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Aortic and Arterial Mechanics
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
Hypertension or HBP is the most common cardiovascular disease, affecting a quarter of the global population. It is defined by an SBP greater than 140 mmHg and a DBP greater than 90 mmHg. The short-term response of a large artery to an increase in pressure consists of a distension of the arterial wall and a decrease in its thickness. The circumferential wall stress is then increased. To normalize the circumferential stress, adaptive phenomena take place in the medium term. An increase in the internal diameter and thickening of the media are observed, mainly by hypertrophy and hyperplasia of SMCs and by an increase in the synthesis of collagen, elastin, and proteoglycans [34,35]. This type of remodeling has been observed both in experimental studies in animal models and in clinical studies [36]. Interestingly, despite the increase in elastin and collagen content, their relative mass densities and elastin-to-collagen volume ratios are not altered [37]. Peripheral resistance arteries may exhibit variable levels of hypertrophy and remodeling [38]. Remodeling contributes to an increase in peripheral vascular resistance, generally associated with hypertension. This increase in resistance leads to an increase in pulse pressure, which, in turn, is an arterial remodeling trigger that leads to enlargement and thickening of the large arteries [3]. Therefore, the remodeling induced by initial HBP is amplified; this maintains HBP, thus forming a vicious circle [39].
The Isolated Perfused Porcine Skin Flap
Published in Rhoda G. M. Wang, James B. Knaak, Howard I. Maibach, Health Risk Assessment, 2017
To date, our laboratory has perfused over 1700 IPPSFs. Biochemical viability has been assessed by monitoring glucose utilization (arterial-venous glucose extraction), lactate production, enzyme leakage, perfusate flow, pressure, vascular resistance, and pH.35,37-39’40 Glucose utilization from a series of control flaps is depicted in Figure 4 and is the parameter primarily used during an experiment to monitor flap viability. Note the relative stability of this parameter over an experiment. In a series of 255 flaps, mean (± SD) glucose utilization was 0.8 ± 0.2 mg/h/g flap. Viability for 8 to 12 h has been confirmed through extensive light and electron microscopic histological studies.38 A final sensitive real-time indicator of IPPSF viability and function is the vascular resistance profile (pressure/flow) over the course of an experiment. This remains constant unless toxicity occurs or vasoactive drugs are administered. When vasodilators such as tolazoline are administered, vascular resistance decreases while vasoconstrictors such as norepinephrine increase vascular resistance.
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Published in William H. Bush, Karl N. Krecke, Bernard F. King, Michael A. Bettmann, Radiology Life Support (Rad-LS), 2017
Diffuse vasodilation causes lowering of systemic vascular resistance. Leaky capillary beds allow plasma to pour into the extravascular space, further lowering the blood pressure and causing reflex tachycardia.
Correlation between time lag of arterial–plethysmographic waveforms and systemic vascular resistance: a prospective study
Published in Journal of Medical Engineering & Technology, 2018
Radhakrishnan Muthuchellappan, Ramesh V. J., Umamaheswara Rao Ganne S., Thennarasu K., Anjana Jacob, Sripathy G., Bhadrinarayan V., Mohanvelu K.
Systemic vascular resistance is the total resistance which the blood must overcome to maintain flow along the systemic vasculature. This SVR is determined by the length and radius of the vessel through which the blood flows and the viscosity of the blood. The large arteries such as aorta and arteries of the forearm and leg do not offer much resistance. It has been seen that there is only a drop of 2–4 mmHg pressure from ascending aorta to the arteries of the leg and forearm in supine position [4]. The major resistance to the circulation is offered by the arterioles [1]. Viscosity determines SVR only when the blood flows in large arteries as compared to flow in the arterioles and in the capillaries. Therefore, the travel of the pulse wave from the radial artery to thumb may theoretically represent the resistance of the peripheral vascular system. This study has proved that in an individual patient, the TLi indirectly represents the SVR. As the vascular system network is different in each patient, the relationship between the time lag and the SVR also differs across patients. However, for a given patient, changes in SVR can be monitored by looking at the trend changes in TLi.
Mathematical modeling of the Fontan blood circulation supported with pediatric ventricular assist device
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
Ekaterina Rubtsova, Aleksandr Markov, Sergey Selishchev, Jamshid H. Karimov, Dmitry Telyshev
Patient activity directly affects the systemic vascular resistance (Ferreira et al. 2005). The pressure-flow characteristics of pediatric VAD Sputnik were simulated in the presented interaction model (Figure 5) depending on the patient activity level. Pressure and flow rate values in the biotechnological system vary with the pressure-flow characteristic of the pump. The greater the vascular resistance, the higher the pressure and lower the flow rate. In a biological system without a pump, this phenomenon is compensated by the baroreceptor reflex. Moreover, in a biotechnological system, it can be compensated for by increasing the rotor speed at the moment of increased patient activity, and vice versa, by decreasing speed at low activity, e.g., at sleep.