Abstract:
A tubular medical fluid flow set comprises a pressure sensing chamber connected in flow-through relation to fluid flow tubing of the set. The pressure sensing chamber defines a movable, flexible, impermeable diaphragm dividing the chamber into two separate compartments. The fluid flow tubing communicates with one of the compartments and is isolated from the other of the compartments. A port is carried on the chamber, the port having a seal therein, and communicating with the other of the compartments. Thus, the other of the compartments is hermetically sealed until the port is opened for connection with a pressure measuring device, to keep the flexible diaphragm in a desired, initial position prior to opening of the seal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of U.S. application Ser. No. 13/928,454, filed Jun. 27, 2016, which is a division of U.S. application Ser. No. 13/299,868, filed Nov. 18, 2011, which is a division of U.S. application Ser. No. 11/270,080, filed Nov. 9, 2005, now U.S. Pat. No. 8,092,414, all of which are hereby incorporated by reference herein in their entireties. 
     
    
     BACKGROUND 
       [0002]    Sets for extracorporeal blood handling, and also parenteral solution sets, generally require flow-through chambers, often called drip chambers, which, in use, utilize an upper liquid level of the medical liquid passing through it, with an air space on top. Such chambers generally have a permanently connected, branching, hollow-bore, flexible, branch line communicating with said air space for an air pressure line which connects via a reversible connector at its remote end to an equipment pressure port on the permanent equipment, which in turn communicates with a pressure monitor transducer for measuring air-pressure in the chamber as a surrogate for blood-pressure. A pressure-transmitting sterility barrier or diaphragm separates the sterile, disposable set and the unsterile permanent equipment. 
         [0003]    These sets generally need to be initially primed with saline or another parenteral solution, where the proper upper liquid level is provided in each drip chamber present. Then, in the field of extracorporeal blood handling such as in hemodialysis, connection may be made with a fistula set or other means of access to the patient&#39;s bloodstream, and the saline in the primed set is replaced by blood, which is transferred to and from an extracorporeal blood processing device. These devices may comprise hemodialyzers, hemofilters and other devices for extracting components in the blood and returning the balance to the donor. 
         [0004]    Alternately, it is also known for a flow-through chamber to incorporate a diaphragm as the pressure-transmitting sterile barrier which may be in direct contact with blood or another parenteral solution, or may only be in contact with air above the upper liquid level. For example, see Madsen et al. U.S. Pat. No. 3,713,341, Borsanyi U.S. Pat. No. 3,863,504, and Gangemi U.S. Pat. No. 4,077,882. 
         [0005]    As taught in Brugger et al. U.S. Pat. No. 5,693,008, a flow-through chamber or “pod” is provided, having a diaphragm that transmits pressure but prevents passage of blood across said diaphragm. The pod comprises a rigid chamber in which said diaphragm is mounted and which further comprises a reversible connector which communicates with an airspace between said connector and the non-sterile side of said diaphragm. Said reversible connector, air space and non-sterile diaphragm side are open to atmosphere prior to medical treatment. To prepare for treatment, the reversible connector is connected directly to the pressure port on the face of the dialysis machine. Thus, a pressure tight system is attained and the machine&#39;s pressure transducer can measure pressure in the sterile set&#39;s flow-through blood pathway. Flow-through blood tubing must convey blood to and from that pod mounted on the face of the machine. 
         [0006]    As a disadvantage of these diaphragmatic systems, the great majority of over 100,000+ dialysis machines which are clinically used at the present time have their pre-pump arterial, post pump arterial and/or venous pressure ports for measuring blood pressure positioned on the face of the machine remote from other sites to which the blood tubing must be routed, such as the to the blood pump, the dialyzer (in the case of hemodialysis), the safety shut-off clamp, etc. Thus there is a disadvantage in the use of this system. It is always desirable to minimize the length of the extracorporeal blood flow path, both for reasons of simple economy, to minimize extracorporeal pressure drop and clottable surface area, as well as to minimize the total extracorporeal blood volume. 
         [0007]    It is a further disadvantage of the current diaphragmatic system that the non-sterile side of the diaphragm is open to atmosphere prior to being brought into sealing relation with the equipment&#39;s pressure port, and therefore may be displaced prior to use. Such displacement results in pressure measurement errors and/or limited pressure measurements. 
         [0008]    It is a disadvantage of sets which fit the great majority of the world&#39;s dialysis machines that they have drip chambers and permanently attached branch lines. Such branch lines complicate the sets&#39; construction, packaging and use and are expensive. 
         [0009]    By this invention, a generally airless pressure chamber (called a “pod”) which contains a diaphragm may be used as a substitute for a pressure monitoring drip chamber regardless of the front panel placement of necessary equipment. By this invention the pod is not connected to the pressure port on the face of a dialysis machine, but is spaced therefrom, and the important function of pressure monitoring still takes place. This achieves numerous advantages when compared with the prior drip chamber. Specifically, in the pod of this invention, it becomes unnecessary to set a liquid level as in many prior art chambers, and a blood-air interface can be completely avoided. At the same time, the chamber of this invention may be significantly smaller than the drip chambers of the prior art, and thus may have a reduced priming volume. Also, the volume of the chamber can be temporarily further reduced by manipulation of the diaphragm, for example during the rinse back step in extracorporeal blood handling procedures such as dialysis, to reduce the amount of solution needed in the rinse back process. 
         [0010]    Also by this invention there are achieved important advantages when compared with the pods of the prior art. Compared with the priming volume and tubing costs of extracorporeal circuits using pods of the prior art, this invention saves cost because less large-bore blood tubing, but more small bore air pressure monitoring tubing, is used, the latter not containing blood. Thus it can be of a much finer, and cheaper, gauge than blood tubing, resulting in a net savings of plastic and cost, with less blood volume. 
         [0011]    Sets utilizing the pod of this invention are easier to prime and operate, because there is no liquid level needed to be set in a chamber, as in the prior art. The pod of this invention may have branch connections for access to parenteral solutions such as saline or heparin solution, and it also may carry a connected, blood-free pressure monitor line (pressure tubing) for connection to a remote pressure port, for the monitoring of particularly blood pressure in the tubular set which carries the chamber. Cost may be saved in the manufacture and assembly of the set of this invention, since the blood tubing may be shortened, as it does not have to extend to the face of the dialysis machine, while also reducing extracorporeal blood volume (priming volume), as a clinical advantage. 
         [0012]    The pod of this invention may be positioned precisely where pressure needs to be determined. For example, to detect line kinks or leaks, the pressure measuring chamber or pod should be upstream of the tubing which may leak or become kinked. Where a dialyzer is remotely monitored from a machine (as is generally the case) the placing of a pressure measuring chamber or pod immediately downstream from it is impossible in the case of drip chambers or prior art pods. As a further advantage, the pressure chamber of this invention does not require a permanently connected pressure monitor line. Rather, it can connect with a reusable pressure monitor line. Thus the set utilizing the chamber is less expensive, and there is an overall saving of cash because many disposable sets may be sequentially used with a single pressure monitor line, if desired. 
       SUMMARY 
       [0013]    In accordance with this invention, a tubular blood flow set is provided which comprises a pressure sensing pod connected in flow-through relation to fluid flow tubing of said set, typically blood tubing. The pressure sensing pod defines a movable, flexible, impermeable diaphragm dividing the pod into two separate compartments. The fluid flow tubing communicates with one of the compartments for fluid flow through the compartment. The fluid flow tubing is isolated from the other of the compartments by the diaphragm. A pod connector carried on the pod communicates with the other of the compartments. In one embodiment of this invention a hollow-bore branch line is permanently attached to and communicates with the pod connector. The branch line is long enough, and terminates in a releasable connector such that it mates with the machine&#39;s pressure port. In another embodiment, the pod connector is releasable, and may be temporarily attached to a separate branch line bearing an appropriate mating connector for the pod connector. As before, the branch line is long enough, and terminates in a releasable or non-releasable connector to the pressure sensing machines pressure port. Preferably, the pod connector is sealed prior to attachment to either the machine port directly, or preferably to said separate branch line. Such sealing may be permanently breached, as in a frangible barrier, or it may be reversibly opened such as attained by a slit disc of U.S. Patent Publication No. US 2005/0159710 A1, the disclosures of which are incorporated by reference. 
         [0014]    Thus, the one compartment of the pod is part of a fluid flow path, typically blood, through the fluid flow set and the pressure sensing chamber. The other of the compartments is preferably hermetically sealed by a sealed port, until opened for connection with a pressure measuring device. The effect of this is to keep the movable, flexible diaphragm in a desired, initial position prior to said opening. The diaphragm, when the hermetic seal is broken, is capable of moving between a first position and a second, opposed position in which the diaphragm in the first position can bow outwardly from the blood pathway, to maximize blood volume in the chamber, while the diaphragm in the second position can bow inwardly to minimize, but typically not eliminate, blood volume in the chamber. In some embodiments, the diaphragm has a central, domed portion which can flip between the two positions. 
         [0015]    In an arterial, pre-pump pod embodiment where the pod is generally subjected to negative pressure [but sometimes positive pressure when priming], the diaphragm may be moveable between the first and second positions when the hermetic seal is broken, but not before. The same holds for the post pump, positive pressure situation. 
         [0016]    In some embodiments, the sealed port is opened by engagement with a connector which is carried on an end of a length of separate pressure tubing. This connector may be, for example, a male luer lock connector or any other desired connector that is compatible for connection with the sealed port carried on the pod. Also, the pressure tubing connects at an opposed end thereof with the pressure measuring device, either permanently or separably, as may be desired. 
         [0017]    Specifically, in some embodiments the sealed port of the pod may be so sealed by a partition having a peripheral connection with a lumen wall of the sealed port. A major portion of the peripheral connection is relatively thin, capable of being easily broken open, while a minor portion of the peripheral connection is thicker than the major portion of the peripheral connection, so that the minor portion functions as a hinge. Thus the partition can pivot, but it cannot separate from the rest of the sealed port as it is torn open by an advancing connector such as a male luer. 
         [0018]    In some embodiments, the sealed port partition is relatively thin in a line of tearing weakness extending across the partition, as well as around most of the periphery so that, when broken, there are two hinges and half partitions which distend a lesser distance inwardly than the previous embodiment. 
         [0019]    Further, by this invention in some embodiments, a first section of the partition adjacent to the major portion (but radially inwardly therefrom) is thicker than the corresponding, opposite section of the partition adjacent to the periphery thereof. The effect of this is to focus rupturing force provided by pressure from a male luer or other tubular connector to the periphery of the partition at the first section. Thus, when a normal, flat-ended tubular connector is inserted into the sealed port and pressed inwardly, it encounters the first section and presses against it, without contact with the opposite section. Accordingly, the rupturing force is focused against only a portion of the periphery of the partition, that portion being at least part of the major portion of the peripheral connection, thin enough to be easily broken open. This force is focused because the tubular connector is engaging only the first section of the partition because of its increased thickness, and not the corresponding, opposite section. Thus the total force required for frangibility of the partition is less. The partition easily opens and pivots about the minor portion of the peripheral connection, to open the sealed port. 
         [0020]    Typically the first section of the partition is at least twice as thick as the corresponding, opposite section. 
         [0021]    Thus, a blunt tube such as a male luer can easily open the partition. 
         [0022]    Further in accordance with this invention, a pressure sensing chamber or pod for a tubular medical flow set described above may be directly and permanently attached to an inlet or outlet connector, for direct, typically releasable, connection with an extracorporeal blood processing device. The set that carries the chamber is for handling extracorporeal blood flow, with the pressure sensing chamber being directly attached, preferably to the downstream end of, the extracorporeal blood processing device such as a hemodialyser. The pressure monitor system that utilizes the pressure sensing pod is thus capable of monitoring pressure of the entire length of the blood flow tubing extending downstream from the extracorporeal blood processing device, typically a dialyzer. This is a significant area for pressure monitoring, because it is typically the majority of the extracorporeal blood flow circuit that operates under positive pressure. A serious blood leak or kink anywhere along the line downstream of the dialyser can thus be detected by a pressure fluctuation, if there is constant monitoring through the pressure sensing chamber. 
         [0023]    Generally, the diaphragm of the pod occupies substantially a first position when the interior of the flow set is filled with a blood at close to atmospheric pressure, as when the pump is stopped or during priming, and the diaphragm is urged towards the second position whenever the blood side pressure on the diaphragm is less than the air side pressure on the diaphragm. Such greater air side pressure may be intentionally applied through said pressure tubing, which may be flexible, by a machine system having an air pump communicating with said tubing, or the pressure tubing may be disconnected from the machine&#39;s port and reconnected to a device such as a syringe. In either case, positive pressure may intentionally be applied to the chamber to drive the diaphragm towards the second position, which may be desirable during a blood rinseback procedure, involving rinsing blood from the tubular set, back to the patient, since the internal volume of the chamber is minimized by such intentional pressurization, thus reducing the hydration that must be provided to the patient. The tubing may carry a clamp or valve to retain the positive pressure at the diaphragm. 
         [0024]    Alternately, the pod of this invention may comprise an arterial post-pump and/or venous pod embodiment where the pod is generally subjected to positive pressure. The diaphragm may substantially initially occupy the second position when the interior of the flow set is filled with blood at close to atmospheric pressure; and the diaphragm is urged towards the first position whenever the blood side pressure is greater than the air side pressure on the diaphragm, so that the greater the blood pressure, the more the diaphragm is driven from the second position toward the first position. 
         [0025]    Movement of the diaphragm between the first and second positions is restricted by the fact that, in the pressure sensing process, a sealed, fixed volume of air exists between the diaphragm and a pressure sensing transducer, with the branch line pressure tubing extending therebetween. Thus, movement of the diaphragm toward one position or another position will reflect a change of the level of compression of the air or other compressible fluid in the fluid flow path between the diaphragm and the pressure sensing transducer, thus transmitting the pressure of the blood to the transducer. Thus, in this circumstance, the diaphragm does not flip back and forth with ease between the first and second positions because of the sealed volume of air or other compressible fluid in the flow path between the diaphragm and the pressure transducer. 
         [0026]    Further in accordance with a preferred embodiment of this invention, the sealed port communicating with the other of the compartments of the pressure sensing chamber facilitates the priming of the medical fluid flow set, since it provides the sealed, fixed volume of air discussed above that holds the diaphragm in the desired position. This desired position may vary, depending on whether the pod is to be exposed to reduced pressure or elevated pressure during normal operation. 
         [0027]    One can see that if the other of the compartments separated from fluid flow by the diaphragm is not sealed, the diaphragm will flip from one position to the other in accordance with pressures that are encountered in the fluid (blood) flow path during shipping, installation or priming. If the diaphragm winds up in the wrong position at the end of priming, inconvenient steps will have to be taken, while maintaining sterility, to remedy it. 
         [0028]    Thus, the sealed port holds the diaphragm in its desired position, which position depends upon its contemplated use, until priming or other desired step(s) has been completed. Then, one can open the seal of the pressure sensing pod port as a sealed connection is made with a pressure line, so that now the pod is again sealed with the pressure line communicating between the chamber and the pressure monitor. 
         [0029]    Specifically, when the blood flow set of this invention is being used as an arterial set for hemodialysis, upstream from the roller pump tubing so as to encounter negatively pressurized blood (i.e., blood under suction pressure from the roller pump), it may be preferred for the pod diaphragm at ambient pressure to initially occupy a position substantially close to the first, volume maximizing position. Thus, as negative (subatmospheric) bloodline pressure increases, the diaphragm moves incrementally toward the second position, with that movement being resisted by the sealed, fixed volume of air, which is being expanded in response to the negative (subatmospheric) pressure of the blood acting upon the diaphragm. Thus, the negative pressure is duplicated in the fixed volume of air or other compressible fluid, and may be sensed by the pressure transducer, which is positioned remotely from the pressure sensing chamber and diaphragm used in this invention. Under positive pressure blood line conditions, the diaphragm starts generally at the opposite, first position. However, when there is open or ambient pressure on both sides of the diaphragm, the diaphragm may flip back and forth between its first and second positions relatively easily. 
         [0030]    The above-described chamber or pod may have a bottom wall, which further defines a channel having a wall of U or V-shaped cross section. Accordingly, when the diaphragm is forced into its extreme, second position, fluid flow is not blocked through the channel, so that flow is provided in all circumstances through the medical fluid flow set. Specifically, the channel wall may be U-shaped and substantially contiguous with the internal diameter wall of the flow tubing of the set, preferably being substantially aligned with, and of a size similar to, the inner diameter wall of the flow tubing of the set where it connects with the chamber. This can promote efficient fluid flow through the entire set, even when the diaphragm is held in its second, blood volume minimizing position. 
         [0031]    Also, one or more access ports may be provided to the pod&#39;s inlet or outlet connection or the pressure chamber communicating with its blood pathway. These ports may be used to provide parenteral solution, heparin, or other medicaments to the blood or for withdrawing blood or air or saline from the flowpath. 
         [0032]    The pod may be connected at one end via a flowthrough port with the pump tubing of the set, which comprises typically roller pump tubing, which is carried on many extracorporeal blood transport sets. Alternately, the flowthrough port may connect with another pump apparatus, or it may connect to a venous air-trapping chamber, or any other flowthrough component of an extracorporeal set. The pressure chamber (pod) then has another end with another flowthrough port which may fit tubing of same or different diameter from pump tubing or to another flowthrough component. Thus, this pod may serve the additional function of a pump segment connector, a tube connector, or a device connector, as well as providing other function as described herein. 
         [0033]    Further by this invention, blood may be rinsed from the extracorporeal blood flow tubing and returned to the patient, after an extracorporeal blood flow procedure such as hemodialysis. The blood flow tubing is connected to the pod having the flexible diaphragm, which defines a blood holding volume. The diaphragm is sealingly mounted within the chamber. This method comprises the steps of pressurizing the chamber to move the diaphragm, to cause the blood holding volume of the chamber to be substantially minimized, without blocking blood flow through the blood flow tubing and chamber. Then, parenteral solution such as saline is caused to pass into the tube and chamber to replace the blood, while the blood is returned to the patient. The substantially minimized blood holding volume of the chamber reduces the fluid volume of the extracorporeal blood flow tube, which provides clinical advantage, and requires the use of less solution to provide the desired rinseback. 
         [0034]    Typically, this method is practiced after the step of using the pod to sense blood pressure in the blood flow tube during extracorporeal blood processing, with the diaphragm being positioned to enlarge the blood-holding volume in the chamber above the minimum volume, a length of pressure tubing extending from the chamber to a pressure monitor device 
         [0035]    Further by this invention, a pressure transmitting pod defines a chamber, the pod being for connection and flow-through relation to fluid flow tubing of the fluid flow set. The pod has a flexible fluid impermeable diaphragm dividing the pod into separate compartments. The first of the compartments communicates with flow connectors for the fluid flow tubing. A second of the compartments communicates with a pressure connection port for connection with the length of pressure tubing at one end thereof. The tubing is for sealed connection at its other end to a remote pressure connector of a pressure sensing machine, to transmit pressure from the second of the compartments through the pressure tubing to the pressure sensing machine for pressure monitoring. The diaphragm has a dome shape, and is sufficiently flexible to easily distort in a manner reflective of pressure changes, to vary the volumes of the two compartments. In some embodiments, the diaphragm of dome shape can vary the volume of the respective compartments at a pressure variation of 500 mm mercury by at least 3 cc. 
         [0036]    The pressure tubing may be permanently connected to the connection port, the pod, or releasably connected as previously described. The pressure tubing at its other end can connect to a remote tubing connector for connection to the machine remote pressure port during medical treatments, or permanently, if desired. As previously described, the pod connection port is sealed from the atmosphere by an internal partition, the seal being openable by sealing attachment with a connector of the pressure tubing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    In the drawings,  FIG. 1  is a partially diagrammatic, sectional view of a portion of a first embodiment of a tubular blood flow set using the pressure sensing pod and flexible diaphragm disclosed. 
           [0038]      FIG. 2  is an exploded, perspective view of the pressure sensing pod of  FIG. 1   
           [0039]      FIG. 3  is a plan view of the pressure sensing pod of  FIG. 1 . 
           [0040]      FIG. 4  is a longitudinal sectional view taken along line  4 - 4  of  FIG. 3 . 
           [0041]      FIG. 5  is a transverse, sectional view taken along line  5 - 5  of  FIG. 3 . 
           [0042]      FIG. 6  is an end elevational view of the chamber of  FIG. 3 . 
           [0043]      FIG. 7  is a plan view of a hemodialysis set, making use of another embodiment of this invention. 
           [0044]      FIG. 8  is an exploded, longitudinal sectional view of a pressure sensing pod of the set of  FIG. 7 . 
           [0045]      FIG. 9  is a sectional view taken along line  9 - 9  of  FIG. 8 . 
           [0046]      FIG. 10  is a fragmentary, enlarged plan view of a portion of  FIG. 7 , showing the connection of the pressure sensing pod of  FIG. 8 . 
           [0047]      FIG. 11  is a detailed view of  FIG. 8 , showing how a connector such as a male luer lock connector can rupture the partition for access to the pressure sensing pod. 
           [0048]      FIG. 12  is a view similar to  FIG. 9  of another embodiment of the sealed port partition 
           [0049]      FIG. 13  is a sectional view taken along line  13 - 13  of  FIG. 12 . 
           [0050]      FIG. 14  is a fragmentary view of the sealed port of  FIG. 13 , carried on a pod as in previous embodiments, about to be connected with a pressure tube as in previous embodiments. 
           [0051]      FIG. 15  is a sectional view showing an initial connection (of luer lock type) of the components of  FIG. 14 . 
           [0052]      FIG. 16  shows a fully advanced, sealed connection of the components of  FIG. 14 , with the partition of  FIG. 12  being opened by advancement of the male luer lock connector. 
           [0053]      FIG. 17  is a perspective view of the connector of  FIG. 14 , showing internal parts. 
           [0054]      FIG. 18  is a plan view of another embodiment of the pod of this invention. 
           [0055]      FIG. 19  is a sectional view taken along line  18 - 18  of Fig. A. 
       
    
    
     DETAILED DESCRIPTION 
       [0056]    Referring to the drawings,  FIG. 1  shows a portion of a venous set  10  for hemodialysis, conventional except as otherwise shown. Set  10  is shown to comprise a length of roller pump tubing  11 , which is conventionally attached to one end of pressure sensing pod chamber  12  of this invention. The opposed end  14  of pod  12  may connect to a length of set tubing  16 , which may connect to other set components, which may be of conventional design for an extracorporeal blood conveying set. Particularly, tubing  16  may fit within the inner diameter of end portion  14  so that such tubing is of a different inner diameter from that of pump tubing  11 , if desired. Thus, pressure pod  12  also includes the function of a connector for joining together tubing of differing diameters in the blood set. 
         [0057]    Similarly, the end  18  of pump tubing  11  may connect through a conventional connector, such as one shown in U.S. Pat. No. 5,360,395, (the disclosures of which are incorporated by reference) to a length of tubing  20  to connect additional, conventional portions of a tubular blood set for hemodialysis or another extracorporeal blood treatment procedure. For both tubes  20  and  16  these may include injection sites, Y sites, and end connectors, which may connect in this present embodiment respectively with a dialyzer and the patient, but in other embodiments could connect with a different, extracorporeal blood processing device, or any other conventional connection. 
         [0058]      FIG. 2  shows an exploded view of pressure pod  12 , comprising a lower compartment-defining portion  22 , an upper compartment-defining portion  24 , and a flexible diaphragm  26 , which defines a convex, central portion  28  shown to be bulging outwardly from the blood flow portion of the chamber. Compartment defining portion  22  defines a blood inlet port  30  and a blood outlet port  32 , as well as an access port  34 , which communicates with the interior of the chamber. Each of these ports  30 ,  32 ,  34  may be connected to flexible tubing in a conventional manner. As shown in  FIG. 1 , ports  30 ,  32  connect with blood flow tubing, while port  34  can connect with tubing  35  which, in turn, may connect with a source of parenteral solution such as saline, or a source of heparin solution, or any other desired or conventional use. Tubing  35  connects with the interior of pressure pod  12  through aperture  38 . 
         [0059]    The three components  22 ,  24 ,  26  of pressure pod  12  seal together with peripheral, circumferential connection, and may be conventionally bonded together by conventional means such as ultrasound sealing or solvent bonding, the components being made typically of conventional thermoplastic and/or thermoset materials, to form the completed chamber as shown in  FIGS. 3 to 6 . Upper compartment-defining portion  24  as shown in  FIG. 2  may be rotated by 180 degrees to form the assembled device shown in  FIGS. 1, 3 and 4 . 
         [0060]    Thus, flexible diaphragm  26  is shown in the assembled pod  12  as being sealingly mounted within a pressure sensing pod between connections of the blood flow tubing  30 ,  32  and a connection port  40 , which may have a seal such as a known valve, or a frangible barrier. Port  40  may connect with a length of pressure tubing  42  ( FIG. 1 ), which is thus connected with the interior of upper compartment-defining portion  24  of pressure sensing pod  12 . In  FIG. 1 , diaphragm  26  is shown to be occupying its first position as previously described, where diaphragm  26  initially bows outwardly to maximize the chamber volume communicating with the blood flow tubing  11 ,  16 . When the blood flow within pod  12  is under negative or subatmospheric pressure, as is the case for portions of set  10  which are upstream of roller pump tubing  11 , a suction is induced on diaphragm  26 , causing it to be urged downwardly toward inlet and outlet ports  30 ,  32  in position  26   a . Pressure tubing  42  is long enough so that it will reach pressure measuring equipment connector  41  mounted anywhere on the equipment. Equipment pressure connector  41  communicates with a pressure transducer  43  as in a conventional hemodialysis machine, for example, communicating by the joined end connector  44  of tube  42  and connector  41  with the air space within tube  42  and above diaphragm  26 . This air space can be sealed when connectors  44  and  41  are joined, so that air neither is added to nor escapes from the volume of air present. 
         [0061]    Thus, as suction from the negatively pressurized blood below diaphragm  26  is exerted, an expansion of the fixed volume of air described above takes place, which will allow diaphragm  26  to move downwardly until the negative (subatmospheric) pressures on both sides of the diaphragm are balanced. Thus, the air pressure in tube  42  will match the pressure of the blood below diaphragm  26 , and that air pressure can be sensed by pressure sensor  43 , and reported by an appropriate signal on preferably a moment-by-moment, real time basis, as is important in the field of extracorporeal blood handling. 
         [0062]      FIG. 4  shows how diaphragm  26  can be moved to its second position  26   a , in which it bows inwardly with respect to the blood flow path, to significantly reduce the blood volume in chamber  10 . Diaphragm  26  may be initially held in this position for the measurement of positive, super-atmospheric pressures in the blood flow path  46 , where increases in pressure urge diaphragm  28  outwardly from near the second position  26   a  ( FIG. 4 ) toward the first position  26  ( FIG. 1 ). However, as before, this movement is resisted by the fact that there is a constant amount of air the space  48  above diaphragm  26  and in pressure tube  42 . The air pressure in pressure tube  42  equals the blood pressure in flow path portion  46 , with diaphragm  26  moving to make it so, so that the blood pressure can be monitored by transducer  43  while the unsterile pressure connectors  41 ,  44  remain remote from any blood, being conventionally carried on the face of a dialysis machine or the like at a position spaced from the arrangement of the roller pump, pump tubing  11 , and chamber  12 . Because of the presence of pressure tubing  42 , which extends to connector  41  and pressure transducer  43 , wherever it may be located on or in the dialysis machine, it is possible to shorten the overall length of the blood tubing  16 ,  11 ,  20 , which is desirable for reasons stated above. 
         [0063]    The lower compartment portion  22  of pod  12  has a bottom wall which defines a transverse channel  50 , which extends between blood inlet port  30  and blood outlet blood port  32  Channel  50  is shown to be of U-shaped cross-section, being substantially aligned with, and having a size similar to, the inner diameter of the blood flow port  30 ,  32  and the tubing which they carry, to provide efficient fluid flow, even when diaphragm  26  is in its second position, as shown in  FIG. 4  as diaphragm  26   a . The presence of channel  50  assures that there will not be major blocking of blood flow when diaphragm  26  is in its second position. 
         [0064]    When the extracorporeal blood processing procedure is complete, it is necessary to rinse the blood back to the patient in a step known as “rinse back.” To accomplish this, pressure tubing  42  may be disconnected from the pressure monitor transducer  43 , and the portion of the set which draws blood from the patient can be removed from the patient. Then, pressure tubing  42  is connected with a conventional syringe  52  ( FIG. 1 ), which is depressed to add air or other fluid to the system to cause diaphragm  26  to assume its second position as shown in  FIG. 4  ( 26   a ). A slide clamp  54  or other type of clamp then may close off pressure tubing  42 , to keep diaphragm  26  under pressure and firmly in its second position  26   a  during the rinse back process, so that the blood containing volume of pod  12  is minimized Saline solution or the like flows into the system through an access site such as parenteral solution line  35 , to replace blood in the set with saline solution, and to return blood back to the patient through the remaining patient connection. Alternatively or additionally, saline solution may be added to the separated end of the set of set portion  16  for rinseback, to terminate the procedure. 
         [0065]    Thus, by one embodiment of this invention, blood pressure in a blood flow tube may be monitored through a length of pressure tubing  42  connecting to a diaphragm pod  12  as described, with the diaphragm being positioned near a first position that essentially maximizes the blood holding volume in the pod, although varying, for example negative, pressures in the chamber can result in differing positions of the diaphragm. Then, at the end of the extracorporeal blood flow procedure, pressure sensing pod  12  may be pressurized to move diaphragm  26  to its second position  26   a , to cause the blood holding volume of the pod to be substantially minimized, without blocking flow through the blood flow tube and pod. Parenteral solution such as saline is then passed into the tube and pod to replace the blood, while the blood is returned to the patient. 
         [0066]    Referring to  FIGS. 7-11 , another embodiment of the invention is shown for an extracorporeal system for hemodialysis. 
         [0067]    Arterial set  60 , for removing blood from the patient, comprises a connector  62  for connection with a patient fistula. A length of flexible tubing  64  communicates with an injection site  66  which, in turn, is directly connected to a pressure sensing pod  68 , similar to that shown in  FIG. 8 . Pressure sensing pod  68  connects with pump tubing  70 , having a larger diameter than tubing  64 . Tubing  70 , in turn connects with a connector  72  for connection with lesser diameter blood flow tubing  74 , which, in turn, connects with dialyzer  76 . The dialysis solution flow lines are eliminated for clarity of disclosure. Solution line  69  connects with pod  68  in a manner similar to line  35  of  FIG. 2 . 
         [0068]    Dialyzer  76 , in turn, connects directly to a connector  78 , of conventional design, which, in turn, connects directly to another pressure sensing pod  80  of a type disclosed in  FIG. 8  and other drawings. Thus, pressure sensing pod  80  can be disconnected from dialyzer  76  to permit reuse of dialyzer  76 , coupled with disposability for pressure sensing pod  80  and the connected venous set  82 . 
         [0069]    Connector  78  may be an appropriate threaded, locking connector or the like, preferably one that meets the DIN specifications or any other means for a secure connection, including an adhesively bonded connection, to dialyzer  76  via its conventional connector  77 . 
         [0070]    Pressure sensing pod  80  connects with blood flow tubing  84  which, in turn, connects with an air trap chamber  86  which may be conventional, for example of a design similar to that disclosed in U.S. Pat. No. 6,517,508, the disclosures of which are incorporated by reference, in which bubbles are separated by centrifugal flow without suction of the bubbles downwardly by the formation of a vortex. Preferably, air trap chamber  86  may be operated with no upper liquid level or airspace for a completely airless extracorporeal system, but for bubbles collected. Tubing  88  connects to the bottom of air trap chamber  86  at one end, and connects to a conventional patient fistula connector  90 . Connector port  87  is also provided. 
         [0071]    Turning to  FIG. 8 , an exploded view of pressure sensing pod  80  is shown, the structure of pressure sensing pod  68  being also similar to it, except for the elements to which it is connected. 
         [0072]    Pressure sensing pod  80  defines a lower compartment portion  22   a , generally similar to the embodiment shown in  FIG. 2 , including the bottom flow groove  50   a  similar to groove  50 . Diaphragm  26   a  is generally of similar design to diaphragm  26 , having a bulge  28   a  of slightly different design. Pressure sensing pod  80  is then closed with upper compartment portion  24   a , the peripheries of the portions being sealed together in a conventional manner. 
         [0073]    Port  112  may be used for testing in manufacturing, and may be sealed with an amount of sealant  114 . 
         [0074]    Pressure sensing pod  80  carries sealed port  116 , which may be generally of the design of a female luer lock connector, having lugs or screw threads  118  in conventional manner, or other sealing and/or locking means. Port  116  is sealed by partition  120 , so that the volume  92 , which is spaced by diaphragm  28   a  from flow ports  30   a ,  32   a , is hermetically sealed when the periphery  94  of pressure sensing pod  80  is sealed. Partition  120  has a peripheral connection with lumen wall  96  of sealed port  116 . 
         [0075]    The pressure sensing diaphragm in pod  80  defines a dome  28   a  which has a maximum depth  29  of about 6-7 mm (such as 6.3 mm), and a width of the chamber defined by the dome of about 23-25 mm., specifically 24 mm. 
         [0076]    As shown particularly in  FIG. 9 , partition  120  has a 360° peripheral connection with lumen wall  96 , with a major portion  98  of the peripheral connection being relatively thin, typically a film of sealing material about 0.2 to 0.4 mm thick. This thin, frangible peripheral band  98  comprises the major portion of the circumference of partition  120 , for example extending from about 270°-330° of the circumference, specifically about 300°. 
         [0077]    At the periphery of the remaining portion of the circumference of partition  120 , a minor portion  100  of the peripheral connection may be thicker, on the order of 1 mm thick, so that it is not frangible but, rather, serves as a hinge to permit partition  120  to pivot as it is broken open by the pressure of an advancing tubular member, such as a male luer lock connector, advancing through lumen wall  96  of connector  116 . 
         [0078]    Additionally, as shown in  FIGS. 8 and 9 , a first section  102  of partition  120  is positioned adjacent to at least some of the major, thin, peripheral portion  98 . This first section  102  is thicker than the corresponding, opposite section  104  of partition  120  adjacent to the periphery of minor portion  100 . Thus, when a tubular connector  106 , as shown in  FIG. 11 , is advanced into the lumen of connector  116 , in the normal circumstance when tubular male luer lock connector  106  has a flush, tubular end, it engages first, thickened portion  102  of partition  120 , which is positioned adjacent to major, peripheral portion  98 , to focus rupturing force to at least some of major peripheral portion  98 . Thus, inward pressure of tubular connector  106  causes rupturing force that is focused onto at least a portion of the thin, major, peripheral portion  98 , causing major portion  98  to rip open. Minor peripheral portion  100 , however, is thick enough, typically on the order of 1 mm, to not rip, but rather to bend as a hinge, to open connector  116 . It is accordingly desirable for connector  116  and particularly partition  120  to be made of a material such as polyethylene, which is capable of forming a reliable, strong hinge upon bending at the hinge thickness used. 
         [0079]    As shown in  FIG. 8 , pressure sensing pod  80  is attached to a blood flow connector  78 , and thus may be directly, releasably or permanently connected with an extracorporeal blood processing device such as dialyzer  76  ( FIG. 10 ). Connector  78  may be a connector that complies with DIN standards in a conventional manner. 
         [0080]    As shown in  FIG. 11 , male luer connector  106  may be carried on the end of pressure tubing  42   a  in a manner similar to tubing  42  of  FIG. 1 , except that pressure tubing  42   a  is not shown permanently bonded to pod  80 . Thus, pod  80  may be reversibly or permanently attached to a connector  41  ( FIG. 1 ) which communicates with an electronic pressure monitor  43  of the machine. In this present embodiment of  FIGS. 10 and 11 , tubing  42   a , end connector  44   a , and male luer connector  106 , having locking sleeve  108 , may be reusable for a large number of connections with different pressure sensing pods  80 , since connector  116  communicates with volume  92  inside of pressure sensing pod  80 , which volume is sealed from the blood flow path  31   a , by diaphragm  26   a . Thus, sterility does not have to be an attribute of pressure tubing  42   a . This permits the long term or even permanent communication of tubing  42   a  and electronic pressure sensing device  43 , wherever remotely located on the machine, and its sequential use with a large number of separate blood flow sets, such as that of  FIG. 7 . 
         [0081]    Saline line  69  of set  60  provides a connection with pressure chamber or pod  68  in a manner similar to the saline line connection  34  of  FIG. 2 . Pressure sensing pod  68  also carries a connector  116   a  similar in structure and function to connector  116 . 
         [0082]    The particular design of partition  120  and sealed connector  116  and other disclosed designs, may be used in other modes of use for medical fluid flow sets, for example, as a sealed port for a Y or T connector, or a connector to another kind of pod or chamber for any of various uses. The connectors disclosed may be connected to a pump tubing segment connector  72  to receive a heparin branch line (not shown), and/or the connectors may be carried on arterial inlet connectors to receive an attachable injection site. In this way, branch tubing components of the blood set can be reduced or eliminated, for cost savings. 
         [0083]    Referring to  FIGS. 12-17 , a diaphragm chamber or pod  80   a  is similar to chamber  80  except as otherwise described. Pod  80   a  carries a sealed port  116   a , similar to port  116 , attached to pod  80   a , and generally of the design of a female luer lock connector, having lugs or screw threads  118   a  in conventional manner or other sealing and/or locking means. Port  116   a  is sealed by partition  120   a , so that the volume  92   a  which is spaced by the diaphragm of pod  80   a  (similar to diaphragm  28   a  in the previous embodiment) is hermetically sealed when the periphery of pod  80   a  is sealed, as in the previous embodiment. Partition  120   a  has a peripheral connection with the lumen-defining wall  96   a  of port  116   a.    
         [0084]    As shown particularly in  FIG. 12 , partition  120   a  has 360 degree peripheral connection with lumen wall  96   a , with a diametrically opposed pair of peripheral, thin walled tear lines  130 , being positioned adjacent to lumen wall  96   a  and comprising a major portion of the circumference of partition  120   a . These tear lines are relatively thin, comprising lines partition wall of material typically about 0.2-0.4 mm thick, depending of course upon the particular plastic used. These thin, frangible peripheral tear lines may extend, for example, at least about 250 degrees of the total circumference, and typically no more than about 340 degrees. 
         [0085]    Partition  120   a  also defines a similarly thin-walled tear line  132  extending substantially as a diameter across partition  120   a , to generally bisect partition  120   a  by separating it into two, generally similar halves. 
         [0086]    At the periphery of the remaining portions of the circumference of partition  120   a , minor portions of the periphery  134 , which are the remaining portions of the circumference, may be thicker than portions  130  and  132 , being generally on the order of 1 mm thick or more, so as not to be frangible, but, rather, to serve as hinges to respectively permit the two halves of partition  120   a  on either side of central, thin tear line  132  to pivot as partition  120   a  is broken open by the pressure of an advancing tubular member such as male connector  136 , which may be connected to pressure connection tubing  138 , for similar purpose as tubing  42 ,  42   a , or for any other desired medical purpose. 
         [0087]    Connector  136  may define a projecting, frustoconical sealing member  140  which mates in the manner of a luer connector with tapered, frustoconical lumen wall  96   a . Projecting member  140  further carries a partition opening member  142  at its forward end, which, in turn, may comprise a frustoconical member of greater wall angle to the axis of connector  136 , or it may comprise a pointed member with open lumen flow ports positioned beside it, or any member which can press against partition  120   a  to rupture lines  130 ,  132 , to open partition  120   a.    
         [0088]    Thus, instead of a thickened partition broken by a regular male luer or other tube having a flush end, as in the previous embodiment, in this embodiment, a partition is provided without thick sections (but having the thinned tear lines  130 ,  132 ) and which uses an extension  142  on a male connector  140  to break partition  120   a . This has advantage when one does not want a regular male luer lock connector or the like to mistakenly access the device, since it can be formed so that a male connector engages and seals with frustoconical lumen surface  96   a  before the male luer can reach partition  120   a  to press it, to cause possible premature opening. Thus, a special set with a special connector  136  may be required to open sealed port  116   a.    
         [0089]    This special male connector  136  is carried on the end of pressure tubing  138 , which may be similar to pressure tubing  42   a  of  FIG. 10 , except that pressure tubing  138  is not permanently bonded to pod  80   a  and upper compartment portion  92   a , and may be reversibly or permanently attached to a pressure port similar to port  41 , which communicates with an electronic pressure monitor  43  of a pressure measuring machine. 
         [0090]    In the embodiment of  FIGS. 12-17 , tubing  138  and special male connector  136 , having locking sleeve  143 , may be reusable for a large number of connections with different diaphragmatic chambers or pods  80   a , since connector  116   a  is sealed from the blood flow path by its diaphragm. Sterility thus does not have to be an attribute of pressure tubing  138  (or tubing  42   a ), permitting the long term and even permanent connection of tubing  138  to electronic pressure sensing system  41 ,  43 , wherever remotely located on the machine, such as a dialysis machine. Thus, a significant economy may be achieved by the sequential use of tubing  138  and connector  136  with a large number of separate blood flow sets. 
         [0091]    Referring to  FIGS. 18 and 19 , a pod  150 , defining a chamber  152  and a flexible diaphragm  154 , defining a dome in a manner similar to those of previous embodiments such as diaphragm  26 , is disclosed. Pod  150  may be used in a manner described with respect to pods of the previous embodiments, being connected through tubular connectors  156 ,  158  to tubular components of an extracorporeal blood set, or directly connected at one of the connectors  156 ,  158  to a dialyzer or the like, as previously described. Port  160  is provided, being for a similar purpose as is port  116 ,  116   a  of the previous embodiment, carrying a partition  163 , which may be of design similar to the partitions of the previous embodiments and for similar purpose. 
         [0092]    It can be seen that pod  150  is elongated, and in some embodiments of this invention, the length of pod chamber  152  along its longest axis  153  may be at least twice its width  162 . This provides a greater volume to pod  150  compared with a round pod having a diameter similar to the width  162  of pod  150 . The dome of diaphragm  154  can flip back and forth in a manner described with respect to previous embodiments, and thus, the overall volume of the air side  164  of the chamber and go from essentially zero as shown in  FIG. 19  to a volume which is at least 2.5 cc, preferably 3.0 cc., and specifically more than 3.2 cc., typically, so that an air volume of that amount can form when flexible diaphragm  154  is displaced to its maximum position on the right of  FIG. 19 , to minimize the volume of blood compartment  166  in pod  150 , for the advantages previously discussed. 
         [0093]    Thus, as flexible diaphragm  154  flips its dome between its two positions, there is a volume displacement, displacing at least 2.5 cc. of air and typically greater amounts as specified above. This amount of displacement assures that a broad pressure range in pod  150  can be monitored despite using a lengthy tube several feet in length which connects port  160  with a pressure transducer mounted within a pressure sensing component of, for example, an extracorporeal blood processing machine, as in previous embodiments. Specifically, it is desirable for the system to be able to register a range of 500 mmHg of positive pressure to minus 250 mmHg of reduced or negative pressure without the dome of diaphragm  154  coming into contact with a wall of pod  150  so that it can no longer move its position responsive to pressure change. It can also be seen that stretching of the elastomer of diaphragm  154  is minimized by the dome configuration as the dome moves back and forth. In fact, in some embodiments, flexible but non elastomeric materials may be used for the dome  154 . 
         [0094]    Specifically, to achieve the desired volumes in a small pod, the width  162  of diaphragm  154  (essentially the same as the chamber width) should be at least twice the depth  168  of the dome of diaphragm  154  and in some embodiments the width  162  should be at least three times the depth  168  of dome  164 . This helps to provide a blood flow path, having a maximum thickness which is not too deep, causing a risk of blood stagnation and clotting, while at the same time providing an adequate amount of air displacement on the air side of diaphragm  154  so that a wide range of pressures can be measured. 
         [0095]    The above has been offered for illustrative purposes only, and is not intended to limit the scope of the invention of this application, which is as defined in the claims below.