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Anesthetic Outcome and Cardiopulmonary Resuscitation
Published in Michele Barletta, Jane Quandt, Rachel Reed, Equine Anesthesia and Pain Management, 2023
The goal of post-cardiac arrest care is to avoid hypotension and maintain adequate perfusion to the tissues. Perfusion depends on blood flow not blood pressure alone.It is advisable to not only monitor blood pressure but also to measure global perfusion metrics such as central venous oxygen saturation (ScvO2) and blood lactate.
Grafts and Flaps in Head and Neck Reconstruction
Published in R James A England, Eamon Shamil, Rajeev Mathew, Manohar Bance, Pavol Surda, Jemy Jose, Omar Hilmi, Adam J Donne, Scott-Brown's Essential Otorhinolaryngology, 2022
First 72 hours to 1 week are critical. Monitor for flap (artery and vein), theatre (anesthetic, neuropraxia) and systemic (clot, chest, cardiac) complications. Suboptimal systemic factors (e.g. blood pressure) or local factors (e.g. compression, haematoma) affect perfusion. Flap monitoring is done clinically (e.g. colour, capillary refill, turgor, temperature), by hand-held or implantable Doppler.
Principles behind Magnetic Resonance Imaging (MRI)
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
The most established MRI technique for assessment of cerebral blood flow (CBF) is dynamic susceptibility contrast MRI (DSC-MRI). A Gd-based contrast agent is injected intravenously, and the signal time course is monitored by rapid T2*-weighted EPI (approximately 1 image/second for 1–2 minutes) during the first passage of the contrast agent bolus in the brain. The contrast agent concentration is quantified, as a function of time, in the tissue (pixel by pixel) as well as in a brain-feeding artery (providing the arterial input function, AIF). Perfusion-related parameters such as cerebral blood volume (CBV), CBF (Figure 32.22b), and mean transit time (MTT) can be calculated using kinetic theory for intravascular tracers, most commonly by using deconvolution of the tissue concentration time curve with the AIF to obtain CBF and MTT. The basic concept is often referred to as ‘bolus tracking’ (applicable also to, for example, computed tomography). Quantification in absolute terms has, so far, been problematic due to difficulties in obtaining accurate AIFs and uncertainties concerning the transverse relaxivities in tissue and blood.
Application of HIPEC simulations for optimizing treatment delivery strategies
Published in International Journal of Hyperthermia, 2023
Daan R. Löke, H. Petra Kok, Roxan F. C. P. A Helderman, Bella Bokan, Nicolaas A. P. Franken, Arlene L. Oei, Jurriaan B. Tuynman, Pieter J. Tanis, Johannes Crezee
The heat sink, due to perfusion, is given by [22]: 3], blood specific heat [J/kg/K ], core temperature [K] and local tissue temperature [K], respectively. The core temperature was updated continuously during simulations and the local heat was redistributed according to Equation (5). The perfusion can vary significantly per organ and therefore organ specific perfusion terms were used, as listed in Table 1. Metabolic heat generation and cutaneous heat loss were included with a volumetric and core component to account for the body parts not explicitly modeled. Therefore, the core temperature was updated at each iteration using the following equation: q represents the heat added or removed by a specific process [J/s], 3], 3], and s].
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.
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