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Vascular Impedance
Published in Wilmer W Nichols, Michael F O'Rourke, Elazer R Edelman, Charalambos Vlachopoulos, McDonald's Blood Flow in Arteries, 2022
This is the opposition to flow at the end of a vascular bed, immediately upstream from its termination. This termination is taken to represent the high-resistance arterioles. Properties of the arterioles are almost purely resistive (with little effect of blood inertia or vessel distensibility), that is, where Womersley’s nondimensional factor α is miniscule and resistance completely dominates reactance (see Figure 8.11). Terminal impedance is thus considered in terms of modulus only and takes the form, like peripheral resistance, of mean pressure divided by mean flow. It is not, however, strictly identical to peripheral resistance, since there is some (albeit small) drop of pressure along the arterial tree from the point of pressure measurement in a large artery to arteriolar origin (Figure 11.1) and also because mean pressure is not zero in the capillaries beyond, even though the transmission of pulsatile pressure through to these vessels is extremely small. Because of the finite pressure drop along the arterial system and finite pressure in the capillaries, terminal impedance is somewhat less than peripheral resistance as measured from the mean arteriovenous pressure difference. This point is of considerable relevance when venous pressure is high, as is normally the case for the pulmonary circulation and for the systemic circulation in heart failure (see Chapters 13 and 14).
Motion of blood in the venous system—novel findings
Published in Dinker B. Rai, Mechanical Function of the Atrial Diastole, 2022
During the early part of the 20th century, Harvey Cushing introduced the sphygmomanometer for the clinical use in this country despite enormous resistance and criticism from the rest of the medical fraternity. Ever since then physicians have been dependent upon the measurement of pressure not only of the arteries but also of the veins in order to understand the hemodynamics during both the states of health and disease. The law that governs the motion of blood is the same in the venous and arterial systems. However, the conditions under which it moves in the venous system are totally different. Most of the time it has to move against the gravitational force, and it has to move in negative pressure tubes that are potentially collapsible. Hence the flow of blood from a higher to a lower positive pressure is not a quality of venous hemodynamics. However, physicians are still dependent upon the measurement of venous pressure to understand that of the venous hemodynamics. Despite its limitations there are no other better parameters available. Many modifications of venous pressure have been reported, each claiming to be better than the other, which is a natural outcome.
Anesthesia for Minimally Invasive Cardiac Surgery
Published in Theo Kofidis, Minimally Invasive Cardiac Surgery, 2021
Ti Lian Kah, Sophia Ang Bee Leng, Wei Zhang, Lalitha Manickam, Jai Ajitchandra Sule
Baseline pulmonary artery systolic pressure is estimated by adding the peak regurgitant pressure of the tricuspid regurgitation to the central venous pressure (Figure 5.17).
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
Impact of Three Methods of Ischemic Preconditioning on Ischemia-Reperfusion Injury in a Pig Model of Liver Transplantation
Published in Journal of Investigative Surgery, 2022
Alessandro Rodrigo Belon, Ana Cristina Aoun Tannuri, Daniel de Albuquerque Rangel Moreira, Jose Luiz Figueiredo, Alessandra Matheus da Silva, Suellen Serafini, Raimundo Renato Guimarães, Caroline Silverio Faria, Alcione Sanches de Alexandre, Josiane Oliveira Gonçalves, Vitor Ribeiro Paes, Uenis Tannuri
The animals (donors and recipients) were fasted for 12 hours, then at 7 a.m. injected with intramuscular xylazine (2.0 mg/Kg) and ketamine (10.0 mg/Kg) as pre-anesthetic 15 minutes before anesthesia, which was induced with propofol (5.0–10.0 mg/Kg) and maintained with endotracheal intubation, 40% oxygen supply, and isoflurane (1.3 to 2.0%) in inspired air, along with a continuous intravenous infusion of fentanyl (0.05 µg/Kg/min). Catheters were introduced into the jugular vein for fluid infusion and central venous pressure (CVP) measurement, and into the carotid artery for invasive mean arterial pressure (iMAP) measurement and blood sampling for biochemical analyses. The catheters were sutured to the skin with mononylon sutures to prevent its release during the postoperative period. Recipient animals were continuously monitored until the end of the surgery and post-surgery recovery with electrocardiogram, oximetry, end tidal carbon dioxide monitoring (EtCO2), respiratory rate, and pressure measurements - CVP and iMAP.
Impact of tetraplegia vs. paraplegia on venoarteriolar, myogenic and maximal cutaneous vasodilation responses of the microvasculature: Implications for cardiovascular disease
Published in The Journal of Spinal Cord Medicine, 2022
Michelle Trbovich, Yubo Wu, Wouter Koek, Joan Zhao, Dean Kellogg
No validated tests quantify the remaining autonomic function post-SCI, so it is problematic to classify groups based on SNS integrity. More specifically, how autonomic impairment impacts the relative contribution of VAR and MYO responses during cuff inflation and limb dependency is unknown. We reported ISAFSCI results as the best comprehensive assessment of the remaining autonomic function, however, its subjectivity (based on patient report/accuracy as a historian) limits its power. In addition, for the women participants we did not control for menstrual cycle, which can impact vascular responsiveness. Regarding calculations of SkVR we did not directly measure venous pressure via intravenous catheter during and after the formation of the hydrostatic column as some studies have done in AB persons,56 but to minimize invasiveness, we assumed it based on methods/values used in other studies.37,39–41