Using a classic paper by Robin Fåhraeus and Torsten Lindqvist to teach basic hemorheology

2013 ◽  
Vol 37 (2) ◽  
pp. 129-133 ◽  
Author(s):  
Linea Natalie Toksvang ◽  
Ronan M. G. Berg
Keyword(s):  
Apparent Viscosity ◽  
Peripheral Resistance ◽  
Tissue Perfusion ◽  
Vessel Diameter ◽  
Glass Capillary ◽  
Capillary Tubes ◽  
Cell Deformability ◽  
Blood Flows ◽  
Classic Paper

“The viscosity of the blood in narrow capillary tubes” by Robin Fåhraeus and Torsten Lindqvist ( Am J Physiol 96: 562–568, 1931) can be a valuable opportunity for teaching basic hemorheological principles in undergraduate cardiovascular physiology. This classic paper demonstrates that a progressive decline in apparent viscosity occurs when blood flows through glass capillary tubes of diminishing radius, which was later designated as the “Fåhraeus-Lindqvist effect.” Subsequent studies have shown that apparent viscosity continues to decline at diameters that correspond to the arteriolar segments of the systemic vascular tree, where the majority of the total peripheral resistance resides and is actively regulated in vivo. The Fåhraeus-Lindqvist effect thus reduces microvascular resistance, thereby maintaining local tissue perfusion at a relatively lower blood pressure. The paper by Fåhraeus and Lindqvist can be used as a platform for a plenary discussion of these concepts as well as of the relationships among hematocrit, vessel diameter, red blood cell deformability, and resistance to blood flow and how these factors may affect the work of the heart.

Regional circulatory responses to head-out water immersion in conscious dogs

1987 ◽  
Vol 253 (2) ◽  
pp. R254-R263 ◽  
Author(s):  
G. Hajduczok ◽  
K. Miki ◽  
J. R. Claybaugh ◽  
S. K. Hong ◽  
J. A. Krasney
Keyword(s):  
Blood Flow ◽  
Regional Blood Flow ◽  
Water Immersion ◽  
Local Heating ◽  
Peripheral Resistance ◽  
Tissue Perfusion ◽  
Conscious Dogs ◽  
Metabolic Demand ◽  
Blood Flows ◽  
Total Brain

We determined the regional blood flow responses to head-out water immersion (WI) in intact (INT) and cardiac-denervated (CD) conscious dogs. Immersing dogs in thermoneutral water (37 degrees C) in the quadruped position for 100 min resulted in significant increases in cardiac output (Qco) above control values by 38.7% in the INT dogs and 39.2% in the CD dogs (P less than 0.01). Arterial pressure increased by 32 and 34.7% in the INT and CD groups, respectively, during WI, with no significant changes occurring in the calculated total peripheral resistance. Regional blood flow responses were measured with 15-microns radiolabeled microspheres. Flows in the INT and CD groups increased significantly to the heart (40, 38%), skin (93, 96%), fat (79, 83%), diaphragm (44, 48%), and intercostal muscles (58, 55%), whereas there were no changes in renal cortical blood flows during WI. Total brain blood flows did not change significantly on immersion; however, blood flows in both INT and CD animals were increased to the cerebellum (19, 22%), but a significant decrease in pituitary flow (52%) was observed only in the CD group during WI. Gastrointestinal tissue flows increased only during early WI in both INT (45%) and CD (47%) animals. However, blood flows to the skeletal muscles increased only during late WI in the INT (53%) and CD (47%) groups. There were no significant differences between the INT and CD groups. Rectal temperatures and systemic O2 consumption (VO2) were unchanged during WI in both groups of animals. These observations indicate that WI leads to a sustained elevation of Qco accompanied by selective increases in regional tissue perfusion that may be accounted for in some tissues by an increase in metabolic demand or by local heating responses and produces a time-dependent redistribution of blood flow away from the gastrointestinal tissues toward skeletal muscle tissues, which may be due to a partial uncoupling of the normal Q/VO2 relationship. This may be caused by thermal or central neurohumoral mechanisms. These regional circulatory responses are not dependent on the presence of the cardiac nerves.

Mesenteric baroreceptors

1975 ◽  
Vol 229 (6) ◽  
pp. 1514-1519 ◽  
Author(s):  
RS Tuttle ◽  
M McCleary
Keyword(s):  
Peripheral Resistance ◽  
Receptor Activity ◽  
Pacinian Corpuscle ◽  
Blood Flows ◽  
Vasomotor Reflexes ◽  
Mesenteric Vessels ◽  
Large Vessels ◽  
Intravascular Pressure ◽  
Vascular Region

Occlusion of the mesenteric vessels in the cat and injection of catecholamines produced significant changes in skin and muscle blood flows. These were abolished by cutting the mesenteric nerves. The occurrence of systemic pressure and peripheral resistance changes in cross-perfused mesenteric preparations indicates that hemodynamic factors alone, such as might result from occlusion of a large vascular region, were not initiating the reflex. This also excludes extramesenteric receptors within the heart and large vessels from the reflex. Since both intravascular pressure and catecholamines have been shown to modify Pacinian receptor discharge in vivo, the evidence suggests that the mesenteric Pacinian corpuscle is the baroreceptor probably initiating the vasomotor reflexes in skin and muscle. The net effect of mesenteric receptor activity appears to be an inhibition of vasomotor neurons supplying skin and muscle.

scholarly journals Perivascular vital cells in the ablation center after multibipolar radiofrequency ablation in an in vivo porcine model

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
F. G. M. Poch ◽  
C. A. Neizert ◽  
B. Geyer ◽  
O. Gemeinhardt ◽  
S. M. Niehues ◽  
...  
Keyword(s):  
Radiofrequency Ablation ◽  
Early Stage ◽  
Pringle Maneuver ◽  
Vessel Diameter ◽  
Inflow Occlusion ◽  
White Zone ◽  
Cell Vitality ◽  
Internally Cooled ◽  
Hepatic Vessels

AbstractMultibipolar radiofrequency ablation (RFA) is an advanced ablation technique for early stage hepatocellular carcinoma and liver metastases. Vessel cooling in multibipolar RFA has not been systematically investigated. The objective of this study was to evaluate the presence of perivascular vital cells within the ablation zone after multibipolar RFA. Multibipolar RFA were performed in domestic pigs in vivo. Three internally cooled bipolar RFA applicators were used simultaneously. Three experimental settings were planned: (1) inter-applicator-distance: 15 mm; (2) inter-applicator-distance: 20 mm; (3) inter-applicator-distance: 20 mm with hepatic inflow occlusion (Pringle maneuver). A vitality staining was used to analyze liver cell vitality around all vessels in the ablation center with a diameter > 0.5 mm histologically. 771 vessels were identified. No vital tissue was seen around 423 out of 429 vessels (98.6%) situated within the central white zone. Vital cells could be observed around major hepatic vessels situated adjacent to the ablation center. Vessel diameter (> 3.0 mm; p < 0.05) and low vessel-to-ablation-center distance (< 0.2 mm; p < 0.05) were identified as risk factors for incomplete ablation adjacent to hepatic vessels. The vast majority of vessels, which were localized in the clinically relevant white zone, showed no vital perivascular cells, regardless of vessel diameter and vessel type. However, there was a risk of incomplete ablation around major hepatic vessels situated directly within the ablation center. A Pringle maneuver could avoid incomplete ablations.

scholarly journals Endothelin 1-induced retinal ganglion cell death is largely mediated by JUN activation

2020 ◽  
Vol 11 (9) ◽  
Author(s):  
Olivia J. Marola ◽  
Stephanie B. Syc-Mazurek ◽  
Gareth R. Howell ◽  
Richard T. Libby
Keyword(s):  
Transcription Factor ◽  
Molecular Mechanisms ◽  
Ganglion Cells ◽  
Retinal Vessel ◽  
Vessel Diameter ◽  
Retinal Ganglion ◽  
Retinal Ganglion Cell Death ◽  
Ganglion Cell Death

Abstract Glaucoma is a neurodegenerative disease characterized by loss of retinal ganglion cells (RGCs), the output neurons of the retina. Multiple lines of evidence show the endothelin (EDN, also known as ET) system is important in glaucomatous neurodegeneration. To date, the molecular mechanisms within RGCs driving EDN-induced RGC death have not been clarified. The pro-apoptotic transcription factor JUN (the canonical target of JNK signaling) and the endoplasmic reticulum stress effector and transcription factor DNA damage inducible transcript 3 (DDIT3, also known as CHOP) have been shown to act downstream of EDN receptors. Previous studies demonstrated that JUN and DDIT3 were important regulators of RGC death after glaucoma-relevant injures. Here, we characterized EDN insult in vivo and investigated the role of JUN and DDIT3 in EDN-induced RGC death. To accomplish this, EDN1 ligand was intravitreally injected into the eyes of wildtype, Six3-cre+Junfl/fl (Jun−/−), Ddit3 null (Ddit3−/−), and Ddit3−/−Jun−/− mice. Intravitreal EDN1 was sufficient to drive RGC death in vivo. EDN1 insult caused JUN activation in RGCs, and deletion of Jun from the neural retina attenuated RGC death after EDN insult. However, deletion of Ddit3 did not confer significant protection to RGCs after EDN1 insult. These results indicate that EDN caused RGC death via a JUN-dependent mechanism. In addition, EDN signaling is known to elicit potent vasoconstriction. JUN signaling was shown to drive neuronal death after ischemic insult. Therefore, the effects of intravitreal EDN1 on retinal vessel diameter and hypoxia were explored. Intravitreal EDN1 caused transient retinal vasoconstriction and regions of RGC and Müller glia hypoxia. Thus, it remains a possibility that EDN elicits a hypoxic insult to RGCs, causing apoptosis via JNK-JUN signaling. The importance of EDN-induced vasoconstriction and hypoxia in causing RGC death after EDN insult and in models of glaucoma requires further investigation.

Vasomotion of basilar arteries in vivo

1990 ◽  
Vol 258 (6) ◽  
pp. H1829-H1834 ◽  
Author(s):  
K. Fujii ◽  
D. D. Heistad ◽  
F. M. Faraci
Keyword(s):  
Moderate Hypertension ◽  
Vessel Diameter ◽  
Base Line ◽  
Large Artery ◽  
Cranial Window ◽  
Basilar Arteries ◽  
The Mean ◽  
Rhythmic Change ◽  
The Brain

Vasomotion is a rhythmic change in vascular caliber that has been described in vivo mainly in peripheral arterioles. In this study, we have characterized vasomotion in a large artery of the brain in vivo. In anesthetized rats, spontaneous vasomotion was observed in 38 of 47 basilar arteries visualized through a cranial window. Base-line arterial diameter was 259 +/- 9 (means +/- SE) microns. Under control conditions, the frequency of vasomotion was 4.8 +/- 0.2 cycles/min, and the amplitude was 19 +/- 2% of the mean diameter. Vasomotion usually occurred simultaneously along the entire length of the vessel, but in some arteries it propagated in either direction. Moderate hypertension (phenylephrine) or vasoconstriction induced by topical application of serotonin, vasopressin, or the thromboxane analogue U 46619 increased the frequency of vasomotion. Moderate hypotension or vasodilation induced by nitroglycerin, adenosine, or acetylcholine decreased the frequency. Marked hypertension, hypotension, or vasodilatation abolished vasomotion. Thus vasomotion of the basilar artery in vivo 1) is common and of relatively large amplitude, 2) does not seem to be driven by a single pacemaker, and 3) is dependent on vessel diameter or vasomotor tone.

scholarly journals Exploring the Relationships Between Hemodynamic Stresses in the Carotid Arteries

2021 ◽  
Vol 7 ◽  
Author(s):  
Magnus Ziegler ◽  
Jesper Alfraeus ◽  
Elin Good ◽  
Jan Engvall ◽  
Ebo de Muinck ◽  
...  
Keyword(s):  
Vessel Wall ◽  
Carotid Arteries ◽  
Carotid Bifurcation ◽  
Vessel Diameter ◽  
Atherosclerotic Plaques ◽  
Shear Stresses ◽  
Strongly Correlated ◽  
4D Flow ◽  
Bifurcation Angle

Background: Atherosclerosis manifests as a focal disease, often affecting areas with complex hemodynamics such as the carotid bifurcation. The magnitude and regularity of the hemodynamic shear stresses acting on the vessel wall are thought to generate risk patterns unique to each patient and play a role in the pathogenesis of atherosclerosis. The involvement of different expressions of shear stress in the pathogenesis of carotid atherosclerosis highlights the need to characterize and compare the differential impact of the various expressions of shear stress in the atherosclerotic carotid bifurcation. Therefore, the aim of this study is to characterize and compare hemodynamic wall shear stresses (WSS) in the carotid arteries of subjects with asymptomatic atherosclerotic plaques. Shear stresses were also compared against vessel diameter and bifurcation angle to examine the relationships with the geometry of the carotid bifurcation.Methods: 4D Flow MRI and contrast-enhanced MRA data were acquired for 245 subjects with atherosclerotic plaques of at least 2.7 mm in conjunction with the Swedish CArdioPulmonary bioImage Study (SCAPIS). Following automatic segmentation and geometric analysis, time-resolved WSS and near-wall turbulent kinetic energy (nwTKE) were derived from the 4D Flow data. Whole-cycle parameters including time-averaged WSS and nwTKE, and the oscillatory shear index (OSI) were calculated. Pairwise Spearman rank-correlation analyses were used to investigate relationships among the hemodynamic as well as geometric parameters.Results: One hundred and seventy nine subjects were successfully segmented using automated tools and subsequently geometric and hemodynamic analyses were performed. Temporally resolved WSS and nwTKE were strongly correlated, ρ = 0.64. Cycle-averaged WSS and nwTKE were moderately correlated, ρ = 0.57. Cycle-average nwTKE was weakly correlated to OSI (ρ = −0.273), revealing that nwTKE provides information about disturbed flow on the vessel wall that OSI does not. In this cohort, there was large inter-individual variation for both WSS and nwTKE. Both WSS and nwTKE varied most within the external carotid artery. WSS, nwTKE, and OSI were weakly correlated to vessel diameter and bifurcation angle.Conclusion: The turbulent and mean component of WSS were examined together in vivo for the first time, and a strong correlation was found between them. nwTKE presents the opportunity to quantify turbulent wall stresses in vivo and gain insight into the effects of disturbed flow on the vessel wall. Neither vessel diameter nor bifurcation angle were found to be strongly correlated to the turbulent or mean component of WSS in this cohort.

In vivo characterization of vasocontractile activities in erythrocytes

1983 ◽  
Vol 58 (3) ◽  
pp. 356-361 ◽  
Author(s):  
Michael P. McIlhany ◽  
Lydia M. Johns ◽  
Thomas Leipzig ◽  
Nicholas J. Patronas ◽  
Frederick D. Brown ◽  
...  
Keyword(s):  
Vascular Resistance ◽  
Peripheral Resistance ◽  
Content Type ◽  
Control Value ◽  
Arterial Blood ◽  
Anesthetized Dogs ◽  
Chronic Cerebral Vasospasm ◽  
In Vivo Characterization

✓ Partially purified protein from washed and artificially hemolyzed erythrocytes, known to cause significant contractions of isolated canine cerebral vessels in vitro, was injected into the cisterna magna of intact anesthetized dogs. Cerebral blood flow, measured by the xenon-133 washout technique, decreased from a control value of 49.5 ± 1.17 ml/100 gm/min to an experimental value of 34.1 ± 1.65 ml/100 gm/min at 2 hours. Cerebral vascular resistance rose from a control value of 2.05 ± 0.17 PRU (peripheral resistance units) to an experimental value of 2.91 ± 0.25 PRU at 2 hours. Mean arterial blood pressure, heart rate, intracranial pressure, and cerebral perfusion pressure remained stable. Cardiac output also fell significantly (in 2-hour control animals it was 2.89 ± 0.37 liter/min, and in 2-hour experimental animals 1.43 ± 0.13 liter/min) and peripheral vascular resistance rose. These changes were evident by 10 minutes after the cisternal injection of the hemolysate protein, and remained for the duration of the 2-hour monitoring period. Serial vertebrobasilar angiograms demonstrated marked narrowing of the intracranial basilar artery when compared to control values. The narrowing persisted for several days in most animals, and tended to increase with time. Relaxation occurred by the 10th through the 14th day. The authors conclude that this experimental preparation may be a useful model for both in vitro and in vivo investigation of chronic cerebral vasospasm.

Evaluation of an infrared laser-Doppler blood flowmeter

1987 ◽  
Vol 252 (6) ◽  
pp. G832-G839 ◽  
Author(s):  
A. P. Shepherd ◽  
G. L. Riedel ◽  
J. W. Kiel ◽  
D. J. Haumschild ◽  
L. C. Maxwell
Keyword(s):  
Rotational Velocity ◽  
Rotating Disk ◽  
Tissue Perfusion ◽  
Infrared Laser ◽  
Blood Oxygenation ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Flow Signal

Several laser-Doppler blood flowmeters are now commercially available; however, only one utilizes an infrared laser diode (Laserflo, TSI, St. Paul, MN). Because of this and other unique features such as its microprocessor-based signal analyzer, we evaluated this device's ability to measure tissue perfusion. Initially, we determined whether laser illumination directly affected the microvasculature. Intravital microscopic observations in the hamster cremaster muscle indicated that neither He-Ne nor infrared laser light affected the diameters of arterioles that were responsive to vasoactive agents. To test the flowmeter for linearity and repeatability, we used a rotating disk to simulate a light-scattering, flowing medium. The "flow" signal was highly correlated (r = 0.99) with the rotational velocity of the disk, was consistent among flow probes, and showed a high degree of reproducibility. The second model consisted of microsphere suspensions pumped through cuvettes. The laser-Doppler velocimeter (LDV) flow signal was linear with respect to pump output. With red blood cells in the perfusate, we examined the effects of blood oxygenation on the flowmeter's performance. The LDV flow signal was unaffected by changes in blood oxygenation. We evaluated linearity in vivo in isolated, perfused rat livers and in isolated canine gastric flaps. We observed linear relationships between total flow and laser-Doppler flow measured on the surface of the liver (r = 0.98) and in the gastric mucosa (r = 0.98), but the slopes of the relationships between total and local LDV flow showed considerable variability not noted in the in vitro studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular peripheral resistance and compliance in the lobster Homarus americanus

1997 ◽  
Vol 200 (3) ◽  
pp. 477-485 ◽  
Author(s):  
J Wilkens ◽  
G Davidson ◽  
M Cavey
Keyword(s):  
Striated Muscle ◽  
Peripheral Resistance ◽  
Systolic Pressure ◽  
Body Part ◽  
Homarus Americanus ◽  
Arterial System ◽  
Flow Rates ◽  
Flow Through ◽  
Lateral Walls

The peripheral resistance to flow through each arterial bed (in actuality, the entire pathway from the heart back to the pericardial sinus) and the mechanical properties of the seven arteries leaving the lobster heart are measured and compared. Resistance is inversely proportional to artery radius and, for each pathway, the resistance falls non-linearly as flow rate increases. The resistance of the hepatic arterial system is lower than that predicted on the basis of its radius. Body-part posture and movement may affect the resistance to perfusion of that region. The total vascular resistance placed on the heart when each artery is perfused at a rate typical of in vivo flow rates is approximately 1.93 kPa s ml-1. All vessels exhibit adluminal layers of fibrils and are relatively compliant at pressures at or below heart systolic pressure. Arteries become stiffer at pressures greater than peak systolic pressure and at radii greater than twice the unpressurized radius. The dorsal abdominal artery possesses striated muscle in the lateral walls. This artery remains compliant over the entire range of hemolymph pressures expected in lobsters. These trends are illustrated when the incremental modulus of elasticity is compared among arteries. All arteries should function as Windkessels to damp the pulsatile pressures and flows generated by the heart. The dorsal abdominal artery may also actively regulate its flow.

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