Massive blood loss leading to hypovolemic shock is still a life-threatening situation. Recently, a great number of investigations have been conducted in order to understand the pathophysiological and immunological changes taking place during shock and to develop treatment strategies. These preclinical trials are based on animal studies. Although a wide spectrum of species and experimental models are available to researchers, it is rather difficult to create an ideal animal model to study hemorrhagic shock. A major challenge for investigators is the generation of a system which is simple, easily reproducible and standardized, while being an accurate replica of the clinical situation. The goal of this review is to summarize the current experimental models of hemorrhagic shock, highlighting their advantages and disadvantages to help researchers find the most appropriate model for their own experiments on hypovolemic shock.
Molecular clusters of a wide variety of substances have been generated by'homogeneous nucleation in nozzle flow and studied by electron diffraction. Clusters were the order of 100 Á in diameter. The majority of the clusters were found to be liquidlike.Two examples could be produced as either liquid or crystalline clusters by adjusting flow conditions. Several others could be induced to organize into two or more different crystalline packings by controlling mole fraction, carrier gas, and/or stagnation pressure. Substances exhibiting large ranges of liquid existence in the bulk gave liquid clusters while those with small or null ranges gave solid aggregates. In intermediate cases the entropy of fusion, representing a measure of difficulty of molecular reorientation, helped to sharpen the diagnostic rule of thumb regarding cluster form. Approximate computations of the temperatures of clusters growing in their supersaturated vapor during nozzle flow indicate that the condensing clusters are appreciably warmer than the gaseous medium and much warmer than the grown clusters exiting the nozzle. In a number of cases, the clusters appear to have undergone phase changes in the course of some microseconds of cooling in adiabatic flow after they were fully grown.
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