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Diagnostics of Functional Abnormalities in the Microcirculation System Using Laser Doppler Flowmetry
Published in Andrey V. Dunaev, Valery V. Tuchin, Biomedical Photonics for Diabetes Research, 2023
Irina A. Mizeva, Elena V. Potapova, Elena V. Zharkikh
In the cutaneous vascular system, the diameter of arterioles and blood pressure within them are two major factors affecting the changes in blood flow. Maintaining a constant blood flow despite an increase in blood pressure is called autoregulation of blood flow and usually occurs at pressures between 70 and 170 mm Hg. Both the metabolic state of the tissue (e.g., hypoxia) and the myogenic response prevent the blood vessel walls from excessive stretching under high pressure, thus providing constant tension in the vessel wall.
Cerebral Circulation
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Autoregulation of the cerebral circulation refers to the phenomenon in which CBF is kept constant over a mean arterial blood pressure range of 50–150 mmHg (6.7–20 kPa). Changes in perfusion pressure are thought to invoke a myogenic response (Bayliss effect) in the vascular smooth muscle. This myogenic response is sensitive to mean blood pressure and to changes in pulse pressure. Nitric oxide appears to mediate basal vascular tone, but it is unlikely to be directly involved in pressure autoregulation. Above a mean arterial pressure of 150 mmHg, CBF passively increases with CPP and arterial pressure (Figure 6.1).
Diseases of the Nervous System
Published in George Feuer, Felix A. de la Iglesia, Molecular Biochemistry of Human Disease, 2020
George Feuer, Felix A. de la Iglesia
The decline of cerebral blood flow by vascular block or reduction of cardiac output initiates autoregulatory mechanisms. The large brain vessels adjust to this situation and attempt to maintain constant blood flow. Local changes including a mechanical myogenic response to decreased pressure and modification of the metabolism are important factors in this regulation. An increase of tissue pCO2 and decrease of pO2 cause vasodilatation. In addition to lower pH, lower affinity of hemoglobin for oxygen raises the level of oxygen retained locally. When this mechanism fails due to inadequate blood supply, major tissue changes result.
Increased mean perfusion pressure variability is associated with subsequent deterioration of renal function in critically ill patients with central venous pressure monitoring: a retrospective observational study
Published in Renal Failure, 2022
Yudie Peng, Buyun Wu, Changying Xing, Huijuan Mao
When the body’s BP fluctuates, the kidney maintains its own perfusion mainly through two mechanisms which are the myogenic response and the tubuloglomerular feedback response. However, this classic curve of automatic blood flow regulation was obtained from the experiment, which gradually reduces the renal perfusion pressure. Therefore, this description is valid only for very slow changes in BP and the effect of faster BP fluctuations on renal blood flow cannot be correctly described. Critically ill patients are known for high incidence of anxiety [34], delirium [35], sleep loss [36], abnormal central and autonomic nervous regulation [37]. Under such situations, patients tend to have difficulty maintaining stable renal perfusion, then exhibiting deterioration of subsequent renal function. Further physiological studies are required to reveal the potential mechanism between increased MPPV and deterioration of renal function.
Kidney physiology and pathophysiology during heat stress and the modification by exercise, dehydration, heat acclimation and aging
Published in Temperature, 2021
Christopher L. Chapman, Blair D. Johnson, Mark D. Parker, David Hostler, Riana R. Pryor, Zachary Schlader
There is great interest in accurately quantifying changes in renal blood flow because it is a highly controlled variable that has implications for the regulation of blood pressure and water and electrolytes. Thus, it is also important to note that the kidneys have an intrinsic ability to maintain blood flow at varying arterial pressures (i.e., autoregulate). Renal blood flow autoregulation is mediated by actions of the afferent arterioles and interlobular arteries and their myogenic response to constrict or relax in response to changes in perfusion pressure [173-175]. Approximately, 50% of the total autoregulatory response [176,177] rapidly occurs within 3-10 seconds [178,179], which is contributed to by unloading of the renal baroreceptors and tubuloglomerular feedback provided by the juxtaglomerular apparatus [180,181]. Tubuloglomerular feedback also results in renin release by the afferent arterioles in response to sensation of decreased NaCl delivery to the macula densa in the distal tubule [182], which ultimately ensures a relatively stable renal blood flow and glomerular filtration rate (see Glomerular filtration rate). These neural (discussed previously in Autonomic control of kidney function), hormonal (discussed previously in PHYSIOLOGY AND ASSESSMENT OF BODY WATER REGULATION), and autoregulatory mechanisms offer a complex and highly redundant control of renal blood flow to maintain homeostasis utilizing many systems.
Effect of perivascular low dose ethanol on rat femoral vessels: Preliminary study
Published in Journal of Plastic Surgery and Hand Surgery, 2020
Soysal Bas, Seyhan Hascicek, Ramazan Ucak, Alican Gunenc, Aysin Karasoy Yesilada
Vasospasm, one of the body's defense system, is affected by many factors and is caused by smooth muscle contraction in the tunica media. Iatrogenic or traumatic intimal injury leads to smooth muscle activation by local mediators such as endothelin-1 and thromboxane A2 secreted from the endothelium [1]. Vascular preparation, handling and anastomosis tension trigger myogenic response as a result of smooth muscle depolarization and cause vasoconstriction [2]. The sympathetic system mediates vasoconstriction caused by cold exposure both in digital ischemia in Raynaud’s phenomenon (RF) and in reconstructive microsurgery. Increased sympathetic activity as a result of systemic cold exposure is mediated by norepinephrine, and local cold exposure causes vasoconstriction by directly stimulating alpha 2 adrenergic receptors [3]. Systemic hormones include the renin-angiotensin-aldosterone system triggered by hypovolemia. Angiotensin 2 (AT-2) causes contractions by stimulating AT-2 receptor type 1 on vascular smooth muscle [4].