DE3333461A1 - Flow-adapted dialyser lid - Google Patents

Abstract

Dialysers for artificial kidneys using hollow fibre bundles possess terminal connections for the blood flowing in and the blood flowing out, the connections being designed as lids on both ends of the cylindrical housing for the hollow fibres. Usually, these lids have a centrally located nozzle for the blood hose and form a distribution space for distribution of the blood entering at that point to the ends of the hollow fibres in the bundle and, correspondingly, at the outflow end. Previous configurations of these lids were unsuitable from a flow point of view because they caused large variations in the flow rate of the blood within the distribution space and, furthermore, led to detachment of the flow from the axial lid wall. The present invention presents a calculation method for lid configurations without such deficiencies, as a result of which corresponding novel lid contours having improved properties are obtained. For this purpose, the flow fields of 1) the rotationally symmetrical stagnation flow and 2) an extended, circular sink flow are combined, after which the group of flow lines is selected as the lid contour by the edge of the sink region. For calculation purposes, a flow line defining the contour cross-section is determined.

Description

Strömunqsanoeoasster dialyzer cover

The present invention relates to a cover for hollow fiber dialyzers with a central flow of blood, which has a shape adapted to the hemodynamics and thus reduces the tendency of the blood to clot.

Cylindrical hollow fiber dialyzers with a full bundle have a cylindrical Housing in which a bundle of hollow fibers - on the order of 10 ODO pieces - is inserted. For sealing between the hollow fibers at the ends of the housing, the bundle is here, at both ends, filled with a synthetic resin. To get to the The end faces of the cylinder open the hollow fibers so that their interior is accessible the resin is cut across the dialyzer #. The resulting circular, flat cut surface has a variety of round holes through which internal cavities formed by the cut hollow fibers, in which the blood should be introduced. To do this, a lid is placed on the end of the cylinder mounted, which has a central nozzle (for the hose connection), and from here the blood is distributed radially over the fiber openings. The conventional design, up to the date of the invention it was also the only one on the market with a central Nozzle, is shown in Fig. #.

The importance of the flow condition in the lid space for blood coagulation is mostly overlooked so far. The first or current inventor has in own work on the so-called "Hemoflow" dialyzer, which does not have a central feed to the lid, but a tangential blood supply, one for blood coagulation A significantly more favorable flow condition is generated, which in practice results in the resulting the following reduction in the tendency to clot has been proven. With the present Invention is (in separate and independent work) a hemodynamically correct one Design of lid with central feed achieved, thereby also for this Lid type results in a lower tendency to coagulate.

Lids of conventional design have the following zones inferior Blood flow velocity on: - the stagnation point on the Cut surface opposite the nozzle, - the edge zone.

It is also here that clots are preferred to be found in the lid space, when clotting occurs. Correspondingly, the blood coagulates in the hollow fibers, emanating from these zones.

The reason for this is that the platelets of the blood are in such zones lower flow velocity a longer contact time with the foreign surface has, and thus the greater chance of adhering to this surface, which then a clot is started. For observations on this: see Agishi et al., Proc. EDTA Vol. 12, pp. 535-550.

The separation of the flow from the inner surface also plays a role here of the lid, which is the case with blood viscosity in all conventional lids can be proven (e.g. 8.

by injecting dye into the flow for visualization a 33% glycerine solution at 37 OC, which simulates the blood viscosity). This creates undesirable eddies in the lid space, mostly concentric Vortex rings.

In the present invention, the former inventor has a novel one Established design principle, which is checked by the second named inventor at the same time as calculations to solve the equations. This allows the Detachment, when the flow is deflected from the axial nozzle flow to the radial flow across the cut surface, can be reduced or avoided. Further a higher flow velocity is achieved in the edge area, and the effect the congestion zone in the center is reduced. In principle, this makes the lid contour streamlined forms.

Two rotationally symmetrical flows are used to design the cover superimposed, and the streamline of the resulting flow field, which goes through the edge of the cut surface, chosen as the cover contour. These currents are: - the rotationally symmetrical stagnation point flow, - the sink flow of a spread out (evenly distributed) circular depression.

(See J.H. Spurk: Lecture Fluid Mechanics II, T.H. Darmstadt, 1975).

The streaming potential ~ of the rotationally symmetrical stagnation point flow is = a2 (r2 - 2z2), where r is the radial coordinate and z is the axial coordinate from the stagnation point. a is a constant. The streaming potential of the spread, evenly distributed sink flow into a circular sink with radius R is where r and z have the same meaning as above (from the center point of the sink circle), p and ç are integration variables and E is a constant.

If these two flows are now superimposed, a differential equation for the flow lines ensues: where E (k) and K (k) are complete elliptic integrals 2.

or 1st type are: and no parameter: ~ is a constant here and r 'an integration variable.

In this formula, R = 1 was set, i.e. the radius of the circular depression chosen as the unit of length.

A contour of this kind, at o (= 25, is shown in Fig. 2. It is obtained by numerical solution of the above differential equation. By Adapting a continuous function, one finds that a very good approximation the exact solution is given by z = 0.0259 (# 1 - 1 ~ 195) r2. Therefore be the solution according to fig. 2 is only given in this way, for the sake of simplicity, instead of an expensive one Table for the exact solution.

In these calculations, the friction of the flow on the lid contour neglected because an exact solution of the Navier-Stokes equations in this Case requires an enormous amount of computing power. The friction in the edge zone acts focus on the flow field. A compensation for this can, however, be done experimentally be made by removing the lid a small amount from the Cut surface away. Tests with different intermediate layers showed that the advantageous Edge flow is well preserved up to an axial displacement of the cover by approx. 0.5 mm remain. The effect of the edge flow on the mm central flow is only negligible with a shift of 1-2 mm.

The choice of a distance of 0.5-1 mm turns out to be a better good compromise can be made with α = 1000.

A better contour can be found with α = 1000, where the Solution approximated by z = 0.0280313 # + 0.0172962r- 0.0071258 r r is given. This contour fulfills the two more easily by adapting the axial cover position Low radial flow velocity drop requirements, and a central flow undisturbed by the edge state. It is shown in Fig. 3.

It is clear that various improvements to this contour calculation, with the invention corresponding effort, are possible without departing from the principle of the invention to deviate. An exact solution of the Navier-Stokes equations, based on the desired flow condition, to find the corresponding contour, is practically impossible for reasons of effort. It is, however, possible to use an iterative Method to apply, whereby one proceeds from a given contour, the calculates the resulting flow condition taking into account the friction, and on Hand of the results corrected the contour. With the contour corrected in this way, this becomes Repeat the process until no further corrections are necessary.

This procedure also requires a certain amount of effort, and it was We have therefore not yet been able to do this with the means available to us to be carried out even though the process is theoretical and the procedure is clear. Therefore, we can only go so far from the experimentally carried out correction, by adjusting the axial cover position, results can be given.

Another alternative is an approximate consideration of the Friction, e.g. according to the Osén process.

It is clear that this type of streamlined lid is for everyone Types of devices suitable for extracorporeal circulation, such as hemoperfusion cartridges, Hemofilters, plasma filters, dialyzers, etc. It is also clear that continuous Approach formulas not only, as above, by adapting to numerically calculated ones exact solutions can be obtained, but also by approximated analytical Solutions of the occurring equations.

The specified values of the parameter oC are only examples here.

In principle, any value can be selected for this.

Explanations of the figures: Figure 1 shows in cross section a schematic diagram of a conventional lid with an inlet nozzle (above), which widens (downwards) into a distribution space above the one with hollow fiber openings provided cut surface (this cut surface, not shown, closes the lid directly below) Figure 2 shows half a cross-section of a Lid design with an inner contour that according to the invention at oc = 25 and R = 1 was calculated. For the sake of simplicity, the outer contour is made up of straight pieces shown. The axial displacement mentioned in the text to correct for friction losses is in the drawing not taken into account (the drawing shows the contour without this shift). A cylindrical coordinate system (r, h) is also drawn in, with the h-axis in the center of the lid.

Figure 3 is basically the same as Figure 2, but with # = = 1000. Here, however, the contour was continued vertically (parallel to the z-axis) from z = 0.5, for the purpose of forming a nozzle.

Claims (7)

Claims 1, cover for a device for extracorporeal blood treatment, characterized in that the cover has a streamlined transition from a central nozzle flow has a radial distribution flow, its Contour from the edge streamline when a stagnation point flow is superimposed with a spread sink current is calculated. 2. Lid according to claim 2, characterized in that the contour is corrected experimentally for the effect of friction. 3. Lid according to claim 2, characterized in that the contour is corrected mathematically for the effect of friction, with the help of the equations by Navier-Stokes, in an exact or approximate solution. 4. Lid according to claim 3, characterized in that the contour corrected by an iterative process so that for a given contour the corresponding flow condition is calculated and the contour is corrected accordingly is used to approach the desired state, and this process is repeated until no further correction is necessary. 5. Lid according to one of claims 1-4, characterized in that the contour is given by a continuous approximation formula, by adaptation a continuous function obtained from the numerical solution. 6. Lid according to one of claims 1-3, characterized in that the contour is given by a continuous approximation formula, by analytical Approximate solution of the current equations obtained. 7. Lid according to claim 4, characterized in that the contour is given by a continuous approximation formula, which is obtained by that the contour specified for the calculation of the flow condition, if necessary corrected, is defined by a continuous function.