CONTRIBUTIONS OF SUSPENDING MEDIUM TO ELECTRICAL-IMPEDANCE OF BLOOD

Blood cells from ten normal subjects, anticoagulated with dried sodium heparin, were washed twice with phosphate-buffered saline (PBS) and r esuspended with autologous plasma, serum, serum plus sodium heparin, a nd PBS. The resistance R(p) and capacitance C-m of these suspensions w ere determined by measuring the impedances at three frequencies 100 kH z, 800 kHz and 1.2 MHz, and found to be dependent on the proteins and electrolytes of the suspending medium. Two suspensions with the same m edium resistivity might have different resistances if the contents of the two mediums are different. The fibrinogen, serum proteins, sodium heparin and membrane contributed to C-m by 20%, 14%, 2% and 64%, respe ctively. For the samples with buffered sodium citrate as anticoagulant and in the haematocrit range 30-60%, the group washed and resuspended with PBS had a consistently decreased R(p) and C-m compared to the or iginal group. Sodium heparin seemed to be the best anticoagulant when studying the electrical impedance of blood. The influence of suspendin g medium might result in part from the altered interfacial polarisatio n. The results might be useful for understanding the origin of the imp edance of blood, and imply that impedance measurement may be an altern ative method for screening purposes for diseases that involve abnormal compositions of certain plasma proteins.