Method of determining cavity compliance of an elastomeric medical product for leak testing

Abstract

The invention relates to a method for determining the volume of a cavity of a rubber-elastic medical product, such as a latex product, for a non-destructive leakage test, and a device for carrying out the method.

Description

Technical Field

[0001] The present invention relates to a method for determining the cavity compliance of a rubber elastic medical product (e.g., a latex product) for non-destructive leakage testing, and an apparatus for carrying out the method. Background Technology

[0002] Rubber-elastic medical products (such as rubber gloves, balloon catheters, condoms, etc.) undergo several tests before being placed on the market. These tests look for uniform defects, but also include puncture and burst tests. To test rubber-elastic medical products, they are typically filled with gas or liquid. Depending on the size of the resulting chamber (cavity), different volumes of fluid (such as N2, CO2, water, saline solution) are used to expand the product to a level suitable for testing for manufacturing defects (especially leaks).

[0003] In the case of using gaseous fluids (such as CO2), the equipment used employs a pressure reducer to set the necessary volumetric flow rate, which is then introduced into the medical product.

[0004] The situation is different when using liquid fluids (such as a saline solution). For example, a peristaltic pump, which allows the volumetric flow rate to be changed by controlling the pump's rotation, is used in this case.

[0005] By introducing a volumetric flow rate into the cavity, the chamber is filled with fluid, and the pressure inside the cavity increases. Simultaneously, the cavity of the medical product expands.

[0006] The so-called cavity compliance (extensibility) C c It can be used as a static characteristic curve based on volume V c And the resulting pressure P c The relationship between them is expressed by equation C. c =V c / P c (See Figure 1a) to determine it.

[0007] Compliance C c The reciprocal of the elasticity E is called the elasticity E. c =1 / C c .

[0008] The fundamental requirement here is that the specific pressure within the cavity must not have a harmful effect on the medical product (except for burst tests intended to damage the product). For this reason, a pressure sensor is typically used to measure the cavity pressure. With proper adjustment, the necessary volumetric flow rate can be calculated without creating cavity pressures harmful to the product. Therefore, the necessary volumetric flow rate is achieved by adjusting a pressure regulator or peristaltic pump. However, it must be considered that pressure is not measured during fluid supply: when measuring pressure, the fluid supply is briefly interrupted to establish a pressure balance that represents the actual pressure within the medical product. Fluid supply resumes after the measurement is completed.

[0009] Depending on the medical product and its size, a significant change in volume is required to expand the rubber elastic product to achieve the desired pressure (see...). Figure 1b ).

[0010] Currently, users of the equipment must perform some necessary setup to communicate information about the product and its dimensions to the equipment. Within the scope of quality assurance measures, it is often necessary to take a small number of products from a product line and perform appropriate tensile or burst tests on a separate test bench. In this case, manually entering individual product parameters (such as product type and dimensions) will lead to errors. This also applies to small-batch manufacturing.

[0011] This allows us to derive parameters and limits, particularly for controlling / regulating equipment. For example, the loaded dataset can quantify the maximum permissible flow rate of the fluid.

[0012] If the product is larger than initially assumed, the expansion will continue for a long time and cause undesirable measurement delays. Conversely, if the product is smaller than initially assumed, it may quickly reach stress levels that are detrimental to the product.

[0013] The device may malfunction if the user sets the wrong product and its size on the testing equipment (e.g., pre-selecting the wrong glove size or selecting a balloon catheter instead of a glove).

[0014] The devices and methods known in the prior art have so far failed to solve the above problems. Relevant prior art includes US2007 / 0083126A1, US 2010 / 0236555 A1, DE 4309380 A1, DE 19809867 C1 and other publications, such as Balloon-based measuring Systems for compliance investigations published by Tautorat, C. et al. in Current Directions in Biomedical Engineering 4(1), 2018.

[0015] Therefore, a regulating system for a technical device that automatically measures the critical characteristic parameters of a cavity is needed. Summary of the Invention

[0016] This invention discloses a technical device for delivering fluid into a rubber elastic medical product. The device measures the characteristic parameters of the cavity, thereby autonomously determining the necessary operating parameters. Attached Figure Description Detailed Implementation

[0017] Figure 2 A medical device (3) for delivering fluid according to the present invention is shown, having the following components:

[0018] A fluid reservoir (1) from which fluid is extracted and delivered to a conveying unit (4) via a connecting element (2). The fluid may be a gas (e.g., CO2 or N2) or a liquid (e.g., a salt solution).

[0019] Controlled pumps (actuators or delivery units) used to deliver fluids in a controlled manner (4).

[0020] Measuring device for measuring volumetric flow rate (5)

[0021] Pressure sensor (6) used to measure the dynamic and static pressure of fluids.

[0022] Connection element (7) (e.g., hose) for delivering fluid from device to medical product (8).

[0023] Electronic storage elements (not explicitly illustrated) are used to acquire measurement data. Additionally, there are electronic computing units (e.g., microcontrollers) used to set necessary control commands to the actuators, evaluate data, and load / write parameter datasets from the storage elements.

[0024] By using a medical device containing the aforementioned components, the compliance of a cavity can be automatically determined based on values ​​such as volumetric flow rate and pressure, thereby preventing human error. Various measurement methods can be employed for this purpose, which will be described below.

[0025] Method Ia

[0026] First, the rubber-elastic medical product is connected to the device using a connecting element (fluid tubing). Then, the device is turned on. Before the initial volumetric flow rate is introduced, the pressure within the cavity is measured. Subsequently, an actuator generates a predefined time-varying volumetric flow rate q (e.g., a pulsed volumetric flow rate with a defined time length). This flow rate creates a pressure boost q within the cavity. c .

[0027] Volume V can be determined by integrating a volumetric flow rate measurement unit. The equipment stops conveying after completing the defined volumetric flow rate and measures the static pressure within the cavity. This can then be achieved through partial pressure boosting (dp). c / dV c To measure elasticity.

[0028] This process can be repeated until the desired target pressure is reached within the cavity. A PV diagram, or purported PV curve, can then be derived from the partial pressurization. This curve provides information about the cavity dimensions (i.e., the dimensions of the medical device). Parameterization can then be performed by comparing these parameters with system parameters, allowing for the selection of optimal system parameters (e.g., maximum delivery rate, control parameters, and adjustment parameters). Automatic cavity identification can be confirmed via optional user confirmation.

[0029] Figure 4 An example of this method is shown. Two volumes, V1 and V2, are delivered into a chamber at staggered intervals. The pressure inside the chamber subsequently increases by p. c This can be achieved using a pressure sensor p d The cavity pressure is measured. This determines the operating point V. c1 =V1,P c1 =P d1 and V c2 =V2+V1,p c2 =P d2 Then, for example, an approximation of the PV diagram can be calculated using a linear approximation (see...). Figure 4 ). In the measurement diagram (below) Figures 5 to 7 The pressure measurement signal exhibits "transient oscillations" at the start and stop points of the volumetric flow rate.

[0030] Method Ib

[0031] In real-world product manufacturing, leaks sometimes occur at cavities. Such leaks, due to the unknown fluid outflow rate, can distort the procedures described in Method Ia. To compensate for the impact of leaks using measurement data, Method Ia is extended as follows:

[0032] A pressure is generated within the cavity by a pressure regulator. In this case, the volumetric flow rate required to reach the desired pressure is specified. In a closed (leak-free) cavity, the pressure regulator will adjust the volumetric flow rate to zero when the desired pressure is reached (see...). Figure 6 ).

[0033] If a leak exists in the medical product, the pressure regulator will continuously adjust the volumetric flow rate to compensate for the leak. The volumetric flow rate required to maintain the pressure is the leakage volumetric flow rate q at the current cavity pressure. l . Figure 7 An illustrative diagram is provided for this purpose. This allows for the measurement of the volumes V2 and V3 of medical product flowing out from the leak. The injected volume can then be adjusted based on the leakage situation.

[0034] This can be achieved by knowing the pressure drop on the connecting element in advance and by measuring the pressure p. d1 To measure the pressure p inside the cavity when the volumetric flow rate stops c1 Or calculate its approximate value. At this point in time, p d ≈p c1 .

[0035] At this point, an evaluation method similar to that in Method Ia can be used. To achieve multiple working points for calculating the PV diagram, the target pressure can always be (temporarily) increased.

[0036] By repeating the operation for different target pressure values, different operating points of the PV diagram can be determined, thereby determining the cavity size.

[0037] Method II

[0038] During equipment operation, the current operating point in the PV diagram of the medical product can be measured. Partial capacity value (ΔC) c =ΔV c / Δp c A lower value indicates a large product, while a larger value indicates a small product. To obtain this information, a measurement pause is performed during equipment operation. During this pause, the volumetric flow rate is briefly interrupted, and a steady-state cavity pressure p is measured. c1Subsequently, a predefined time-varying volumetric flow rate (e.g., a pulsed volumetric flow rate with a defined time length) is generated using an actuator. This volumetric flow rate creates pressure within the cavity. The volume V2 supplied during this time period can be measured by integrating a volumetric flow rate measurement unit. The device stops delivery after completing the delivery of the defined volumetric flow rate and measures the static pressure p within the cavity. c2 Then the device returned to normal function (see...). Figure 7 The measurement result is ΔC. c =V2 / (p c2 -p c1 The difference from Method I is that no complete information about the cavity dimensions or PV diagram is available. Therefore, this information is only valid at the current operating point where the volumetric flow rate required to maintain the cavity pressure is known. However, at this operating point, the fidelity can be adjusted based on the user-selected default settings and the actual measured characteristic values ​​(see [link to method]). Figure 8 In this way, the device can autonomously adjust its parameter set in the event of discrepancies, providing the user with the optimal system settings needed for intervention.

[0039] This method is particularly well-suited for testing balloon catheters. Depending on their intended use, balloon catheters may have openings that form the site of leakage. Despite the openings, the method can also test compliance C. c (C c =V c / p c It can be used for measurement. In addition, it can perform burst tests (or tear tests).

[0040] Method III

[0041] The pressure is temporarily increased during equipment operation. Active pressure control / regulation is used for this purpose. The additional volume required to maintain the desired pressure within the cavity is measured during the pressurization phase. This allows for the determination of a partial volume value (ΔC = ΔV / Δp). The process is the same as in Method II. However, Method III can also be used for the initial filling phase of the cavity. For this purpose, the desired target pressure is increased in a quasi-smooth manner (very slowly or stepwise). Measurement interruption is not required when system parameters regarding the equipment and the connection unit between the equipment and the medical product are available. This allows the volume data and the resulting pressure data to be transferred to a PV diagram. As in Method I, this provides a basis for determining the cavity size or product type. This enables parameterization and selection of optimal system parameters (e.g., maximum delivery rate, control parameters, and regulation parameters). Automatic cavity identification can be confirmed via optional user confirmation.

[0042] Method IV

[0043] One variation of Method II is that, when measuring the current cavity pressure p...c1 Then increase the volumetric flow rate. The rising pressure at the sensor is related to the pressure rise within the cavity (see...). Figure 9 Therefore, for cavity pressure p c2 Measurement is therefore unnecessary (see Method II). For this reason (see...) Figure 10 ), and measure the rise Δp related to volume V2. c After these values ​​are measured, the equipment resumes its previous operation.

[0044] Unlike Method II, this will result in a lack of information regarding the cavity pressure value p. c2 While not having a precise understanding, it will produce the same partial rise, allowing comparison of that value with the measured cavity value to compare the device parameters set by the user. Figure 11 ), and this value can be modified if necessary to ensure optimal parameterization of the device.

[0045] Explanation of reference numerals in the attached figures

[0046] (1) Fluid storage tank

[0047] (2) Fluid connection (fluid supply hose between the reservoir and the medical device (3) for delivering fluid)

[0048] (3) Medical devices for delivering fluids

[0049] (4) Conveying device

[0050] (5) Measuring device for measuring fluid volumetric flow rate

[0051] (6) Pressure sensor

[0052] (7) Fluid connection

[0053] (8) Rubber elastic medical products.

Claims

1. A method for determining the cavity compliance of a leaking rubber-elastic medical product using a medical device in the following manner: c Method: a) Controlled introduction of fluid into the cavity. b) Measure the leakage volumetric flow rate, which is the volumetric flow rate of the fluid required to maintain the pressure within the cavity at a predetermined pressure. c) Set a target pressure within the cavity. d) Control the fluid to be introduced into the cavity at an additional volumetric flow rate greater than the leakage volumetric flow rate. e) Controlling the pressure within the cavity to increase from the predetermined pressure to the target pressure in a quasi-smooth manner. f) Measure the additional volume ΔV required from step e) until the pressure inside the cavity reaches the target pressure. c , g) Determine compliance C c C c =ΔV c / Δp c , Where ΔV c It is determined by the integral of {(the additional volumetric flow rate) - (the leakage volumetric flow rate)} over the time taken to increase the pressure within the cavity from the predetermined pressure to the target pressure in step e). Δp c =(the target pressure) - (the predetermined pressure).

2. A method for determining the cavity compliance of rubber elastic medical products. c The device includes the following components: At least one fluid reservoir (1) is used to extract fluid, and the fluid is delivered to the delivery unit (4) via a connecting element (2). At least one delivery unit (4) for delivering the fluid in a controlled manner, At least one measuring device (5) for measuring the volumetric flow rate of the fluid. At least one pressure sensor (6) for measuring the dynamic and static pressure of the fluid. At least one connecting element (7) for conveying the fluid from the delivery unit (4) to the cavity (8), and at least one electronic storage element for recording measurement data. At least one electronic computing unit is used to set necessary control commands to the actuator. Its features are, The apparatus is configured to perform the method according to claim 1 and to load a parameter dataset from the storage element or write a parameter dataset to the storage element.

3. The device according to claim 2, wherein the connecting element (7) is a flexible hose.

4. The apparatus of claim 2, wherein the electronic computing unit is a microcontroller.

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