scholarly journals Remodeling of Resistance Arteries in Renal Failure: Effect of Endothelin Receptor Blockade

2001 ◽  
Vol 12 (10) ◽  
pp. 2040-2050 ◽  
Author(s):  
KERSTIN AMANN ◽  
GABRIEL MIL TENBERGER-MIL TENYI ◽  
AURELIA SIMONOVICIENE ◽  
ANDREAS KOCH ◽  
STEPHAN ORTH ◽  
...  
Keyword(s):  
Renal Failure ◽  
Blood Flow ◽  
High Flow ◽  
Mesenteric Arteries ◽  
Low Flow ◽  
Normal Flow ◽  
Flow Conditions ◽  
First Order ◽  
The Media ◽  
Intimal Thickness

Abstract. Remodeling of vessels is a known feature of renal failure, but it is unclear whether this represents an appropriate or inappropriate response to the known changes in blood flow, shear stress, and wall tension. To investigate remodeling in response to variations in blood flow, first-order mesenteric arteries were exposed to high- and low-flow conditions via the ligation of second-order branches, according to the technique described by Pour-ageaud and De Mey. The resulting changes in vessel geometric features, relative proportions of intima and media, submicroscopic structure, and immunostaining for proliferating cell nuclear antigen (PCNA), endothelin-1 (ET-1), and ETAreceptors were assessed in first-order mesenteric arteries under low-flow and high-flow conditions. Subtotally nephrectomized (SNX) animals were compared with sham-operated rats. Animals either were left untreated or were treated with the ETAreceptor antagonist (ET-RA) LU-135252, because of suggestions in the literature that ET is involved in vascular remodeling in uremia. A highly significant increase in intimal thickness was noted in low-flow arteries (4.21 ± 1.39 μm) of SNX animals, compared with normal-flow arteries (2.06 ± 0.61 μm), but this increase was not observed in sham-operated rats (1.38 ± 0.77 in low-flow arteriesversus2.40 ± 0.35 μm in normal-flow arteries). The increase in intimal thickness in low-flow arteries was abrogated by ET-RA. The medial thickness was increased in untreated SNX animals (19.5 ± 3.61 μm), compared with sham-operated rats, and this increase was also prevented by ET-RA. The medial thickness was not affected by low flow in either sham-operated or SNX animals. In parallel, the number of PCNA-positive intimal cells was higher in low-flow, but not high-flow, arteries of SNX rats, compared with sham-operated rats. No significant change was observed in sham-operated animals. In the media, the number of PCNA-positive cells was higher in untreated SNX animals than in sham-operated rats. The number was even more markedly increased in high-flow, but not low-flow, vessels. This increase was abrogated by ET-RA. It is concluded that, in uremic animals, the response of the intima to low flow and the response of the media to high flow are exaggerated. Both responses are apparently mediated by ET.

The Arterial Lumen Is Controlled by Flow-Related Shear Stress

Physiology ◽  
1993 ◽  
Vol 8 (1) ◽  
pp. 34-38 ◽  
Author(s):  
V Smiesko ◽  
PC Johnson
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Blood Flow Velocity ◽  
Flow Regulation ◽  
High Flow ◽  
Normal Flow ◽  
Flow Conditions ◽  
Flow Rates ◽  
Arterial Lumen ◽  
Significant Mechanism

An increase in blood flow velocity through both arteries and arterioles induces a dilation that is mediated by the endothelium. This is a significant mechanism of flow regulation at normal flow rates and is critically important during high flow conditions.

scholarly journals Persistent splanchnic hyperemia during upright tilt in postural tachycardia syndrome

2006 ◽  
Vol 290 (2) ◽  
pp. H665-H673 ◽  
Author(s):  
Julian M. Stewart ◽  
Marvin S. Medow ◽  
June L. Glover ◽  
Leslie D. Montgomery
Keyword(s):  
Blood Flow ◽  
Blood Volume ◽  
Supine Position ◽  
High Flow ◽  
Splanchnic Blood Flow ◽  
Low Flow ◽  
Postural Tachycardia Syndrome ◽  
Lower Body ◽  
Normal Flow ◽  
Postural Tachycardia

Previous investigations have allowed for stratification of patients with postural tachycardia syndrome (POTS) on the basis of peripheral blood flow. One such subset, comprising “normal-flow POTS” patients, is characterized by normal peripheral resistance and blood volume in the supine position but thoracic hypovolemia and splanchnic blood pooling in the upright position. We studied 32 consecutive 14- to 22-yr-old POTS patients comprising 13 with low-flow POTS, 14 with normal-flow POTS, and 5 with high-flow POTS and 12 comparably aged healthy volunteers. We measured changes in impedance plethysmographic (IPG) indexes of blood volume and blood flow within thoracic, splanchnic, pelvic (upper leg), and lower leg regional circulations in the supine posture and during incremental tilt to 20°, 35°, and 70°. We validated IPG measures of thoracic and splanchnic blood flow against indocyanine green dye-dilution measurements. We validated IPG leg blood flow against venous occlusion plethysmography. Control subjects developed progressive vasoconstriction with incremental tilt. Splanchnic blood flow was increased in the supine position in normal-flow POTS, despite marked peripheral vasoconstriction, and did not change during incremental tilt, producing progressive splanchnic hypervolemia. Absolute hypovolemia was present in low-flow POTS, all supine flows and volumes were reduced, there was no vasoconstriction with tilt in all segments, and segmental volumes tended to increase uniformly throughout tilt. Lower body (pelvic and leg) flows were increased in high-flow POTS at all angles, with consequent lower body hypervolemia during tilt. Our main finding is selective and maintained orthostatic splanchnic vasodilation in normal-flow POTS, despite marked peripheral vasoconstriction in these same patients. Local splanchnic vasoregulatory factors may counteract vasoconstriction and venoconstriction in these patients. Lower body vasoconstriction in high-flow POTS was abnormal, and vasoconstriction in low-flow POTS was sustained at initially elevated supine levels.

scholarly journals Soil microbial inoculation during flood events shapes headwater stream microbial communities and diversity

2021 ◽  
Author(s):  
Florian Caillon ◽  
Katharina Besemer ◽  
Peter Peduzzi ◽  
Jakob Schelker
Keyword(s):  
Microbial Diversity ◽  
Bacterial Diversity ◽  
Soil Water ◽  
Headwater Streams ◽  
High Flow ◽  
Low Flow ◽  
Flood Events ◽  
Flow Conditions ◽  
Soil Microbial ◽  
Microbial Inoculation

AbstractFlood events are now recognized as potentially important occasions for the transfer of soil microbes to stream ecosystems. Yet, little is known about these “dynamic pulses of microbial life” for stream bacterial community composition (BCC) and diversity. In this study, we explored the potential alteration of stream BCC by soil inoculation during high flow events in six pre-alpine first order streams and the larger Oberer Seebach. During 1 year, we compared variations of BCC in soil water, stream water and in benthic biofilms at different flow conditions (low to intermediate flows versus high flow). Bacterial diversity was lowest in biofilms, followed by soils and highest in headwater streams and the Oberer Seebach. In headwater streams, bacterial diversity was significantly higher during high flow, as compared to low flow (Shannon diversity: 7.6 versus 7.9 at low versus high flow, respectively, p < 0.001). Approximately 70% of the bacterial operational taxonomic units (OTUs) from streams and stream biofilms were the same as in soil water, while in the latter one third of the OTUs were specific to high flow conditions. These soil high-flow OTUs were also found in streams and biofilms at other times of the year. These results demonstrate the relevance of floods in generating short and reoccurring inoculation events for flowing waters. Moreover, they show that soil microbial inoculation during high flow enhances microbial diversity and shapes fluvial BCC even during low flow. Hence, soil microbial inoculation during floods could act as a previously overlooked driver of microbial diversity in headwater streams.

scholarly journals Increased plasma angiotensin II in postural tachycardia syndrome (POTS) is related to reduced blood flow and blood volume

2006 ◽  
Vol 110 (2) ◽  
pp. 255-263 ◽  
Author(s):  
Julian M. Stewart ◽  
June L. Glover ◽  
Marvin S. Medow
Keyword(s):  
Blood Flow ◽  
Angiotensin Ii ◽  
Blood Volume ◽  
High Flow ◽  
The Other ◽  
Low Flow ◽  
Postural Tachycardia Syndrome ◽  
Peripheral Blood Flow ◽  
Ang Ii ◽  
Postural Tachycardia

POTS (postural tachycardia syndrome) is associated with low blood volume and reduced renin and aldosterone; however, the role of Ang (angiotensin) II has not been investigated. Previous studies have suggested that a subset of POTS patients with increased vasoconstriction related to decreased bioavailable NO (nitric oxide) have decreased blood volume. Ang II reduces bioavailable NO and is integral to the renin–Ang system. Thus, in the present study, we investigated the relationship between blood volume, Ang II, renin, aldosterone and peripheral blood flow in POTS patients. POTS was diagnosed by 70° upright tilt, and supine calf blood flow, measured by venous occlusion plethysmography, was used to subgroup POTS patients. A total of 23 POTS patients were partitioned; ten with low blood flow, eight with normal flow and five with high flow. There were ten healthy volunteers. Blood volume was measured by dye dilution. All biochemical measurements were performed whilst supine. Blood volume was decreased in low-flow POTS (2.14±0.12 litres/m2) compared with controls (2.76±0.20 litres/m2), but not in the other subgroups. PRA (plasma renin activity) was decreased in low-flow POTS compared with controls (0.49±0.12 compared with 0.90±0.18 ng of Ang I·ml−1·h−1 respectively), whereas plasma Ang II was increased (89±20 compared with 32±4 ng/l), but not in the other subgroups. PRA correlated with aldosterone (r=+0.71) in all subjects. PRA correlated negatively with blood volume (r=−0.72) in normal- and high-flow POTS, but positively (r=+0.65) in low-flow POTS. PRA correlated positively with Ang II (r=+0.76) in normal- and high-flow POTS, but negatively (r=−0.83) in low-flow POTS. Blood volume was negatively correlated with Ang II (r=−0.66) in normal- and high-flow POTS and in five low-flow POTS patients. The remaining five low-flow POTS patients had reduced blood volume and increased Ang II which was not correlated with blood volume. The data suggest that plasma Ang II is increased in low-flow POTS patients with hypovolaemia, which may contribute to local blood flow dysregulation and reduced NO bioavailability.

Vasomotor responses in chronically hyperperfused and hypoperfused rat mesenteric arteries

1998 ◽  
Vol 274 (4) ◽  
pp. H1301-H1307 ◽  
Author(s):  
Fabrice Pourageaud ◽  
Jo G. R. De Mey
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Sodium Nitroprusside ◽  
Arginine Vasopressin ◽  
Side Branch ◽  
Mesenteric Arteries ◽  
Low Flow ◽  
Basal Diameter ◽  
Lower Shear ◽  
Altered Blood

We evaluated the reactivity of small arteries after remodeling induced by elevated or reduced blood flow. In 6-wk-old rats, every other first-order side branch of the superior mesenteric artery was ligated near the bifurcation of second-order branches. Four weeks after surgery, vessels that had been exposed to high flow (HF) or low flow (LF) were isolated and mounted in a pressure myograph at 100 mmHg and were compared with vessels from sham-operated rats (Sham). In HF: 1) basal lumen diameter was increased; 2) sensitivity to norepinephrine, arginine vasopressin, and perivascular nerve stimulation was not modified; 3) maximal constrictor responses (Δ diameter) to these stimuli and 125 mM K+ were increased; and 4) sensitivity and maximal dilator responses to sodium nitroprusside, acetylcholine, and flow were not modified. In LF: 1) basal diameter was reduced; 2) sensitivity to constrictor stimuli was not altered; 3) maximal responses to all vasoconstrictors except arginine vasopressin were reduced; and 4) sensitivity but not maximal dilator responses to sodium nitroprusside and acetylcholine was reduced. During acute flow-induced dilatations, lower shear stress was maintained in HF (48 ± 7 dyn/cm2) than in Sham (63 ± 10 dyn/cm2), but no shear stress regulation was observed in LF. These observations indicate that arterial structural responses to altered blood flow are accompanied by modified reactivity of the arterial smooth muscle, which entails changes in responsiveness to neurogenic and endothelium-dependent stimuli.

The Effect of Altered Cerebral Blood Flow on the Cerebral Kinetics of Thiopental and Propofol in Sheep

2000 ◽  
Vol 93 (4) ◽  
pp. 1085-1094 ◽  
Author(s):  
Richard N. Upton ◽  
Guy L. Ludbrook ◽  
Cliff Grant ◽  
David J. Doolette
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Random Order ◽  
High Flow ◽  
Low Flow ◽  
Flow State ◽  
Concentration Difference ◽  
Blood Flows ◽  
Kinetics Of ◽  
The Brain

Background Thiopental and propofol are highly lipid-soluble, and their entry into the brain often is assumed to be limited by cerebral blood flow rather than by a diffusion barrier. However, there is little direct experimental evidence for this assumption. Methods The cerebral kinetics of thiopental and propofol were examined over a range of cerebral blood flows using five and six chronically instrumented sheep, respectively. Using anesthesia (2.0% halothane), three steady state levels of cerebral blood flow (low, medium, and high) were achieved in random order by altering arterial carbon dioxide tension. For each flow state, 250 mg thiopental or 100 mg propofol was infused intravenously over 2 min. To quantify cerebral kinetics, arterial and sagittal sinus blood was sampled rapidly for 20 min from the start of the infusion, and 1.5 h was allowed between consecutive infusions. Various models of cerebral kinetics were examined for their ability to account for the data. Results The mean baseline cerebral blood flows for the "high" flow state were over threefold greater than those for the low. For the high-flow state the normalized arteriovenous concentration difference across the brain was smaller than for the low-flow state, for both drugs. The data were better described by a model with partial membrane limitation than those with only flow limitation or dispersion. Conclusions The cerebral kinetics of thiopental and propofol after bolus injection were dependent on cerebral blood flow, despite partial diffusion limitation. Higher flows produce higher peak cerebral concentrations.

Abstract 271: Continuous Amplitude Spectral Area May Reflect Adequacy of Myocardial Perfusion Before Attempting Defibrillation

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Raúl J Gazmuri ◽  
Christopher L Kaufman ◽  
Herbert K Whitehouse ◽  
Alvin Baetiong ◽  
Jeejabai Radhakrishnan
Keyword(s):  
Blood Flow ◽  
Myocardial Perfusion ◽  
High Flow ◽  
Low Flow ◽  
Swine Model ◽  
Coronary Perfusion ◽  
Electrical Shock ◽  
Spectral Area ◽  
Electrical Shocks ◽  
Initial Shock

Background: Previous studies have shown that analysis of the VF amplitude-spectral area (AMSA) contains information predictive of electrical shock success. However, the underlying factors that determine AMSA remain elusive. We developed an open-chest swine model of VF in which we modeled “average CPR” followed by “highly effective CPR” using extracorporeal circulation (ECC) and assessed AMSA in relation to adequacy of coronary perfusion. Methods: VF was electrically induced and left untreated for 8 min in 8 pigs after which ECC was started and maintained for 10 min adjusting the flow to generate a coronary perfusion pressure (CPP) of 10 mmHg (low-flow ECC). After delivery of an initial shock, the ECC flow was increased and titrated to secure a mean aortic pressure of 40 mmHg (high-flow ECC) delivering additional electrical shocks at 60 s intervals. Blood flow through the left anterior descending (LAD) artery was reported relative to baseline (LAD rel). AMSA was measured continuously with a 2.1 s timeframe and a Tukey window that moved ahead every 0.5 s, and was averaged every min for this report (Figure). Results: AMSA increased during the initial 5 min of low-flow ECC, but subsequently decreased (Figure). The initial shock uniformly failed to terminate VF prompting increases in ECC to high-flow, which then resulted in the return of spontaneous circulation in each instance after 3 to 5 shocks. During the high-flow ECC, AMSA initially increased but then gradually decreased for reasons that are not clear. Before attempting defibrillation, AMSA was positively correlated with LAD rel (r=0.73, p=0.04). Conclusion: The study provides intriguing data showing changes in AMSA that are time dependent and likely influenced by myocardial perfusion and the effects of electrical shocks on the myocardium. The present study also suggests that the level of AMSA prior to attempting defibrillation may be influenced by the efficacy with which the CPR intervention generates coronary blood flow.

Plasma viscosity and cerebral blood flow

2000 ◽  
Vol 279 (4) ◽  
pp. H1949-H1954 ◽  
Author(s):  
Yoshinobu Tomiyama ◽  
Johnny E. Brian ◽  
Michael M. Todd
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Blood Viscosity ◽  
Blood Cells ◽  
Exchange Transfusion ◽  
Ringer Solution ◽  
Plasma Viscosity ◽  
High Flow ◽  
Flow Conditions ◽  
Whole Blood Viscosity

We hypothesized that the response of cerebral blood flow (CBF) to changing viscosity would be dependent on “baseline” CBF, with a greater influence of viscosity during high-flow conditions. Plasma viscosity was adjusted to 1.0 or 3.0 cP in rats by exchange transfusion with red blood cells diluted in lactated Ringer solution or with dextran. Cortical CBF was measured by H2 clearance. Two groups of animals remained normoxic and normocarbic and served as controls. Other groups were made anemic, hypercapnic, or hypoxic to increase CBF. Under baseline conditions before intervention, CBF did not differ between groups and averaged 49.4 ± 10.2 ml · 100 g−1 · min−1 (±SD). In control animals, changing plasma viscosity to 1.0 or 3.0 cP resulted in CBF of 55.9 ± 8.6 and 42.5 ± 12.7 ml · 100 g−1 · min−1, respectively (not significant). During hemodilution, hypercapnia, and hypoxia with a plasma viscosity of 1.0 cP, CBF varied from 98 to 115 ml · 100 g−1 · min−1. When plasma viscosity was 3.0 cP during hemodilution, hypercapnia, and hypoxia, CBF ranged from 56 to 58 ml · 100 g−1 · min−1 and was significantly reduced in each case ( P < 0.05). These results support the hypothesis that viscosity has a greater role in regulation of CBF when CBF is increased. In addition, because CBF more closely followed changes in plasma viscosity (rather than whole blood viscosity), we believe that plasma viscosity may be the more important factor in controlling CBF.

scholarly journals Care of Maintenance Hemodialysis Patients through Intelligent Algorithm-Based Low-Dose Digital Subtraction Angiography

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Jianhua Hong
Keyword(s):  
Heart Failure ◽  
Blood Flow ◽  
Digital Subtraction Angiography ◽  
Low Dose ◽  
High Flow ◽  
Conventional Group ◽  
Low Flow ◽  
Maintenance Hemodialysis ◽  
Cardiac Complications ◽  
Digital Subtraction

Objective. The study aimed to explore the application value of artificial intelligence (AI)-based low-dose digital subtraction angiography (DSA) in the care of maintenance hemodialysis (MHD) patients. Methods. The characteristics of DSA imaging were analyzed, and the refinement efficiency of the AI algorithm was discussed, expected to assist clinicians in the care and treatment of patients. 100 MHD patients who were in the hospital were selected as the research subjects. They were randomly divided into the conventional DSA group (conventional group) and the AI algorithm-based DSA group (AI-based DSA group). The conventional group used conventional DSA images to guide the care of HM patients, and the AI-based DSA group used the AI algorithm to optimize DSA images. Results. It was found that the AI-based DSA group was better than the conventional DSA group in terms of image sharpness and shaded areas, and the image mean square error (MSE) loss value was smaller ( P < 0.05 ). The patients were followed up for 3 months. In the AI-based DAS group, the blood flow of the drainage vein (DV), the blood flow of the proximal vein (PA), and the blood flow of the brachial artery (BA) were greater than those of the conventional group ( P < 0.05 ). During the 3-month follow-up period, in the conventional group, thrombosis occurred in 4 patients, low-flow AVF occurred in 5 patients, high-flow AVF occurred in 3 patients, and heart failure occurred in 5 patients. In the AI-based DSA group, thrombosis occurred in 2 patients, low-flow AVF occurred in 2 cases, high-flow AVF occurred in 1 case, and heart failure occurred in 3 cases. There were no other cardiac complications in both groups. Conclusion. DSA images optimized by the AI algorithm are suitable for clinical diagnosis and have practical application value.

scholarly journals Longitudinal scattering coefficient obtained by hydroacoustic measurement and by conservative tracer

2021 ◽  
pp. 75-86
Author(s):  
Ana F. Nadal ◽  
José M. Díaz Lozada ◽  
Gonzalo P. Barbero Medina ◽  
Karen M. Moro ◽  
Mariana N. Melchiorre ◽  
...  
Keyword(s):  
Dispersion Coefficient ◽  
Flow Characteristics ◽  
Chemical Reactor ◽  
High Flow ◽  
Low Flow ◽  
Flow Conditions ◽  
Dry Period ◽  
Longitudinal Dispersion Coefficient ◽  
Transport Models ◽  
Conservative Tracer

The objective of the present work was to determine the value of the longitudinal dispersion coefficient (DL) of the Chicamtoltina stream (Alta Gracia) by means of two different techniques, in order to compare the values obtained. The first technique consisted of applying a developed formula that includes a detailed description of hydrodynamic parameters obtained by gauging with a hydroacoustic instrument, while the second technique consisted of injecting a conservative tracer, using the same approach as the non-ideal chemical reactor theory of flow with dispersion. This work was carried out at low flow conditions (dry period) and at high flow conditions (wet period). It was found that, either for high flow or low flow, the values of the dispersion coefficient obtained by both techniques have good agreement, fitting better in the dry period than in the wet period. Due to the fact that frequent gauging campaigns are carried out in this stream, it is concluded that with similar flow characteristics and morphology of the section, the gauging data can be used to determine the DL coefficient, in order to incorporate reliable data that can be applied to pollutant transport models.

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