Membranes and their constituents as promoters of calcium oxalate crystal formation in human urine.

We have proposed that membranes of cellular degradation products are a suitable substrate for the nucleation of calcium oxalate (CaOx) crystals in human urine. Human urine is generally metastable with respect to CaOx. To demonstrate that cellular membranes present in the urine promote nucleation of CaOx we removed these substrates by filtration or centrifugation and induced crystallization by adding sodium oxalate, before and after filtration or centrifugation. In a separate experiment, membrane vesicles isolated from rat renal tubular brush border were added into the filtered or centrifuged urine before crystal induction. Crystals were counted using a particle counter. Urine, the pellet, and retentate were analyzed for the presence of membranes, lipids, and proteins. Lipids were further separated into different classes, identified, and quantified. Both filtration and centrifugation removed lipids, proteins, and membrane vesicles, causing a reduction in lipid and protein contents of the urine. More crystals formed in whole than in filtered or centrifuged urine. The number of crystals significantly increased when filtered urine was supplemented with various urinary components such as the retentate and phospholipids, which are removed during filtration. We also determined the urinary metastable limit with respect to CaOx. Filtration and centrifugation were associated with increased metastable limit which was reduced by the addition of membrane vesicles. These results support our hypothesis that urine normally contains promoters of CaOx crystal formation and that membranes and their constituents are the most likely substrate for crystal nucleation in the urine.

Evaluation of glucose monitoring devices in the hyperbaric chamber.

Diabetic patients may experience fluctuations in whole blood glucose (WBG) levels while receiving hyperbaric oxygen therapy (HBO) resulting in seizure-like activity. Therefore, hyperbaric medical attendants must accurately monitor the WBG levels of these patients during HBO. In addressing this concern, this study evaluated the accuracy and reliability of commercially available glucometers (Glucometer M+, Companion 2, HemoCue, One Touch II, and ExacTech Pen) in the hyperbaric environment. WBG samples were prepared, ranging from 25 to 250 mg/dl, for testing glucometers at ground level and at 2.36 atmospheres absolute (ATA). It was noted that at 2.36 ATA, glucose values increased using the Glucometer M+, but decreased with the Companion 2 and HemoCue. The One Touch II values decreased in the hyperglycemic ranges (> 150 mg/dl), whereas the ExacTech Pen monitor readings increased in the hypoglycemic ranges (< 100 mg/dl). The accuracy of WBG monitors is significantly affected by changes in atmospheric pressure.