Experimental models and measurements to study cardiovascular physiology
Neil Herring, David J. Paterson in Levick's Introduction to Cardiovascular Physiology, 2018
The ability to dissect multicellular preparations consisting of part of or an entire organ and maintain their viability was made possible by the introduction of artificial solutions resembling extracellular fluid by Sydney Ringer in the 1880s (Ringer, 1882). Tyrode’s solution resembles Ringer’s original solution, but contains bicarbonate and phosphate as a buffer (rather than lactate) and can be bubbled with 95% O2 and 5% CO2 to maintain a physiological pH. While isolated multicellular preparations allow more complex physiological behaviours to be studied without the influence of changes in circulating hormones and haemodynamics experienced in vivo, they also have limitations. Tyrode’s solution contains glucose rather than free fatty acids, the heart’s main energy supply. It also lacks proteins. Therefore, during long experimental protocols, the lack of oncotic pressure can lead to tissue swelling. The lack of plasma proteins and haemoglobin also means that local signalling molecules which may bind to either of these may not behave in the same way as they do in vivo. In the following section we discuss some of the commonly used multicellular preparation used in cardiovascular physiology.
Renal Medicine
Timothy G Barrett, Anthony D Lander, Vin Diwakar in A Paediatric Vade-Mecum, 2002
This occurs early in the nephrotic episode or in relapse, precipitated by a rapid fall in plasma albumin levels. This reduces capillary oncotic pressure to such an extent that there is an efflux of plasma water from the circulation which may outstrip homeostatic mechanisms to conserve vascular volume. The clinical features consist of abdominal pain, vomiting, tachycardia, hypotension and signs of poor peripheral perfusion. Diuretics are contraindicated, as they further contract vascular volume, leading to acute renal failure. Hypovolaemic crisis can be easily confused with peritonitis or sepsis. Check the PCV as increased PCV indicates volume contraction. Give isotonic saline 10 ml/kg body weight IV. A rapid resolution of abdominal pain and vomiting suggests that hypovolaemia is the likely explanation. Saltpoor albumin can also be used to expand vascular volume. The dose is 0.5–1.0 g/kg given over a minimum of 4 h. Note that increased oncotic pressure can cause rapid refilling of the vascular volume and carries the potential risk of fatal pulmonary oedema. Monitor HR and respiratory rate closely during and for 8 h after the albumin infusion. Frusemide 2–4 mg/kg by slow IV injection will improve diuresis and reduce the risk of volume overload.
Confusion on terminology: Primary lymphedema and lymphangioma (lymphatic malformation)
Byung-Boong Lee, Peter Gloviczki, Francine Blei, Jovan N. Markovic in Vascular Malformations, 2019
High-output failure (also known as dynamic insufficiency) occurs when excessive lymphatic fluid formation exceeds the transport capacity of the intact lymphatic system. Increases in lymphatic fluid production may arise when Starling forces shift net pressure to favor flow of fluid into the interstitium. Increases in venous pressure result in increased hydrostatic pressure within the venules, and capillaries increase the driving force for ultrafiltration.7–9 Loss of oncotic pressure as seen in hypoproteinemic states such as malnutrition, has a similar effect. Elevated venous pressure occurs in patients with right heart failure, deep vein thrombosis, and venous insufficiency. Local inflammation increases capillary permeability, accelerating the loss of fluid and plasma proteins into the interstitium.7–9
A Review of Lens Biomechanical Contributions to Presbyopia
Published in Current Eye Research, 2023
Wade Rich, Matthew A. Reilly
During fiber cell compaction and water loss fiber cell protein concentration increases. This process occurs over time and results can be seen in more nuclear lens cells.46,124 At higher concentrations lens proteins are more likely to interact and could bind together more frequently. Additionally, degraded protein products and insoluble protein fractions, which are more prevalent in nuclear portions of the lens, are known to associate with cytoskeletal elements of fiber cells. Truncated crystallin protein elements, small peptides associated with beta and gamma crystallin fragments, and insoluble protein fractions all interact tightly with fiber cell cytoskeletal elements, intermediate filament proteins, and membrane associated proteins.33 Membrane associated processes of fiber cells, such as organized control of sodium ion flow in and out of the cell, create microcirculation gradients within the lens. These gradients can be utilized to control water content in the fiber cell, cell volume, protein concentration, and thus other properties like GRIN. Oncotic pressure between concentric fiber cell layers is also generated by control of cellular colloidal contents which is determined by the cytoplasmic makeup of each fiber cell. This oncotic pressure influences cellular water content as a result of cellular protein content. In this case, the concentration of protein leads to water loss, not the other way around.124
Flow balance optimization and fluid removal accuracy with the Quanta SC+ hemodialysis system
Published in Expert Review of Medical Devices, 2020
Clive Buckberry, Nicholas Hoenich, Paul Komenda, Mark Wallace, John E Milad
Based on low flux or low hydraulic permeability of the membrane, the relationship between fluid removal rate and applied pressure is linear, although in practice variability is present due to fluctuations of pressure with time induced by variations of flow and the deposition of blood proteins on the membrane surface. In contrast, for the mid- and high-flux hemodialysis membranes in clinical use today, a non-linear relationship exists between fluid flux and transmembrane pressure (TMP) as there is a rapid transfer of plasma water across the membrane at the inlet of the dialyzer when blood enters the dialyzer blood compartment. The concentration of proteins (oncotic pressure) rapidly rises and leads to the development of ‘concentration polarization’, whereby plasma proteins in the blood deposit on the membrane surface. This has the effect of disproportionately increasing the oncotic pressure at the interface between the blood compartment and the surface of the membrane, which inhibits ultrafiltration to the extent that, toward the blood outlet of dialyzers, ‘reverse filtration’ may occur, in which dialysis fluid traverses the membrane from the dialysis fluid pathway of the dialyzer into the blood pathway, resulting in a non-linear relationship at high operating pressures [19].
Management of priming fluids in cardiopulmonary bypass for adult cardiac surgery: network meta-analysis
Published in Annals of Medicine, 2023
Chen-Yang Xian-Yu, Jian-Bo Xu, Yu-Tong Ma, Nian-Jia Deng, Yu-Ting Tao, Hui-Jun Li, Teng-Yu Gao, Jing-Ying Yang, Chao Zhang
Compared with other fluids, patients who used iso-oncotic HA had the shortest ICU stay, the least blood loss at 24h after surgery, and the lowest chest tube output within 24h after surgery. In contrast to the good results of iso-oncotic HA, hyperoncotic HA had the longest hospital stay and mean CPB time, which clearly indicated the poor effect of hyperoncotic HA. Albumin is an ideal humanized colloid with minimal side effects while having less effect on platelet count [45]. Compared to synthetic colloids, it can better reduce the risk of bleeding after CPB [46]. Total chest tube drainage would decrease the platelet count and decrease aggregation in patients undergoing CPB surgery [44]. This is identical to our finding that iso-oncotic HA during CPB is associated with the least output from the thoracic duct within 24h after surgery, resulting in less postoperative nonoperative bleeding due to platelet depletion and dysfunction. Furthermore, the reduction in urine volume due to the use of albumin is associated with osmotic pressure. The osmolality of iso-oncotic HA was analogous to that of plasma osmolality, and hyperoncotic HA was higher than plasma osmolality [47]. Compared with iso-oncotic HA, hyperoncotic HA increases osmotic pressure higher, leading to intraglomerular oncotic force changes or severe renal injury, such as osmotic nephropathy [48]. However, no results of either iso-oncotic HA or hyperoncotic HA regarding urine output were collected in this study.
Related Knowledge Centers
- Albumin
- Blood Pressure
- Body Fluid
- Extracellular Fluid
- Glomerulus
- Lymph
- Osmotic Pressure
- Capillary
- Blood
- Blood Protein