Thermal Physiology and Thermoregulation
James Stewart Campbell, M. Nathaniel Mead in Human Medical Thermography, 2023
Temperature of the skin's surface largely reflects blood flow through the dermal microvasculature, though larger superficial veins may also warm the skin surface enough to be detected by thermal imagers (Figure 5.3b). Approximately 4% of cardiac output flows through the skin under thermoneutral conditions. This perfusion can increase by more than tenfold via maximal cutaneous vasodilation in response to heat stress, or quickly drop to near zero under severe cold stress.30 Cutaneous blood flow depends mainly on blood circulation in the smallest blood vessels (between 10 and 100 μm in diameter), primarily the arterioles, capillaries, and venules. Whereas the capillary network supplies nutrients and oxygen to the dermal structures, the arterioles are essential for blood flow regulation.31 The regulatory mechanisms include flow-induced vasodilation from wall shear stress, arteriolar myogenic response, and metabolic and autonomic nervous control.32
Properties of the Arterial Wall
Wilmer W Nichols, Michael F O'Rourke, Elazer R Edelman, Charalambos Vlachopoulos in McDonald's Blood Flow in Arteries, 2022
The function of the systemic arterial system is to deliver blood at high pressure and in a continuous stream to peripheral vascular beds. From a simplistic perspective, it can be separated into three anatomical regions to serve the left ventricle as a pulsatile pump and the tissues that need a supply of blood. Each region has a distinct and separate function: (1) The large arteries, especially the elastic arteries (aorta, brachiocephalic, carotid, etc.), serve predominately as a cushioning reservoir, or “Windkessel,” that stores blood during systole and expels it to the tissue during diastole. (2) The long muscular arteries act predominately as conduits, distributing blood to the extremities; these arteries also actively modify wave propagation by changing smooth muscle tone and diameter with little change in mean arterial blood pressure. (3) The arterioles, by changing their caliber, alter peripheral resistance and therefore aid in the maintenance of mean arterial blood pressure, as well as the delivery of a steady or continuous flow of blood to the organs and tissues according to their need. Major changes in the central elastic arteries occur over long periods of time, while acute alterations in wall properties (e.g. with rise or fall in dis-tending pressure) are passive (Nichols and Edwards, 2001; Giannattasio and Mancia, 2002). Changes in the muscular arteries and arterioles most often occur acutely, and alterations in wall properties are active (Boutouyrie et al., 2000; Nichols and Edwards, 2001; Safar et al., 2003).
The patient with acute cardiovascular problems
Peate Ian, Dutton Helen in Acute Nursing Care, 2020
The flow of blood down the arterioles can be controlled by regulating the diameter of the vessel. Contraction (vasoconstriction) of the vessels narrows the lumen and reduces blood flow, and relaxation causes dilation of the lumen, increasing the diameter and allowing an increase in blood flow. Control of vascular tone occurs both centrally and peripherally. The autonomic nervous system (ANS) utilises hormones such as adrenaline and nor-adrenaline, which cause vasoconstriction and antidiuretic hormone (ADH) that regulates fluid loss via the kidneys. Vasoconstriction and dilation may occur locally to preserve blood flow to vital organs such as the heart, brain and lungs, but in doing so, divert blood flow from other less essential areas. In addition to collecting blood from the capillary beds and returning it to the heart, veins and venules can expand to act as reservoirs for blood or constrict in order to divert the flow of blood elsewhere.
Dynamic Changes in Retinal Vessel Diameters and Arteriovenous Ratio within 10 Days of Birth
Published in Current Eye Research, 2023
Previous studies in adults have shown that the retinal artery’s diameter decreases with the onset of diabetes while the retinal vein’s diameter widens.3 In addition, when systemic blood pressure continues to rise, self-regulating vessels narrow the arterioles.4 Moreover, retinal vascular morphological changes may predict age-related cognitive decline,5 and a low AVR may indicate adverse pregnancy outcomes.6 Similarly, newborns experience parturition from inside to outside in the neonatal period. Whole-body microcirculation is influenced by sudden changes in the environment, the gradual establishment of pulmonary circulation, and changes in blood oxygen content. These changes may theoretically lead to severe relaxation and contraction of the retinal blood vessels shortly after birth. With the development of fundus photography systems and semi-automatic measurement software for newborns, the diameter of the retinal vessels in newborns can also be quantitatively analyzed. Kandasamy et al. measured the retinal blood vessels of 20 full-term newborns within 7 days of birth using digital software and found that the average AVR was 0.66. However, there are no studies on early changes in the retinal vessel diameter and AVR with age in full-term newborns.
Arteriolar hyalinosis and renal outcomes in patients with immunoglobulin A nephropathy
Published in Renal Failure, 2022
Yunzhu Shen, Tangli Xiao, ZhiKai Yu, Yinghui Huang, Ting He, Haiyang Li, Jun Zhang, Jiachuan Xiong, Jinghong Zhao
Meanwhile, there are striking differences between the prognosis of the two groups, which implies that arteriolar hyalinosis is a pathological feature of poor prognosis. Furthermore, as the degree of arteriolar hyalinosis increases, the prognosis worsens. In addition, we have observed the relationship between arteriolar hyalinosis and hypertension. Wang et al. [35] analyzed that hypertensive IgAN patients with ischemic renal injury has a poorer prognosis. And this study has showed that the patients with arteriolar hyalinosis and hypertension in IgAN suffer a worse prognosis. And at the same time, hypertension seemed not to be an independent risk factor to the patients with arteriolar hyalinosis in this study, which is inconsistent with the study of Miyabe et al. [36]. The possible reasons are that pathological scoring systems for IgAN, such as Oxford classification, without considering arteriolar hyalinosis, and the MESTC primary are also included, while arteriolar hyalinosis is not included in multivariate regression analysis. Furthermore, the primary pathological manifestation of renal damage caused by the essential hypertension is arteriolar hyalinosis [37]. The possible reason for the results of our subgroup is that part of the effect of hypertension on the prognosis of IgAN works by causing hyaline changes in renal arterioles. However, it still needs further research on the internal mechanism of hypertension and arteriolar hyalinosis in IgAN.
New Insights into Diabetic and Vision-Threatening Retinopathy: Importance of Plasma Long Pentraxine 3 and Taurine Levels
Published in Current Eye Research, 2021
Hülya Güngel, Füsun Erdenen, Isil Pasaoglu, Duygu Sak, Tülin Ogreden, Ilkay Kilic Muftuoglu
PTX-3 is one of the endothelium-specific inflammatory cytokines, representing the tissue inflammatory response, especially the one involving the vascular bed, and may reflect the inflammatory status of the vasculature. PTX-3 enhances the procoagulant effect of the endothelial cells and reduces the endothelial repair by disabling the effect of the fibroblast growth factor. It may modulate inflammation-associated tissue damage and offer protection against AS. The maximum plasma level of PTX-3 varies depending on the time of the vascular event.7 Clinical studies have shown conflicting results about the role of PTX-3 as an active mediator of endothelial dysfunction, AS, and ischemic events.22 PTX-3 may have a dual role in the activation of pro- and anti-inflammatory pathways as determined by time, space, and environmental signals. The association of PTX-3 and DR is correlated with an important retinal microvascular dysfunction, characterized by capillary leakage or closure, leading to ischemia.23 Reportedly, PDR patients had the highest PTX-3 levels.24 Further, high PTX-3 levels are related to vascular dysfunction in patients with type 2 DM. The perfusion pressure of the precapillary arterioles, that suddenly rise for any reason, causes damage to the vessel walls as a result of impaired autoregulatory mechanism. It is characterized by soft exudates that form sclerosis in the precapillary arteriole, creating an obstruction in the vascular lumen and ischemia in the nerve fiber layer. This mechanism is known to cause hypertensive retinopathy.25