Previous studies investigated the effects of pressure on red blood cel
ls, 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 du
ring pressurization. Fresh human blood was divided into 2 ml samples i
n polypropylene tubes and exposed to either negative or positive press
ure for 5 min at 37 degrees C. The plasma free hemoglobin was measured
and compared to controls (0 mmHg) exposed to the same environment. Th
is procedure was duplicated with a 1 ml layer of mineral oil on each s
ample, 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 n
ot 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 pressu
re, but rather with the susceptibility of blood to cavitation.