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Principal Investigator:
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Jay C. Buckey, Jr., M.D.
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Organization:
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Dartmouth College
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Project Ended:
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2009
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Astronauts who perform spacewalks are at risk for decompression sickness ("the bends"). If decompression sickness occurs, it can cause severe joint pain, coughing, skin irritation, cramps and even paralysis due to nitrogen bubbles in the blood and tissue. Dr. Jay C. Buckey and Creare, Inc., are testing an ultrasonic instrument that detects and sizes small nitrogen bubbles in both blood and tissue to monitor for and prevent decompression sickness. If successful, these instruments will improve spacewalk efficiency and safety, and lead to better understanding and detection of decompression sickness in astronauts as well as deep-sea divers and pilots.
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Principal Investigator:
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Jay C. Buckey, Jr., M.D.
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|
Organization:
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Dartmouth College
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Project Ended:
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2009
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Decompression sickness can be a significant operational issue for NASA during extravehicular activity. Improved bubble detection and sizing technology could enhance safety and promote understanding of decompression sickness. The goal of this project was to develop and demonstrate a novel bubble detection and sizing techniquedual-frequency ultrasound (DFU).
In this project we:
- Demonstrated the ability of the DFU to detect stationary microbubbles in tissue.
- Performed a comprehensive calibration of the sizing capabilities of the device using bubbles of known size.
- Performed a mix of human and animal experiments to explore the usefulness of tissue bubble detection.
First, we demonstrated that DFU could detect both ultrasonic contrast agent and decompression bubbles in tissue. This demonstrated the ability of DFU to detect small bubbles in tissue. The next step was to assess whether bubbles could be detected after exercise in normal humans. Exercise has been postulated to create small bubbles in tissue, and these bubbles are thought to increase bubble formation and decompression sickness risk during subsequent decompression stress after exercise. But these small bubbles had never been directly detected in tissue.
To do this, in the past year we surveyed for bubbles in the legs of human subjects before and after cycle ergometer exercise using DFU. Six normal human subjects aged 28-52 were studied. Eleven marked sites on the left thigh and calf were imaged on each subject using standard imaging ultrasound. Subjects then rested in a reclining chair for two hours prior to exercise. For the hour before exercise, a series of baseline measurements were taken at each site using DFU. A minimum of six baseline measurements was taken at each site. The subjects then exercised at 80 percent of their age-adjusted maximal heart rate for 30 minutes on an upright bicycle ergometer.
After exercise, the subjects returned to the chair and multiple post-exercise measurements were taken at the marked sites with the Creare dual-frequency instrument. Measurements continued until no further signals consistent with bubbles were returned or one hour had elapsed. All the subjects had signals consistent with bubbles in at least one site after exercise.
The most likely explanation for these results is that exercise does produce gas-filled micronuclei (bubbles). This is the first demonstration that these micronuclei can be detected after exercise, and these results have important implications for decompression sickness diagnosis and treatment.
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Principal Investigator:
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Jay C. Buckey, Jr., M.D.
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|
Organization:
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Dartmouth College
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Project Ended:
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2009
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The results from this study are applicable to divers, aviators, high-altitude parachutists and others who are exposed to the risk of decompression sickness.
Another application for this technology is bubble monitoring during coronary artery bypass surgery or valve replacement surgery. Patients who have coronary artery bypass surgery are at risk for having solid and gaseous emboli reach the brain when they are on the "pump" (the cardiopulmonary bypass circuit). The Creare dual-frequency ultrasound unit could be used to monitor for bubbles in the bypass circuit and could distinguish between solid and gaseous emboli.
Creare is also applying the knowledge gained on the bubble acoustics and expertise gained in this effort to a Department of Energy project to mitigate cavitation damage in the Spallation Neutron Source (SNS) being developed at Oak Ridge National Laboratory. In this facility, a large acoustic wave is produced in the mercury spallation target when proton pulses very rapidly and repeatedly enter the mercury. The acoustic wave reflects off the vessel walls and causes the mercury to cavitate which results in severe damage to the vessel when the SNS is operated at the desired full power level. Creare is characterizing the ability of various stabilized bubbles to dampen the large acoustic wave and, thereby, mitigate the resulting cavitation damage.
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