CA1106770A

CA1106770A - Hollow fiber dialysis

Info

Publication number: CA1106770A
Application number: CA359,854A
Authority: CA
Inventors: Kyu H. Lee
Original assignee: Extracorporeal Medical Specialties Inc
Current assignee: Extracorporeal Medical Specialties Inc
Priority date: 1975-11-05
Filing date: 1980-09-08
Publication date: 1981-08-11
Also published as: FR2330429A1; SE7611942L; JPS5697458A; MX143979A; FR2330429B1; IT1063433B; SE434120B; JPS5616687B2; CA1100887A; NL165058C; BR7607355A; CA1106771A; SE8100863L; GB1569182A; DE2650588A1; NL165058B; NL7612323A; AR215452A1; JPS5258079A; BE847969A

Abstract

Abstract of the Disclosure Improved dialyzer construction has elongated tubular casing with enlarged casing ends and longitudinally-extending partitioning that divides its interior into a plurality of generally parallel passageways containing hollow dialysis fibers, the casing ends containing di-alyzate flow manifolding and directing means for re-ceiving dialyzate from a supply thereof, directing it from one casing end to the other through one of the passageways around the fibers, and so to and fro through the successive passageways, finally directing the dialy-zate out through a discharge opening. The dialyzate flow can in each fiber-containing passageway be counter-current to the flow within the fibers of the liquid being dialyzed. A gas by-pass can be provided in the partitioning at one end to bleed out gas that tends to accumulate at the high point of the to-and-fro dialyzate travel.

Description

~.3~.`1I~7~

The present invention relates to dialysis, particularly dialysis of liquids such as blood.
There have been many suggestions for improving dialysis equipment especially of the artificial kidney type. A great many so-called coil-type artificial kidneys are in use in which the dialysis element is a tube many inches in diameter, but flattened and spirally wound with a spacer to separate the turns of the winding. An artificial kidney so made is relatively large in size, and there have been suggestions for smaller constructions having bundles of thousands of hollow fibers each a very narrow tube that functions as a dialysis element, but this modified con-struction still presents problems. An example of hollow fiber apparatus is shown in U.S.P. 3,442,002, and a fiber which has recently come into use for hollow fiber dialyzers in the deacety-lated cellulose acetate fiber referred to in U.S.P. 3,545,209.
These fibers are generally required to be kept wet with water at all times after the de-acetylation, in order to maintain their dialytic permeability. This has led to the awkwardness of ship-ping and storing dialyzers based on such hollow fibers while the fibers are filled with water and with the water containing form-aldehyde to keep it from developing microbial growth. Before each use it then becomes necessary to flush out all the formaldehyde.
According to the present invention, there is provided a hollow fiber dialyzer which has an elongated tubular casing which containS partitioning that divides the interior into a plurali-ty of separate longitudinally-extending passageways with dialyzate flow directing means for receiving dialyzate from an external source and directing it to flow from one casing end to the other through one of the passageways an then back -through the one casing and through another of the passageways and so to and fro length-wise through the other passageways and finally out of the casing.

~t least two of the passageways each has a longitudinally-extend-~4 ~ .

~677~

ing bundle of elongated hollow blood dialysis fibers which extend lengthwise therethrough with means connected to deliver blood to be dialyzed from an inlet to the fiber ends of each of the bundles at the same end of the casing and to receive the blood from the other ends of the hollow fibers for delivery to an outlet. Each of the passageways which have a bundle of fibers has the fibers packed in it and the dialyzate flow directing means further includes manifolding of enlarged cross-section to direct dialyzate into contact with the outer layers of fibers and in each of the bundles as the dialyzate enters each passage-way thereby to reduce undesirable channeling of the dialyzate.
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:-Fig. 1 is an elevational view partly in section and partly broken away, of a hollow fiber dialyzer in accordance with the present invention;
Figs. 2, 3 and 4 are sectional views of the construction of Fig. 1, taken along the lines 2-2, 3-3 and 4-4, respectively;
Fig. 5 is a view similar to Fig. 1 of a modified hollow fiber dialyzer representative of the present invention;
Figs. 6, 7 and 8 are sectional views of the construction of Fig. 5 taken along the lines 6-6, 7-7 and 8-8, respectively;
Figs. 9, 10, 11 and 12 are views similar to Figs. 1, 2, 3 and 4 of a further modified dialyzer typical of the present invention;
Fig. 13 is a sectional view of a cap suitable for use with the construction oE Fig. 9; and Figs. 14, 15 and 16 are views similar to Figs. 1, 2 and 3 of yet another embodiment of the present invention.
The following examples illustrate very desirable manners of preparing hollow fiber dialyzers in accordance ~3-~' .

6 ~ o ~4~

with the present application.

A dialysis casing such as shown at 10 in Fig. 1 and molded or cemented together ~rom polyc,arbonate or polystgrene 5 resin) is first provided. This casing has an over-all length of about 7-1/2 inches with its intermediate portion 12 having an internal diameter of 1-3/8 inches, each end 14 ~ 16 belng of enlarged bore having internal diameters about 1-7/8 inches.
The tubular length of the interior of the casing is divided into three individual passageways 2~, 22~ 23 by an axial ~,veb 25 of threa flange3J 31J 32 and 33. An inlet tube 36 opens into enlarged end 14, and a discharge tube 3~ leads out from end 16.
~ reb 26 has flow control means at each end ~4, 16 arranged so that fluid entering inlet 36 flows upwardly through passage-way 21 ~rom end 14 to end 16, then at end 16 moves from the top of pa~sageway 21 to the top of passageway 22, then down~Yardly through passageway 22 to lower end 14 where it then trans~ers to the bottom of' passageway 23 along which it moves upwardly to end 16 for discharge through outlet 38. To effect this ~low control, flange 31 is arranged as a barrier seal against the outer wall OI the casing throughout the length of lower end 14 as well as throughout the length of the intermediate portion 12~ but not at the upper end 16. Instead at that upper snd flange 31 is cut out as shown at 40 to provide a ~low-through space l~l that thus opens between the upper ends of passageways 21 and 22.
Flange 32 is similarly shaped in an opposite sense 30 that at its lower portion it provides an edge 50 spaced from the lowest point o~ casing end 14 to provide a flow through space ~1 between the lower ends of passageways 22 and 23.

^~ 77 A batch o~ hollow cupra~mon~um rsgenerated cellulose ~ibers having a wall thickness o~ about 12 microns plu3 or minus 2 microns and an internal diameter o~ about 200 microns plus or minus 50 microns is unspooled, pre~erably ~rom a plurality o~ spools in parallel strands~ cut to a length o~
about 9 inches and care~ully cleaned. As generally supplied these ~ibers are made by extruding cuprammonium cellulose solution through an annular die into a regenerating bath while introducing a water-immiscible liquid into the bore of the hollow extrudate. A typical water-insoluble liquid is isopropylmyristate. A~ter regeneration is completed care~ul ~ashing with isopropanol removes such liquid. The lnteriors of the fibers can then be wet with a so~tening agent such as glycerine, preferably leaving about 5% of the so~tening agent by weight of the clean ~iber~ This so~tening is not essen-tial but helps guard the ~ibers against breakage or damage during subsequent handling, and does not detract from the e~fectiveness by which the fibers are sealed into the casing 10.
A bundle of two to three thousand ~ibers so prepared is then inserted into one of the passageiiays 21, 22~ 23, and additional bundles in each of the rem~ining passageways. This insertion can be expedited by first sliding over the bundle a tapered sleeve of polyethylene, then introducing the ~illed sleeve, narrow end ~irst~ into one o~ the passageways, and ~inally pulling the sleeve of~ the introduced bundle. At the narrow end of the taper the ~ibers are arranged to project from the sleeve so they can be gripped to help pull the sleeve o~ the other ends o~ the ~ibers~

When all the passageway~ are ~illed with ~ibers, the ~6~7 ..6--potting can be QtartedO At each end oF the casing each bundle o~ fibers projects a short distance. 'Each o~ these pro~ecting end~ is dlpped in melted carnauba wax which is then permitted to solidi~y after the carnauba wax has penetrated a very short distance into all of the individual fibers. ~he casing iB then clamped longitudinall~ between potting heads connec~ed to a potting compound container as illustrated in Fig. 19 o~ Patent 3,442,oo2) and centri~uged as also indicated in that patent whils the uncured liquid freshly mixed potting mixture i9 poursd into the potting compound container. This mixture csn be a polyurethane prepolymer resin with a chain extender, or an epo~y cement mixture as described in Patent 3,442,002, or a hardenable polysiloxane liquid or other settable resin.
When a hardenable polysiloxane liquid with a curing agent such as chlorplatinic acid is used, the centrifuging is conducted at about 350 g while the mixture is heated 7 and after about 1/2 hour at 150F. the potting mixture is cured to the point that it no longer ~lows. The potting heads are then unclamped and removed, and the curing completed by holding the dialyzer in an air oven at 150F for two hours. A~ter that the potting mixture is a cleanly cutting solid and a sh~rp metal blade is used to cut the potting mixture flush with the open ends 14, 16 o~ the casing. This leaves the construction as illustrated in ~ig. 1, the potting composition being sho~n at 56 and 57. Covers 61, 62 each equipped with a ~low connection 64, 65 are then ~itted to the casing ends 14, 16 as by welding or cementing, although they can also be threaded in place i~ desired~ The construction ls then complete and only needs a ~lushing through to remove the water-soluble softening agent ~rom the inside of the hollow flbers _7~ 67~

be~ore it is placed in servioe. The dialyzers can be ~tored either before or a~ter washing out the softening agent, without significantly a~ecting ~ts dialysis properties.
When the dialyzer is used it is generally held with end 16 up, a source of dialyzate is conneoted to inlet 36, discharge 38 is connected to waste, and a supply o~ blood to be dialyzed connected to inlet 65 with a blood return to outlet 64. In use bubbles of air or other ghses can form in the dialyzate and tend to rise toward the upper end 16 o~ the dialyzer. To keep those bubbles ~rom becoming trapped at the upper ends o~ passageways 21 and 22 and collecting there in an amount that could interfere with the dialysis~ a small bleed 59 i9 ShO'NIl as provlded at the upper end o~ web ~lange 32. For a flanga with a wall thickness o~ 1/16 inch a round opening as 15 little as 1/2 millimeter in diameter will enable the gas trapped at the abo~e-mentioned ends to readily make its wa~
lnto the upper end of passageway 23 and out through discharge opening 38, without significantly reducing the er~ectiveness of tne dialysis. The gas vent can even be made slightly smaller as for example 0v3 mm. in diameter~ The optimum width of the vent is related to the thickness of the wall through which it penetrates. For wall thiclmesses greater than 1/16 inch the vent width is pre~erably a little larger than 1/2 millimeter.
A feature OL the dialyzer construction of Fig. 1 is that such dialyzers are readily manufactured with more uniform dialysis e~ectiveness than corresponding dialyzers in which there is no partitioning and web 26 is completely omitted.
Notwithstanding the enlarged ends 1l~, 16 which serve as dialyzate manirolds that bring the dialyzate into direct 6~7~

contact with the outer layers o~ ~iber~ in the ~iber bundles~
the dialyzate has a tendency to make its way through one end of the dialyzsr to the other through the easiest path and thus find and establish a channelg even when the flbers are ~alrly well packed in place. Such channeling greatly reduees the e~ectlveness of the dialy~is particularly through the walls of those ~ibers that are some distance laterally spaced from the channel. ~nlen this happens with a dialyæer oontaining only a single dialyzate passageway~ lts efficiency becomes 50 poor that it generally has to be discarded.
Such channeling i9 more likely to take place as the wall thickness of the hollow fibers diminishes and as the riber diameter decreases; these cause the ~ibers to be more fle~ible so that it is easier ~or the dialyzate to create a channel by de~lecting the fibers. Wall thicknesses o~ about 5 to about 20 microns are suitable ~or e~ective use ~nd thioknesses of ~rom about 10 to about 15 microns are pre~erred. Fibers with internal passageways not over about 500 microns wide~ pre~er-ably ranging ~rom about 100 to about 300 microns in width~ are very e~fective. Cuprammonium regenerated hollow fibers o~ this type are relatively sti~f, particularly when dry~ and are accordingly very easy to handle in the assembling o~ a bundle ~or insertion in a dialyzer~ and in the insertion itself.
In the construction o~ Fig. 1 a channeling-induced drop ln e~ficiency o~ passageway 21 can also occur9 but when that happens the dialyzate emerging from passageway 21 is less loaded with contaminant~ 90 that it be¢omes more ef~ective in lts subsequent passage through passageways 22 and 23.
In addition el~ch of the passageways 21, 22 and 23 is narrower than lt would be without the web 26, and channeling ~ 7 _9 becomes less likely in narrower passQgeways. Also the total length of ~ibers contacted by the dialyzate ln the construction o~ Fig. 1 is three times the length contacted i~ web 26 were omitted, and the e~lciency loss through channeling diminishes as such length lncreases.
Because of the more reproducible greater e~iciencies of the construction of Fig. 1, dialyzers having an operating length between potting seals 56, 57, of only about 15 centi-meters can be readily manufactured with the desired high qualities. This small bulk is particularly de3irable, desirable, although in general overall lengths of from about 6 to about 12 inches can be attractlve for hospital uss.

Figs. 5, 6, 7 and 8 illustrate a modified dialyzer 110 pursuant to the present inventlon. In this dialyzer there are three parallel dialyzer passageways along the lines of Fig. 1 but the flow o~ dialyzate is arranged so that throughout its fiber-oontacting path it moves on the outside of the individual ~ibers in a direction countercurrent to the ~low o~ blood or other medium being dialyzed within the ~ibers.
As in the construction of Fig. 1, dialyzer 110 has a central tubular section 112 with enlarged ends 114, 116 and with a partitioning web 126 inserted or molded in section 112.
Web 126 has ~langes 131, 132, 133 ~imilar to the three ~langes ~ web 26) and in addition also has two supplemental ~lange~
134, 135 that define ~upplemental passageways 124, 125.
The bundleq of hollow ~ibers are contained in pa~sage-ways 121, 122, 123; passageways 124, 125 being unfilled so that they provide paths ~or the dialyzate to ~low while out 7~
~lo of contact with the fibers~
The flow of dialyzate is controlled by appropriate shaping of the web flanges in the construction of Fig. 5 so that it enters and flows upwardly first through passage 121 then downwardly through passage 124 then back upwardly through passageway 122 returning this time to the bottom ~ia passageway 125, and finally completing the dialy9is by an upward travel through passageway 123 and discharge at outlet 138. For this result, the upper ends of webs 13~ and 135 are spaced from the inside wall of casing end 116 and the lower ends o~ webs 131 and 132 are spaced from the inside surface of casing end 114, as more clearly illustrated in Figs. 7 and ~ -No gas vent is provided in the construction of Fig. 5 inasmuch as the dialyzate flow rate is fairly high in the very narrow return passageways 124, 125. Thus a flow rate of only about one ~oot a second is generally sufficient to sweep out gas bubbles that tend to form. For slower flow rates, as for example when the dialyzate is discarded after a single passage through the dialyzer and is not recirculated from outlet 138 back to inlet 136, gas venting can be provided in the construc-tion of Fig. 5.
Gas venting can be eliminated where the dialyzate iB
treated to reduce gas evolution, as for example by boiling it under reduced pressure before it is introduced into the dialyzer. This removes almost all of the dissolved gases, and the maintenance o~ some pressure on the dialyzate as it is impelled through the dialyzer acts as an additional preventive to ga~ evolution.
The dialyzer casings of the present invention need not be circular in cross-section but can be oval, rectangular or 7~3 triangular if desired, both in their external shape as well as ln the shape of the passagewayqO Similarly~ they do not have to be perfectly linear in longitudinal direction.

Figs, 9 through 13 illustrate a dialyzer 210 according to the present invent~on which is generally triangular in cross-section, particularly at its ends 214, 216. Those ends each have a mounting rib 217 which helps in positioning end connector covers 262. ~oreover each rib 217 can be provided with a ridge 219 which need only be about 15 to about 20 mils high that helps in welding the cover in place as by sonic or ultrasonic vibration of the mounted cover against that ridge~
Upon vibration in this manner the ridge and the ridge-engaging portion of the cover ruse as a result of the ~rictional heating effects of the vibration between them, and weld together making a very effective fluid-tight seal.
The construction and operation of Figs. 9 through 13 generally corresponds to that of Figs. 5 through 8, and similar portions such as partitloning web 2269 passageways 221J 222 and 223 for receiving the hollow fibers, passageways 224 and 225 for dialyzate return, and inter-passage spacings 241, are similarly numbered. However, to better seal the blood or other dialyzand away from undesired crevices and the like, covers 262 are each provided with an internal sealing lip 263 shaped to engage the potting seal 257 outside the fiber-containing æone.
The dialyzand is thus kept from penetrating into the crevice 265 between the internal surface of the cover and external surface of the casing wall.
To further help with such sealing, the potting seal 257 can be arranged to project out a short distance 2673 such as -12~ 7 1/8 inch, beyond the C8S ing end.

EXA~PLE 4 Figs. 14, 15 and 16 illustrate a dlalyzer 412 having a generally rectangular configuration both in its external aspect as well as in its passageways. Such a configuration makes better use o, space and can contain more fibers than other com~iguratlons having the same overall dimensions.
The conQtruction and operation of this exemplification, as well as the numbering of its parts, i3 S imilar to that of Figs. 1 through ~, except that its covers 462 and cover engagement are like those of Figs, 9 through 13 without the internal sealing lip. Internal sealing is provided in Fig~ 14 by having its end covers 462 tightly engage the outer margin of the potting seal. Also instead of having the fiber-containing pasQageways 421, 422 and 423 arrayed generally circumferent~ly around casing 410, these passageways are arranged in a simple row all lying in what can be considered the same thick plane~
The fiber bundles can be inserted in the dial-yzer passageways without the help of a sleeve, particularly if the walls of a casing end provide a gradual taper ~rom their large internal bore down to the smaller bore of central portion 12 or 112. Alternatively the bundles can be sleeved and the sleeves left in the dialyzer in position around the bundles, This alternative is particularly desirable when the sleeves are of relatively thin wall section, i.e. about 3 mils, so that they do not occupy much room.
The insertion of the fiber bundles is also made easier if this is done when the casings are hot. The heat expands the casing and thus provides a little more room for more ~'6~

readily sliding the bundles into place, after which the casing cools down and tightly encloses the fibers, thus making for added efficiency. Instead of an elongated sleeve to help the fiber insertion, a single narrow length of plastic or even wire can be looped around a fiber bundle ad~acent one end, and tied or crimpea against the fibers so as to provide a tail for the bundle. The bundle can then be pulled through a passageway by first passing the tail through the passageway and then pull-ing on the tail.
It is generally desirable to clean the hollow fibers for the dialysis as by washing or rinsing them with a readily volatilizable solvent, particularly where the bores in the fibers contain a liquid which should not contact the dialyzand or dialyzate.
The advantages of partitioning are obtained when the dialyzer is partitioned to provide only two parallel dialyzing passageways. A very simple construction of this type has inlet and outlet tubes 36, 38 on opposite sides of the upper casing 16 with a single central web extending longitudinally the entire length of the casing but with an opening in its lower portion.
The partitioning can even be more subdivided than is shown in the drawings so as to provide 4 or 5 parallel dialysis passageways, but the use of more partitions takes away some of the space for fibers so that the bulk of the casing has to be increased to maintain the dialyzing effectiveness.
The partitioning of the present invention simplifies the mechanical handling in the manufacture of the dialyzer. The reduced width of the individual passageways, e.g. one to three ~1 677~

centimeters, as compared to an unpartitioned dialyzer, reduces the number o~ ~ibers per passageray and thus simpli~ies the preparation o~ the individual bundles. By way o~ illustration, the task of preparing a 6000~iber bundle for an unpartitioned dialyzer is more complex than that o~ preparing three 2000-~iber ~undles ~or use in the dialyzer of Fig. 1 or Fig. ~ or Fig. 9.
The fiber-containing passageways can also be double tapered as illustrated at 211 in Fig. 9 so that they provide a constriction in their central portions. Such a constriction o~
about 1/2 to 1 millimeter helps grip the ~ibers and keep them ~rom being de~lected by the ~low around them, thus reducing the te~dency to channelling.
Another feature of the present invention i9 that the different compartments o~ the described dialyzers need not be used ~or the same function. One of the compartments can for example be used to hold an absorbent such as activated charcoal or the lil~e, instead o~ ~ibers, so as to absorb impurities or other undesirable ingredients in the dlalyzand. Different kinds of ~ibers can be used in dif~erent passageways to obtain di~ferent dialysis ef~ects on the dialyzand as it passes through the dialyzer. Indeed some o~ the passageways, such as passageway 124, can be filled with absorbent for the purpose o~ treating the dialyzate as it moves through the dialyzer and better condition the dialyzate for its passage through the remaining fiber-containing passagewa~s.
The potting Or the ~iber ends can be accomplished with techniques other than that described above. Thus the preliminary dip of the ~ibers to plug their bores can be into melted resin~modi~ied waxes or thermoplastic resins Or -15- ~ 7 ~

compositions that harden to form thermosetting resins. The potting mixture itself can for example be used as a preli~inary dip of shallow depth9 followed by deeper pottin~. Also, by maintaining slightly higher pressure in unplugGed fiber bores 5 as against the pressure over the potting mixture into which the unplugged fiber ends are dipped, the potting mixture is kept at a low level within those bores and the preliminary dip to plug those bores can be completely eliminated. The bores can alternatively be sealed by melting the fiber ends when they are of fusible natureJ and in this ~ay make a prior dip un-necessary.
'~hile centrifugal force applied to the liquid potting mixture hslps assure that such mixture thoroughly impregnates all crevices and pores around and between the fibers and in 15 this ~ay assures thorough sealing of the dialyæate chamber from the dialyzand gas pressure applied over the liquid potting composition during the potting, has a similar effect. One end of a fiber bundle can accordingly be potted at a time, without the need for the centrifugal potting apparatus.
Also the covers 61, 62 can be arranged to snap on over the potted ends of the dialyzer, as shown in Fig. 5 at 161, 162 for example. Such covers can be relatîvely flexible and the potted ends they snap over can be fitted with ridges as at 163 to help lock the snap-on covers in place.
The dialysis discussed above is to be distinguished from osmosis in that tha dialysis uses fibers whose walls are extremely porous, much too porous for use in osmosis. This comparison is more clearly shown by the fact that a reverse osmosis process desalinating brackish water for instance, requires membranes of relativel~J non-porous material such as -16~ 6 ~ ~

polyvinyl chlorideg as well as the use of a driving pressure greater than the osmotic pressure and as high as practicable.
An attempt to carry out such a reverse osmosis with the cupr-mmonium regenerated cellulose as described above, will merely cause the brackish water to rapidly filter through the regenerated cellulose fibers and emerge at the discharge face of the cellulose in substantially the same condition as it entered the entrance face.
The dialyzer construction of the present invention can also be used with the dialyzate passing through the bores of the hollow fibers and the dialyzand moving along the outside of the fibers, although this arrangement is not desirable where blood is the dialyzand. However with osmosis-type fibers, the structural arrangement of the present invention is suitable for osmotic processes such as reverse osmosis~ and in such use it is preferred to pass the fluid being treated around the hollow fibers so that the high pressures used on such fluids in reverse osmosis is applied to the exteriors of the fibers. Fiber failures are then not likely to cause leakage.
The apparatus of the present invention is also suitable for use in gas separation, again with an appropriate type of fiber, or in gas treatment of liquids as in the oxygenation of blood where silicone fibers are preferred.
Obviously many modifications and variations of the present invention are possible in the light o~ the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than a~ specifically described.

Claims

the embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A hollow fiber dialyzer having an elongated tubular casing containing partitioning that divides its interior into a plurality of separate longitudinally-extending passageways, dialyzate flow directing means for receiving dialyzate from an external source and directing it to flow from one casing end to the other through one of the passageways and then back to said one casing end through another of the passage-ways and so to and fro lengthwise through the other passageways and finally out of the casing, at least two of the passageways each having a longitudinally-extending bundle of elongated hollow blood dialysis fibers extending lengthwise therethrough, and means connected to deliver blood to be dialyzed from an inlet to the fiber ends of each of said bundles at the same end of the casing and to receive the blood from the other ends of the hollow fibers for delivery to an outlet, characterized in that each of the passageways having a bundle of fibers has the fibers packed in it, and the dialyzate flow directing means further includes manifolding of enlarged cross-section to direct dialyzate into contact with the outer layers of fibers in each of said bundles as the dialyzate enters each said passageway whereby to reduce undesirable channeling of dialyzate.

2 The hollow fiber dialyzer as in claim 1 wherein the manifolding of enlarged cross-section is defined by laterally enlarged casing ends.