Biomedical Imaging Magnetic Resonance Imaging
Lawrence S. Chan, William C. Tang in Engineering-Medicine, 2019
Perfusion is a process that brings nutritive blood supply to the tissue through the arterial system and drains the metabolic byproducts into the veins. Perfusion measurement using MRI can be divided into two categories, those employing exogenous agents as a tracer, and those using water protons in the arterial blood as an endogenous label. Among exogenous agents for perfusion MRI, gadolinium chelates are most frequently used. To perform perfusion measurements, a bolus of gadolinium contrast agent is intravenously administered, followed by the rapid acquisition of a series of snap-shot images with either -weighting or T1-weighting. The former is known as dynamic susceptibility contrast (DSC) imaging, while the latter dynamic contrast-enhanced (DCE) imaging. In DSC, the time-series images are processed to extract perfusion-related parameters, such as cerebral blood volume, mean transient time, and time to peak. In DCE, the images are analyzed with a pharmacokinetic model to yield a number of parameters relating to permeability, surface area, transfer constants, etc. (Jahng et al. 2014).
Integrated Cardiovascular Responses
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
In early septic shock, much of the hypotension is due to generalized vasodilatation. Cardiac output may be high initially and tissue oxygen delivery may be normal or even above normal. However, tissue hypoxia occurs as a result of the inadequate perfusion pressures. Arteriovenous shunting occurs as a result of vasodilatation and capillary thrombosis and damage. As fluid leaks out of the circulation and as myocardial depression begins to take effect, cardiac output decreases, compounding the hypoperfusion states. Mediators from septic shock also cause arterial hypoxaemia as a result of increased V/Q mismatch, pulmonary hypertension and right ventricular failure. As the kidneys begin to fail, the clinical state is exacerbated and eventually multiple organ failure occurs.
Surgical Complications of Kidney and Pancreas Transplantation
Stephen M. Cohn, Matthew O. Dolich in Complications in Surgery and Trauma, 2014
Graft thrombosis may occur after the development of reperfusion-induced graft pancreatitis, which is caused when pancreatic blood flow is reduced to a critical level. Multiple factors may be involved in graft pancreatitis including the following [36]. Donor risk factors include hemodynamic instability, brain injury, and vasopressor administration; procurement injury may be due to excessive intraoperative manipulation. Perfusion injury may also occur when excessive flush volumes or perfusion pressures are used. Also, total cold and warm ischemia times may have an effect on preservation and the occurrence of reperfusion injury. Grewal et al. [37] demonstrated that postoperative treatment of the recipient with calcium-channel blockers, combined with the administration of steroids to the donor at the time of procurement, protects against the development of pancreatitis.
Mechanistic links between systemic hypertension and open angle glaucoma
Published in Clinical and Experimental Optometry, 2022
Ying-kun Cui, Li Pan, Tim Lam, Chun-yi Wen, Chi-wai Do
In contrast, the blood supply to an organ is generally regulated by the perfusion pressure. The perfusion pressure is defined as the difference between arterial and venous pressure. The higher the perfusion pressure, the greater the blood flow to the organ and the less likely the organ becomes ischaemic. In most cases, the pressure outside the vein is considered to be atmospheric,39 as shown in Figure 1A. Nevertheless, under certain circumstances, the tissue outside the vein could exert pressure on the vein. For example, whilst standing, there is blood pooling in the veins of the lower limbs due to gravity. To facilitate blood return to the heart, the skeletal muscle contracts, enhancing blood circulation in the presence of one-way venous valves.40
Thermophysical and mechanical properties of biological tissues as a function of temperature: a systematic literature review
Published in International Journal of Hyperthermia, 2022
Leonardo Bianchi, Fabiana Cavarzan, Lucia Ciampitti, Matteo Cremonesi, Francesca Grilli, Paola Saccomandi
Another fundamental factor affecting the thermal outcome during hyperthermia treatments concerns the blood flow in perfused tissues. Blood perfusion refers to the passage of a certain blood volume through vessels embedded in biological tissues, in order to provide oxygen and deliver important nutrients to tissues, as well as remove waste substances [178]. The blood flow can be expressed as the volume of blood, which is forced to flow within a tissue, per tissue mass per unit of time [179], i.e., mL/100 g/min. Moreover, knowing the tissue density, the blood perfusion rate (i.e., the volumetric rate per unit tissue volume, often expressed in 1/s [180]) can be attained as the product of blood flow and the tissue density [181]. The blood flow has been investigated at both normothermic conditions and at temperatures that do not lie in the physiological range, by imposing a temperature variation to biological media through different methods. Likewise, the temperature sensitivity of the blood perfusion has been assessed in different tissues; preclinical studies on healthy tissues and on tumor models have been set, as well as evaluations on blood flow upon temperature changes during clinical trials.
Electrolyte handling in the isolated perfused rat kidney: demonstration of vasopressin V2-receptor-dependent calcium reabsorption
Published in Upsala Journal of Medical Sciences, 2020
Krister Bamberg, Lena William-Olsson, Ulrika Johansson, Anders Arner, Judith Hartleib-Geschwindner, Johan Sällström
A microcontroller was constructed using the Arduino UNO device (www.arduino.cc). The pressure signal from the transducer is fed into the controller via a bridge amplifier. The pressure sensor was placed at the level of the kidney. The output from the microcontroller determines the speed of the peristaltic pump. A computer programme on the controller was developed that continuously calculates the difference between the desired perfusion pressure and the actual perfusion pressure, and applies a correction to the pump rate using a proportional–integral–derivative (PID) regulator (Arduino PID library) in order to maintain the user-set pressure level. Before an experiment was commenced, a calibration function was activated on the controller which runs the pump through a number of pre-defined flow rates. The pressure at each level was recorded by the controller, which generates a calibration curve, using a second order polynomial fit, that is used in the consecutive experiment. This procedure thus allows for a flow-independent control of the perfusion pressure. Flow data from the experiments were collected and stored using a Powerlab data acquisition system (ADInstruments, Bella Vista, NSW, Australia) connected to a personal computer. Ten-minute mean values of the collected perfusion data were calculated for further analysis.