Crystal sedimentation and stone formation

Abstract

Mechanisms of crystal collision being the first step of aggregation (AGN) were analyzed for calcium oxalate monohydrate (COM) directly produced in urine. COM was produced by oxalate titration in urine of seven healthy men, in solutions of urinary macromolecules and in buffered distilled water (control). Crystal formation and sedimentation were followed by a spectrophotometer and analyzed by scanning electron microscopy. Viscosity of urine was measured at 37°C. From results, sedimentation rate (vS), particle diffusion (D) and incidences of collision of particles in suspension by sedimentation (IS) and by diffusion (ID) were calculated. Calculations were related to average volume and urinary transit time of renal collecting ducts (CD) and of renal pelvis. vS was in urine 0.026 ± 0.012, in UMS 0.022 ± 0.01 and in control 0.091 ± 0.02 cm min−1 (mean ± SD). For urine, a D of 9.53 ± 0.97 μm within 1 min can be calculated. At maximal crystal concentration, IS was only 0.12 and ID was 0.48 min−1 cm−3 which, even at an unrealistic permanent and maximal crystalluria, would only correspond to less than one crystal collision/week/CD, whereas to the same tubular wall being in horizontal position 1.3 crystals/min and to a renal stone 624 crystals/cm2 min could drop by sedimentation. Sedimentation to renal tubular or pelvic wall, where crystals can accumulate and meet with a tissue calcification or a stone, is probably essential for stone formation. Since vS mainly depends on particle size, reducing urinary supersaturation and crystal growth by dietary oxalate restriction seems to be an important measure to prevent aggregation.

From crystalluria to kidney stones, some physicochemical aspects of calcium nephrolithiasis

“…In CS which in scanning microscopy performed at the end of Ox titration showed large crystal aggregates ( Figure 6C), a rapid OD decrease immediately after the end of titration was observed, whereas in urine without AGN ( Figure 6B) this rapid OD decrease was lacking or occurred with a delay of 15 and more minutes. Analysis of crystallization curves and scanning electron microscopy of crystal sediments revealed a good correlation between OD decrease and particle sizes [30] . Crystals produced by Ox titration showed in urine of 63% of healthy controls but only in urine of 33% of stone patients during 30 min observation time a complete inhibition of AGN (P < 0.05) [7] .…”

“…The natural driving forces for particle collision without shaking or stirring are diffusion by Brownian motion and sedimentation. The effect of these two forces recently was studied in the context of high physiological crystal concentrations, renal tubular and pelvic dimensions and urinary transit times in the kidney [30] . Crystals are even at the maximal concentration of 24000/cm 3 assumed in idiopathic Ca stone formers [9] on average in a distance of about 350 µ.…”

“…an accumulation of 624 crystals per cm 2 surface and min. can be calculated [30] . Crystal accumulation on kidney calcifications or stones seems to be an important mechanism in stone formation.…”

The infectious factor in the genesis of urinary stone formation

“…Некоторыми авторами инфекция рассматривается как фактор, усугубляющий течение болезни, являясь одновре-менно дополнительной местной причиной фор-мирования и поддержания хронического течения мочекаменной болезни. При этом продукты жизне-деятельности микроорганизмов расцениваются как фактор неблагоприятного влияния на мочу за счет ее резкого ощелачивания и бурного образования кристаллов аморфных фосфатов, если же имеет ме-сто наличие ядра кристаллизации, то определяют быстрый рост камней [1,13,15]. По мнению дру-гих авторов, инфекционный компонент является этиологическим фактором формирования камней [11][12][13]21].…”

Litíase Urinária E Sua Relação Com Os Achados De Cristalúria E Hematúria Na Urinálise

“…Ademais, um grande número de pacientes com litíase por oxalato de cálcio não apresenta níveis urinários elevados de cálcio e oxalato [7][8] . O citrato, componente normal da urina, desempenha um papel importante na redução da formação e recorrência dos cálculos urinários, pois, ao se ligar ao cálcio, ele inibe a nucleação espontânea e a cristalização do oxalato de cálcio [9][10] . Este estudo teve como objetivo verificar a frequência de cristalúria e a relação entre litíase urinária e os achados de cristalúria e hematúria em pacientes da região noroeste do estado do Rio Grande do Sul.…”