Blood vessel pressing cuff, blood pressure measuring apparatus including the blood vessel pressing cuff, and blood pressure measuring method using the blood pressure measuring apparatus

A blood vessel pressing cuff includes a strap surrounding a body part, a first actuator disposed on the strap and including a first shape memory alloy which changes to a first shape memorized in advance, at a temperature equal to or higher than a first temperature, and a second actuator disposed on the strap and including a second shape memory alloy which changes to a second shape memorized in advance, at a temperature equal to or higher than a second temperature that is different from the first temperature. If the first shape memory alloy changes to the first shape, pressure applied to the body part surrounded by the strap is increased. Even when the first shape memory alloy changes to the first shape, if the second shape memory alloy changes to the second shape, the pressure applied to the body part surrounded by the strap is reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Korean Patent Application No. 10-2009-0066389, filed on Jul. 21, 2009, and all the benefits accruing therefrom under 35 U.S.C. §119, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

Provided is a blood vessel pressing cuff for pressing a blood vessel in order to measure blood pressure, a blood pressure measuring apparatus including the blood vessel pressing cuff, and a blood pressure measuring method using the blood pressure measuring apparatus.

2. Description of the Related Art

As people's interest in health continuously increases, various blood pressure measuring apparatuses are being developed. Blood pressure measurement methods include a Korotkoff sound method, an oscillometric method, a tonometric method, and the like. In the Korotkoff sound method, which is a typical pressure measurement method, when pressure is sufficiently applied to a body part where arterial blood flows, to stop the flow of the arterial blood and then is released, pressure at a moment when an initial pulse is heard is measured as systolic pressure and pressure at a moment when no more pulse is heard is measured as diastolic pressure.

The oscillometric method and the tonometric method are used in digital blood pressure measuring apparatuses. Like the Korotkoff sounds method, in the oscillometric method, a sphygmus wave generated when pressure is sufficiently applied to a body part where arterial blood flows to stop the flow of the arterial blood and then is released at a uniform speed, or a sphygmus wave generated when pressure is applied to the body part to raise the pressure at a uniform speed, is sensed so as to measure systolic pressure or diastolic pressure. When compared to a moment at which the sphygmus wave has a maximum amplitude, pressure when the sphygmus wave is at a certain level of the maximum amplitude may be measured as the systolic pressure or the diastolic pressure.

Alternatively, pressure when amplitudes of the sphygmus wave greatly vary may be measured as the systolic pressure or the diastolic pressure. When pressure is applied and then is released at a uniform speed, the systolic pressure is measured before the sphygmus wave reaches the maximum amplitude and the diastolic pressure is measured after the sphygmus wave has reached the maximum amplitude. On the other hand, when applied pressure is raised at a uniform speed, the systolic pressure is measured after the sphygmus wave has reached the maximum amplitude and the diastolic pressure is measured before the sphygmus wave has reached the maximum amplitude. In the tonometric method, blood pressure may be continuously measured by using the amplitude and shape of a sphygmus wave generated when pressure that does not completely stop the flow of arterial blood is applied to a body part.

SUMMARY

Provided is a blood vessel pressing cuff using shape memory alloys, which is capable of being easily formed in a small size and delicately controlling application and release of pressure, a blood pressure measuring apparatus including the blood vessel pressing cuff, and a blood pressure measuring method using the blood pressure measuring apparatus.

Provided is a blood vessel pressing cuff including a strap surrounding one body part, a first actuator disposed on the strap and including a first shape memory alloy that changes to a first shape memorized in advance, at a temperature equal to or higher than a first temperature, and a second actuator disposed on the strap and including a second shape memory alloy that changes to a second shape memorized in advance, at a temperature equal to or higher than a second temperature that is different from the first temperature. If the first shape memory alloy changes to the first shape, pressure applied to the one body part surrounded by the strap is increased, and even when the first shape memory alloy changes to the first shape, if the second shape memory alloy changes to the second shape, the pressure applied to the one body part surrounded by the strap is reduced.

Provided is a blood pressure measuring apparatus including a blood vessel pressing cuff, a sensing unit sensing a sphygmus wave and a pressure of a blood vessel of a person when the blood vessel pressing cuff presses one body part of the person, and a processor calculating blood pressure of the person based on the sphygmus wave and the pressure of the blood vessel.

Provided is a blood pressure measuring method including surrounding one body part of a person with a strap of a blood pressure measuring apparatus, the blood pressure measuring apparatus including the strap, a first actuator including a first shape memory alloy, and a second actuator including a second shape memory alloy, applying pressure to the one body part surrounded by the strap, by changing a temperature of the first actuator to a temperature equal to or higher than a first temperature and thus changing the first shape memory alloy to a first shape memorized in advance, calculating blood pressure of the person based on a sphygmus wave and a pressure of a blood vessel of the person, which are sensed while the one body part is pressed, and releasing the pressure applied to the one body part surrounded by the strap, by changing a temperature of the second actuator to a temperature equal to or higher than a second temperature that is different from the first temperature and thus changing the second shape memory alloy to a second shape memorized in advance.

The first shape may be a shape of the first shape memory alloy, in which a length of the first actuator is reduced when the first shape memory alloy is changed to the first shape, and the second shape may be a shape of the second shape memory alloy, in which a length of the second actuator is increased when the second shape memory alloy is changed to the second shape.

The second shape memory alloy may return to a third shape memorized in advance, at a temperature equal to or lower than a third temperature that is between the first and second temperatures, and may have no shape memorized in advance at a temperature between the second and third temperature.

The third shape may be a shape of the second shape memory alloy, in which a length of the second actuator is reduced when the second shape memory alloy is changed to the second shape.

The first temperature may be higher than room temperature, and the second temperature may be higher than the first temperature.

The first shape may be a shape of the first shape memory alloy, in which the first actuator protrudes toward the one body part when the first shape memory alloy is changed in the first shape, and the second shape may be a shape of the second shape memory alloy, in which a length of the second actuator is increased when the second shape memory alloy is changed to the second shape.

The first shape memory alloy or the second shape memory alloy may be self-heated due to a supplied current.

The first actuator may include wires of the first shape memory alloy, which are extended in a length direction of the first actuator.

The second actuator may include wires of the second shape memory alloy, which are extended in a length direction of the second actuator.

The first actuator or the second actuator may further include heaters heating the first shape memory alloy or the second shape memory alloy.

The blood vessel pressing cuff may further include a length control unit disposed on the strap and controlling a length of the strap according to a size of the one body part surrounded by the strap.

The first actuator or the second actuator may further include an adiabatic unit including an adiabatic material that surrounds the first shape memory alloy or the second shape memory alloy, respectively.

DETAILED DESCRIPTION

Hereinafter, the invention will be described in detail with reference to the accompanying drawings.

FIG. 1is a cross-sectional view of an exemplary embodiment of a blood pressure measuring apparatus100according to the present invention.FIG. 2is a structural block diagram of the blood pressure measuring apparatus100illustrated inFIG. 1.

Referring toFIGS. 1 and 2, the blood pressure measuring apparatus100may be worn on a wrist1through which a radial artery5passes, so as to easily sense a sphygmus wave and a pressure of a blood vessel of a person. The blood pressure measuring apparatus100includes a blood vessel pressing cuff101pressing the radial artery5in the wrist1, e.g., a target part of the person, a sensing unit109sensing the sphygmus wave and the pressure of the radial artery5in the wrist1when the wrist1is pressed using the blood vessel pressing cuff101, and a processor110calculating blood pressure of the person based on the sphygmus wave and the pressure of the radial artery5, which are sensed by the sensing unit109.

The blood pressure measuring apparatus100may further include a memory112storing data and a program which are required when the processor110calculates the blood pressure, an input unit107inputting instructions such as a blood pressure measurement instruction, a display unit113visually showing a blood pressure measurement result, and a communication unit114transmitting the blood pressure measurement result to a receiver (not shown) m such as through a wired or wireless method. The input unit107, the processor110, the memory112, the display unit113, and the communication unit114are included in a measurement block105(FIG. 1).

The blood vessel pressing cuff101includes a strap102surrounding the wrist1, and a first actuator120, a second actuator180, and a length control unit190which are disposed on the strap102. The first actuator120is disposed at a distance and separated from the second actuator180along a longitudinal direction of the strap102. InFIG. 1, the first actuator120is disposed directly on a skin portion (e.g., an outermost surface) of the wrist1adjacent to the radial artery5, and the measurement block105is disposed on the first actuator120so as to overlap with the first actuator120. However, the measurement block105may not always overlap with the first actuator120in an alternative embodiment. Also, the sensing unit109may or may not overlap with the first actuator120. The strap102may be a single unitary indivisible member of the blood pressure measuring apparatus100.

The first actuator120includes a first shape memory alloy122that changes to a first shape memorized in advance, at a temperature equal to or higher than a first temperature that is higher than room temperature, and a first adiabatic unit127including an adiabatic material that completely surrounds the first shape memory alloy122.

Likewise, the second actuator180includes a second shape memory alloy182and a second adiabatic unit187including an adiabatic material that completely surrounds the second shape memory alloy182. The second shape memory alloy182changes to a second shape memorized in advance, at a temperature equal to or higher than a second temperature that is higher than the first temperature, and returns to a third shape memorized in advance, at a temperature equal to or lower than a third temperature that is between the first and second temperatures. The second shape memory alloy182returning to the third shape memorized in advance has no shape memorized in advance at a temperature between the second and third temperature.

A shape memory alloy, such as nitinol (“NiTi”) that is an alloy of nickel (Ni) and titanium (Ti), is an alloy that memorizes a shape and changes back to the memorized shape at a shape return temperature, after being deformed from the memorized shape, such as due to an external force. The shape return temperature of the shape memory alloy may be variously set by appropriately controlling a process for memorizing the shape of the alloy. The adiabatic material of the first and second adiabatic units127and187may be, for example, meta-aramid fiber or rubber.

FIG. 3is a plan view showing an exemplary embodiment of a first shape122(ii) previously memorized by the first shape memory alloy122illustrated inFIG. 1. The first shape memory alloy122is a single unitary indivisible member.

Referring toFIG. 3, the first shape memory alloy122may have a substantially wire shape and may longitudinally extend in a lengthwise direction of the first actuator120illustrated inFIG. 1, e.g., along a circumferential direction of the wrist1illustrated inFIG. 1. The first shape memory alloy122is installed in the first actuator120with an initial shape122(i) represented by a virtual (dotted) line inFIG. 3. However, the previously memorized first shape122(ii) of the first shape memory alloy122is a shrunken shape compared to the initial shape122(i). As shown inFIG. 3, the previously memorized first shape122(ii) has a smaller length than the initial shape122(i). Thus, if an internal temperature of the first actuator120is between room temperature and a first temperature, plastic deformation occurs in the first shape memory alloy122due to an external force. However, if heated to above the first temperature that is higher than room temperature, the first shape memory alloy122shrinks from the initial shape122(i) to the first shape122(ii), and the length of the first actuator120is also reduced from the initial shape122(i) to the previously memorized first shape122(ii).

FIG. 4is a plan view showing an exemplary embodiment of second and third shapes182(ii) and182(i) previously memorized by the second shape memory alloy182illustrated inFIG. 1. The second shape memory alloy182is a single unitary indivisible member.

Referring toFIG. 4, the second shape memory alloy182may also have a substantially wire shape and may longitudinally extend in a length direction of the second actuator180illustrated inFIG. 1, e.g., along a circumferential direction of the wrist1illustrated inFIG. 1. The second shape182(ii) of the second shape memory alloy182is an extended shape, and the third shape182(i) of the second shape memory alloy182is a shrunken shape compared to the second shape182(ii).

The second shape memory alloy182is initially installed in the second actuator180with the third (e.g., initial) shape182(i) represented by a virtual (dotted) line inFIG. 4. Thus, if an internal temperature of the second actuator180is room temperature, the second shape memory alloy182is maintained in the third shape182(i) until a third temperature is reached.

If the internal temperature of the second actuator180exceeds the third temperature, the second shape memory alloy182may not be maintained in the third shape182(i) any more, such that plastic deformation occurs in the second shape memory alloy182due to an external force.

If the internal temperature of the second actuator180is further increased from the third temperature to a second temperature, the second shape memory alloy182rapidly extends to the second shape182(ii). As such, the length of the second actuator180is increased. The second shape memory alloy182returns to the third shape182(i) memorized in advance from the second shape182(ii), at a temperature equal to or lower than the third temperature, and has no shape memorized in advance at a temperature between the second and third temperature.

Referring back toFIGS. 1 and 2, the first and second shape memory alloys122and182are self-heated due to supplied currents, and change to previously memorized shapes if the temperatures in the first and second actuators120and180are accordingly increased. The processor110may control the currents supplied to the first and second actuators120and180. As described above, the first and second shape memory alloys122and182are respectively surrounded by the first and second adiabatic units127and187. Thus, malfunctions of the first and second shape memory alloys122and182may be prevented despite an external temperature increase caused by, for example, strong direct rays of the sun.

FIG. 5is a graph showing an exemplary embodiment of correlations between temperature and displacements of the first and second shape memory alloys122and182illustrated inFIG. 1.FIG. 5will be described in conjunction withFIGS. 1,3and4.

Referring toFIG. 5, for example, a first temperature at which the first shape memory alloy122changes from initial shape122(i) to the first shape122(ii) may be about 45° C., a second temperature at which the second shape memory alloy182changes from the third shape182(i) to the second shape182(ii) may be about 55° C., and a third temperature at which the second shape memory alloy182returns to the third shape182(i) from the second shape182(ii) may be about 50° C.

In order to measure blood pressure of a person, the blood pressure measuring apparatus100is worn around the wrist1of the person. In more detail, the strap102completely surrounds the wrist1. The second shape memory alloy182is maintained in the third shape182(i) at room temperature. Then, the temperatures in the first and second actuators120and180are increased by applying currents to the first and second actuators120and180. If an internal temperature of the first actuator120reaches about 45° C., e.g., the first temperature, the length of the first actuator120is reduced due to the first shape memory alloy122that changes from the initial shape122(i) to the first shape122(ii), and thus the wrist1starts to be pressed by the blood pressure measuring apparatus100.

If an internal temperature of the second actuator180is increased and exceeds about 50° C., e.g., the third temperature, the second shape memory alloy182is not maintained in the third shape182(i) any more, and plastic deformation occurs in the second shape memory alloy182due to an external force. In this case, the amount of the plastic deformation of the second shape memory alloy182is proportional to the strength of the external force. Since the length of the first actuator120is continuously reduced between about 50° C., e.g., the third temperature, and about 55° C., e.g., the second temperature, a tensile force (as the “external force”) is applied to the second actuator180and thus the length of the second actuator180is increased. Accordingly, the pressure applied to the wrist1is smoothly increased in the temperature range from about 50° C. to about 55° C., where the length of the first actuator120is decreased at substantially a same time as the length of the second actuator180is increased. If a temperature equal to or higher than about 55° C., e.g., the second temperature, is reached, the second shape memory alloy182rapidly changes to the second shape182(ii) as shown by the relatively steep slope of the line inFIG. 5, and thus the length of the second actuator180is rapidly increased. As such, the pressure applied to the wrist1is rapidly reduced.

Since the pressure applied to the wrist1by the blood vessel pressing cuff101is gradually increased during a period after the temperatures in the first and second actuators120and180start to be increased and until about 55° C., e.g., the second temperature, is reached, this period is defined as a pressing period I (seeFIG. 6). Since the pressure applied to the wrist1by the blood vessel pressing cuff101is rapidly reduced during a period after the temperature about equal to or higher than the second temperature is reached, this period is defined as a pressure releasing period D (seeFIG. 6).

With reference to the illustrated embodiment, the blood pressure of the person is calculated based on the sphygmus wave and the pressure of the radial artery5of the person. After the blood pressure is calculated, if the temperatures are decreased to room temperature by blocking the currents supplied to the first and second actuators120and180, the second shape memory alloy182shrinks and returns to the (initial) third shape182(i). Due to a restoring force of the second shape memory alloy182that shrinks to the third shape182(i), the first shape memory alloy122returns to the initial shape122(i) that is the shape before shrinking to the first shape122(ii).

An exemplary embodiment of a method of calculating blood pressure by using an oscillometric method will now be described.

FIG. 6illustrates graphs for describing an exemplary embodiment of a method of measuring blood pressure by using an oscillometric method, and the blood pressure measuring apparatus100illustrated inFIG. 1.

Referring toFIG. 6, the sphygmus wave of a person during the pressing period I may be represented by, for example, a line WO. Pressure sensed by the sensing unit109illustrated inFIG. 1, at a time after a time when the line WO has a maximum amplitude Amax is determined as systolic pressure Psys of a person, and pressure sensed by the sensing unit109at a time before the time when the line WO has the maximum amplitude Amax is determined as diastolic pressure Pdia of the person. In alternative embodiments, the systolic pressure Psys and the diastolic pressure Pdia may be determined as pressures measured when the sphygmus wave has certain levels of amplitudes with reference to the maximum amplitude Amax, or may be determined as pressures measured when an envelope line of the sphygmus wave has rapidly-varying slopes.

FIGS. 7A and 7Bare plan views showing an exemplary embodiment of internal states of the first actuator120illustrated inFIG. 1.FIG. 7Aillustrates a case when a first shape memory alloy132is shrunken, andFIG. 7Billustrates a case when the first shape memory alloy132is extended and includes a longer length than that ofFIG. 7A.

Referring toFIGS. 7A and 7B, the first actuator120may have a woven structure in the plan view, in which a plurality of wires of the first shape memory alloy132is longitudinally extended in a single first direction, and a plurality of strands of thread134is longitudinally extended in a single second direction crossing the first shape memory alloy132wires. In addition to crossing the first shape memory alloy132wires, threads134may be disposed alternating above and below individual first shape memory alloy wires132, respectively. A current is directly supplied to the first shape memory alloy132through terminals (not shown) connected to two (e.g., opposing) ends of the first shape memory alloy132. If temperature is increased, in the woven structure, the first shape memory alloy132shrinks from an initial state illustrated inFIG. 7Bto a state illustrated inFIG. 7A. In an embodiment, the second actuator180illustrated inFIG. 1may also have the woven structure illustrated inFIGS. 7A and 7B.

FIGS. 8A and 8Bare plan views showing another exemplary embodiment of internal states of the first actuator120illustrated inFIG. 1.FIG. 8Aillustrates a case when a first shape memory alloy136is shrunken, andFIG. 8Billustrates a case when the first shape memory alloy136is extended and includes a longer length than that ofFIG. 8A.

Referring toFIGS. 8A and 8B, the first actuator120may have a woven structure in the plan view, in which a plurality of wires of the first shape memory alloy136is longitudinally extended in a single first direction, and a plurality of heaters138is longitudinally extended in a single second direction crossing the first shape memory alloy136wires. In addition to crossing the first shape memory alloy136wires, heaters138may be disposed alternating to above and below individual first shape memory alloy wires136, respectively. A current may be supplied to the heaters138through terminals (not shown) connected to two (e.g., opposing) ends of the heaters138, and thus an internal temperature of the first actuator120may be increased. If the internal temperature of the first actuator120is increased, the first shape memory alloy136shrinks from an initial state illustrated inFIG. 8Bto a state illustrated inFIG. 8A. In an embodiment, the second actuator180illustrated inFIG. 1may also have the woven structure illustrated inFIGS. 8A and 8B.

FIGS. 9A and 9Bare plan views showing exemplary embodiments of the length control unit190illustrated inFIG. 1. The length control unit190is a component that controls the length of the strap102illustrated inFIG. 1according to the size of the wrist1illustrated inFIG. 1, and more particularly, according to a circumferential length of the wrist1.

Referring toFIG. 9A, the length control unit190includes a plurality of connection blocks192,194and196that are connected to each other substantially linearly, such as in a row. Every neighboring (e.g., directly adjacent) two of the connection blocks192,194and196includes convex and concave portions that fit together, such as by having complementing profiles. If the convex portion of each of the connection blocks192,194and196fits into the adjacent concave portion of a neighboring one of the connection blocks192,194and196, pin holes195aand197aof convex portions and pin holes193band195bof concave portions are correspondingly aligned, and the connection blocks192,194and196may be connected to each other by removably inserting pins198into the aligned pin holes193band195a, and195band197a, respectively.

In one exemplary embodiment, if the wrist1of a person has a long circumferential length, all three of the connection blocks192,194and196may be connected. If the wrist1of the person has a short circumferential length, the connection block194in the middle may be removed from connection with the remaining connection blocks192and196, and only the connection blocks192and196may be directly connected to each other. The pins198combined with the pin holes195a,197a,193band195bmay solely fix the connection blocks192,194and196to each other. An overall length of the length control unit190is adjustable due to the pins198being removably disposed in the pin holes195a,197a,193band195bof the connection blocks192,194,196, respectively. As such, the blood vessel pressing cuff101illustrated inFIG. 1may be customized to a user's wrist1, such that excessive pressing of the wrist1by the blood vessel pressing cuff101is reduced or effectively prevented.

Referring toFIG. 9B, alternatively, a length control unit290includes first and second brackets292and295separated from each other in a longitudinal direction of the strap102, and connected to two (e.g. opposing) ends of the strap102. The first and second brackets292and295are connected to each other so as to control the distance therebetween and allow the blood vessel pressing cuff101illustrated inFIG. 1to be customized to a user's wrist1.

In more detail, the first and second brackets292and295are connected to each other by screws298that penetrate both the first and second brackets292and295. As illustrated inFIG. 9B, external threads may not be disposed on portions of the screws298, which are kept in (e.g., overlap with) screw holes293disposed extending completely through the first bracket292, and may be disposed on the other remaining portions of the screws298which do not overlap with the screw holes293. The screws298may have a head portion disposed outside of the screw holes293of the first bracket292. The head portion does not include any external threads, and may have a dimension larger than a dimension of the screw holes293.

Also, internal threads corresponding to the external threads of the screws298may be disposed only in screw holes296disposed extending completely through the second bracket295. In one exemplary embodiment, if the wrist1of the person has a long circumferential length, the screws298may be rotated in one direction so as to increase the distance between the first and second brackets292and295. If the wrist1of the person has a short circumferential length, the screws298may be rotated in an opposite direction so as to decrease the distance between the first and second brackets292and295. As such, the blood vessel pressing cuff101may be customized to a user's wrist1, such that excessive pressing of the wrist1by the blood vessel pressing cuff101is reduced or effectively prevented.

FIG. 10is a magnified cross-sectional view of an exemplary embodiment of the first actuator included in the blood pressure measuring apparatus100illustrated inFIG. 1, according to the present invention.FIGS. 11A and 11Bare perspective views respectively showing an initial shape222(i) and a first shape222(ii) previously memorized by a first shape memory alloy222illustrated inFIG. 10.

FIG. 12is a graph showing an exemplary embodiment of correlations between temperature and displacements of the first shape memory alloy222illustrated inFIG. 10, and the second shape memory alloy182illustrated inFIG. 1.

Referring toFIG. 10, a first actuator220according to the illustrated embodiment may be included in the blood pressure measuring apparatus100, instead of the first actuator120illustrated inFIG. 1. The first actuator220includes the first shape memory alloy222that changes to the first shape222(ii) at a first temperature higher than room temperature, and an adiabatic unit227including an adiabatic material that completely surrounds the first shape memory alloy222. Due to the adiabatic unit227, malfunctions of the first shape memory alloy222may be reduced or effectively prevented despite an external temperature increase caused by, for example, strong direct rays of the sun. A current may be directly supplied to the first shape memory alloy222.

Referring toFIGS. 11A and 11B, the first shape memory alloy222is installed in the first actuator220with the initial shape222(i). The initial shape222(i) may be a spiral coil shape, where portions of the initial shape222(i) are disposed substantially coplanar with each other. The spiral coil shaped first shape memory alloy222is a single unitary indivisible member. However, the first shape222(ii) of the first shape memory alloy222is a shape in which one end of the spiral coil shape protrudes in one direction, e.g., portions of the first shape222(ii) are not coplanar with each other. Thus, if an internal temperature of the first actuator220is between room temperature and the first temperature, plastic deformation occurs in the first shape memory alloy222due to an external force. However, if heated to above the first temperature, the first shape memory alloy222changes from the initial shape222(i) to the first shape222(ii) that protrudes in one direction. Where the first shape memory alloy is included in the first actuator220, the first actuator220protrudes toward the wrist1illustrated inFIG. 1, since the strap102provides resistance to the moving of the first actuator220away from the wrist1. As such, the first actuator220presses a skin (e.g., an outermost surface) portion of the wrist1, which is close to the radial artery5illustrated inFIG. 1.

Referring toFIGS. 10,11A,11B and12, the first temperature at which the first shape memory alloy222changes to the first shape222(ii) may be, for example, about 40° C., a second temperature at which the second shape memory alloy182changes to the second shape182(ii) illustrated inFIG. 4may be, for example, about 55° C., and a third temperature at which the second shape memory alloy182returns to the third shape182(i) illustrated inFIG. 4may be, for example, about 50° C.

In an embodiment of measuring a blood pressure, in order to measure blood pressure of a person, the blood pressure measuring apparatus100is worn around the wrist1of the person. At room temperature, the second shape memory alloy182is maintained in the third shape182(i), e.g., a shrunken shape. If currents are supplied to the first and second actuators220and180, internal temperatures of the first and second actuators220and180are increased. If the internal temperature of the first actuator220reaches about 40° C., e.g., the first temperature, the first actuator220protrudes due to the first shape memory alloy222that changes to the first shape222(ii), and thus one portion of the wrist1, which is close to the radial artery5, starts to be pressed.

If the internal temperature of the second actuator180is increased and exceeds about 50° C., e.g., the third temperature, the second shape memory alloy182is not maintained in the third shape182(i) any more and plastic deformation occurs in the second shape memory alloy182due to an external force. In this case, the amount of the plastic deformation of the second shape memory alloy182is proportional to the strength of the external force. Since the first actuator220continuously protrudes toward the wrist1between about 50° C., e.g., the third temperature, and about 55° C., e.g., the second temperature, a tensile force is applied to the second actuator180and thus the length of the second actuator180is increased. Accordingly, the pressure applied to the wrist1is smoothly increased in the temperature range from about 50° C. to about 55° C.

If a temperature equal to or higher than about 55° C., e.g., the second temperature, is reached, the second shape memory alloy182rapidly changes to the second shape182(ii) and thus the length of the second actuator180is rapidly increased. As such, the pressure applied to the wrist1is rapidly reduced. If the internal temperatures of the first and second actuators220and180are reduced to room temperature by blocking the supplied currents after the blood pressure is calculated, the first and second shape memory alloys222and182respectively return to the initial shape222(i) and the third shape182(i).

FIG. 13is a magnified cross-sectional view of another exemplary embodiment of a first actuator included in the blood pressure measuring apparatus100illustrated inFIG. 1, according to the present invention.

Referring toFIG. 13, a first actuator240according to the illustrated embodiment may be included in the blood pressure measuring apparatus100, instead of the first actuator120illustrated inFIG. 1or the first actuator220illustrated inFIG. 10. The first actuator240includes a first shape memory alloy242that changes to a first shape memorized in advance, at a first temperature higher than room temperature, and an adiabatic unit247including an adiabatic material that completely surrounds the first shape memory alloy242. Due to the adiabatic unit247, malfunctions of the first shape memory alloy242may be reduced or effectively prevented despite an external temperature increase caused by, for example, strong direct rays of the sun. A current may be directly supplied to the first shape memory alloy242.

The first shape memory alloy242is installed in the first actuator240with an initial shape represented by virtual (dotted) lines, and portions of the first shape memory alloy242are substantially coplanar with each other. As represented by solid lines inFIG. 13, the first shape of the first shape memory alloy242is a shape in which a center portion of the first shape memory alloy242protrudes toward the wrist1illustrated inFIG. 1, such that the portion of the first shape memory alloy242are not coplanar with each other. Thus, if the first actuator240is heated from room temperature to the first temperature, the first shape memory alloy242changes to the first shape that protrudes toward the wrist1, and the first actuator240also protrudes toward the wrist1. As such, the first actuator240presses a skin (e.g., an outermost surface) portion of the wrist1, which is close to the radial artery5illustrated inFIG. 1.