IN-VITRO ESTIMATION OF RED-BLOOD-CELLS AGGREGATION USING ULTRASOUND DOPPLER TECHNIQUES

Aggregation of red blood cells (RBCs) is one of the principal hemorheo logical factors which plays an important role in capillary circulation . In order to study RBC's aggregation, an ultrasound Doppler in vitro technique, using pulsed wave monoelement pencil 4 MHz probes, was desi gned. A hydraulic pump system has been implemented, using an electric step motor that establishes in a certain distance, a laminar blood flo w profile into a rectangular cross-section plexiglass tube. Blood comi ng from blood collection bags was used and following certain typical m easuring protocols, red blood cells' samples of various parameters and conditions were acquired. Adding dextrans to the blood samples, red b lood cells aggregation was achieved and observed for various hematocri t values. Both the emitted and the backscattered signals were driven t o a system containing a multi-channel digital oscilloscope - of high s ampling rate and processing capabilities - and a powerful PC with a hi gh acquisition A/D card and special control software. The estimation o f mean aggregates size - by measuring the mean ultrasonic intensity sc attered by the blood sample - led us to a qualitative, in vitro ultras onic method.