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Specialized Circulations in Susceptible Tissues
Published in Wilmer W Nichols, Michael F O'Rourke, Elazer R Edelman, Charalambos Vlachopoulos, McDonald's Blood Flow in Arteries, 2022
Decreased diastolic perfusion pressure may result from arterial hypotension (as in cardiogenic shock, where it is a major factor in the vicious circle of cardiac decompensation), from increased left ventricular diastolic pressure (in left ventricular failure), from increased right atrial pressure (in right ventricular failure) or from left ventricular dysfunction with slowed ventricular relaxation (Frohlich et al., 1992a). These factors are rarely the cause of myocardial ischemia entirely by themselves but usually act in combination with coronary narrowing or with ventricular hypertrophy (Frohlich et al., 1992b; Gould, 1997; Thomas et al., 2019). Aortic stiffening causes a reduction in coronary perfusion pressure and coronary flow reserve and predisposes to myocardial ischemia (Weber et al., 2006; Galderisi, 2008; Guelen et al., 2008; Ikonomidis et al., 2008; Nemes et al., 2008), but this usually requires other factors, including increased myocardial demand (from increased left ventricular systolic pressure or relatively increased systolic period from tachycardia; (O'Rourke et al., 2019c) or a minor degree of coronary narrowing (Watanabe et al., 1992, 1993; Kass et al., 1996; Nichols et al., 2013, 2015; Thomas et al., 2019).
Hemodynamic and Microcirculatory Aspects of Genetically Abnormal Red Cells
Published in Ronald L. Nagel, Genetically Abnormal Red Cells, 2019
HS is characterized by hemolytic anemia and by the presence of stomatocytic (cup-shaped) red cells and significant number of spherocytic forms.53 Reduced red cell deformability in HS has been reported by a number of workers using a variety of in vitro techniques.47,54,55 The reduced surface area to volume ratio55 as well as increased MCHC57 of spherocytic forms accounts for reduced red cell deformability, although density-dependent analysis of deformability of HS cells has not been performed. HS red cells also show a reduced intrinsic membrane deformability (shear modulus).58 LaCelle50 has reported that in the mouse cremaster muscle capillaries, infused HS cells behave normally except for the most spherocytic forms which could cause occasional obstruction especially at low flow rates. However, increase in the perfusion pressure could dislodge the obstructive cells. Since the HS, the spleen selectively removes spherocytes and other rigid cells from circulation, splenectomy performed to alleviate anemia often results in an increase in number of circulating spherocyte population. The microcirculatory passage of HS cells may itself result in the membrane loss, sphericity, and increase in MCHC.
Rheology of Peripheral Arterial Disease
Published in Gordon D. O. Lowe, Clinical Blood Rheology, 2019
The hemorheological changes in ischemic tissues, such as the calf muscle of a claudicant, may be both a cause and a consequence of the ischemia. The decreased pO2 and pH, increased pCO2 and other metabolites like lactic acid, and decreased temperature or red cell adenosine triphosphate (ATP) concentration, have all been shown to cause decreased blood cell filterability. Most recently, the possibility of oxygen-derived free radicals playing a similar role has been suggested. The resulting rheological changes in turn will tend to increase the ischemia, resulting in a vicious cycle that may spiral either way. The triggering mechanism initiating this vicious cycle in the vast majority of cases is a decreased perfusion pressure and only rarely a primary rheological defect. The decreased perfusion pressure may be chronic, due to established atherosclerosis; or acute, due to a superimposed thrombosis. (A possible rheological role in atherogenesis and thrombogenesis is discussed in Chapter 13, this volume). It is this hypothesis of a vicious, viscous spiral which may be the basis of the prognostic significance of rheological factors in peripheral circulatory disease and is also partly the justification for rheological treatment of peripheral ischemia.
Dynamic Changes in Retinal Vessel Diameters and Arteriovenous Ratio within 10 Days of Birth
Published in Current Eye Research, 2023
This study found that the retinal artery diameter was distinct at different times after birth by comparing the CRAE in different groups. This result suggests that the retinal artery in newborns undergoes changes in relaxation and contraction after birth, and it mainly shows a narrowing trend. Placental circulation with low resistance stops when the fetus is born owing to umbilical cord clamping, and pulmonary circulation is rapidly established. The physiological state of the newborn undergoes immediate changes. When it begins to inhale air, the alveoli gradually expand, and respiratory movement is gradually and firmly established. After birth, resistance to pulmonary blood flow decreases, ensuring increased pulmonary blood flow. Simultaneously, the resistance of peripheral blood vessels increases, and peripheral blood vessels contract, thus increasing blood pressure. Perfusion pressure changes when blood pressure persistently rises. The retinal arterioles self-regulate and narrow to maintain a constant blood flow or change the blood flow to meet local metabolic needs.7,8
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
Additionally, the association between MPPV and deterioration of renal function may be heterogeneous in patients with cardiac surgery, medical sepsis and others. Critically ill patients with medical sepsis are characterized with endothelial dysfunction [38]. Thus, the same rise and fall in MPP may lead to greater fluctuation of renal blood flow compared to those diseases without marked endothelial dysfunction. And for patients undergoing cardiac surgery, they presented with decreased perfusion pressure characterized by renal venous congestion [39]. The correlation between absolute level of MPP and the deterioration of renal function may be more significant [40]. After adjusting for TWA-MPP, the correlation between MPPV and the deterioration of renal function weakened. In patients after abdominal surgery, intra-abdominal pressure may have a greater effect on renal perfusion [41]. However, our study excluded patients with acute compartment syndrome, and the number of patients undergoing abdominal surgery was limited, so they were not discussed separately.
Effects of perioperative dexmedetomidine infusion on renal function and microcirculation in kidney transplant recipients: a randomised controlled trial
Published in Annals of Medicine, 2022
Yin-Chin Wang, Ming-Jiuh Wang, Chih-Yuan Lee, Chien-Chia Chen, Ching-Tang Chiu, Anne Chao, Wing-Sum Chan, Meng-Kun Tsai, Yu-Chang Yeh
Dexmedetomidine is a highly selective alpha-2 agonist with sedative and analgesic effects [5]. It modulates inflammation by enhancing parasympathetic tone while reducing sympathetic tone [6,7]. Dexmedetomidine has been reported to confer renal protection effects in patients undergoing coronary artery bypass surgery [8,9]. The protective effects of dexmedetomidine against ischemia-reperfusion injury have been described in many studies [10–12]. Moreover, the sympatholysis effect of dexmedetomidine induced vasodilation [5], and our previous animal study showed that dexmedetomidine prevented alterations of intestinal microcirculation in rats with surgical stress and pain [13]. However, the most common side effects of dexmedetomidine are bradycardia and hypotension. Low cardiac output and low perfusion pressure may deteriorate microcirculation [14,15]. We hypothesised that dexmedetomidine could attenuate the ischemia-reperfusion injuries and preserve transplanted kidneys’ function. In addition, the issue that the effects of dexmedetomidine on perioperative microcirculation were protective or detrimental remained unknown. Thus, this study investigated postoperative renal function and perioperative sublingual microcirculation in patients undergoing kidney transplantation.