1. Field of the Invention
The present invention relates to a blood pressure monitor cuff with an air bag for squeezing a living body to interrupt the blood flow through an artery and a blood pressure monitor including the same.
2. Description of the Background Art
Usually, in order to measure blood pressure, a cuff containing a fluid bag for squeezing an artery in a living body is first wrapped around the surface of the living body. Pressure is then applied to the wrapped fluid bag and reduced as appropriate, so that an artery pulse pressure and wave in the artery is detected. The blood pressure is thus measured.
Here, a cuff refers to a hollow strap-like structure that can be wrapped around a part of a living body. Fluid such as gas or liquid is injected into the cuff in order to measure an artery pulse pressure of the arm or leg of a living body. Therefore, a cuff implies the concept including a fluid bag and wrapping means for wrapping the fluid bag around a living body. In particular, a cuff wrapped around and fitted on the wrist or upper arm of a human body is sometimes called an armband or a manchette.
A fluid bag used in such a cuff is formed by two-dimensionally joining a pair of flexible sheet materials formed of a resin or the like and welding the peripherals thereof together. The fluid bag formed in this manner is wrapped around the upper arm or wrist of a human body and a fluid is injected into the fluid bag to apply pressure. Here, the difference in circumferential length between an inner circumferential sheet and an outer circumferential sheet forming the fluid bag causes slacks and wrinkles on the inner peripheral sheet.
The position of an artery varies for each subject of measurement because of variations among individual living bodies. For reliable squeeze, the fluid bag wrapped around a living body is preferably inflated evenly along its entire length. However, when the above-noted wrinkle appears above the artery to be squeezed, the wrinkle obstructs sufficient inflation of the fluid bag. Thus, the artery may be squeezed insufficiently. This state will be described in detail with reference to
In particular, in a wrist blood pressure monitor, a radius of curvature of a fluid bag fitted on the wrist is smaller as compared with an upper arm blood pressure monitor. Therefore, the difference in circumferential length between the outer circumferential sheet and the inner circumferential sheet has a significant impact on the inner circumferential sheet, so that big wrinkles are likely to appear on the inner circumferential sheet.
Japanese Patent Laying-Open No. 62-072315 discloses a blood pressure monitor cuff including an air bag as described above. In this document, the outer peripheries of a pair of sheet materials are welded together in the shape of a bag. In addition, joint portions formed by welding these sheet materials together are provided at appropriate intervals inside the fluid bag. Provision of joint portions at appropriate intervals encourages wrinkles to be formed at locations provided with the joint portions and prevents deep wrinkles.
In the blood pressure monitor cuff disclosed in Japanese Patent Laying-Open No. 62-072315, the joint portions are provided by joining the inner circumferential sheet and the outer circumferential sheet together at appropriate intervals, thereby to encourage wrinkles to be formed at the joint portions. However, the upper arm or wrist wearing a cuff varies in size and shape among individuals. For example, there is a considerable difference between a relatively big adult male and a small female or a child. Therefore, if a female or child uses a cuff having an interval between joint portions that is set relatively wide based on an adult male, deep wrinkles are rather formed at the joint portions, and these wrinkles may prevent arteries from being squeezed sufficiently. In addition, these wrinkles divide the fluid bag, so that the fluid is not distributed over the entire fluid bag and the inflation of the fluid bag becomes uneven. As a result, arteries may not be squeezed stably. On the other hand, if an adult male uses a cuff having an interval between joint portions that is set relatively narrow based on a relatively small female or a child, a sufficient thickness cannot be secured for the fluid bag, so that the arteries may not be squeezed sufficiently.
Moreover, if the position of a wrinkle is fixed by providing a joint portion as described above, the position of the artery may correspond to the position of the fixed wrinkle in some subjects. In such a case, the artery cannot be squeezed stably, which may adversely affect the precision in measurement.
It is an object of the present invention to provide a blood pressure monitor cuff and a blood pressure monitor, in which big deep wrinkles in the inner face of the fluid bag of the cuff fitted on a living body can be prevented.
A blood pressure monitor cuff in accordance with the present invention includes a fluid bag being inflated and deflated as a fluid comes in and out. The fluid bag is formed of a flexible sheet material. The fluid bag has at least an inner circumferential sheet positioned inside when the blood pressure monitor cuff is wrapped around a living body, and an outer circumferential sheet positioned on the outer circumferential side of the inner circumferential sheet. The sheet material forming the fluid bag has a thickness of 0.15 mm or less.
The present invention is made based on a completely new knowledge over prior arts in that a fluid bag is formed of a sheet material thinner than a conventionally used sheet material, so that a difference in circumferential length between an outer circumferential sheet and an inner circumferential sheet is reduced when the blood pressure monitor cuff is wrapped around a living body, thereby reducing the influence of the wrinkle formed on the inner circumferential sheet.
This knowledge will now be described in detail. A certain thickness is required for a fluid layer in order to absorb protrusions and depressions on the surface of a living body and to allow a fluid to flow smoothly in the fluid layer inside the fluid bag. However, the thickness of the sheet material forming the fluid bag is essentially not limited, as long as the sheet material can hold the fluid layer. Then, in the present invention, the thickness of the sheet material of the fluid bag for forming the fluid layer is reduced, so that the entire thickness of the fluid bag is reduced while the thickness of the fluid layer is kept equal to the conventional one. Accordingly, when this fluid bag is wrapped around a living body, the difference in circumferential length between the outer circumferential sheet and the inner circumferential sheet can be reduced. As a result, the slacks on the inner circumferential sheet can be reduced and the big deep wrinkles appearing on the inner circumferential sheet can be decreased, thereby allowing stable squeeze on arteries.
In the present invention, the inventors conducted an elaborate study to find that the effect as described above is sufficiently brought about when the thickness of the sheet material forming the fluid bag is equal to or less than 0.15 mm. With the thickness of the sheet material equal to or less than 0.15 mm, the difference in circumferential length between the outer circumferential sheet and the inner circumferential sheet can be reduced enough when the fluid bag is wrapped around a living body, thereby surely reducing big deep wrinkles formed on the inner circumferential sheet. As a result, the fluid bag can squeeze an artery stably.
In the blood pressure monitor cuff as described above, the fluid bag may have a plurality of fluid layers radially overlapping with each other when the blood pressure monitor cuff is wrapped around a living body. When the fluid bag has a plurality of fluid layers, the number of sheet materials increases. Thus, wrinkles appearing on the inner circumferential sheet may be a problem. However, the reduced thickness of the sheet material can effectively prevent deep big wrinkles.
In the blood pressure monitor cuff as described above, the sheet material forming the fluid bag may be made of polyurethane. When the sheet material forming the fluid bag is reduced in thickness, its strength should be ensured. In particular, the strength in the welding portion of the sheet material is important. Using the sheet material made of polyurethane, sufficient strength can be secured particularly at the welding portion even when the thickness is reduced.
As described above, in a wrist blood pressure monitor, wrinkles tend to adversely affect the measurement of blood pressure due to a small radius of curvature of a wrist portion. However, when the blood pressure monitor cuff as described above is used for a wrist blood pressure monitor, big deep wrinkles can be reduced effectively, thereby avoiding any inconvenience in measurement caused by wrinkles.
A blood pressure monitor may be formed of the blood pressure monitor cuff as described above with provision of an inflation/deflation unit inflating and deflating the fluid bag, a pressure detection unit detecting a pressure in the fluid bag, and a blood pressure value calculation unit calculating a blood pressure value based on information of the pressure detected by the pressure detection unit.
In the blood pressure monitor cuff and the blood pressure monitor using the same in accordance with the present invention, big deep wrinkles can be reduced on the inner face of the fluid bag fitted on a living body. Therefore, an artery can be squeezed reliably, and blood pressure can be measured stably.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
In the following, an embodiment of the present invention will be described in detail with reference to the figures. It is noted that although in the following embodiment a wrist blood pressure monitor will be described by way of illustration, the blood pressure monitor cuff and the blood pressure monitor in accordance with the present invention is not limited to a wrist blood pressure monitor and may be applied to other blood pressure monitors such as an upper arm blood pressure monitor.
Cover body 140 includes an inner cover 142 positioned inside in a fitted state and formed of a highly stretchy cloth or the like, and an outer cover 141 positioned outside of inner cover 142 and formed of a less stretchy cloth or the like. These inner cover 142 and outer cover 141 are superposed and stitched together at their peripheries thereby to form a bag. A hook-and-loop fastener 165 is provided on the inner circumferential surface side of cover body 140 at one end thereof in the longitudinal direction. A hook-and-loop fastener 166 engaging the hook-and-loop fastener 165 is affixed on the outer circumferential surface of cover body 140 on the other end thereof in the longitudinal direction. These hook-and-loop fasteners 165, 166 are means for stably fixing blood pressure monitor 100 on the wrist.
Air bag 150 is formed of a bag-like member formed of a resin sheet as a sheet material and includes an inflation/deflation space 157 therein. The inner circumferential surface of air bag 150 functions as a squeezing surface 158 for squeezing the wrist. Inflation/deflation space 157 is connected to an air system 121 for blood pressure measurement of apparatus body 110 described later through a tube 120 (see
Curled elastic member 160 is arranged outside air bag 150. Curled elastic member 160 is formed of a flexible member elastically deformable in the radial direction when being annually wound around. Curled elastic member 160 is adhered to the outer surface of air bag 150 by not-shown adhesion means such as a double-sided tape. The curled elastic member 160 is formed in such a manner as to keep its annular shape and acts such that air bag 150 tightly fits on a living body in a fitted state. The curled elastic member 160 is formed, for example, of a resin member such as polypropylene so as to develop sufficient elasticity.
Apparatus body 110 also includes a CPU (Central Processing Unit) 113 for intensively controlling and watching each unit, a memory unit 114 for storing a program causing CPU 113 to execute prescribed operations and a variety of information such as a measured blood pressure value, a display unit 111 for displaying a variety of information including a blood pressure measurement result, an operation unit 112 operated to input a variety of instructions for measurement, and a power supply unit 115 for supplying power to CPU 113 in response to a power-on instruction from operation unit 112. CPU 113 functions as blood pressure value calculation means for calculating a blood pressure value.
Air system 121 for blood pressure measurement includes a pressure sensor 122 for measuring a pressure in air bag 150 (referred to as “cuff pressure” hereinafter), a pump 123 for supplying air to air bag 150, and a valve 124 opened and closed for exhausting or introducing air for air bag 150. Pressure sensor 122 functions as pressure detection means for detecting the cuff pressure. Oscillation circuit 125 outputs to CPU 113 a signal of an oscillation frequency according to an output value from pressure sensor 122. Pump driving circuit 126 controls driving of pump 123 based on a control signal applied from CPU 113. Valve driving circuit 127 controls opening and closing of valve 124 based on a control signal applied from CPU 113.
As shown in
Then, CPU 113 calculates a blood pressure (a systolic blood pressure value and a diastolic blood pressure value) in a well-known procedure (step S104). Specifically, in the process of gradually decreasing the cuff pressure, CPU 113 extracts pulse wave information based on an oscillation frequency obtained from oscillation circuit 125. Then, a blood pressure value is calculated based on the extracted pulse wave information. When a blood pressure value is calculated at step S104, the calculated blood pressure value is displayed on display unit 111 (step S105). It is noted that the measurement scheme as described above is based on a so-called depressurization measurement scheme in which a pulse wave is detected during depressurization of the air bag. Alternatively, a so-called pressurization measurement scheme may also be employed, as a matter of course, in which a pulse wave is detected during pressurization of the air bag.
Blood pressure monitor 100 and blood pressure monitor cuff 130 in this embodiment are characterized by the structure of air bag 150 arranged in blood pressure monitor cuff 130. In the following, the structure of air bag 150 will be described in detail with reference to the figure. Here, an air bag having two air layers will be described by way of example.
Resin sheet 154 serves as an inner circumferential sheet 162 positioned on the inner circumferential side when blood pressure monitor cuff 130 is fitted on the wrist. On the other hand, resin sheet 151 serves as an outer circumferential sheet 161 positioned on the outer circumferential side when blood pressure monitor cuff 130 is fitted on the wrist. Resin sheets 152 and 153 serve as an intermediate sheet 164.
Desirably, the material of the resin sheet forming air bag 150 is highly stretchy and free from leakage of air from inflation/deflation space 157 after welding. Such a material includes, for example, ethylene vinyl acetate copolymer (EVA), flexible polyvinyl chloride (PVC), polyurethane (PU), thermoplastic elastomer-olefinic (TPE-O), and crude rubber. Here, the present invention is characterized by air bag 150 formed of a sheet material thinner than the conventional one. Therefore, the sheet material needs to have a sufficient strength even if the thickness is reduced. In this respect, the inventors have found through an elaborate study that polyurethane is the most preferable sheet material for air bag 150. The use of a resin sheet made of polyurethane ensures a sufficient strength particularly at the welding portion.
As described above, the present invention is made based on a completely new knowledge over prior arts in that air bag 150 is formed of a sheet material thinner than the conventionally used sheet material. Accordingly, the difference in circumferential length between outer circumferential sheet 161 and inner circumferential sheet 162 is reduced when blood pressure monitor cuff 130 is wrapped around a living body, thereby decreasing big deep wrinkles formed on inner circumferential sheet 162.
This knowledge will be described in detail.
L1=2π(r+kt+α)
L2=2πr
Here, if the circumferential difference between the outer circumferential sheet and the inner circumferential sheet is Ld, Ld can be expressed as follows.
Ld=2π(kt+α)
Assuming the thickness a of the air layers is constant, the expression above suggests that the circumferential difference Ld can be reduced by decreasing the thickness t of the sheet material or the number of sheets k.
Here, when a plurality of air layers are provided, the thickness of air bag 150 becomes uniform in the width direction when air bag 150 is inflated, as compared with a single air layer. Therefore, a squeezing force is less likely to be distributed, so that arteries 51, 52 can be squeezed more reliably. In this respect, it is preferable to provide a plurality of air layers. When two air layers are provided, the number of sheets k is four. Therefore, as compared with a single layer (k=2), the effect brought by reducing the thickness t of the sheet material is even more remarkable.
In the following, the effect of the present invention will be verified by calculating Ld in an illustrative example. The thickness t of a sheet material forming an air bag that is most frequently used at present is in the range from 0.3 mm to 0.5 mm. It is thus assumed that the thickness t of the conventional sheet material is 0.4 mm, and the thickness t of the sheet material in the example of the present invention is 0.15 mm. With two air layers and α=0, the circumferential difference Ld0.4 and Ld0.15 with t=0.4 and t=0.15 are as follows.
Ld0.4=2π(4×0.4)=10.1 mm
Ld0.15=2π(4×0.15)=3.0 mm
This calculation result shows that there is a very big difference between Ld0.4 and Ld0.15. As wrinkles are formed depending on the magnitude of Ld, reduction in the thickness of the sheet material can significantly minimize slacks on inner circumferential sheet 162, thereby reducing big deep wrinkles appearing on inner circumferential sheet 162.
Furthermore, the following experiment was conducted in order to verify this knowledge. The following three kinds of sheet materials of highly compressible PU were prepared as sheet materials forming air bag 150: a material of stretch PU having a thickness t of 0.2 mm; a material of stretch PU having a thickness t of 0.15 mm; and a material of stretch PU having a thickness t of 0.1 mm. Air bag 150 having two air layers was fabricated using each of these materials.
FIGS. 10 to 12 show the results of this experiment, in which (a) is a photograph of the inner circumferential surface of the air bag, and (b) is an illustration based on the photograph, showing the wrinkles on the inner circumferential surface of the air bag.
As described above, the trouble in squeezing an artery is a deep big wrinkle (see
This experiment shows that thickness t of 0.15 mm or less mostly prevents big deep wrinkles. In order to prevent big deep wrinkles more reliably, preferably, thickness t of the sheet material may further be reduced. Although a thinner sheet material is preferable to reduce big deep wrinkles, considering the strength of the sheet material, it is particularly preferable that thickness t is 0.08 mm or more and 0.12 mm or less. With thickness t of less than 0.08 mm, the air bag may be broken, for example, when a great force that is not normally exerted is applied to the air bag. On the other hand, with thickness t of more than 0.12 mm, the effect of reducing big deep wrinkles may be insufficient, depending on the conditions of blood pressure measurement.
It is noted that, considering the strength of the presently available sheet material, actually, it is difficult to secure the strength of air bag 150 formed by welding unless the thickness is about 0.05 mm or more. Therefore, the minimum value of the thickness of the sheet material is 0.05 mm, if specified. It should be noted that this value may possibly be further reduced if a sheet material having a superior characteristic were found.
In this embodiment, the case of two air layers has mainly been described. However, needless to say, the present invention may be applied to the cases of a single air layer and three or more air layers. Furthermore, in the embodiment described above, the air bag is formed by welding a pair of sheet materials together at the peripheries in the shape of a bag by way of illustration. Alternatively, the air bag may be formed by folding one sheet of sheet material into half and welding the three sides together.
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.
Number | Date | Country | Kind |
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2005-036066 | Feb 2005 | JP | national |