NASA Human Research Program Investigators' Workshop (2012)
4040.pdf
A Combined Transport-Kinetics Model for Growth of Renal Calculi in 1G
and Microgravity
Mohammad Kassemi* Ilana Iskovitz and Robert Brock
National Center for Space Exploration Research (NCSER)
NASA Glenn Research Center
Cleveland Ohio 44135
Abstract
Renal stone disease is not only a concern on earth but could conceivably pose as a serious risk to
the astronauts’ health and safety in Space. In this paper, a combined transport-kinetics model for
growth of calcium oxalate crystals is presented. The model is used to parametrically investigate
the growth of renal calculi in urine with a focus on the coupled effects of transport and surface
reaction on the ionic concentrations at the surface of the crystal and their impact on the resulting
growth rates. It is shown that under nominal conditions of low solution supersaturation and low
Damkohler number that typically exist on Earth, the surface concentrations of calcium and
oxalate approach their bulk solution values in the urine and the growth rate is most likely limited
by the surface reaction kinetics. But for higher solution supersaturations and larger Damkoeler
numbers that may be prevalent in the microgravity environment of Space, the calcium and
oxalate surface concentrations tend to shift more towards their equilibrium or saturation values
and thus the growth process may be limited by the transport through the medium. Furthermore, it
is shown that as the crystal size increases a shift towards a transport-limited growth process is
likely. In this situation beyond a critical radius that is a function of the physiochemical
parameters of the renal environment, the growth rate will not be independent of the radius as in a
reaction-limited situation but will decrease as the crystal size increases.