A direct technique was developed to estimate parameters related to half life (T1/2) and rate constants of embolization (RCE) and to quantitate emboli of three sizes (small, medium, and large) shed from the oxygenator and arterial filter during cardiopulmonary bypass (CPB). Cardiopulmonary bypass was performed in 16 Yorkshire pigs divided as follows: systemic heparin group (SHG:6), systemic heparin/heparinized circuit group (SH/HCG:5), and Iloprost (Bentley) (2 ng/kg/min)/heparinized circuit group (IHCG:5) with In-111 labeled autologous platelets. The anesthetized pigs (20-25 kg) underwent CPB at 2.5-3.0 L/min for 3 hours. Pigs were injected with In-111 platelets (300-420 microCi) 24 hours before CPB. Cardiopulmonary bypass was instituted with a roller pump and hollow-fiber oxygenator, and thrombosis and embolization on the oxygenator and filter were monitored by a calibrated Geiger probe (WMB Johnson Associates, Montvale, NJ). The radioactivity in the oxygenator and filter reached peak values at 25-45 min after CPB; the radioactivity then declined in the oxygenator but remained at a steady state in the filter, suggesting continuous embolization at the same rate of trapping. The curve stripping technique of the normalized radioactivity time curve of the oxygenator was used for RCE estimation of different sized emboli shed from the oxygenator; 42% of thrombus embolized from the oxygenator in SHG with three rate constants, with T1/2s of 12 min, 42 min, and 13 hr; the SH/HCG embolized 35% with T1/2 of 78 min, and the IHCG embolized 30%, with a T1/2 of 22 min. This indicates that there is less embolization in the IHCG.(ABSTRACT TRUNCATED AT 250 WORDS)