GB1464651A - Method and circuit arrangement for determining the coagulation time of blood or blood plasma - Google Patents

Abstract

1464651 Measuring coagulation times; voltage measuring KOMBINAT MEDIZIN-UNDLABORTECHNIK VEB 28 Jan 1974 [26 Jan 1973] 03797/74 Headings G1A and G1U The coagulation time of a liquid such as blood or blood plasma, i.e. the time taken for the liquid to coagulate after a reagent is added to it, is measured by producing an electric signal representing an optical, electric or mechanical property of the liquid, monitoring the signal to determine an extreme value when it corresponds to the minimum turbidity of the liquid, and measuring the time interval between the addition of the reagent and the moment when the signal has fallen below the extreme by a predetermined adjustable amount. The property measured may be viscosity, conductivity or turbidity, only the latter being described. Fig. 2 shows an electric signal produced by a turbidity measurement; this is the inverse of the turbidity, and passes through a maximum 9 some time after the addition of reagent at 4. A circuit having a store is supplied with this signal via a diode, so that the stored signal follows the electric signal, but is lower by an amount equal to the drop across the diode; the diode ensures that the stored signal remains at its maximum when the electric signal starts to drop. Thus in Fig. 2 the store is activated at time 5 after the initial fluctuations have died out, and the stored signal levels off at a voltage 11 below the maximum level of the electric signal. A timer is activated when the reagent is added, and is switched off when the electric signal has fallen to the stored value, at point 6. The total time is the coagulation time. In Fig. 4 the turbidity is measured by light source and detector 40, 13. After amplification at 14 the electric signal passes via diode 15 to store 16, thence to transformer 18 and diodes 19. Thus the signal at the + input of differential amplifier 22 is less than the maximum value by the amounts dropped across diodes 15 and 19, and is adjustable by switch 20. The detector signal also passes via amplifier 14 and transformer 20 to the - input of 22. When the + and - inputs become equal, timer 23 is switched off. In an alternative embodiment, Fig. 5, the amplified detector signal passes to the - input of 26, then to filter 28, threshold switch 30, amplifier 32 and relay 34. While the detector signal increases, the relay contact 37 stays closed, and motor 38 adjusts potentiometer 39 so that the + input of 26 follows the detector signal; at the maximum detector signal the relay opens, and the + input of 26 remains at a voltage equal to this maximum signal. The voltage is applied via two diodes 35 to the + input of 27 where it is compared with the detector signal. When the latter has fallen below its maximum by an amount equal to the drop across diodes 35, the inputs to 27 become equal and timer 23 is switched off via filter 29, trigger 31 and amplifier 33.