title: Cardiogenic mixing increases aerosol deposition in the human lung in the absence of gravity.
abstract: BACKGROUND
  Exposure to extraterrestrial dusts is an almost inevitable consequence of any proposed planetary exploration. Previous studies in humans showed reduced deposition in low-gravity compared with normal gravity (1G). However, the reduced sedimentation means that fewer particles deposit in the airways, increasing the number of particles transported to the lung periphery where they eventually deposit albeit at a smaller rate than in 1G. In this study, we determined the role that gravity and other mechanisms such as cardiogenic mixing play in peripheral lung deposition during breath holds.
  
  
  METHODS
  Eight healthy subjects inhaled boluses of 0.5 μm-diameter particles to penetration volumes (Vp) of 300 and 1200ml that were followed by breath holds of up to 10 sec. Tests were performed in 1G and during short periods of microgravity (μG) aboard the NASA Microgravity Research Aircraft. Aerosol deposition and dispersion were calculated from these data.
  
  
  RESULTS
  Results show that, for both Vp, deposition in 1G was significantly higher than in μG. In contrast, while dispersion was significantly higher in 1G compared to μG at Vp=1200ml, there was no significant gravitational effect on dispersion at Vp=300ml. Finally, for each G level and Vp, deposition and dispersion significantly increased with increasing breath-hold time.
  
  
  CONCLUSIONS
  The most important finding of this study is that, even in the absence of gravity, aerosol deposition in the lung periphery increased with increasing residence time. Because the particles used in this study were too large to be significantly affected by Brownian diffusion, the increase in deposition is likely due to cardiogenic motion effects.
authors: Dept. of Medicine, UCSD, La Jolla, CA, USA ; Dept. of Radiology, UCSD, La Jolla, CA, USA.
authors: G Kim
authors: GK
authors: Prisk
authors: Rui Carlos
authors: RC
authors: Sá
authors: Chantal
authors: C
authors: Darquenne
keywords: aerosol bolus; cardiogenic mixing; dust; planetary exploration; reduced gravity
references: J Appl Physiol Respir Environ Exerc Physiol. 1982 Dec;53(6):1603-7
references: 7153156
references: J Appl Physiol (1985). 2004 Dec;97(6):2083-9
references: 15298988
references: J Appl Physiol (1985). 1999 Apr;86(4):1402-9
references: 10194229
references: J Appl Physiol (1985). 1997 Dec;83(6):2029-36
references: 9390977
references: J Appl Physiol (1985). 2000 Nov;89(5):1787-92
references: 11053327
references: Exp Lung Res. 1991 Jul-Aug;17(4):763-87
references: 1935835
references: J Appl Physiol. 1973 Jul;35(1):9-17
references: 4716169
references: Eur J Appl Physiol. 2008 Aug;103(6):687-95
references: 18488244
references: J Appl Physiol (1985). 1998 Oct;85(4):1252-9
references: 9760313
references: Respir Physiol Neurobiol. 2005 Aug 25;148(1-2):207-16
references: 15890563
references: J Appl Physiol Respir Environ Exerc Physiol. 1977 Jan;42(1):5-12
references: 833076
references: J Appl Physiol. 1961 Jul;16:697-702
references: 13784582
references: Inhal Toxicol. 2002 Sep;14(9):901-16
references: 12396402
references: J Clin Pharmacol. 1989 Jul;29(7):615-27
references: 2760255