Autoregulation assessment by direct visualisation of pial arterial blood flow in the piglet brain

Abstract Impairment of cerebrovascular autoregulation (CAR) is common after brain injury, although the pathophysiology remains elusive. The mechanisms of vascular dysregulation, their impact on brain function, and potential therapeutic implications are still incompletely understood. Clinical assessment of CAR remains challenging. Observational studies suggest that CAR impairment is associated with worse outcomes, and that optimization of cerebral blood flow (CBF) by individual arterial blood pressure (ABP) targets could potentially improve outcome. We present a porcine closed cranial window model that measures the hemodynamic response of pial arterioles, the main site of CBF control, based on changes in their diameter and red blood cell velocity. This quantitative direct CAR assessment is compared to laser Doppler flow (LDF). CAR breakpoints are determined by segmented regression analysis and validated using LDF and brain tissue oxygen pressure. Using a standardized cortical impact, CAR impairment in traumatic brain injury can be studied using our method of combining pial arteriolar diameter and RBC velocity to quantify RBC flux in a large animal model. The model has numerous potential applications to investigate CAR physiology and pathophysiology of CAR impairment after brain injury, the impact of therapeutic interventions, drugs, and other confounders, or to develop personalized ABP management strategies.

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Hemodynamic Shear Stress and Endothelial Dysfunction in Hemodialysis Access

The Open Urology & Nephrology Journal ◽

10.2174/1874303x01407010033 ◽

2014 ◽

Vol 7 (1) ◽

pp. 33-44 ◽

Cited By ~ 28

Author(s):

Michelle K Fitts ◽

Daniel B Pike ◽

Kasey Anderson ◽

Yan-Ting Shiu

Keyword(s):

Blood Flow ◽

Shear Stress ◽

Neointimal Hyperplasia ◽

Vascular Wall ◽

Chronic Hemodialysis ◽

Arterial Blood Flow ◽

Venous Anastomosis ◽

Arterial Blood ◽

Arteriovenous Access ◽

The Impact

Surgically-created blood conduits used for chronic hemodialysis, including native arteriovenous fistulas (AVFs) and synthetic AV grafts (AVGs), are the lifeline for kidney failure patients. Unfortunately, each has its own limitations; AVFs often fail to mature to become useful for dialysis and AVGs often fail due to stenosis as a result of neointimal hyperplasia, which preferentially forms at the graft-venous anastomosis. No clinical therapies are currently available to significantly promote AVF maturation or prevent neointimal hyperplasia in AVGs. Central to devising strategies to solve these problems is a complete mechanistic understanding of the pathophysiological processes. The pathology of arteriovenous access problems is likely multi-factorial. This review focuses on the roles of fluid-wall shear stress (WSS) and endothelial cells (ECs). In arteriovenous access, shunting of arterial blood flow directly into the vein drastically alters the hemodynamics in the vein. These hemodynamic changes are likely major contributors to non-maturation of an AVF vein and/or formation of neointimal hyperplasia at the venous anastomosis of an AVG. ECs separate blood from other vascular wall cells and also influence the phenotype of these other cells. In arteriovenous access, the responses of ECs to aberrant WSS may subsequently lead to AVF non-maturation and/or AVG stenosis. This review provides an overview of the methods for characterizing blood flow and calculating WSS in arteriovenous access and discusses EC responses to arteriovenous hemodynamics. This review also discusses the role of WSS in the pathology of arteriovenous access, as well as confounding factors that modulate the impact of WSS.

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Cardiovascular and hemorheological effects of three modified human hemoglobin solutions in hemodiluted rabbits

Journal of Applied Physiology ◽

10.1152/jappl.1999.86.2.541 ◽

1999 ◽

Vol 86 (2) ◽

pp. 541-548 ◽

Cited By ~ 29

Author(s):

Alexis Caron ◽

Patrick Menu ◽

Beatrice Faivre-Fiorina ◽

Pierre Labrude ◽

Abdu I. Alayash ◽

...

Keyword(s):

Blood Flow ◽

Cardiovascular Effects ◽

Human Albumin ◽

Arterial Blood Flow ◽

Human Hemoglobin ◽

Shear Rates ◽

Arterial Blood ◽

High Shear Rates ◽

Abdominal Aortic ◽

The Impact

The cardiovascular effects of human albumin (Alb) and three human hemoglobin (Hb) solutions, dextran-benzene-tetracarboxylate Hb, αα-crosslinked Hb, and o-raffinose-polymerized Hb were compared in anesthetized rabbits undergoing acute isovolemic hemodilution with Hct reduction from 41.4 ± 2.7 to 28.8 ± 1.6%. The impact of the vasoconstricting properties of Hb was examined by measuring heart rate (HR), mean arterial pressure (MAP), abdominal aortic, and femoral arterial blood flow, vascular resistance (VR), and aortic distension during the first 3 h after hemodilution. The impact of the hemorheological parameters was assessed by measurements of hemodiluted blood viscosity. In contrast to Alb, the Hb solutions elicited an immediate increase in MAP (20–38%). The effects of Alb and Hb solutions on HR, as well as on aortic and femoral arterial blood flow, were similar. VR decreased with Alb (20–28%) and increased with all three Hb solutions (30–90%), but the MAP and VR rising trends were different with each Hb solution. Aortic distension decreased in Hb groups compared with the Alb group for the first 60 min. The viscosity of hemodiluted blood was similar for all groups at high shear rates but was dependent on the viscosity of the solutions at low shear rates. We conclude that the vasoconstriction elicited by the Hb solutions overrides the vasodilation associated with viscosity changes due to hemodilution and would be the major factor responsible to the cardiovascular changes.

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Krogh’s capillary recruitment hypothesis, 100 years on: Is the opening of previously closed capillaries necessary to ensure muscle oxygenation during exercise?

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00384.2019 ◽

2020 ◽

Vol 318 (2) ◽

pp. H425-H447 ◽

Cited By ~ 3

Author(s):

Hugo Angleys ◽

Leif Østergaard

Keyword(s):

Blood Flow ◽

Capillary Flow ◽

Compartment Model ◽

Muscle Oxygenation ◽

Arterial Blood Flow ◽

Oxygen Extraction ◽

Model Calculations ◽

Capillary Recruitment ◽

Arterial Blood ◽

The Impact

In 1919, August Krogh published his seminal work on skeletal muscle oxygenation. Krogh’s observations indicated that muscle capillary diameter is actively regulated, rather than a passive result of arterial blood flow regulation. Indeed, combining a mathematical model with the number of ink-filled capillaries he observed in muscle cross sections taken at different workloads, Krogh was able to account for muscle tissue’s remarkably efficient oxygen extraction during exercise in terms of passive diffusion from nearby capillaries. Krogh was awarded the 1920 Nobel Prize for his account of muscle oxygenation. Today, his observations are engrained in the notion of capillary recruitment: the opening of previously closed capillaries. While the binary distinction between “closed” and “open” was key to Krogh’s model argument, he did in fact report a continuum of capillary diameters, degrees of erythrocyte deformation, and perfusion states. Indeed, modern observations question the presence of closed muscle capillaries. We therefore examined whether changes in capillary flow patterns and hematocrit among open capillaries can account for oxygen extraction in muscle across orders-of-magnitude changes in blood flow. Our four-compartment model of oxygen extraction in muscle confirms this notion and provides a framework for quantifying the impact of changes in microvascular function on muscle oxygenation in health and disease. Our results underscore the importance of capillary function for oxygen extraction in muscle tissue as first proposed by Krogh. While Krogh’s model calculations still hold, our model predictions support that capillary recruitment can be viewed in the context of continuous, rather than binary, erythrocyte distributions among capillaries. NEW & NOTEWORTHY Oxygen extraction in working muscle is extremely efficient in view of single capillaries properties. The underlying mechanisms have been widely debated. Here, we develop a four-compartment model to quantify the influence of each of the hypothesized mechanisms on muscle oxygenation. Our results show that changes in capillary flow pattern and hematocrit can account for the high oxygen extraction observed in working muscle, while capillary recruitment is not required to account for these extraction properties.

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A magnetic resonance imaging-compatible small animal model under extracorporeal circulation

Interactive CardioVascular and Thoracic Surgery ◽

10.1093/icvts/ivz139 ◽

2019 ◽

Vol 29 (4) ◽

pp. 612-614

Author(s):

Anna Kathrin Assmann ◽

Payam Akhyari ◽

Florian Demler ◽

Artur Lichtenberg ◽

Alexander Assmann

Keyword(s):

Magnetic Resonance Imaging ◽

Animal Model ◽

Blood Flow ◽

Magnetic Resonance ◽

Extracorporeal Circulation ◽

Arterial Blood Flow ◽

Flow Profile ◽

Resonance Imaging ◽

Arterial Blood ◽

The Impact

Abstract The impact of different extracorporeal circulation (ECC) scenarios on arterial blood flow profiles has not yet been revealed. To allow for exact measurements, magnetic resonance imaging (MRI) during ECC is required. Therefore, the present study addressed the feasibility of a high-resolution MRI-compatible animal model of ECC. For usage in New Zealand White rabbits, we developed an ECC device, the tubes of which were long enough to eliminate impacts of the magnetic field on the blood pump and heart–lung control machine. The miniaturized ECC system via thoracic access comprised an infant oxygenator, a pulsatile centrifugal pump, 1/8″ tubes, a 10-Fr aortic cannula and a 12-Fr venous cannula for vacuum-assisted drainage. This miniaturized ECC system has very low priming volume (230–255 ml) to reduce the system-inherent haemodilution to 50%. Consequently, haemoglobin rates remained high enough to guarantee adequate oxygenation (arterial pressure of oxygen >200 mmHg). Optimized venous drainage by an additionally inserted pulmonary artery vent catheter resulted in sufficient blood flow (31.6–65.8 ml/min/kg) that was maintained for 60 min with pulsatility. The current study demonstrates the feasibility of MRI-compatible ECC in rabbits, and this model allows for real-time blood flow profile measurements during different ECC scenarios in future projects.

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P1333PULSE WAVE ANALYSIS UNDER THE CONDITIONS OF HIGH ARTERIAL FLOW: ASSESSMENT OF SHUNT FUNCTION AND REACTIVE HYPEREMIA

Nephrology Dialysis Transplantation ◽

10.1093/ndt/gfaa142.p1333 ◽

2020 ◽

Vol 35 (Supplement_3) ◽

Author(s):

Niklas Mueller ◽

Joachim Streis ◽

Sandra Müller ◽

Hermann Josef Pavenstädt ◽

Stefan Reuter ◽

...

Keyword(s):

Blood Flow ◽

Endothelial Function ◽

Pulse Wave ◽

Statistical Significance ◽

Reactive Hyperemia ◽

Duplex Sonography ◽

Arterial Blood Flow ◽

Reactive Hyperaemia ◽

Arterial Blood ◽

The Impact

Abstract Background and Aims Fistula-creation as well as reactive hyperaemia increase local arterial blood flow. We wanted to analyse the impact of these haemodynamic changes on pulse wave (PW) morphology to assess fistula- and endothelial function. Method We conducted a clinical pilot study including 56 patients with functioning forearm fistula. PW morphology in the A. brachialis was assessed tonometrically at the non-fistula and fistula arm using the SpygmoCor® device. We also performed a PW analysis on the non-fistula arm under the condition of reactive hyperaemia (possible in 43 patients). Duplex-sonography was used as a complementary and reference method. Results In comparison to measurements under physiologic conditions, both the fistula arm (a) and the non-fistula arm with reactive hyperemia (b) showed marked differences in the pulse wave morphology (figure). The changes in PW morphology were most prominent in the area of the diacrotic notch and could be assessed as the differences of the sum of the mean slope (Δλ in mmHg/ms) between the diacrotic notch and the main preceding and subsequent inflexion point. Measurement with duplex-sonography confirmed increased peak blood flow velocity in the arteria brachialis (ΔVmax in cm/s) under both conditions. Statistical significance could be proved for Δλ and for ΔVmax (table). Finally, bivariate regression analysis revealed a correlation of Δλ with ΔVmax (figure; c: p=0.001 and r=-0,483 for interarm-differences of the fistula and non-fistula arm; d: p= 0.030 and r=-0.343 for the differences between the physiologic state and reactive hyperaemia at the non-fistula arm). Conclusion PW analysis under high flow conditions has the potential to be a new useful clinical tool in nephrology to monitor fistula- as well as endothelial function assessed by reactive hyperaemia. The findings should be verified in a trial with clinical endpoints.

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The Impact of Varicocelectomy on Testicular Arterial Blood Flow

Fayoum University Medical journal ◽

10.21608/fumj.2021.183650 ◽

2021 ◽

Vol 8 (2) ◽

pp. 9-19

Author(s):

Mohamed Amin ◽

Hamdy Ibrahim ◽

Khaled Mohamed ◽

Hossam Shaker

Keyword(s):

Blood Flow ◽

Arterial Blood Flow ◽

Arterial Blood ◽

The Impact

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Impact of intrinsic blood flow regulation in cirrhosis: maintenance of hepatic arterial buffer response

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.2000.279.2.g454 ◽

2000 ◽

Vol 279 (2) ◽

pp. G454-G462 ◽

Cited By ~ 82

Author(s):

Sven Richter ◽

Isabella Mücke ◽

Michael D. Menger ◽

Brigitte Vollmar

Keyword(s):

Blood Flow ◽

Venous Blood ◽

Blood Perfusion ◽

Flow Regulation ◽

Arterial Blood Flow ◽

Venous Blood Flow ◽

Total Blood ◽

Arterial Blood ◽

Blood Flow Regulation ◽

The Impact

The hepatic arterial buffer response (HABR) effectively controls total blood perfusion in normal livers, but little is known about blood flow regulation in cirrhosis. We therefore studied the impact of HABR on blood perfusion of cirrhotic livers in vivo. After 8-wk CCl4 treatment to induce cirrhosis, 18 anesthetized rats (and 18 noncirrhotic controls) were used to simultaneously assess portal venous and hepatic arterial inflow with miniaturized ultrasonic flow probes. Stepwise hepatic arterial blood flow (HAF) or portal venous blood flow (PVF) reduction was performed. Cirrhotic livers revealed a significantly reduced total hepatic blood flow (12.3 ± 0.9 ml/min) due to markedly diminished PVF (7.3 ± 0.8 ml/min) but slightly increased HAF (5.0 ± 0.6 ml/min) compared with noncirrhotic controls (19.0 ± 1.6, 15.2 ± 1.3, and 3.8 ± 0.4 ml/min). PVF reduction caused a significant HABR, i.e., increase of HAF, in both normal and cirrhotic livers; however, buffer capacity of cirrhotic livers exceeded that of normal livers ( P < 0.05) by 1.7- to 4.5-fold (PVF 80% and 20% of baseline). Persistent PVF reduction for 1, 2, and 6 h demonstrated constant HABR in both groups. Furthermore, HABR could be repetitively provoked, as analyzed by intermittent PVF reduction. HAF reduction did not induce changes of portal flow in either group. Because PVF is reduced in cirrhosis, the maintenance of HAF and the preserved HABR must be considered as a protective effect on overall hepatic circulation, counteracting impaired nutritive blood supply via the portal vein.

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Effect of Selected Manual Therapy Interventions for Mechanical Neck Pain on Vertebral and Internal Carotid Arterial Blood Flow and Cerebral Inflow

Physical Therapy ◽

10.2522/ptj.20120477 ◽

2013 ◽

Vol 93 (11) ◽

pp. 1563-1574 ◽

Cited By ~ 15

Author(s):

Lucy C. Thomas ◽

Darren A. Rivett ◽

Grant Bateman ◽

Peter Stanwell ◽

Christopher R. Levi

Keyword(s):

Blood Flow ◽

Magnetic Resonance ◽

Manual Therapy ◽

Therapeutic Interventions ◽

Arterial Blood Flow ◽

Large Individual ◽

Serious Adverse Events ◽

Arterial Blood ◽

Significant Difference ◽

The Brain

Background Manual therapy of the cervical spine has occasionally been associated with serious adverse events involving compromise of the craniocervical arteries. Ultrasound studies have shown certain neck positions can alter craniocervical arterial blood flow velocities; however, findings are conflicting. Knowledge about the effects of neck position on blood flow may assist clinicians in avoiding potentially hazardous practices. Objective The purpose of this study was to examine the effects of selected manual therapeutic interventions on blood flow in the craniocervical arteries and blood supply to the brain using magnetic resonance angiography (MRA). Design This was an experimental, observational magnetic resonance imaging study. Method Twenty adult participants who were healthy and had a mean age of 33 years were imaged using MRA in the following neck positions: neutral, rotation, rotation/distraction (similar to a Cyriax manipulation), C1–C2 rotation (similar to a Maitland or osteopathic manipulation), and distraction. Results The participants were imaged using 3T MRA. All participants had normal vascular anatomy. Average inflow to the brain in neutral was 6.98 mL/s and was not significantly changed by any of the test positions. There was no significant difference in flow in any of the 4 arteries in any position from neutral, despite large individual variations. Limitations Only individuals who were asymptomatic were investigated, and a short section of the arteries only were imaged. Conclusions Blood flow to the brain does not appear to be compromised by positions commonly used in manual therapy. Positions using end-range neck rotation and distraction do not appear to be more hazardous to cerebral circulation than more segmentally localized techniques.

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