scholarly journals Two-compartment model of inner medullary vasculature supports dual modes of vasopressin-regulated inner medullary blood flow

2010 ◽  
Vol 299 (1) ◽  
pp. F273-F279 ◽  
Author(s):  
Julie Kim ◽  
Thomas L. Pannabecker
Keyword(s):  
Blood Flow ◽  
Blood Flow Rate ◽  
Outer Zone ◽  
Compartment Model ◽  
Transverse Dimension ◽  
Vessel Diameter ◽  
Functional Coupling ◽  
Vascular Bundles ◽  
Transport Pathways ◽  
Vasa Recta

The outer zone of the renal inner medulla (IM) is spatially partitioned into two distinct interstitial compartments in the transverse dimension. In one compartment (the intercluster region), collecting ducts (CDs) are absent and vascular bundles are present. Ascending vasa recta (AVR) that lie within and ascend through the intercluster region (intercluster AVR are designated AVR2) participate with descending vasa recta (DVR) in classic countercurrent exchange. Direct evidence from former studies suggests that vasopressin binds to V1 receptors on smooth muscle-like pericytes that regulate vessel diameter and blood flow rate in DVR in this compartment. In a second transverse compartment (the intracluster region), DVR are absent and CDs and AVR are present. Many AVR of the intracluster compartment exhibit multiple branching, with formation of many short interconnecting segments (intracluster AVR are designated AVR1). AVR1 are linked together and connect intercluster DVR to AVR2 by way of sparse networks. Vasopressin V2 receptors regulate multiple fluid and solute transport pathways in CDs in the intracluster compartment. Reabsorbate from IMCDs, ascending thin limbs, and prebend segments passes into AVR1 and is conveyed either upward toward DVR and AVR2 of the intercluster region, or is retained within the intracluster region and is conveyed toward higher levels of the intracluster region. Thus variable rates of fluid reabsorption by CDs potentially lead to variable blood flow rates in either compartment. Net flow between the two transverse compartments would be dependent on the degree of structural and functional coupling between intracluster vessels and intercluster vessels. In the outermost IM, AVR1 pass directly from the IM to the outer medulla, bypassing vascular bundles, the primary blood outflow route. Therefore, two defined vascular pathways exist for fluid outflow from the IM. Compartmental partitioning of V1 and V2 receptors may underlie vasopressin-regulated functional compartmentation of IM blood flow.

scholarly journals A Simplified Model for Predicting Friction Factors of Laminar Blood Flow in Small-Caliber Vessels

Fluids ◽  
2018 ◽  
Vol 3 (4) ◽  
pp. 75 ◽  
Author(s):  
Aikaterini Mouza ◽  
Olga Skordia ◽  
Ioannis Tzouganatos ◽  
Spiros Paras
Keyword(s):  
Blood Flow ◽  
Pressure Drop ◽  
Friction Factor ◽  
Small Diameter ◽  
Numerical Data ◽  
Blood Flow Rate ◽  
Vessel Diameter ◽  
Simplified Model ◽  
Glycerol Solution ◽  
Fanning Friction Factor

The aim of this study was to provide scientists with a straightforward correlation that can be applied to the prediction of the Fanning friction factor and consequently the pressure drop that arises during blood flow in small-caliber vessels. Due to the small diameter of the conduit, the Reynolds numbers are low and thus the flow is laminar. This study has been conducted using Computational Fluid Dynamics (CFD) simulations validated with relevant experimental data, acquired using an appropriate experimental setup. The experiments relate to the pressure drop measurement during the flow of a blood analogue that follows the Casson model, i.e., an aqueous Glycerol solution that contains a small amount of Xanthan gum and exhibits similar behavior to blood, in a smooth, stainless steel microtube (L = 50 mm and D = 400 μm). The interpretation of the resulting numerical data led to the proposal of a simplified model that incorporates the effect of the blood flow rate, the hematocrit value (35–55%) and the vessel diameter (300–1800 μm) and predicts, with better than ±10% accuracy, the Fanning friction factor and consequently the pressure drop during laminar blood flow in healthy small-caliber vessels.

Renal medullary blood flow: its measurement and physiology

1986 ◽  
Vol 64 (7) ◽  
pp. 873-880 ◽  
Author(s):  
W. A. Cupples
Keyword(s):  
Blood Flow ◽  
Renal Medulla ◽  
Vascular Bundles ◽  
Medullary Blood Flow ◽  
Vasa Recta ◽  
Countercurrent Exchange ◽  
Renal Medullary Blood Flow ◽  
Urinary Concentrating Ability ◽  
Velocity Tracking ◽  
Uptake Method

The vasculature of the mammalian renal medulla is complex, having neither discrete input nor output. There is also efficient countercurrent exchange between ascending and descending vasa recta in the vascular bundles. These considerations have hampered measurement of medullary blood flow since they impose pronounced constraints on methods used to assess flow. Three main strategies have been used: (i) indicator extraction; (ii) erythrocyte velocity tracking; and (iii) indicator dilution. These are discussed with respect to their assumptions, requirements, and limitations. There is a consensus that medullary blood flow is autoregulated, albeit over a narrower pressure range than is total renal blood flow. When normalized to gram tissue weight, medullary blood flow in the dog is similar to that in the rat, on the order of 1 to 1.5 mL∙min−1∙g−1. This is considerably greater than estimated by the radioiodinated albumin uptake method which has severe conceptual and practical problems. From both theoretical and experimental evidence it ssems that urinary concentrating ability is considerably less sensitive to changes in medullary blood flow than is often assumed.

Autoregulation in vasa recta of the rat kidney

1983 ◽  
Vol 245 (1) ◽  
pp. F32-F40 ◽  
Author(s):  
H. J. Cohen ◽  
D. J. Marsh ◽  
B. Kayser
Keyword(s):  
Blood Flow ◽  
Arterial Pressure ◽  
Flow Velocity ◽  
Volume Expansion ◽  
Collecting Duct ◽  
Rat Kidney ◽  
Extracellular Fluid ◽  
Vessel Diameter ◽  
Video Adaptation ◽  
Vasa Recta

Vasa recta blood flow autoregulation was studied by measuring flow velocity in individual vessels on the papilla surface with a video adaptation of the dual-slit erythrocyte velocity method. Vessel diameter did not vary with arterial pressure in the range of 60-150 mmHg, allowing the calculation of the ratio of flows in a single vessel at two pressures from the ratio of velocities. Flow velocity in single vasa recta increased with arterial pressure to 75 mmHg, remained constant in the range of 75-125 mmHg, and increased with higher pressures. In a second series of animals, whole kidney blood flow auto-regulated above 90 mmHg. Vasa recta and whole kidney flow patterns were not changed by extracellular fluid volume expansion. Volume expansion caused a greater increase in ascending than in descending vasa recta flow, reflecting the volume load from enhanced collecting duct reabsorption in diuresis. In a final series, Na excretion varied with arterial pressure in the range of 90-130 mmHg. Because vasa recta velocity remains constant within this range, pressure diuresis cannot be caused by the lack of autoregulation of vasa recta blood flow, at least to 130 mmHg.

scholarly journals Impact of nitric oxide-mediated vasodilation on outer medullary NaCl transport and oxygenation

2012 ◽  
Vol 303 (7) ◽  
pp. F907-F917 ◽  
Author(s):  
Aurélie Edwards ◽  
Anita T. Layton
Keyword(s):  
Nitric Oxide ◽  
Blood Flow ◽  
Supply And Demand ◽  
Vascular Bundles ◽  
Concentration Gradients ◽  
Outer Medulla ◽  
Nacl Transport ◽  
Reciprocal Interactions ◽  
Medullary Blood Flow ◽  
Vasa Recta

The present study aimed to elucidate the reciprocal interactions between oxygen (O2), nitric oxide (NO), and superoxide (O2−) and their effects on vascular and tubular function in the outer medulla. We expanded our region-based model of transport in the rat outer medulla (Edwards A, Layton AT. Am J Physiol Renal Physiol 301: F979–F996, 2011) to incorporate the effects of NO on descending vasa recta (DVR) diameter and blood flow. Our model predicts that the segregation of long DVR in the center of vascular bundles, away from tubular segments, gives rise to large radial NO concentration gradients that in turn result in differential regulation of vasoactivity in short and long DVR. The relative isolation of long DVR shields them from changes in the rate of NaCl reabsorption, and hence from changes in O2 requirements, by medullary thick ascending limbs (mTALs), thereby preserving O2 delivery to the inner medulla. The model also predicts that O2− can sufficiently decrease the bioavailability of NO in the interbundle region to affect the diameter of short DVR, suggesting that the experimentally observed effects of O2− on medullary blood flow may be at least partly mediated by NO. In addition, our results indicate that the tubulovascular cross talk of NO, that is, the diffusion of NO produced by mTAL epithelia toward adjacent DVR, helps to maintain blood flow and O2 supply to the interbundle region even under basal conditions. NO also acts to preserve local O2 availability by inhibiting the rate of active Na+ transport, thereby reducing the O2 requirements of mTALs. The dual regulation by NO of oxygen supply and demand is predicted to significantly attenuate the hypoxic effects of angiotensin II.

scholarly journals The Natural-Mineral-Based Novel Nanomaterial IFMC Increases Intravascular Nitric Oxide without Its Intake: Implications for COVID-19 and beyond

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1699
Author(s):  
Tomohiro Akiyama ◽  
Takamichi Hirata ◽  
Takahiro Fujimoto ◽  
Shinnosuke Hatakeyama ◽  
Ryuhei Yamazaki ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Blood Flow ◽  
Flow Rate ◽  
Vascular System ◽  
Vascular Complications ◽  
Blood Flow Rate ◽  
Vessel Diameter ◽  
Human Hand ◽  
Natural Mineral ◽  
Living Body

There are currently no promising therapy strategies for either the treatment or prevention of novel coronavirus disease 2019 (COVID-19), despite the urgent need. In addition to respiratory diseases, vascular complications are rapidly emerging as a key threat of COVID-19. Existing nitric oxide (NO) therapies have been shown to improve the vascular system; however, they have different limitations in terms of safety, usability and availability. In light of this, we hypothesise that a natural-mineral-based novel nanomaterial, which was developed based on NO therapy, might be a viable strategy for the treatment and prevention of COVID-19. The present study examined if it could induce an increase of intravascular NO, vasodilation and the consequent increase of blood flow rate and temperature in a living body. The intravascular NO concentration in the hepatic portal of rats was increased by 0.17 nM over 35.2 s on average after its application. An ultrasonic Doppler flow meter showed significant increases in the blood flow rate and vessel diameter, but no difference in the blood flow velocity. These were corroborated by measurements of human hand surface temperature. To our knowledge, this result is the first evidence where an increase of intravascular NO and vasodilation were induced by bringing a natural-mineral-based nanomaterial into contact with or close to a living body. The precise mechanisms remain a matter for further investigation; however, we may assume that endothelial NO synthase, haemoglobin and endothelium-derived hyperpolarising factor are deeply involved in the increase of intravascular NO.

scholarly journals Blood Flow Velocity in the Pial Arteries of Cats, with Particular Reference to the Vessel Diameter

1984 ◽  
Vol 4 (1) ◽  
pp. 110-114 ◽  
Author(s):  
Masahiro Kobari ◽  
Fumio Gotoh ◽  
Yasuo Fukuuchi ◽  
Kortaro Tanaka ◽  
Norihiro Suzuki ◽  
...  
Keyword(s):  
Blood Flow ◽  
Flow Velocity ◽  
Flow Rate ◽  
Blood Flow Velocity ◽  
Blood Flow Rate ◽  
Video Camera ◽  
Vessel Diameter ◽  
Pial Arteries ◽  
Cross Sectional ◽  
Pial Artery

The blood flow velocity and diameter of feline pial arteries, ranging in diameter from 20 to 200 μm, were measured simultaneously using a newly developed video camera method under steady-state conditions for all other parameters. There was a linear relationship between blood flow velocity and pial artery diameter ( y = 0.340 x + 0.309), the correlation coefficient being 0.785 (p < 0.001). The average values for blood flow velocity in pial arteries <50 μm, ≧50 but <100 μm, ≧100 but <150 μm, and ≧150 μm in diameter were 12.9 ± 1.3, 24.6 ± 3.4, 42.1 ± 4.7, and 59.9 ± 5.3 mm/s, respectively. Blood flow rate was calculated as a product of the cross-sectional area and the flow velocity. The blood flow rate increased exponentially as the pial artery diameter increased ( y = 2.71 × 10−4 x2.98). The average values for blood flow rate in pial arteries <50 μm, ≧50 but <100 μm, ≧100 but <150 μm, and ≧150 μm in diameter were 12.8 ± 1.5, 122.1 ± 24.8, 510.2 ± 74.8, and 1524.2 ± 174.4 10−3 mm3/s, respectively. Hemorheological parameters such as the wall shear rate and Reynolds' number were also calculated. The data obtained provide a useful basis for further investigations in the field of cerebral circulation.

Measurements of blood flow to individual glomeruli in the ophidian kidney

1990 ◽  
Vol 258 (6) ◽  
pp. R1313-R1319 ◽  
Author(s):  
S. D. Yokota ◽  
W. H. Dantzler
Keyword(s):  
Blood Flow ◽  
Plasma Osmolality ◽  
Blood Flow Rate ◽  
Vessel Diameter ◽  
Intermittent Flow ◽  
Thamnophis Sirtalis ◽  
Instantaneous Rate ◽  
Single Nephron ◽  
The Difference

Continuous measurements of the instantaneous rate of blood flow to individual glomeruli in a normal vertebrate kidney were made in the garter snake Thamnophis sirtalis. Epifluorescence video microscopy was used to visualize and record blood flow in the afferent arterioles of superficial nephrons. The dual-slit method was used for the determination of red blood cell (RBC) velocity from the video replay. Simultaneous measurements of the vessel diameter allowed the continuous determination of the instantaneous rate of blood flow. A total of 100 glomeruli was surveyed in 12 animals. These glomeruli displayed both constant and highly variable rates of blood flow, with 21% of all nephrons displaying intermittent glomerular perfusion. The mean single-nephron blood flow rate (SNBFR) for all individuals was 23.9 +/- 10.3 (SD) nl/min (n = 12). The percentage of nephrons with intermittent flow for an individual animal increased significantly with increasing plasma osmolality. Intermittency was associated with low SNBFR values; SNBFR averaged 13.5 +/- 10.2 (SD) nl/min (n = 21) in intermittent nephrons and 29.2 +/- 19.0 (SD) nl/min (n = 79) in continuous flow nephrons, the difference being significant (P less than 0.001). Nephrons with continuous perfusion displayed a much greater range of SNBFR values than intermittent nephrons. This suggests that, although changes in whole kidney glomerular filtration rate (GFR) in reptiles need not involve glomerular intermittency, intermittency may lower GFR.

Physiology of the renal medullary microcirculation

2003 ◽  
Vol 284 (2) ◽  
pp. F253-F266 ◽  
Author(s):  
Thomas L. Pallone ◽  
Zhong Zhang ◽  
Kristie Rhinehart
Keyword(s):  
Blood Flow ◽  
Contractile Function ◽  
Renal Medulla ◽  
Urinary Concentration ◽  
Vascular Bundles ◽  
Ang Ii ◽  
Physiological Mechanisms ◽  
Vasa Recta ◽  
Water Efflux ◽  
Salt And Water Balance

Perfusion of the renal medulla plays an important role in salt and water balance. Pericytes are smooth muscle-like cells that impart contractile function to descending vasa recta (DVR), the arteriolar segments that supply the medulla with blood flow. DVR contraction by ANG II is mediated by depolarization resulting from an increase in plasma membrane Cl− conductance that secondarily gates voltage-activated Ca2+ entry. In this respect, DVR may differ from other parts of the efferent microcirculation of the kidney. Elevation of extracellular K+ constricts DVR to a lesser degree than ANG II or endothelin-1, implying that other events, in addition to membrane depolarization, are needed to maximize vasoconstriction. DVR endothelial cytoplasmic Ca2+ is increased by bradykinin, a response that is inhibited by ANG II. ANG II inhibition of endothelial Ca2+ signaling might serve to regulate the site of origin of vasodilatory paracrine agents generated in the vicinity of outer medullary vascular bundles. In the hydropenic kidney, DVR plasma equilibrates with the interstitium both by diffusion and through water efflux across aquaporin-1. That process is predicted to optimize urinary concentration by lowering blood flow to the inner medulla. To optimize urea trapping, DVR endothelia express the UT-B facilitated urea transporter. These and other features show that vasa recta have physiological mechanisms specific to their role in the renal medulla.

Effect of blood flow rate and donor vessel diameter on the patency of carotid venous bypass grafts in dogs

1989 ◽  
Vol 31 (3) ◽  
pp. 195-199 ◽  
Author(s):  
Bryan M. Pereira ◽  
Philip R. Weinstein ◽  
Enrique Zea-Longa ◽  
Mohammed El-Fiki
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Blood Flow Rate ◽  
Vessel Diameter ◽  
Bypass Grafts ◽  
Venous Bypass

scholarly journals Urine concentrating mechanism: impact of vascular and tubular architecture and a proposed descending limb urea-Na+ cotransporter

2012 ◽  
Vol 302 (5) ◽  
pp. F591-F605 ◽  
Author(s):  
Anita T. Layton ◽  
William H. Dantzler ◽  
Thomas L. Pannabecker
Keyword(s):  
Blood Flow ◽  
Interstitial Fluid ◽  
Collecting Duct ◽  
Rat Kidney ◽  
Renal Medulla ◽  
Fluid Composition ◽  
Vascular Bundles ◽  
Vasa Recta ◽  
Countercurrent Exchange ◽  
Thin Limb

We extended a region-based mathematical model of the renal medulla of the rat kidney, previously developed by us, to represent new anatomic findings on the vascular architecture in the rat inner medulla (IM). In the outer medulla (OM), tubules and vessels are organized around tightly packed vascular bundles; in the IM, the organization is centered around collecting duct clusters. In particular, the model represents the separation of descending vasa recta from the descending limbs of loops of Henle, and the model represents a papillary segment of the descending thin limb that is water impermeable and highly urea permeable. Model results suggest that, despite the compartmentalization of IM blood flow, IM interstitial fluid composition is substantially more homogeneous compared with OM. We used the model to study medullary blood flow in antidiuresis and the effects of vascular countercurrent exchange. We also hypothesize that the terminal aquaporin-1 null segment of the long descending thin limbs may express a urea-Na+ or urea-Cl− cotransporter. As urea diffuses from the urea-rich papillary interstitium into the descending thin limb luminal fluid, NaCl is secreted via the cotransporter against its concentration gradient. That NaCl is then reabsorbed near the loop bend, raising the interstitial fluid osmolality and promoting water reabsorption from the IM collecting ducts. Indeed, the model predicts that the presence of the urea-Na+ or urea- Cl− cotransporter facilitates the cycling of NaCl within the IM and yields a loop-bend fluid composition consistent with experimental data.

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