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A pulsed Doppler instrument running at 1.5 MHz resonance frequency was used for detection of microbubbles within a recirculating fluid line. Glass beads of nominal 200 microns were injected to get a statistical calibration level of the set-up. This is achieved by identifying the peak intensity of the bubble size histogram which reflected the microsphere size.

The anticoagulant effect of heparin was studied in 20 patients undergoing aortocoronary bypass surgery. The protamine dose necessary to reverse heparin after extracorporeal circulation (ECC) was assessed in ten patients from individual heparin dose-response curves (HDR group). The other ten patients received protamine according to a routine protocol (control group). The protamine administration was followed in both groups by injection of 3-5 g tranexamic acid (Cyklokapron). A wide range of sensitivity to heparin was shown by the patients. Although almost twice as much protamine was given to the control group as to the HDR group, the effect on heparin reversal was similar. The variability of protamine dose did not influence the post-bypass levels of fibrinogen, AT-III, activated coagulation time (ACT) or Cephotest, and fibrinolysis was not observed in either of the groups. During ECC there was poor correlation between ACT and plasma heparin levels, and the use of heparin dose-response curves was grossly misleading in regard to true heparin concentration. The postoperative bleeding was not related to the levels of heparin or coagulation parameters after heparin reversal. The concentrations of fibrinogen and AT-III showed variations dependent on the changes in haematocrit. A number of factors other than heparin that influence ACT are discussed.

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A comparative study of microbubble release from various types of oxygenators was performed using ultrasonic Doppler techniques. Bubble count versus amplitude histograms were calculated to derive the statistical distribution of the relative microbubble sizes. To compare the different oxygenators with respect to differences in microbubble releases, several key parameters as, temperature, liquid flow rate, gas to flow relationship, liquid level within the oxygenator, were altered one at a time to indicate different and oxygenator related sensitivities with respect to variations of the key parameters.