Abstract:
An inflatable cuff for blood pressure measurement includes a first inflatable bag which is inflatable to press an arterial vessel of a body portion of a living subject and stop flow of blood in the arterial vessel which the inflatable cuff is adapted to be wound around the body portion; a second inflatable bag for sensing a pulse wave propagating along the arterial vessel, which is supported by the inflatable cuff such that the second inflatable bag is located inside a downstream-side portion of the first inflatable bag in the direction of the blood flows in the arterial vessel, and which as a dimension as measured in the direction that is smaller than a dimension of the first inflatable bag as measured in said direction; and a fluid-filled bag which is located between the second inflatable bag and the body portion and which is filled with incompressible fluid.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an inflatable cuff for blood pressure measurement, which is adapted to be worn on a body portion of a living subject, and particularly to a cuff having a first inflatable bag for pressing the body portion and a second inflatable bag for sensing a pulse wave.  
           [0003]    2. Description of Related Art  
           [0004]    A cuff, including an inflatable bag, is adapted to be wound around a body portion of a living subject. The bag inflates when a gas or a liquid is supplied into, and consequently the wound cuff presses the body portion.  
           [0005]    A cuff may function not only as a device for pressing a body portion, but also as a device for sensing a pulse wave propagating from an arterial vessel. In general, an oscillometric blood pressure measuring device slowly deflates the cuff wound around a body portion to weaken a force by the cuff against the body portion, and determines a blood pressure based on pulse waves continuously received by the cuff during the slow deflation. The device adopts a static pressure of the inflatable bag as a systolic pressure, at a rising point of an envelope of amplitudes of the pulse waves, that is, a point where the amplitude of the pulse waves suddenly raises.  
           [0006]    The device may determine an indefinite systolic pressure when the cuff has only one inflatable bag because a fluctuation in pressure in the inflatable bag provides with indefinite rising point of the envelope of the amplitudes of the pulse waves.  
           [0007]    To solve the above problem, JP 05-269089 A, U.S. Pat. No. 6,346,083 and U.S. Pat. No. 6,497,668 disclose a cuff having an inflatable bag for pressing a body portion so as to stop a flow of blood in an arterial vessel and an inflatable bag for sensing a pulse wave from the arterial vessel. The cuff disclosed in these references includes an outer bag for pressing the body portion and an inner bag for sensing the pulse waves. A device using this cuff provides a relatively definite systolic pressure with a relatively definite rising point of the envelope of the amplitudes of the pulse waves sensed by the inner bag, because the inner bag is substantially located in the center of and on a body portion side of the outer bag and no pulsation directly propagates to the inner bag when the arterial vessel pulsates again around an upstream end of the outer bag.  
           [0008]    An uneven surface of the body portion, such as an ankle, is difficult to fittingly wind with the cuff. The cuff having the outer bag for pressing the body portion and the inner bag for sensing the pulse waves disclosed in the above references cannot provide with a definite systolic pressure because of an indefinite shape of the envelope of the amplitudes of the pulse waves sensed by the inner bag if the inner bag is not fully wound on the uneven surface of the body portion.  
         SUMMARY OF THE INVENTION  
         [0009]    It is therefore an object of the present invention to provide an inflatable cuff for blood pressure measurement including an inflatable bag for pressing a body portion of a living subject and another inflatable bag for sensing a pulse wave, which is used for determining a definite blood pressure even if the body portion has an uneven surface.  
           [0010]    To attain this object, the present invention provides the inflatable cuff for blood pressure measurement including: (1) a first inflatable bag which is inflatable to press an arterial vessel of a body portion of a living subject and stop flow of blood in the arterial vessel which the inflatable cuff is adapted to be wound around the body portion; (2) a second inflatable bag for sensing a pulse wave propagating along the arterial vessel, the second inflatable bag is supported by the inflatable cuff such that the second inflatable bag is located inside a downstream-side portion of the first inflatable bag as seen in the direction in which the blood flows in the arterial vessel, and which has a dimension as measured in said direction that is smaller than a dimension of the first inflate bag as measured in said direction; and (3) a fluid-filled bag which is located between the second inflatable bag and the body portion and which is filled with an incompressible fluid.  
           [0011]    According to this feature of the present invention, the fluid-filled bag located on an inner side of the second inflatable bag receives a pressure on its inner surface when a pressure of each of the first and second inflatable bags raises with the inflatable cuff wound around the body portion of the living subject. An inner surface, that is, a surface on the body portion side, of the fluid-filled bag filled with an incompressible fluid changes its form to the same as an uneven surface of the body portion and an outer surface, that is, a surface on the second inflatable bag side, of the fluid-filled bag changes its form to the same as a form of an inner surface of the second inflatable bag by the pressure. Consequently, the shape of the envelope of the amplitudes of the pulse waves sensed through the second inflatable bag is definite and an accurate blood pressure is measured thereby because the combination of the second inflatable bag and the fluid-filled bag fits on the uneven surface of the body portion.  
           [0012]    According to a second feature of the present invention which includes the first feature, the fluid-filled bag has a size and is located such that the fluid-filled bag is present in a whole space between the second inflatable bag and the body portion of the living subject in a state that the inflatable cuff is wound around the body portion. Consequently, the shape of the envelope of the amplitudes of the pulse waves sensed through the second inflatable bag is more definite and an accurate blood pressure is measured thereby because the combination of the second inflatable bag and the fluid-filled bag fits on the uneven surface of the body portion.  
           [0013]    According to a third feature of the present invention which includes the first feature, the fluid-filled bag has a size and is located such that the second inflatable bag and the fluid-filled bag are overlapped in a state that the inflatable cuff is wound around the body portion. Consequently, the shape of the envelope of the amplitude of the pulse waves sensed through the second inflatable bag is most definite and an accurate blood pressure is measured thereby because the combination of the second inflatable bag and the fluid-filled bag fits on the uneven surface of the body portion and the pulse wave does not propagates from the fluid-filled bag to the first inflatable bag. If the fluid-filled bag is too large and a pulsation propagated through the fluid-filled bag is directly propagated to the first inflatable bag without propagating through the second inflatable bag, a pulse wave propagated from the living subject propagates from the fluid-filled bag not only to the second inflatable bag but also to the first inflatable bag and the pulse wave which the first inflatable bag receives further propagates to the second inflatable bag. Accordingly, the shape of the envelope of the amplitudes of the pulse waves sensed through the second inflatable bag is little definite because the pulse wave becomes distorted during the propagation through the first inflatable bag to the second inflatable bag. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The above and optional objects, features, and advantages of the present invention will be better understood by reading the following detailed description of the exemplary embodiments of the invention when considered in conjunction with the accompanying drawings, wherein:  
         [0015]    [0015]FIG. 1 illustrates an inflatable cuff for blood pressure measurement at an ankle in a plan view according to the present invention;  
         [0016]    [0016]FIG. 2 illustrates the inflatable cuff for blood pressure measurement at the ankle in a bottom view,  
         [0017]    [0017]FIG. 3 illustrates the inflatable cuff for blood pressure measurement in a sectional view taken along line  3 - 3  in FIG. 1  
         [0018]    [0018]FIG. 4 illustrates a set of a first inflatable bag, a second inflatable bag and a shield plate in a plan view;  
         [0019]    [0019]FIG. 5 illustrates the set of the first inflatable bag, the second inflatable bag and the shield plate in a front view; and  
         [0020]    [0020]FIG. 6 illustrates the inflatable cuff wound around the ankle and arterial vessels pressed by the first and second inflatable bags. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0021]    Hereinafter, there will be described an inflatable cuff for blood pressure measurement embodying the present invention, by reference to the drawings.  
         [0022]    In FIG. 1, an inflatable cuff  10  which has a belt-like ape is about 14 cm in width and is slightly bent toward a transversal direction to be formed an arch. The cuff  10  has two narrowed portions  12 ,  12  at one end in a longitudinal direction. Each of the narrowed portions  12  is a half in width of the cuff  10  and has a fastener pad  14  on an inner surface, that is, a surface on a body portion side, and a main portion  70  of the cuff  10  also has fastener pads  16  on an outer surface, that is, a surface on the opposite side to the body portion side. The fastener pads  14  and  16  are fastened to each other, and the narrowed portions  12 ,  12  are unfastenably fixed to the main portion  70  at the fastener pads  14  and  16  with the cuff  10  wound around an ankle (not shown) and are on the most outside of the wound cuff  10 . Consequently, the cuff  10  is fixed to the ankle.  
         [0023]    A containing bag  24  consists of an inner cloth member  72  and an outer cloth member  20 , both of which substantially are the same in shape as the cuff  10 . The inner cloth member  72  and the outer cloth member  20  are mutually fixed by sewing with a circumferential cloth member  22 . A portion of the inner cloth member  72  without the narrowed portions  12 ,  12  forms an inner cloth portion  18  which covers substantially from the center of the cuff  10  to the end opposite to the narrowed portion side in a longitudinal direction. The containing bag  24  includes a first inflatable bag  28  and a second inflatable bag  26 , which is located in a transversal end portion, that is, on a downstream side of a blood flow in an arterial vessel and under the bag  28 .  
         [0024]    As shown in FIG. 1, the first inflatable bag  28  for stopping the blood flow in the arterial vessel on the inner side of the cuff  10  has a rectangular shape, is slightly shorter in width than the containing bag  24 , namely, than the cuff  10  and is also slightly shorter in length than the bag  24  in the longitudinal direction. As shown in FIG. 2, the second inflatable bag  26  also has a substantially rectangular shape, is about between a third and a quarter in width of the bag  24  and is slightly shorter than the bag  24  in the longitudinal direction. The bags  28  and  26  are formed of soft resin  
         [0025]    As shown in FIG. 1, the inflatable cuff  10  has a first conduit  34  integratedly connected to the first inflatable bag  28  and a second conduit  32  integratedly connected to the second inflatable bag  26 . To ports of the conduits  34  and  32  protruding outside from the containing bag  24 , pipes (not shown) are connected so as to supply air to the bags  28  and  26 , respectively. The conduits  34  and  32  are connected each other through the pipes with a restriction.  
         [0026]    As shown in FIGS. 2 and 3, the containing bag  24  includes a rectangular inner sheet  30  which has substantially the same length as the inner cloth portion  18  in the longitudinal direction and has a half length of the inner cloth portion  18  in the transversal direction The sheet  30  is disposed such that along side of the sheet  30  on the downstream side of the blood flow in the arterial vessel when the cuff  10  is wound around the ankle is substantially located on a long side on the downstream side of the containing bag  24 . Fixation of both of transversal edge portions of the sheet  30  to the inner cloth portion  18  provides with a cavity  36  which includes the second inflatable bag  26 . The sheet  30  is formed of soft resin.  
         [0027]    The cavity  36  has a shield plate  38  formed of high density polyethylene on an outer side of the bag  26  and a fluid-filled bag  40  on an inner side of the bag  26 . Transversal leg of the shield plate  38  and the fluid-filled bag  40  are substantially the same as that of the second inflatable bag  26 . The bag  40  is filled with an incompressible fluid, such as a gel and a liquid, while filled with water in this embodiment.  
         [0028]    As shown in FIG. 4, the shield plate  38  has a rectangular shape whose long sides extend in the longitudinal direction. The fluid-filled bag  40  also has a rectangular shape whose long sides extend in the longitudinal direction, and is shorter than the second inflatable bag  26  in the longitudinal direction. Furthermore, the bag  40  is located parallel to the second inflatable bag  26 , a width of the bag  40  is substantially equal to that of the bag  26  and a centerline of the bag  40  is on a centerline of the bag  26  in the longitudinal direction.  
         [0029]    As shown in FIG. 5, the shield plate  38 , the second inflatable bag  26  and the fluid-filled bag  40  are integratedly fixed at respectively longitudinal ends, that is, at points A and A in the figure, one another by sewing.  
         [0030]    The length of the fluid-filled bag  40  in the longitudinal direction is slightly shorter than that of the second inflatable bag  26  such that the bags  26  and  40  are overlapped each other when the cuff  10  is wound around the ankle. Each of the bags  26  and  40  substantially forms a part of a cylinder in a state that the cuff  10  is wound around the ankle. A radius, a distance between the center and the circumference of the cylinder, of the bag  40  is slightly shorter than that of the bag  26 . Therefore, the longitudinal length of the fluid-filled bag  40  in a horizontally extended form is determined to be slightly shorter than that of the bag  26  with taking a difference of the radii.  
         [0031]    In FIG. 3, the containing bag  24  includes the first inflatable bag  28  on the outer side of the inner sheet  30 , and a first support plate  24  and a second support plate  44  on the outer side of the bag  28 . The plates  42  and  44  are formed of substantially hard material, such as hard resin to support the cuff  10  to be a cylinder shape when wound around the ankle.  
         [0032]    In FIG. 6, arterial vessels  48  and  48  of an ankle  46  are pressed to stop blood flows with an inner pressure of a predetermined value, such as 250 mmHg, of each of the bags  26  and  28  for stopping the blood flow, wherein the predetermined value is over a systolic blood pressure value of the arterial vessel  48 . Although the cuff  10  includes the shield plate  38 , the first support plate  42  and the second support plate  44 , they are not shown in FIG. 6.  
         [0033]    The fluid-filled bag  40  and the second inflatable bag  26  are substantially overlapped in a state shown in FIG. 6 because the widths of the bag  40  and  26  are substantially equal to each other and the longitudinal length of the bag  40  are appropriately shorter than that of the bag  26  such that overlapping of the bags  40  and  26  are provided in the state that the cuff  10  is wound around the ankle  46  as described above.  
         [0034]    In FIG. 6, the fluid-filled bag  40  filled with water changes its inner side form to the same as a form of an uneven surface of the body portion with being pressed by the second inflatable bag  26  when the pressures of the bags  28  and  26  raise in the state that the cuff  10  is wound around the ankle  46 . And also an outer side surface of the bag  40  changes its form to the same as a form of an inner surface of the bag  26 . Consequently, the shape of the envelope of the amplitudes of the pulse waves sensed through the second inflatable bag  40  is definite and an accurate blood pressure is measured thereby because the combination of the bags  26  and  40  fits on the uneven surface of the body portion.  
         [0035]    Especially, the invention of this embodiment provides with the most definite shape of the envelope of the amplitudes of the pulse waves sensed through the second inflatable bag  26  because the bag  26  sufficiently fits on the uneven surface of the body portion through the fluid-filled bag  40  and the pulse wave does not propagate from the bag  40  to the first inflatable bag  28  due to the size and the location determined such that the bag  26  and  40  are c overlapped in the state that the cuff  10  is wound around the ankle  46 .  
         [0036]    While the present invention has been described in its exemplary embodiment, the present invention may be otherwise embodied  
         [0037]    Although, for example, the longitudinal length of the bag  40  is determined such that the bags  26  and  40  are overlapped in the state that the cuff  10  is wound around the ankle  46  in the embodiment described above, the longitudinal length of the fluid-filled bag  40  may be longer or shorter than that of the bag  40  in the embodiment described above. And the transversal length of the bag  40  also may be longer or shorter than the bag  26 . More accurate blood pressure is provided by measuring through a bag  26  because the combination of the bag  40  and a part of an inner surface of the bag  26  fits on an uneven surface of a body portion, even though the bag  40  is too small and then a part of the bag  26  is not fit on an uneven surface of the body portion through the bag  40 .  
         [0038]    It is to be understood that the present invention may be embodied with other changes, improvements, and modifications that may occur to a person skilled in the art without departing from the scope and spirit of the invention defined in the appended claims.