Fluid-pressure detector

Abstract: A fluid-pressure detector comprising a pillow-­ like body capable of expanding and shrinking depending on pressure of fluid flowing in the pillow-like body, a detecting means for detecting an amount of expansion or shrinkage of the pillow-like body, and a connecting means for detachably connecting a detecting portion of the detecting means to an outer surface of the pillow-like body. Fluid pressure can be detected continuously and accurately both in the case of positive pressure and in the case of negative epressure. The detecting means is detachable from the pillow-like body, so that only the pillow-like body can be discarded while leaving the expensive detecting means as it is.

Description: The present invention relates to a fluid-pressure detector, and more particularly to a disposable fluid-pressure detector used in a fluid-circulating line. As an example of this kind of fluid-circulating line, there is known a blood line provided in a so-called dialysis system or plasma-separating system. In such blood line, there has been generally used a pressure-detecting chamber 10 as a fluid-pressure detector for detecting the pressure of flowing blood. Fig. 4 shows a schematic structure of the pressure-detecting chamber 10. The pressure-detecting chamber 10 has a tubular closed container 11 made of synthetic resin such as soft vinyl chloride. Tubes 12 for flowing blood therein are connected to both upper end and lower end of the closed container 11. A monitoring tube 13 is also connected to the upper end of the closed container 11. A pressure gauge (not shown) is attached to an opening end of the monitoring tube 13. That is, in this pressure-detecting chamber 10, blood which flows in the tube 12 is contained in the lower portion of the closed container 11, and the change in pressure of air in a closed room 14 over the blood B contained in the closed container 11 is detected by means of the pressure gauge. Thus, the pressure of blood flowing in the tube 12 is detected through the pressure of air in the closed room 14. In the above-mentioned pressure-detecting chamber 10, a pressure-detecting portion communicates with the inside of the chamber since the blood pressure is detected through the air in the closed container 11. Accordingly, it is necessary to provide means for preventing bacteria such as a filter for preventing bacteria between the pressure-detecting portion and the chamber 10. Further, it is necessary to provide means for detecting a blood level in the chamber 10 since there is a danger that air in the chamber 10 enters the blood line by the continuous negative pressure. Still further, the chamber 10 is a relatively large part having a volume of 10 to 30 mℓ, so that there is a disadvantage that the placement or positioning of the chamber requires a large space. In order to solve the above-mentioned disadvantages, a fluid-pressure detector comprising the features of the preamble of claim 1 has been used, of which a side sectional view is shown in Fig. 5. The fluid-pressure detector 20 has a pillow-like body 21 which is made expandable. Tubes 22 for flowing blood which constitutes a blood line are connected to both ends of the pillow-like body 21. A detecting means 23 such as a strain gauge capable of detecting the amount of expansion or shringkage of the pillow-like body 21 is fixedly placed outside the pillow-like body 21. A detecting portion 23a of the detecting means 23 is so arranged as to directly contact the outer surface of the pillow-like body 21. Since the blood line is discarded after being used one time, the pillow-like body 21 connected to the blood line and the expensive detecting means 23 are not connected to each other, i.e. are separately placed. According to the fluid-pressure detector 20, there can be effectively solved disadvantages caused by detecting blood pressure through air as in the above-mentioned pressure-detecting chamber 10 of Fig.4. In the fluid-pressure detector 20, the pillow-like body 21 and the detecting means 23 are not connected to each other. Accordingly, the pressure of blood can be accurately detected as long as the pressure is positive. However, a continuous and accurate detection of the pressure of blood cannot be carried out since the outer surface of the pillow-like body 21 comes off from the detecting portion 23a of the detecting means when the pressure of blood becomes negative, whereby the pillow-like body 21 shrinks beyond the projection limit of the detecting portion 23a of the detecting means 23. Negative pressure can of course be detected if the pillow-like body 21 and the detecting portion 23a of the detecting means 23 are connected to each other. In that case, however, the detecting means 23 is discarded when the blood line including the pillow-like body 21 is discarded. The discard of expensive detecting means 23 is very uneconomical. In a blood set for a dialysis system having a drip bulb with flexible side walls it is known (US-A-3 841 157) to measure the pressure within the drip bulb by means of a magnetic transducer having a metal enclosed coil bobbin and a core of magnetically permeable material slidably received within said bobbin. The core is provided with a hard rubber connecting rod which is attached to a flexible metal support strap snapped with one end to a button provided on one of the flexible side walls of the drip bulb. A second flexible metal strip is snapped to a second button provided at the opposite flexible side will of said drip bulb. This known fluid-pressure detector is relatively complicated and encludes the problem that the connecting rod, which is the detecting portion of the detecting means, is not directly connected to the flexible drip bulb so that measurement is relatively inaccurate. Furthermore, in this known system the air-pressure in the drip chamber is measured so that its sensitivity is poor. Finally, in order to be able to measure also negativ pressure within the drip bulb it is necessary to constantly pretension the flexible straps supporting the drip bulb. The object of the present invention is to provide a fluid-pressure detector having the simple design as shown in Fig. 5 and described above in which the accuracy of detection is improved and the space required for the placement of the detector is reduced. This object is met by a fluid-pressure detector comprising the features of the single claim. In the detector of the present invention, a filter for preventing bacteria is not required since the pressure of fluid flowing in the pillow-like body is detected by directly detecting the amount of expansion or shrinkage of the pillow-like body by means of a detecting means and the pillow-like body does not communicate with the detecting means. Further, means for detecting fluid level is not required since no air exists between the fluid and detecting means. Still further, both a filter for preventing bacteria and means for detecting fluid level are not required and the volume of chamber can be reduced as small as not more than 5 mℓ, so that the whole detector can be miniaturized and space required for the placement of the detector can be reduced. Moreover, the pressure of fluid can be detected continuously and accurately regardless of whether it is positive or negative, since a detecting portion of the detecting means is detachably connected to an outer suface of the pillow-like body by means of a connecting means. The detecting means can be detached from the pillow-like body connected to a fluid-circulating line after the fluid pressure is detected, which enables the discard of the pillow-like body connected to the fluid-circulating line with leaving the detecting means as it is. The detector of the present invention can be applied not only to a line circulating body fluid other than blood but also to other fluid-circulating lines. According to the detector of the present invention, no air exists between fluid and the detecting means unlike in the case of conventional detector, since the pressure of fluid flowing in the pillow-like body is detected by directly detecting the expansion or shrinkage of the pillow-like body by the detecting means. Accordingly, accuracy of detection of fluid pressure can be improved, and the whole detector can be miniaturized, whereby the space required for the placement of the detector can be reduced. Further, the fluid pressure can be detected continuously and accurately not only in the case of positive pressure but also in the case of negative pressure, since the detecting portion of the detecting means is detachably connected to an outer surface of the pillow-like body. Moreover, the detecting means is detachable from the pillow-like body, so that only the pillow-like body which is a part of a fluid-circulating line can be discarded while leaving the expensive detecting means at its attachment position. This results in a saving of cost in the case of a system such as plasma-separating system in which a blood line is exchanged for a new one together with the exchange of donor. In the drawings Fig.1 is a schematic side sectional view of an embodiment of the fluid-pressure detector of the present invention, Fig. 2 is a front view of the embodiment along the line II-II of Fig. 1, Fig. 3 is a schematic side sectional view of another embodiment of the fluid-pressure detector, not claimed, Fig. 4 is a schematic sectional view of a conventional pressure-detecting chamber, and Fig. 5 is a schematic side sectional view of the main portion of a conventional fluid-pressure detector. Next, a fluid-pressure detector of the present invention is explained in detail based on the accompanying drawings wherein the detector is applied to a blood line which is an example of fluid-circulating lines. In Fig.1 to 2, a fluid-pressure detector 1 comprises a pillow-like body 2 capable of expanding and shrinking depending on the pressure of blood flowing in the pillow-like body 2. The pillow-like body 2 is composed of a pair of approximately rectangular sheets 2a, 2b made of synthetic resin such as soft vinyl chloride. Two sheets 2a, 2b are adhered to each other at their peripheries. A tube 3 for flowing blood is connected to each end of the pillow-like body 2. An iron plate 4, an example of magnetic material, is attached by adhesive to an approximately central position of an outer surface of at least one of sheets 2a, 2b constituting the pillow-like body. In the embodiment shown in Fig. 1, the iron plate 4 is attached to the left sheet 2a. A detecting means 5 such as a strain gauge or a differential transformer which detects expansion or shrinkage of the pillow-like body 2 is fixedly provided at a prescribed position outside the pillow-like body 2. A magnet 6 for attracting the iron plate 4 adhered to the outer surface of the pillow-like body 2 is provided at a tip of a detecting portion 5a of the detecting means 5. In the present embodiment, a connecting means which directly connects the outer surface of the pillow-like body 2 to the detecting portion 5a of the detecting means 5 is composed of the magnet 6 and the iron plate 4 closely adhered to the magnet 6 by magnetic attraction thereof. Since the connecting means in the present invention is so designed as to be detachable by the use of iron plate 4 and magnet 6, the magnet 6 is left at the tip of the detecting portion 5a as it is if the pillow-like body 2 connected to the blood line is discarded after being used one time. In the above explanation, the connecting means is composed of the iron plate 4 and the magnet 6. It should be noted, however, that, for example, the connecting means might be composed of a pair of connecting members one of which is attached to an outer surface of the pillow-like body and the other of which is attached to the tip of the detecting portion 5a of the detecting means 5. Both connecting members are connected to each other by dovetail joint, as shown in Fig.3. Connecting members connected to each other by screw joint can also be employed.

Claims: Fluid-pressure detector (1), comprising a pillow-like body (2) capable of expanding and shrinking depending on pressure of fluid flowing in the pillow-like body, a detecting means (5) for detecting the amount of expansion or shrinkage of the pillow-like body, the detecting means being fixedly placed outside the pillow-like body, a detecting portion (5a) projecting from the detecting means (5) and contacting the pillow-like body (2), characterized in that the detecting portion (5a) of the detecting means (5) is detachably connected to an outer surface of the pillow-like body (2) by means of an an iron plate (4) attached to the central portion of one of two sheets (2a, 2b) constituting the pillow-like body (2) and a magnet (6) for attracting the iron plate (4) provided at the tip of the detecting portion (5a) of the detecting means (5) for detecting the amount of expansion or shrinkage of the pillow-like body (2).

Inventors: YAMAUCHI TOSHIO, YAMAUCHI, TOSHIO
Applicants: NISSHO KK, NISSHO CORPORATION
Application year: 1989
Main classification: G01L9
IPC codes: G01L7, A61M1, G01L9, A61B5