 8 comprising a SMA wire 8b. In a preferred embodiment, e.g. as shown, the SMA wire 1s connected to the carrier 2 at opposing ends 15,16. A portion, preferably a central portion, of the wire acts on the slider element 6 such that a contraction of the SMA wire, e.g. upon heating above a phase transition temperature, results in a siding movement, i.e. translation, of the slider element 6 with the contact area 5 in a direction towards the inner contact area bounding the cavity, i.e. an inner contact area of the carrier. A first spring 11 acting on the slider element 6 provides an opposing force such that upon removal of the trigger, e.g. upon cooling of the SMA wire the actuating mechanism 8 may be returned to an initial state. in other words, the spring 11 is preferably provided with a spring constant to allow actuation, e.g. contraction, of the spring upon receiving a force from the thermal actuator element 8a, e.g. a triggered SMA wire. At the same the spring constant is preferably sufficiently high to, upon removal of the tripper to the thermal actuator element 8a, e.g. upon cooling of the wire, overcome a hysteresis in the thermal actuator element 8a, e.g. provide an opposing force stronger than the force needed to return a contracted SMA wire to an initial extended length.

In a preferred embodiment, the thermal actuator element 8a is heated by a current running through the element, i.e. by Joule heating. inventors find that the temperature at the thermal actuator element 8a, e.g. a temperature along the SMA wire may correlate to the contact force. Accordingly, in a preferred embodiment, the sensing means 10 may be further arranged to measure a temperature at the actuating mechanism 8.

In one embodiment, the sensing means 10 may be arranged to measure an electrical resistance of the thermal actuator element, e.g. the SMA wire. In other words, the temperature thermal actuator element 8a may be followed by measuring the electrical resistance.

The thermal actuator element 8a may be formed of any SMA material and in any shape, e.g. diameter and/or length of the wire, suitable to provide a force sufficient to occlude an artery in the body extremity 4. A variety of alloys exhibit the shape-memory effect. Some common systems include the following non-limitative list: Cu-Al-Ni: 14-14.5 wt% Al and 3-4.5 wt% Ni Cu-Al-Ni-Hf Cu-Sn: approx. 15 at% Sn Cu-Zn: 38.5 to 41.5 wt.% Zn Cu-Zn-X (X = Si, Al, Sn) Mn-Cu 5/35 at% Cu Fe-Mn-S1 Co-Ni-Al Ni-Ti The ratio between the constituents can be adjusted to control the transformation temperatures and/or transition forces of the SMA.

Preferably the transition (trigger) temperature is well above a normal operation temperature of the blood pressure measurement cuff 1. e.g. at least above a body temperature, preferably at least above 60 °C.

Inventors found that shape memory alloys formed of an alloy comprising nickel and titanium may be particularly suitable. Accordingly, in a preferred embodiment, the shape memory alloy is formed of a composition comprising nickel and titanium wherein the composition comprises between 50 and 70 wt% of Ni, preferably 55 to 60 wt% of Ni and between 50 and 30 wt% of Ti, preferably 45 to 40 wt% of Ti (all weight percentages based on the total weight of constituents). Suitable SMAs may be commercially known under the names Nitinol or Flexinol. Said SMAs may have a trigger temperature in a range between 70 and 90°C. Further, said SMAs were found to provide a contraction force for 2mm diameter wire of about 20N;

and about 2N for a 0.2mm diameter wire . Based on these numbers the spring constant of the first spring may be calculated to preferably be in a range between range 100-1000 N/m based on an displacement length (actuation length) in a range from 1 to 10 mm and a bias force of about 0.5 times the contraction force.

In a preferred embodiment, e.g. as shown in FIG 5, the carrier 2 is provided with one or more support elements 20 on its outer surface. By providing one or more support elements a distance between the shape memory alloy wire 8b and the outer surface area of the carrier 17 may be maintained. As such, the support means reduce friction, e.g. sliding friction between wire and a stationary surface contacting the wire, e.g. the surface area of the carrier 17. Without wishing to be bound by theory, inventors believe that friction may be reduced by providing the support elements 20 since the support elements 20 reduce the combined contact area between the SMA wire and a stationary surface contacting the wire (compared to wire in direct contact with the surface along the outer perimeter of the carrier 17). Inventors find that the support elements, e.g. poles, decrease the contact area between the SMA wire and the outer surface of the carrier, e.g. ring body. Friction increases exponentially with increasing contact area, e.g. as a SMA wire wraps along a substantial portion of a ring. By using the one or more support elements (20), e.g. poles, that separate the actuator wire from the outer surface of the carrier, the contact area is kept within reasonable limits, and/or loss of actuation force due to friction may be minimized.

In other or further preferred embodiments, the blood pressure measurement cuff is a ring. In other words, in some embodiments, the device may be provided in the format of a ring, i.e. a ring in which the carrier and the cavity are dimensioned to fit a digit (finger and/or toe). Optionally, the carrier and the cavity are dimensioned to fit limb at position of wrist, arm, ankle or leg.

FIG 6 provides a perspective view drawing detailing the interior of an exemplary embodiment of a blood pressure measurement cuff 1 in a ring format.

In the embodiment, e.g. as shown, the carrier 2 is a rigid carrier shaped like a ring and defining a cavity 3 dimensioned to fit a human finger, e.g. middle finger or ring finger, between the inner contact area bounding the cavity 7 and the contact area 5 of a slider element 6. Further provided are a actuating mechanism 8 including a shape memory alloy wire 8b acting onto the slider element 6. The shape memory alloy wire 8b (shown overlaying the device) wraps around an outer surface of the carrier 2 and is fixed thereto at opposing ends 15,16. Also acting on the slider element 6 1s a first spring 11 provided between the outer surface of the carrier 2 and the shape memory alloy wire 8b.

Provided adjacent the cavity at a position opposite the contact area 5 is the pressure sensor 14 for measuring a response signal including a contact force imposed by the contact area of the slider element to the body extremity, and a blood pressure variation signal resulting from a blood flow in the artery.

Further provided in the exemplary embodiment are electronic components 21and a battery for powering the system.

FIG 7 depicts a cross-section detail side view drawing of a further exemplary embodiment of a blood pressure measurement cuff 1. In addition to the embodiment as shown in FIG 6, this embodiment is provided with a second spring 12. For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

Also alternative ways may be envisaged by those skilled in the art having the benefit of the present disclosure for achieving a similar function and result.

It will be appreciated that separate elements of the invention may be combined or split up into one or more alternative components.

The various elements of the embodiments as discussed and shown offer certain advantages, such as a device capable performing essential steps in a blood pressure measurement, including providing and determining a force needed to occlude an artery without undesired noise accompanied with conventional commercial inflatable cuffs. Of course, it is to be appreciated that any one of the above embodiments or processes may be combined with one or more other embodiments or processes to provide even further improvements in finding and matching designs and advantages. It is appreciated that this disclosure offers particular advantages to blood pressure measurement methods and devices, and in general can be applied for any application requiring the need to reversible apply and control a force. While embodiments were shown relating to a blood pressure measurement cuff comprising a shape memory alloy wire in combination with a sensing means for measuring a response signal including a contact force imposed by the contact area of the slider element to the body extremity, and a blood pressure variation signal resulting from a blood flow in the artery, also envisioned are embodiments wherein the sensing means need not be completely integrated with the blood pressure measurement cuff 1. For example, part of the sensing means, e.g. part for a blood pressure variation signal resulting from a blood flow in the artery may be provided separately, and/or may be provided by an operator..

In interpreting the appended claims, it should be understood that the word "comprising" does not exclude the presence of other elements or acts than those listed in a given claim; the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements; any reference signs in the claims do not limit their scope; several "means" may be represented by the same or different item(s) or implemented structure or function; any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise. Where one claim refers to another claim, this may indicate synergetic advantage achieved by the combination of their respective features.

But the mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot also be used to advantage.

The present embodiments may thus include all working combinations of the claims wherein each claim can in principle refer to any preceding claim unless clearly excluded by context.

Claims

Conclusions

A sphygmomanometer cuff (1) comprising a support (2) with a cavity (3) for receiving a body end (4) between a contact area (5) of a slider (6) and an inner contact area defining the cavity ( 7) opposite the slider, wherein the slider is reversibly movable relative to the wearer from an initial position away from the inner contact area to a contact position to make contact with the received body end, to initiate a blood pressure measurement, and the slider is engaged with an operating mechanism (8) mounted on the wearer, when activated, to apply a contact force (F) at a first level (F1) to the body end through the contact area of the slider corresponding to a first pressure, higher than a systolic pressure from an artery in the body end, to occlude the artery (9) during an occlusion period, and the blood pressure monitor cuff further is provided with a detection means (10) directed for measuring a response signal formed by: - the contact force exerted by the contact area of the sliding element on the body end.

The blood pressure monitor cuff according to claim 1, wherein the detection means is further arranged to measure a response signal formed by - a blood pressure variation due to flow of blood in the artery.

The blood pressure monitor cuff of claim 1 or 2, comprising a first spring (11) that provides a biasing force on the operating mechanism (8) in a direction opposite to the contact force.

The blood pressure monitor cuff of claim 3, wherein a second spring (12) is provided acting in a direction against the first spring, the second spring having a spring constant greater than the first.

The blood pressure monitor cuff according to any of the preceding claims, wherein the detection means (10) is arranged to measure a sliding distance of the sliding element (6).

The blood pressure monitor cuff of claim 5, wherein the sensing means is configured to measure an actuation distance of the second spring (12).

The blood pressure monitor cuff according to any of the preceding claims, wherein the detection means (10) comprises: - an acoustic sensor (13) for measuring Korotkoff sounds; and / or - a pressure sensor (14) for measuring pressure variations in the artery.

The blood pressure monitor cuff of any one of the preceding claims, wherein the operating mechanism comprises a thermal actuator element (8a) attached to the carrier and acting on the sliding element such that a volumetric change in the thermal actuator element (8a) results in a translation of the sliding element (6).

The blood pressure monitor cuff of claim 8, wherein the thermal actuator (8a) is formed from a composition comprising a shape memory alloy.

The blood pressure monitor cuff of claim 8 or 9, wherein the thermal actuator element (8a) is a shape memory alloy wire (8b).

The blood pressure monitor cuff of any of claims 8-10, configured to heat the thermal actuator element (8a) by passing an electrical current through the element.

The sphygmomanometer cuff according to any of claims 9-11, wherein the shape memory alloy is formed from nickel and titanium alloy, wherein the nickel content in the alloy is between 50 and 70% by weight, preferably between 55 and 60% by weight. . % and the titanium content in the alloy is between 50 and 30% by weight, preferably between 45 and 40% by weight, based on the total weight of the alloy.

The blood pressure monitor cuff of any of claims 9-12, wherein the support includes one or more support members (20) to maintain a distance between the shape memory alloy wire (8b) and an outer surface of the support (17).

The blood pressure monitor cuff of any preceding claim, wherein the cuff is formed as a ring for a human finger.