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Hypertension
Published in Jahangir Moini, Matthew Adams, Anthony LoGalbo, Complications of Diabetes Mellitus, 2022
Jahangir Moini, Matthew Adams, Anthony LoGalbo
Plasma volume usually decreases as BP increases. In rare cases, the plasma volume stays at normal levels or increases. It is usually high in a hypertensive person because of primary aldosteronism or renal parenchymal disease. Plasma volume can be very low as well, because of pheochromocytoma. As the diastolic BP increases and arteriolar sclerosis develops, blood flow through the kidneys gradually decreases. Until much later, the glomerular filtration rate (GFR) remains normal. The filtration fraction increases because of this. Blood flow in the cerebral, coronary, and muscle blood vessels is normal unless severe atherosclerosis is present.
Particles and Radiation
Published in Rob Appleby, Graeme Burt, James Clarke, Hywel Owen, The Science and Technology of Particle Accelerators, 2020
Rob Appleby, Graeme Burt, James Clarke, Hywel Owen
Our last example involve the tokamaks proposed for fusion power, which typically contain a large volume of plasma; we wish to maintain a high plasma temperature, but unfortunately the plasma is cooled by bremsstrahlung that occurs as electrons pass close by nuclei. An interesting feature is that the bremsstrahlung power , where Q is the ionisation state of the plasma ions. One example of a tokamak is JET, the Joint European Torus. This has a plasma volume of around 100 m. A typical temperature during JET operation might be 100 million kelvin (10 K), which corresponds to a kinetic energy of the electrons of around 13 keV. The number density of the electrons/ions in the plasma during fusion would be around 1020 m cm. This density should be compared to the density of a typical solid material, water, which has molecules in a cubic centimetre. A ‘high-density’, ‘high-temperature’ plasma is therefore still rather tenuous, and contains low-energy electrons. Using these values for the JET tokamak, we predict that the lost bremsstrahlung power is quite high: 2 MW. Therefore, it is hard to keep a tokamak plasma hot because free-free radiation will cause it to cool itself down.
Nephrology, including fluid and electrolytes
Published in Jagdish M. Gupta, John Beveridge, MCQs in Paediatrics, 2020
Jagdish M. Gupta, John Beveridge
Proteinuria clears within a period of 2 weeks in more than 75% of cases of nephrotic syndrome. Patients with frequent relapses may respond to treatment with cyclophosphamide. Red blood cell casts in urine are indicative of glomerulonephritis and are not seen in minimal change nephrotic syndrome. Hypertension is unusual. Diuretics are not indicated and may be dangerous because of the decreased plasma volume.
Polycythemia vera: aspects of its current diagnosis and initial treatment
Published in Expert Review of Hematology, 2023
Richard T Silver, Ghaith Abu-Zeinah
The Polycythemia Vera Study Group (PVSG) in 1967 recognized the importance of documenting an RCM above normal for the diagnosis of PV [59], as did others subsequently, emphasizing that a single increased RBC, or HGB or HCT value, cannot be used as surrogates [57]. Decrease in plasma volume causes pseudo-increased values, which can lead to an incorrect diagnosis. Variability of counts depends upon whether vein or finger was the site of obtaining the blood specimen, use of diuretics, alcohol and tobacco intake, the time of day, the tightness of the tourniquet, and menstruation [57]. Variations in the HCT as high as 11 ± 3.6% have occurred from lying to standing positions [60]. RCV obviously increases with altitude. For example, cities where inhabitants have a higher RBC in the northern hemisphere include Mexico City, Salt Lake City, Santa Fe, and Denver [57]. Moreover, the environmental temperature affects HCT values [57] (lower values in warm climates due to vasodilation and higher ones in cold due to vasoconstriction). In current clinical trials in PV, whereby an increase in HCT from 45% to 46% or 47% may stipulate therapeutic phlebotomy, the issues and items mentioned can have potential significance.
Reproducibility of the CO rebreathing technique with a lower CO dose and a shorter rebreathing duration at sea level and at 2320 m of altitude
Published in Scandinavian Journal of Clinical and Laboratory Investigation, 2020
Laura Oberholzer, Thomas Christian Bonne, Andreas Breenfeldt Andersen, Jacob Bejder, Regitse Højgaard Christensen, Nikolai Baastrup Nordsborg, Carsten Lundby
Several pathologies are associated with abnormal blood volume (BV) and anemia [1,2]. Hemoglobin concentration ([Hb]) serves as the primary diagnostic tool for anemia [3]. However, low [Hb] can be caused both by compromised erythropoiesis and elevated plasma volume (PV) [4,5]. Accordingly, in some patient populations, e.g. chronic kidney disease and heart failure patients, excessive PV expansion can lead to low [Hb] masking normal or even exaggerated hemoglobin and red blood cell volume (RBCV) [6,7]. Therefore, assessment of total hemoglobin mass (Hbmass) and intravascular volumes, i.e. BV and its components RBCV and PV, is often required to determine the nature of anemia. Such determination provides the total O2 carrying capacity independent of PV fluctuations and is also relevant in terms of targeting the respective vascular compartment for treatment [6–8].
Selecting emergency therapy for patients with pre-eclampsia
Published in Expert Opinion on Pharmacotherapy, 2020
Intravenous nitroglycerin is the drug of choice when PE is associated with pulmonary edema and/or coronary artery disease, and hydralazine and nitrates in the presence of hypertension, severe left ventricular dysfunction and/or evidence of congestion in decompensated heart failure [3]. Sodium nitroprusside is recommended in hypertensive crises when other treatments have failed to control the BP and delivery is imminent. However, it should be used for the shortest time possible because of the risk of maternal/fetal cyanide and thiocyanate toxicity, transient fetal bradycardia, and intracranial pressure with potential worsening of cerebral edema in the mother. Because plasma volume is reduced in PE, diuretics should be best avoided and plasma volume expansion minimized, limiting total fluids to 80–85 mL/h (1 mL/kg/h) unless there are other ongoing fluid losses (hemorrhages).