Effects of static pressure on red blood cells on removal of the air interface

Previous studies investigated the effects of pressure on red blood cells, but did not address the presence of an air interface. It has been established that an air interface promotes damage to blood. This study was designed to allow for the isolation of the blood-air interface during pressurization. Fresh human blood was divided into 2 ml samples in polypropylene tubes and exposed to either negative or positive pressure for 5 min at 37 degrees C. The plasma free hemoglobin was measured and compared to controls (0 mmHg) exposed to the same environment. This procedure was duplicated with a 1 ml layer of mineral oil on each sample, to remove the air interface. The sample size for each pressure was 15. Results from this study demonstrate that blood is resistant to positive pressures (1,000 mmHg), even on removal of the air interface. However, hemolysis previously attributed to negative pressures was not seen when the air interface was removed by mineral oil. Removal of the air interface halted cavitation, which occurred at pressures equal to or below -680 mmHg in the presence of the air interface. It is the authors' belief that hemolysis is not correlated with negative pressure, but rather with the susceptibility of blood to cavitation.