Researchers at the Johns Hopkins University School of
Medicine have found that a chemical
commonly used in the production of such medical plastic
devices as intravenous bags and catheters can
impair heart function in rats. Reported online last week in
the American Journal of Physiology, these
findings suggest a possible new reason for some of the
common side effects — including loss of taste
and short-term memory loss — of medical procedures
that require blood to be circulated through
plastic tubing outside the body, such as heart bypass
surgery or kidney dialysis. These findings also
have strong implications for the future of medical plastics
manufacturing.
In addition to loss of taste and memory, coronary
bypass patients often complain of swelling and
fatigue. These side effects usually resolve within a few
months after surgery, but they are troubling
and sometimes hinder recovery.
Artin Shoukas' personal experience with coronary
bypass surgery propelled his search for a root
cause for the loss-of-taste phenomenon. "I'm a chocoholic,
and after my bypass surgery, everything
tasted awful, and chocolate tasted like charcoal for
months," said Shoukas, professor of biomedical
engineering,
physiology,
and
anesthesiology and critical care medicine at Johns
Hopkins and principal
investigator on the study.
Shoukas and Caitlin Thompson-Torgerson, a postdoctoral
fellow in Anesthesiology and Critical
Care Medicine, suspected that the trigger for these side
effects might be a chemical compound of
some kind.
To test their theory, Shoukas and his team of
researchers took liquid samples from IV bags and
bypass machines before they were used on patients. The team
analyzed the fluids in a machine that
can identify unknown chemicals and found the liquid to
contain a chemical compound called
cyclohexanone. The researchers thought that the
cyclohexanone in the fluid samples might have
leached from the plastic. Although the amount of
cyclohexanone leaching from these devices varied
greatly, all fluid samples contained at least some
detectable level of the chemical.
The researchers then injected rats with either a salt
solution or a salt solution containing
cyclohexanone and measured heart function. Rats that got
only salt solution pumped approximately
200 microliters of blood per heartbeat and had an average
heart rate of 358 beats per minute, while
rats injected with cyclohexanone pumped only about 150
microliters of blood per heartbeat with an
average heart rate of 287 beats per minute.
In addition to pumping less blood more slowly, rats
injected with cyclohexanone had 50 percent
weaker heart contractions. They also found that the reflex
that helps control and maintain blood
pressure was much less sensitive after cyclohexanone
exposure, and that fluid retention and swelling
increased.
Thompson-Torgerson and Shoukas said that they would
like to figure out how these side
effects — decreased heart function and swelling
— occur and to what degree cyclohexanone is involved.
Despite the findings in this study, they emphasize
that patients should listen carefully to the
advice of their physicians. "We would never recommend that
patients decline this type of treatment if
they need it," Shoukas said. "On the contrary, such
technologies are life-saving medical advances, and
their benefits still far outweigh the risks of the
associated side effects. As scientists, we are simply
trying to understand how the side effects are triggered and
what the best method will be to mitigate,
and ultimately remedy, these morbidities."
This study was funded by the Bernard A. & Rebecca S.
Bernard Foundation, American Heart
Association, W.W. Smith Foundation, National Institutes of
Health, Pulmonary Vascular Research
Institute, American College of Cardiology, Shin Chun-Wang
Young Investigator Award, American
Physiological Society, Joyce Koons Family Cardiac Endowment
Fund and Shoukas.
Authors on the paper are Thompson-Torgerson, Hunter C.
Champion, Lakshmi Santhanam, Z.
Leah Harris and Shoukas, all of Johns Hopkins University
School of Medicine.
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