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X-Ray, MRI, and Ultrasound Agents Basic Principles
Published in George C. Kagadis, Nancy L. Ford, Dimitrios N. Karnabatidis, George K. Loudos, Handbook of Small Animal Imaging, 2018
Michael F. Tweedle, Krishan Kumar, Michael V. Knopp
By the 1920s, the desire for systemic agents that could demonstrate renal physiology led to experimentation with intravenous iodide and other salts, and ultimately to the first widely compelling intravascular CA, Uroselectan®, a monoiodinated pyridone solubilized via a carboxylic acid, launched in 1930 by Schering-Kahlbaum AG (Table 15.2). It represented a true breakthrough in tolerance, but this molecule still caused serious reactions on use. The high doses and concentrations necessary for XRCA, combined with large potential markets, led to continuous research with the goal of improving tolerance for iodine. The evolution of the iodinated X-ray agents used today proceeded from Uroselectan to Iodopyracet, which is a similar pyridone with two iodine atoms per molecule, through acetrizoate, a benzenoid with two iodine atoms, to the widely successful and long-lived diatrizoate, a carboxylate solublized tri-iodobenzenoid launched in 1954, and still in some selected uses today. The final and highly significant improvement over diatrizoate was made in the 1970s by Torsten Almen and Nyegaard A/S, called metrizamide, by replacing the carboxylic acid with hydroxylated hydrocarbons to impart the necessary high solubility. This reduced osmolality and toxicity dramatically. These “nonionic” compounds were so well tolerated that they could even be used intrathecally among sensitive neural tissues. Modern variants of this early agent have nearly now replaced the ionically solublized XRCA, as well as metrizamide. The history of intravenous XRCA is much more richly described by Grainger (1982).
Interfacial Catalysis at Oil/Water Interfaces
Published in Alexander G. Vdlkdv, Interfacial Catalysis, 2002
PC Jordan. Ionic energetics in narrow channels. Proceedings of the IMA Workshop on Membrane Transport and Renal Physiology. New York: Springer-Verlag, 2002. JA Odutola, TR Dyke. J Chem Phys 72:5062-5070, 1980 .R Guidelli. J Chem Phys 92:6152-6160, 1990 .Y Jiang, R MacKinnon. J Gen Physiol 115:269-272, 2000 .
Radionuclide Examination of the Kidneys
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
At first glance, the kidneys filter blood plasma, reabsorb useful substances, and excrete waste matters out from the body. In fact, the kidney function is much more complex. Kidneys participate in the maintenance of overall fluid, mineral, and acid–base balance, regulation of blood-pressure and secretion of hormones. The details of renal physiology, including physiological models of kidney function, are described in dedicated monographs [5–9] and review papers [10, 11].
Urine specific gravity as an indicator of dehydration in Olympic combat sport athletes; considerations for research and practice
Published in European Journal of Sport Science, 2018
Damir Zubac, Reid Reale, Hrvoje Karnincic, Anamaria Sivric, Igor Jelaska
Being able to accurately categorize athletes as dehydrated or euhydrated offers increased confidence in interpreting research findings, as well as appropriately prescribing hydration interventions. In the acute setting, changes in BM alone have been shown to satisfactorily reflect body-water changes (Armstrong, 2005); however, in the absence of repeated measures (such as in the case of cross-sectional research or in the setting of a single athlete consult), biochemical markers are required. Scientists and practitioners use various biochemical markers in order to screen fluid balance in athletes, with urinary indicators being the most commonly reported (Armstrong, 2005; Sawka et al., 2007). The validity of such measures is derived from an understanding of renal physiology; i.e. the kidney’s ability to concentrate urine in response to changes in total body-water volume and subsequent dehydration. Plasma fluid deficit(s) raise sodium concentrations and subsequently elevate anti-diuretic hormone (ADH), which reduces water excretion (urine production), thereby increasing the concentration of dissolved particles in the urine. Taking advantage of this homeostatic mechanism, and the ease in which urine samples can be collected and assessed, field-based assessments of urine concentration and colour have emerged as popular methods to characterize acute dehydration among athletes. While urine colour is a cost-effective and quick measure, it has been shown to be relatively imprecise when compared to other measures (Cheuvront, Ely, Kenefick, & Sawka, 2010); thus measures of urine concentration (i.e. urine osmolality, UOSM) and urine specific gravity (USG) are generally preferred. Urine osmolality is a direct measure of the number of dissolved particles within a urine sample, whereas USG is a measure of the weight of urine and the particles contained in it. In general, the weight of urine will increase similarly to increases in solute numbers; however, as UOSM is a direct measure of solute concentration, it is often considered to better reflect true changes in total body fluid balance (Voinescu, Shoemaker, Moore, Khanna, & Nolph, 2002). The requirement for laboratory equipment and expertise in the measurement of UOSM means the less resource intense, yet commonly suggested to be comparably valid measure of USG via refractometry has traditionally been recommend as a suitable alternative for the scientist or practitioner (Chadha, Garg, & Alon, 2001). In fact, modern refractometer units may be calibrated in mOsmol•kg-1 H2O and show good validity when compared to laboratory-based measures (Sparks & Close, 2013).