WO1993002801A1

WO1993002801A1 - Centrifuge rotor

Info

Publication number: WO1993002801A1
Application number: PCT/GB1992/001443
Authority: WO
Inventors: Laurence Roy Rickman
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-08-03
Filing date: 1992-08-03
Publication date: 1993-02-18
Anticipated expiration: 1994-02-03
Also published as: AU2388992A; GB2273449B; GB2273449A; GB9401308D0; GB9116806D0

Abstract

A centrifuge rotor comprises a base member and a cover member and has axially-disposed rotational drive connection means in a central region thereof, the base member comprising an essentially circular plate having sample tube locating means disposed radially and terminating outwardly in resilient elements, and the cover member having a lower surface which cooperates, in use, with the base to retain sample tubes securely in position, one of the base and cover members including a least one annular groove disposed radially outwardly of the sample tube locating means and the other of the base and cover members including a corresponding annular projection, the projection being sealingly engageable within the groove when the base and cover members are located together for use. The base member is provided with marked annular zones indicating ranges of packed cell volume and the cover member is transparent, whereby the packed cell volume can be assessed by unskilled personnel in developing countries by direct reading through the cover member against the annular zones, thereby enabling anaemia to be quickly and accurately diagnosed

Description

CENTRIFUGE ROTOR

This invention relates to a centrifuge rotor for the centrifugal separation of whole blood samples contained in microcapillary sample tubes, to provide compacted blood cells and plasma.

The centrifugal separation of blood cells from plasma and the measurement of the resulting packed cell volume is known to be a simple diagnostic test for the presence of anaemia.

Anaemia, due mainly to blood loss, malnutrition, disease and dehydration, resulting from AIDS, cholera and other diarrhoeal and febrile diseases, is responsible for much mortality and serious morbidity in developing countries; very young children, pregnant women and the aged are particularly at risk. However, many such cases remain undiagnosed at present due to the lack of simple, practical and inexpensive diagnostic equipment that can be used satisfactorily at the periphery, where it is urgently needed.

Attempts to improve the health and welfare of sick and impoverished rural communities in the tropics have been frustrated in many cases by the intractable nature of the causative factors, principally low productivity and disease. Sadly, in recent times, as a result of famine, civil strife and oppression, this situation has been exacerbated by the movement of many thousands of refugees, most of whom are malnourished and many seriously sick; more recently the AIDS pandemic has added an even more serious and sinister dimension. Education is hampered by poor health, and periods of serious sickness (among which malaria, hookworm and diarrhoeal disease feature prominently) in children or their families are frequently reflected in poor school attendances, while anaemia, from a variety of causes, weakens children and reduces their capacity to learn, further depriving them of their main opportunity to secure a better future.

Dehydration, too, is a major problem where conditions of poor sanitation and overcrowding occur and where diarrhoeal diseases quickly become established, particularly following disasters and among refugees.

It is an object of the present invention to provide a centrifuge rotor of very simple design, which is inexpensive, virtually unbreakable, needs no servicing and is dependent on neither electricity nor batteries for operation. When operated manually or fitted to a high-speed centrifuge, its use in the mission hospital or rural health centre or by primary health care workers in the villages will immediately identify those suffering with anaemia or dehydration with certainty. Its use will also aid the field diagnosis of filariasis and trypanosomiasis.

According to the invention, therefore, a centrifuge rotor comprises a base member and a cover member and has axially-disposed rotational drive connection means in a central region thereof, the base member comprising an essentially circular plate having sample tube locating means disposed radially and terminating outwardly in resilient elements, and the cover member having a lower surface which cooperates, in use, with the base to retain sample tubes securely in position, one of the base and cover members including at least one annular groove disposed radially outwardly of the sample tube locating means and the other of the base and cover members including a corresponding annular projection, the projection being sealingly engageable within the groove when the base and cover members are located together for use.

Preferably, the sample tube locating means terminate inwardly as well as outwardly in resilient elements, which may each comprise an annular element disposed in an annular groove which communicates between the respective inner or outer ends of the sample tube locating means, which may themselves be constituted by radially-disposed grooves formed in the base member or by inner and outer recesses to receive respective inner and outer end regions of the sample tubes.

The annular groove, preferably formed in the base member, is provided for receiving any blood which seeps from the sample tube under centrifugal force and the corresponding annular projection, preferably formed on the cover member, may be adapted for deflecting any free centrifugally directed blood downwards and for containing any blood seepage in the groove, for example by providing the projection with an upper surface which slopes radially outwardly towards the base of the groove. Preferably, two such grooves and corresponding projections are utilized. In use, the groove or grooves may be lined with absorbent material such as a cotton lace which is compressed by the projection and which is kept moistened with a disinfectant solution, in order to kill any viruses present.

The purpose of the resilient elements is to cushion and further seal the outer ends of the sample tubes while centrifugation is taking place. Preferably, the sample tubes are microcapillary tubes one end of which is closed with a plasticized seal after adding blood and prior to centrifugation.

The cover member should be a close fit on the base member, partly because its function is to retain the sample tubes in place in their locating means and partly to provide an overall smooth external profile in order to reduce air resistance to a minimum and to permit faster centrifuging speeds to be attained. A smooth external profile will also minimize injury caused by inadvertently touching a spinning rotor. The cover member is preferably retained in place by a lock-nut which may be screw-threaded to a suitable hub member. Peripheral cut-away portions may be provided to facilitate removal of the cover member from the base member.

It is a particular feature of the invention that the base member is divided into annular zones in order to provide a gauge for assessment of the packed cell volume of the compacted cells and the cover member is transparent. The zones are preferably colour-coded to enable a relatively unskilled or illiterate health worker to report the results accurately by direct observation through the cover member, without needing to remove the sample tubes before assessment.

The rotational drive connection means preferably comprises an array of holes evenly spaced around the rotational axis, to engage, either directly or indirectly via suitable adaptor, with the drive pins on the drive head of a commercially-available centrifuge which would normally be used with swing-out buckets to accommodate the larger centrifuge tubes of capacity 10-15 ml or with other commercially-available manual or portable powered field centrifuges. However, the centrifuge rotors according to the present invention may be manually spun at high speeds in alternating directions by passing lengths of cord or like material through holes disposed symmetrically about or on opposite sides of the axis, attaching the cords at one end to a suitable support, holding the free ends of the cords in the hand, preferably with the aid of a suitable handle, and causing the rotor to begin rotating, thereby twisting the cords together, whereby rotation can be continued in alternating directions at very high speeds by alternately tensioning and relaxing the cords as between the support and the free ends.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which

Figure 1 is a plan view of a centrifuge rotor capable of holding twenty blood sample tubes, and

Figure 2 is a fragmentary cross-sectional view along a diameter of the rotor of Figure 1.

Figure 3 is similar to Figure 1 for a smaller version for holding ten tubes, and

Figure 4 is similar to Figure 2 for the rotor of Figure 3.

Referring firstly to Figure 1, it should initially be understood that the rotor is formed from a transparent plastics material and, hence, the cover plate is not visible in this view. The cover plate is, however. shown in Figure 2.

The rotor 11 consists of a base plate 12 and a cover plate 13. The upper surface of the base plate is formed with twenty radially-disposed inner and outer locating recesses, respectively 14, 15, for receipt of microcapillary blood sample tubes (not shown) . The inner recesses 14 extend from a central boss around which is a resilient annular sealing element 16 and the outer recesses 15 extend to an annular groove 17, also containing a resilient sealing element. The purpose of the sealing elements is to provide a firm location for the ends of the sample tubes. The central boss is formed with a central axial hole 18 and three holes 19 disposed equi-angularly apart and at a common distance from the axis. As shown in Figure 2, these holes are dimensioned and arranged to engage with the central spindle 20 and rotational drive pins 21 of an electrically-driven or a manually-driven centrifuge (not shown) .

Two annular grooves 22, 23 are also formed in the upper surface of the base member, externally of groove 17. Corresponding annular projections 24, 25 are formed on the lower surface of the cover member. The projections engage and partly fill the respective grooves 22, 23 and have a wedge-shaped profile the sloping face of which deflects any blood towards the bottom of the grooves. The lower parts of the grooves beneath the projections contain absorbent cotton liners 26, 27 which have been soaked in a disinfectant solution, for example chlorine at 10,000 ppm, and squeezed to remove excess liquid.

Circular lines are formed on the base member at predetermined distances from the groove 17, to indicate annular zones which are used for evaluation purposes to enable ready assessment of the packed cell volume of the centrifuged blood, according to the band or zone in which the inner end of the packed cell column reaches.

The bands are marked to correspond with human packed cell volumes of 0 to 20%, 21 to 35%, 36 to 50% and 51% and above, and may be correlated to haemoglobin concentration. In order that the blood cell concentration can be read quickly and accurately in situ without recourse to measurement or calculation, the bands are colour-coded, annotated and letter-coded.

For example, the outer band 23 is coloured red and signifies a very low blood cell volume indicative of severe anaemia; this is marked "very low" and "A"; the next inner band 24 is coloured yellow and signifies a low blood cell volume indicative of moderate anaemia; the band is also marked "low" and has the letter "B"; the next inner band 25 is coloured green and is marked

"normal" with the letter "C"; this band signifies a normal blood cell volume indicative that anaemia is not present, and the next inner band is coloured blue and signifies a high blood cell volume, indicative of dehydration or plasma loss; this band is marked "high" and has the letter "D".

The cover plate is secured in place by a threaded nut 28 carried on the threaded end of the central spindle 20 of the centrifuge.

Figures 3 and 4 are similar to Figures 1 and 2 except that the rotor has provision for ten sample tubes and is for use remote from a centrifuge machine. The rotor has an aluminium hub 29 secured by set screws 30. The cover plate is secured by a locking ring 31 which screw-threadedly engages the hub 29. Four holes 32 are provided, through which string, cord or other suitable filamentary material, preferably braided nylon, may be passed to provide a rotary power source in alternate directions, on initially twisting the strands and then alternately tensioning and relaxing them. It has been found that, at a maximum operating traction force of 25 kg, mean rotational speeds of 4,000 rpm may be obtained, with a maximum speed of 5,600 rpm, the optimum working string length being 160 cm. Under these conditions, the average packing time required is

5 minutes which takes 150 pulls on the string.

It has been seen that these rotational speeds give adequate packing, despite the fact that existing commercially-available microhaemocrit centrifuges operate at speeds up to 12,000 rpm. However, to compensate to some extent for the lower speeds, the sample tubes may be filled to less than their total or standard amounts, whereby the separation layer between packed cells and plasma is radially further outwards in relation to its position with a completely filled tube for the same blood sample.

The rotor according to the invention is designed to eliminate handling of charged sample tubes once loaded in the base member, to minimize the chances of infection from contaminated blood. It will be appreciated that direct observation of the tubes in situ is possible for assessment purposes; the grooves for the sample tubes may be made slightly oversize so that, once assessment has taken place, the cover may be removed and the tubes merely tipped directly into a suitable receptacle for disposal.

Claims

1. A centrifuge rotor comprising a base member and a cover member and having axially-disposed rotational drive connection means in a central region thereof, the base member comprising an essentially circular plate having sample tube locating means disposed radially and terminating outwardly in resilient elements, and the cover member having a lower surface which cooperates, in use, with the base to retain sample tubes securely in position, one of the base and cover members including at least one annular groove disposed radially outwardly of the sample tube locating means and the other of the base and cover members including a corresponding annular projection, the projection being sealingly engageable within the groove when the base and cover members are located together for use.

2. A rotor according to claim 1, in which the sample tube locating means terminate inwardly in resilient elements.

3. A rotor according to claim 1 or claim 2, in which the inward and/or outward resilient elements each comprise an annular element disposed in an annular groove which communicates between the respective inner or outer ends of the sample tube locating means.

4. A rotor according to any preceding claim, in which the sample tube locating means comprise radially-disposed grooves formed in the base member.

5. A rotor according to any preceding claim, in which the annular projection is provided with an upper surface which slopes in a radial outward direction towards the base of the annular groove to which the projection corresponds.

6. A rotor according to any preceding claim, in which two annular grooves and corresponding annular projections are provided, the respective grooves/projections being concentric.

7. A rotor according to any preceding claim, in which the or each annular groove carries an absorbent material which is impregnated with a disinfectant material.

8. A rotor according to any preceding claim, in which the base member is marked in annular zones according to predetermined packed cell volume ranges, whereby the packed cell volume of a centrifuged blood sample contained in a sample tube may be readily assessed by reference to the zones, at least the cover member being transparent.

9. A rotor according to claim 8, in which the zones are colour-coded.

10. A rotor according to any preceding claim, in which the rotational drive connection means comprises an array of hole evenly spaced around the rotational axis of the rotor, the holes in use receiving either the drive pins of a centrifuge head or lengths of cord-like material which can be twisted together to cause the rotor to spin in alternate directions by alternately tensioning and relaxing the cords.

11. A method of diagnosis of anaemia, the method comprising supplying a whole blood sample contained in a sample tube, preferably a capillary tube, to a centrifuge rotor according to claim 8 or claim 9, causing the rotor to spin at centrifuging speeds for a time sufficient to cause the cells to separate from the plasma and to be compacted, and assessing the result by direct observation through the cover member in relation to the marked annular zones.