The first model of the manual haematocrit centrifuge was fabricated using the rear wheel of a bicycle.(Figure 1). The pedal to rear wheel ratio is 2. The diameter of the rear wheel is 63cm and that of the pulley of the rotor is 1.4cm giving a pedal to rotor ratio of 90. The radius of the capillary tube holder, the rotor, is 10.5cm.(Figure 2) The rotor (Figure 3) can hold 10 microhaematocrit sodalime glass tubes {(Na-heparinized 80 iu/mL) – Model 161313 NRIS (product of Modulhm A/S. 6-8 Vasekaer, DK – 2730 Herlev, Denmark} and will revolve at 5 400 rpm (equivalent to a centrifugal force of 3360g) with 60 turns of the pedal per minute. Figure 4 shows the schematic diagram of the rotor.
A wide-faced electronic clock with a second hand is placed in front of the cyclist and using two pedals, it is fairly easy to maintain 60 revolutions of the pedal per minute for 5 minutes. The string belt connecting the wheel to the rotor pulley is adapted from the commercial motor fan belt.
Comparative haematocrit readings using the standard electric centrifuge as control have shown no significant difference.

A reviewer of the article on the device published in TROPICAL DOCTOR5 wrote;
‘the author is to be congratulated for designing this piece of equipment’. He went on: ‘I admire the ingenuity’.
When we ran out of plasticine for sealing the capillary tubes, the cheap and readily available candle wax has proved just as effective.6

1. Awojobi O A The manual haematocrit centrifuge. Tropical Doctor 2002; 32: 168.
2. Awojobi OA and Muyibi SA Letter. When there is no plasticine Tropical Doctor 2002; 32: 250.


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