Abstract
A model for calcium oxalate aggregation was developed using the high-molecular-weight polymer poly (acry lamide). The mechanism for aggregation by this polymer was demonstrated to involve mainly nonelectrostatic hydrogen bonding. With the use of settling studies and turbidity measurements, the effect of extracorporeal shock wave lithotripsy (ESWL) on these aggregates was determined. This effect proved to be a function of aggregate size: the smaller the aggregate, the less effect ESWL had on it. This result can be explained by a force analysis of the ESWL wave: when the distance for the wave to rise to maximal pressure is large relative to the size of the particle, the pressure gradient (related to the force) will never be large. For our machine, the waveform rise takes place over a distance of 306.8 μm. This distance should represent a theoretical minimum for a powerful ESWL effect and correlates well with the minimum size of the stone fragments produced by ESWL. The model described here may be useful for studying the effect of stone therapies on calcium oxalate aggregation, a means for the clinician to predict the probability of fragmenting a stone based on its size, and a means of modifying the ESWL waveform to enable it to break up smaller fragments.
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