Dust Inhalation

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Clearance of Particles Depositing in the Human Lung in Low Gravity

Principal Investigator:
G. Kim Prisk, Ph.D., D.Sc.

University of California, San Diego

In addition to making a mess inside a vehicle or habitat, lunar dust poses a health risk to astronauts that visit the moon. Dr. Kim Prisk is studying how lunar dust, which may contain toxic properties, moves in the lungs. On Earth, inhaled matter that is deposited in the lungs is effectively removed from the body by clearance mechanisms. But in reduced gravity, the deposition is reduced allowing particles to go deeper into the lungs and nearer to sensitive tissue, bypassing the normal clearance mechanisms. As a continuation of a previous project, Prisk will assess particle movement during normal gravity conditions and simulated lunar conditions. The research will answer the question of how dangerous lunar dust is to human health. The findings could also benefit health care on Earth by giving doctors a better understanding of how the lungs work and allow more efficient delivery of aerosol medications.

NASA Taskbook Entry

Technical Summary

Original Aims
The deposition of particulate matter (PM, often referred to as aerosols) in the human lung is known to bring with it both long- and short-term adverse health consequences. The deposition of particles in the lung is strongly influenced by gravitational sedimentation. Studies by our group have shown that normal gravity provides a screening effect whereby inhaled PM larger than 0.5 micron is mainly deposited in the larger airways where it is cleared by mucociliary clearance transport within ~one day. However in low gravity, such as that on the surface of the moon (~1/6 gravity) and Mars (~3/8 gravity), this protective 'gravitational screening' is less efficient.

As a result, particles are deposited in the sensitive alveolar regions of the lung where residence times are very much longer. Further, there is evidence that the dust present on the surface of the moon may possess potent toxicological properties. We hypothesize that clearance rates from the lung of particles deposited in low gravity will be substantially reduced compared to that in Earths gravity, resulting in increased residence times of these particles in the periphery of the lung, enhancing their potential to cause lung damage.

To test this hypothesis, we will measure the clearance rates (measured in Earths gravity) over a few hours to ~one-to-two days, of radio-labeled particles deposited in healthy humans both in Earths gravity and in low gravity corresponding to the lunar surface (~1/6 gravity) during parabolic flight. These data will provide a comprehensive assessment of alterations in the clearance rate of particles inhaled under normal gravity conditions compared to particles inhaled under conditions of lunar gravity (~1/6 gravity). Such an assessment is needed to determine the degree of effort and cost required to control lunar dust within a planned lunar outpost.

Key Findings
In this third year of the project we have completed all technical requirements for flight and stand ready to fly. However flight scheduling has been once again virtually impossible. As a consequence we have performed some ground studies in advance of flight studies. These are part of the post-doctoral fellowship work of Dr Rui-Carlo Sa. In addition we attempted to manifest the experiment on the ESA/Novespace A-300 flying out of Bordeaux, France. However the difficulties with the French nuclear regulatory authorities to fly the necessary radioactive tracer proved insurmountable.

Our current status can be summarized as follows:

• CPHS/Radiation approval in place
• Subject certifications complete
• Hardware and procedures fully tested and functional
• Structural issues resolved
• Ready for flight
• Waiting on flight manifesting, which we are informed will not be before July 2011.

Year 4 Plan
We hope to fly both the 4-micron particle size objective AND the 1-micron particle size objective in Year 4 of the project. In response to the extreme difficulty experienced in scheduling reduced gravity flights, we devised and have now fully verified (as part of the ground studies performed for Dr Sa’s studies) a two-subject-per-flight experimental structure that will permit more efficient use of scarce reduced gravity flight opportunities.

Earth Applications

Airborne particulate matter is a health hazard. The deposition of particulate matter (PM, often referred to as aerosols) in the human lung is known to bring with it both long- and short-term adverse health consequences. On Earth, effects of PM-induced lung injury are most readily seen in individuals with pre-existing lung disease (i.e., asthma, chronic obstructive pulmonary disease). Studies suggest that particle-induced inflammation or edema likely enhance underlying pulmonary disease, leading to a worsening of already abnormal pulmonary ventilation/perfusion relationships and gas exchange. Such worsening can result in hypoxemia leading to fatal cardiac arrhythmia. There is also little question that even healthy individuals exposed to PM for extended periods are susceptible to PM-induced lung injury. For example, the increase in risk of death from long-term exposure to PM in six U.S. cities has been shown to be in the area of 17 percent for the general population for a modest increase in total PM load of 24.5 micro-g/m3.

These studies will directly determine the consequences of a more peripheral site of aerosol deposition on the subsequent clearance of PM from the lung. It is well established that the negative health consequences of exposure to environmental PM increase as particle size is reduced. These studies will provide insight into how much of this effect is a consequence of the increased residence time of particles that are deposited more peripherally in the lungs. Such peripheral deposition occurs not only on the lunar surface but also on Earth.

This project's funding ended in 2012