Advances in shock research
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The passage of red cells is more rapid than for plasma through the microcirculation of most tissues. The effects of hemorrhage (13 ml/kg) and endotoxin (3 mg/kg) on this phenomenon were studied in the exposed mesentery of cats anesthetized with Dial-urethane using epi-illumination fluorescence or transillumination television microscopy. Femoral artery pressure, arteriolar pressure, and arteriolar and venular diameters were measured. ⋯ One hour after endotoxin t was significantly increased in all segments and further increased at three hours. However, the labeled red cell values were still exceeded by the FITC-dextran values at both times. It would appear that the differences in t would be abolished by vasoconstriction reducing axial streaming and plasma skimming whereas vasodilation does not change these phenomena.
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A brief review is given for the rheological behavior of blood in the microcirculation in normal and low flow states. Blood viscosity increases in low flow conditions because of the decrease in shear stress which normally causes red cell deformation and disaggregation. The low hematocrit found in the microvessels leads to a decrease in apparent blood viscosity and tends to compensate for the high vascular hindrance due to the narrowness of the vessels. ⋯ Adhesion of white blood cells to microvascular endothelium leads to an increase in flow resistance, especially in low flow states. The optimum hematocrit for myocardial oxygen transport and utilization is shifted from near 40% in normal conditions to 25% in hemorrhagic hypotension. These findings indicate that blood rheology in the microcirculation should be considered in analyzing the pathophysiological disturbances in shock and that improvement of microcirculation rheology offers a promising approach in treatment.
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Fifteen anesthetized rats, 273 +/- 9 gm (SEM), were monitored hemodynamically for six hours following an IV injection of a sublethal (4--5) X 10(8) organisms/100 gm body wt, n = 5) or lethal 12--15 X 10(8) organisms/100 gm body wt, n = 5) dose of live Escherichia coli or saline (control, n = 5). A transpulmonary thermodilution method was used for measurement of cardiac output. Changes in the arterial blood temperature and pressure were recorded on a polygraph. ⋯ The mean arterial blood pressure was decreased in both groups in the early stage but maintained above 100 mm Hg. Essentially, no hemodynamic changes were noted in the control group. These results confirm our hypothesis that an injection of live E coli can produce a hyperdynamic state in the early stage as well as hypodynamic state in the late stage, and that serial hemodynamic studies on bacteremia in rats can be done successfully using the thermodilution method.
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Intensive care of the patient who has acute brain injury has undergone major changes. Neurologic monitoring, particularly continuous recording of the intracranial pressure, appears to have contributed to an improved outcome in head-injured patients. ⋯ Other techniques such as cerebral blood flow measurements, reflectance spectrophotometry, and sophisticated electrophysiologic recording are being utilized in the laboratory and in man as monitoring techniques. There utility and potential applications are discussed, and the present role of monitoring reviewed.