1. Field of the Invention
This disclosure relates generally to a fluid connection for reducing a fluid volume in said connection. Especially the disclosure describes the fluid connection to reduce an extra fluid volume when using tapered connectors. The disclosure relates also to sample tubing connections used in analyzing equipment such as gas analyzing equipment for patient respiratory gas.
2. Description of Related Art
In anesthesia or in intensive care, the condition of a patient is often monitored e.g. by analyzing the air exhaled by the patient for its carbon dioxide content. For this reason a small portion of the respiratory gas is delivered to a gas analyzer. The sample is carried along a sampling tube connected in one end often to a respiratory tube adapter and the other end to the gas analyzer. This sampling tube is typically disposable and must have some kind of reliable and tight but simple and cheap connectors. Almost all pneumatic connectors in the respiratory system have tapered conical contact surfaces. Such connectors are simple, easy to connect and cheap to make and they still provide an airtight and reliable connection. The connection such as a well-known fitting called Luer-Lok, a registered trademark of Becton Dickinson of Franklin Lakes, N.J. USA, has been in general use for gas sampling but also other similar connectors with differing dimensions can be used. The tapered portion of the connector is normally conical with straight cross section sides because it gives a reliable and tight connection using a large contact area. The tapered portion could in principle also have curved cross section sides or one tapered connector in combination with a suitably designed semi-rigid counterpart. The contact surface responsible for the tightness is always on the tapered portion of the connector. Other possibilities would be cylindrical connectors with either axial or radial gaskets but they are more complicated and expensive and, consequently, not suitable as disposable components. Such connectors are typically used e.g. in pressurized gas lines or gas lines of more permanent nature. With this design it would be easier to avoid dead space in the connection bore since they are allowed to touch axially, longitudinally, while still remaining airtight.
A gas analyzer designed to measure respiratory gas in real time has to be fast enough to resolve changes in the gas content. This is especially true for carbon dioxide, which varies from close to zero in the inspiratory phase to about 5% in the expiratory phase of the breathing cycle. It is then very important to streamline the complete gas sampling system. Many portions of the system with slowed down response can easily add up to unacceptable performance of the gas analyzer. The reason for an increased rise time of e.g. carbon dioxide is often an extra fluid volume, a dead space in the pneumatic line, where the gas flow is slowed down. The tapered conical connector is susceptible to such dead space, especially if the inner dimensions are significantly larger than those of the bore or sampling line itself The inherent construction of the conical connector is such that dead space always is introduced and the amount is critically dependent on the tolerance of the conical dimensions. The connectors must allow for axial or longitudinal play in order to avoid the situation of touching axially because then air leak is likely to occur. Therefore, the tolerances always define an axial extra fluid volume in the connection to ensure tightness at the conical surfaces.
Minimal dead space is essential also in gas or liquid chromatography. An attempt to make connections with capillaries is described in U.S. Pat. No. 6,969,095. The female part of the connection is slightly tapered in order to accept the cylindrical capillary tube and make a tight press-fit. This connector fitting is specially designed for conditions encountered in liquid or gas chromatography and is not intended for repeatedly made reliable connections like in gas analyzers. Robustness inevitably adds dead space to the bore of the connection.
In neonatal main ventilation circuit's extra fluid volume has to be as small as possible. There are different solutions to this problem. The connections are also conically tapered even if the dimensions are much larger than what would be used for a gas sampling system. In one solution there is a sliding internal passage filling the dead space and in another solution a compressible member is used to exclude the extra fluid volume. However, especially for small and disposable connectors like those used in sampling lines of gas analyzers such moving or compressible features would be difficult to implement and would add to the expenses of a disposable accessory.
The above-mentioned shortcomings, disadvantages and problems are addressed herein which will be understood by reading and understanding the following specification.
In an embodiment, a fluid connection for reducing a fluid volume in the connection includes a first connector having a first body encircling a first bore allowing a fluid flow along the first bore, the first body having a first sealing surface The fluid connection also includes a second connector having a second body encircling a second bore allowing a fluid flow along the second bore, the second body having a second sealing surface capable to form a tight connection with the first sealing surface when both the first connector and the second connector are mated. The fluid connection also includes a volume between the first connector and the second connector when mated and a protrusion in of one of the first body encircling the first bore and the second body encircling the second bore and which protrusion is encircling one of the first bore and the second bore. The fluid connection further includes a cavity in a remaining one of the first body and the second body and which cavity is configured to receive the protrusion when mating the first connector and the second connector separating the volume into a first volume and a second volume which is at a distance from the first volume.
In another embodiment, a fluid connection for reducing a fluid volume in the connection includes a first connector having a first body encircling a first bore allowing a fluid flow along the first bore, the first body having a first sealing surface The fluid connection also includes a second connector having a second body encircling a second bore allowing a fluid flow along the second bore, the second body having a second sealing surface capable to form a tight connection with the first sealing surface when both the first connector and the second connector are mated. The fluid connection also includes a volume between the first connector and the second connector when mated, a cross-sectional area of the volume being larger compared to a corresponding cross-sectional area of one of the first bore and the second bore in fluid communication with the volume, and a protrusion in of one of the first body encircling the first bore and the second body encircling the second bore and which protrusion is encircling one of the first bore and the second bore. The fluid connection further includes a cavity in a remaining one of the first body and the second body and which cavity is configured to receive the protrusion when mating the first connector and the second connector separating the volume into a first volume and a second volume which is at a distance from the first volume.
In yet another embodiment a fluid connection for reducing a fluid volume in the connection includes a first connector having a first body encircling a first bore allowing a fluid flow along the first bore, the first body having a first sealing surface The fluid connection also includes a second connector having a second body encircling a second bore allowing a fluid flow along the second bore, the second body having a second sealing surface capable to form a tight connection with the first sealing surface when both the first connector and the second connector are mated. The fluid connection also includes a volume between the first connector and the second connector when mated, a cross-sectional area of the volume being larger compared to a corresponding cross-sectional area of one of the first bore and the second bore in fluid communication with the volume, and a protrusion in of one of the first body encircling the first bore and the second body encircling the second bore and which protrusion is encircling one of the first bore and the second bore. The fluid connection further includes a cavity in a remaining one of the first body and the second body and which cavity is configured to receive the protrusion when mating the first connector and the second connector separating the volume into a first volume and a second volume which is at a distance from the first volume. The first volume and the second volume allow a minor gas exchange with each other by means of an exchange channel between the protrusion and the cavity when the first connector and the second connector are mated.
Various other features, objects, and advantages of the invention will be made apparent to those skilled in art from the accompanying drawings and detailed description thereof
Specific embodiments are explained in the following detailed description making a reference to accompanying drawings. These detailed embodiments can naturally be modified and should not limit the scope of the invention as set forth in the claims.
A fluid connection such as a gas connection for reducing an extra fluid volume such as a dead space in this fluid connection is described. This kind of extra fluid volume is especially inherent in a tapered connection, which are commonly used in patient respiratory circuits. Such a respiratory circuit with a medical gas analyzer is shown in
In
For a more or less stable gas composition the extra volume may not have any major impact on the measurement but for fast changes in gas composition the situation is different, especially when using a fast gas analyzer. This is shown in the graph of
In accordance with an embodiment the extra volume of the fluid connection can be reduced to an acceptable level using a rigid or semi-rigid structure, which may be for example cylindrical and which is able to allow for the considerable axial play of a tapered connection. Such embodiment is depicted in
100261 An internal diameter D2 of said cavity 29 has been reduced to a diameter close to the diameter D1 of the sampling line 8, which is operationally connected to said first bore 21 as shown in
The difference in diameter, D2−D4, should be small enough to allow only a minor gas exchange such as a diffusion between said first volume 30 and said second volume 31 and to only slowly enter the sampling flow through an exchange channel 32, which may be narrow and for example annular, joining said first volume and said second volume. The internal diameter D2 of said cavity 29 is typically identical with the diameter of said first volume 30 and this same applies to across-sectional area of said first volume and said cavity which are typically identical. Said second volume's diameter including said protrusion's 28 diameter D4 is in this embodiment longer than said first volume's diameter. This also means that a cross-sectional area of said second volume including said protrusion 28 is wider than a cross-sectional area of said first volume. Further the cross-sectional area of said first volume 30 is wider than across-sectional area of one of said first bore 21 and said second bore 24 having the diameter D1. The cross-sectional area discussed herein is considered to be perpendicular to a main direction of the flow in said first and second bores.
In the embodiment of
The height of the annular exchange channel 32 depends on the allowable gas exchange between said first volume 30 and said second volume 31. The gas exchange or diffusion time depends on the type of gas, the partial pressure difference of this gas and cross section and length of the exchange channel 32. A simple calculation shows that the dimensions of the exchange channel 32 are not very critical because the gas exchange is a very slow process compared to the time scale of concentration change in the sample flow, compare to the time scale of milliseconds in
In general terms, the length of the protrusion 28, L3+L4 should be about the maximum value within the tolerances of L3 with the addition of the minimum acceptable value of the L4, the exchange channel 32. In the example above this would be L3+L4=2.8 mm+0.5 mm=3.3.mm. Observe that if L3 has its minimum value L3=1 mm, then L4 will be 2.3 mm and the exchange channel 32 will separate said second volume 31 very efficiently. The depth of the corresponding cavity 29 with diameter D2 and length L2+L4 could be the maximum needed clearance of the connection within specification with the addition of the minimum acceptable value of L4 and a small distance to avoid axial contact. In the example this would be L2+L4=1.8 mm+0.5 mm+0.2 mm=2.5 mm. The small additional distance of 0.2 mm then ensures airtight connection for all connectors within the specification. If L3 would be 1 mm in the example above then said first volume 30 with diameter D2 would be only 0.2 mm long. The method is effective in cases where the diameter of the second volume 31, corresponding to D3 in the prior art connection of
Said protrusion 28 in said second body 23 of said second connector 22 of
Variations of the two types of connector in
The connector embodiments above have had conically tapered contact surfaces. The same type of connection leading to a possible unacceptable extra volume can also result from other types of tapered connection fittings. The connectors depicted in
One of said first body 20 and said second body 23 could also have in one of said first sealing surface 25 and said second sealing surface 26 one or several annular ridges 33 to accomplish an airtight connection. In the embodiment of
Another type of conically tapered connection is shown in
The protrusion 28 with a cylindrical structure in
Instead of the connection 35 and sampling channel 37 the adapter 7 could be an adapter for a so called mainstream gas sensor, measuring the infrared absorption directly across the second bore 24. In that case the adapter 7 is provided with two infrared windows according to well-known principles.
Only a few embodiments with different types of tapered connection fittings have been shown above to clarify various embodiments. The common feature is that an unacceptable extra fluid volume inherently is located in the flow channel of the connection. It is to be understood that also other types of connections with this same type of the extra fluid volume problem are possible to improve using the additional rigid or semi-rigid cylindrical structure described.
The written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
Number | Date | Country | Kind |
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10168711.9 | Jul 2010 | EP | regional |