Blood, volume

Blood is composed of a cellular portion, the formed elements, suspended in plasma. The formed elements constitute approximately 40—45% of the blood volume, ie, the hematocrit. When a test tube with blood is centrifuged, the formed elements are packed onto the bottom of the tube, leaving plasma on top... 

History. Methods for the fractionation of plasma were developed as a contribution to the U.S. war effort in the 1940s (2). Following pubHcation of a seminal treatise on the physical chemistry of proteins (3), a research group was estabUshed which was subsequendy commissioned to develop a blood volume expander for the treatment of military casualties. Process methods were developed for the preparation of a stable, physiologically acceptable solution of alburnin [103218-45-7] the principal osmotic protein in blood. Eady preparations, derived from equine and bovine plasma, caused allergic reactions when tested in humans and were replaced by products obtained from human plasma (4). Process studies were stiU being carried out in the pilot-plant laboratory at Harvard in December 1941 when the small supply of experimental product was mshed to Hawaii to treat casualties at the U.S. naval base at Pead Harbor. On January 5, 1942 the decision was made to embark on large-scale manufacture at a number of U.S. pharmaceutical plants (4,5). 

Nontraditional Hormones. Novel hormones identified ia cardiovascular tissue have profound effects on maintenance of blood pressure and blood volume ia mammals. Atrial natriuretic hormone (ANH) is a polypeptide hormone secreted from the atria of the heart. When the cardiac atrium is stretched by increased blood volume, secretion of ANH is stimulated ANH ia turn increases salt and water excretion and reduces blood pressure (6). Endothelin is a polypeptide hormone secreted by endothehal cells throughout the vasculature. Although endothelin is released into the circulation, it acts locally in a paracrine fashion to constrict adjacent vascular smooth muscle and increase blood pressure (7). 

A number of different types of ANF have been described, but the original molecule is a polypeptide of 28 amino acids (qv). The prepro-form is released from the atria by stretch, suggesting that increased blood volume in a poody contracting atria compromised by CHF could be one... 

The principal mechanism of the hypotensive effect of diuretics (qv) is salt and fluid depletion, leading to reduction in blood volume (200,240). Acute effects lead to a decrease in cardiac output and an increase in total peripheral resistance. However, during chronic adrninistration, cardiac output and blood volume return toward normal and total peripheral resistance decreases to below pretreatment values. As a result, the blood pressure falls. The usual reduction in blood volume is about 5%. A certain degree of sustained blood volume contraction has to occur before the blood pressure decreases. The usual decrease in blood pressure achieved using a diuretic is about 20/10 mm Hg (2.7/1.3 kPa) (systoHc/diastoHc pressures. 

Diuretics are needed to return to normal the expanded extracellular volume that other antihypertensive agents produce, such as fluid retention and blood volume expansion, via compensatory mechanisms of the body. The loss of efficacy of antihypertensive agents can be restored if a diuretic is used concomitandy. In the treatment of hypertension, high ceiling or loop diuretics, such as furosemide, ethacrynic acid, and bumetanide, are no more efficacious than the thiazide-type of diuretics. In fact, these agents cause more side effects, such as dehydration, metaboHc alkalosis, etc, and therefore, should not be used except in situations where rapid elimination of duid volume is cleady indicated. 

Logically, ADH receptor antagonists, and ADH synthesis and release inhibitors can be effective aquaretics. ADH, 8-arginine vasopressin [113-79-17, is synthesized in the hypothalamus of the brain, and is transported through the supraopticohypophyseal tract to the posterior pituitary where it is stored. Upon sensing an increase of plasma osmolaUty by brain osmoreceptors or a decrease of blood volume or blood pressure detected by the baroreceptors and volume receptors, ADH is released into the blood circulation it activates vasopressin receptors in blood vessels to raise blood pressure, and vasopressin V2 receptors of the nephrons of the kidney to retain water and electrolytes to expand the blood volume. 

The efficacy of these diuretics led to their extensive use in the clinic, particularly in treatment of hypertension. In theory at least, reduction of the blood volume by diuresis should lead to a lowering of pressure (PV=RT). This expectation was in fact met in actual practice. Recent research does, however, seem to indicate that the thiazides have an antihypertensive effect beyond that explainable by a simple lowering of blood volume. 

The average adult has about 16 g of sodium ions in her blood. Assuming a total blood volume of 5.0 L, what is the molarity of Na+ ions in blood ... 

Vasopressin (antidiuretic hormone [ADH]) secretion increases in response to decreased blood volume and/or reductions in effective blood volume via a decrease in inhibitory tone from both low-pressure and high-pressure baroreceptors to the hypothalamus. The neuronal pathways that mediate hemodynamic regulation of... 

In theory, one could utilise GC-A ligands to lower blood pressure and to reduce blood volume as they increase the excretion of water and salt. Nesiritide, human recombinant BNP, is the first member of this new class of drugs approved for the initial intravenous treatment of acutely decompensated congestive heart failure. Whether nesiritide can be a valuable addition to the standard therapy of decompensated heart failure remains to be demonstrated. 

Many antihypertensive drug lower the blood pressure by dilating or increasing the size of the arterial blood vessels (vasodilatation). Vasodilatation creates an increase in the lumen (the space or opening within an arteiy) of the arterial blood vessels, which in turn increases the amount of space available for the blood to circulate Because blood volume (the amount of blood) remains relatively constant, an increase in the space in which the blood circulates (ie, the blood vessels) lowers the pressure of the fluid (measured as blood pressure) in the blood vessels. Although the method by which anti-hypertensive drug dilate blood vessels varies, the result... 

Plasma protein fractions include human plasma protein fraction 5% and normal serum albumin 5% (Albuminar-5, Buminate 5%) and 25% (Albuminar-25, Buminate 25%). Plasma protein fraction 5% is an IV solution containing 5% human plasma proteins. Serum albumin is obtained from donated whole blood and is a protein found in plasma The albumin fraction of human blood acts to maintain plasma colloid osmotic pressure and as a carrier of intermediate metabolites in the transport and exchange of tissue products. It is critical in regulating the volume of circulating blood. When blood is lost from shock, such as in hemorrhage, there is a reduced plasma volume. When blood volume is reduced, albumin quickly restores the volume in most situations. 

Plasma protein fractions are used to treat hypovolemic (low blood volume) shock that occurs as the result of bums, trauma, surgery, and infections, or in conditions where shock is not currently present but likely to occur. Plasma protein fractions are also used to treat hypoproteinemia (a deficiency of protein in the blood), as might be seen in patients with nephrotic syndrome and hepatic cirrhosis, as well as other diseases or disorders. As with human pooled plasma, blood type and crossmatch is not needed when plasma protein fractions are given. 

The volume of blood in the body of a certain deep-sea diver is about 6.00 L. Blood cells make up about 55% of the blood volume, and the remaining 45% is the aqueous solution called plasma. What is the maximum volume of nitrogen measured at 1.00 atm and 37°C that could dissolve in the diver s blood plasma at a depth of 93 m, where the pressure is... 

Metabolic acidosis can also result when a person is severely burned. Blood plasma leaks from the circulatory system into the injured area, producing edema (swelling) and reducing the blood volume. If the burned area is large, this loss of blood volume may be sufficient to reduce blood flow and oxygen supply to all the body s tissues. Lack of oxygen, in turn, causes the tissues to produce an excessive amount of lactic acid and leads to metabolic acidosis. To minimize the decrease in pH, the injured person breathes harder to eliminate the excess C02. However, if blood volume drops below levels for which the body can compensate, a vicious circle ensues in which blood flow decreases still further, blood pressure falls, C02 excretion diminishes, and acidosis becomes more severe. People in this state are said to be in shock and will die if not treated promptly. 

The dangers of shock are avoided or treated by intravenous infusion of large volumes of a salt-containing solution that is isotonic with blood (has the same osmotic pressure as blood), usually one known as lactated Ringer s solution. The added liquid increases blood volume and blood flow, thereby improving oxygen delivery. The HCO / H2C03 ratio then increases toward normal and allows the severely injured person to survive. 

Renin is released by the juxta-glomerular cells when kidney perfusion is impaired. Reduction of the blood volume markedly stimulates release of this enzyme into the blood. The diuretic drug furosemide also markedly stimulates the release of renin. 

Dextrans are produced commercially for use as plasma substitutes (plasma expanders) which can be administered by intravenous injection to maintain or restore the blood volume. They can be used in applications to ulcers or bum wounds where they form a hydrophilic layer which absorbs fluid exudates. 

Hamberg LM, Hunter GJ, Kierstead D, Lo EH, Gilberto Gonzalez R, Wolf GL. Measurement of cerebral blood volume with subtraction three-dimensional functional CT. Am J Neuroradiol 1996 17 1861-1869. 

Sorensen AG, Copen WA, 0stergaard L, Buonanno FS, Gonzalez RG, Rordorf G, Rosen BR, Schwamm LH, Weisskoff RM, Koroshetz WJ. Hyperacute stroke simultaneous measurement of relative cerebral blood volume, relative cerebral blood flow, and mean tissue transit time. Radiology 1999 210 519-527. 

Grubb RL, Jr., Phelps ME, Ter-Pogossian MM. Regional cerebral blood volume in humans. X-ray fluorescence studies. Arch Neurol 1973 28 38-44. 

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