Acceleration of coagulation time by ultrasound

The clotting time of fresh human platelet rich plasma (PRP) was decreased by 50% immediately following ultrasonic irradiation at intensities within the range 0.4-2.2 W/cm². PRP was obtained from adult blood anticoagulated with citrate and irradiated in a cylindrical glass chamber (diameter 1.1 cm, volume 1.5 ml) having acoustically transparent windows of Saran Wrap at each end. This chamber was immersed in a water bath at 30°C and located on axis approximately 0.5 cm in front of a 2.54 cm diam PZT4 1 MHz transducer, operating at its fundamental frequency. Coagulation times after recalcification were measured with a clinical fibrometer, and showed a marked reduction immediately after irradiation. Subsequent clotting measurements on the same irradiated sample throughout the next 20 min showed a time dependent increase in clotting time, presumably due to uptake of clot promoting factors by intact platelets. An increase in the intensity of the ultrasound decreased the rate at which these clotting factors were removed from the plasma, indicating that platelets are damaged during irradiation. Irradiation of PRP for 5 min at intensities greater than those above appears to cause irreversible platelet aggregation.