The dispersion of indicator flowing through simplified models of the circulation and its relevance to velocity profile in blood vessels

G., C.

doi:10.1113/jphysiol.1966.sp007999

Cited by 53 publications

(20 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The findings 18,19 implied the presence of secondary motion in blood flow in curved and branching arteries. In addition, they encouraged consideration of the effects of flow-induced wall shear, including on blood-wall mass transport.…”

Section: Fluid Mechanics and Pathologymentioning

confidence: 99%

“…I met at that time and began to collaborate with James Lighthill, a distinguished mathematical scientist. 16 Recognizing that curvature and branching are major features of the arterial system, he suggested some model studies, reminiscent of Taylor, 17 but comparing indicator dispersion in a curved pipe with that in a straight pipe, under physiological conditions.The findings 18,19 implied the presence of secondary motion in blood flow in curved and branching arteries. In addition, they encouraged consideration of the effects of flow-induced wall shear, including on blood-wall mass transport.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Discovery of the Role of Wall Shear in Atherosclerosis

Caro

2009

ATVB

175

114

View full text Add to dashboard Cite

Abstract-The suggestion was made in the 1870s that mechanical irritation of the arterial wall is a cause of atherosclerosis, because the changes were chiefly found at points "exposed to the full stress and impact of the blood." The mechanical damage theory persisted until well into the 20th century when, with interest increasing in multidisciplinary research, two fluid mechanical proposals were advanced for the patchy distribution of the lesions. One advocated high-and the other low-wall shear. Arterial wall shear stress levels appeared, however, insufficiently high to damage the endothelium. In contrast, examination of cadaver human arteries, combined with flow studies in models and casts of arteries, implied that the lesions occurred preferentially in regions expected to experience low-wall shear; a mechanism, involving arterial wall lipid metabolism and shear-dependent blood-wall mass transport, was suggested to account for that distribution. These proposals helped stimulate extensive investigation of arterial fluid mechanics/mass transport and vascular biology/pathology, revealing mechanisms that may explain the now widely confirmed preferred occurrence of atherosclerosis in low wall shear regions in adult human beings. Fluid Mechanics and PathologyPolymaths, including Leonhard Euler (1707-1783) and Thomas Young (1773-1829), studied wave propagation in arteries, but they do not appear to have investigated the arterial flow field. Interest in atherosclerosis and the mechanisms that underlay its patchy distribution in arteries increased from the later 19th century onward. However, in contrast to the polymath approach, there was then a tendency toward specialization in engineering and biology/pathology/ medicine, a development unfavorable to research in the essentially multidisciplinary field of arterial fluid dynamics. The specialization largely persisted until the middle of the 20th century, when interest increased in multidisciplinary research. Therefore, it was against a background of specialization that much of the research of the 19th century and first half of the 20th century on blood flow and atherosclerosis was undertaken.It is important to appreciate that wall shear stress and wall shear rate are characteristics of the local flow field. The former is the force applied parallel, or tangential, to a boundary, and the latter is the gradient of velocity normal to the boundary. The wall shear stress is the product of the wall shear rate and the viscosity of the fluid. In citing relevant studies, we comment, where indicated, on instances of incomplete understanding of the fluid mechanics.Several workers suggested that flow separation might occur in the arterial system at, for example, sites of curvature, branching or expansion of the cross-section. Suggested links between flow separation and the development of atherosclerosis included mechanical damage to the wall, 1,2 platelet deposition, 3 and fibrin deposition. 4 Flow separation and static zones may occur in arteries and investigation of the issue conti...

show abstract

Section: Fluid Mechanics and Pathologymentioning

confidence: 99%

mentioning

confidence: 99%

Discovery of the Role of Wall Shear in Atherosclerosis

Caro

2009

ATVB

175

114

View full text Add to dashboard Cite

show abstract

“…2A, B) were not found in the peripheral circula tion since turbulence and secondary flow phenomena in the aorta and arterial tree [5] produce a substantial mixing effect. Moreover, constant state NEP infusions into the atria did not produce differential actions on LV contractile state ( fig.…”

Section: Discussionmentioning

confidence: 99%

Physiological Evaluation of Pulmonary Dilutional and Enzymatic Activity on Blood-Borne Catecholamines in Cardiocirculatory Performance

et al. 1977

View full text Add to dashboard Cite

Although the lung is a rich source of monamine oxidase and related catecholamine metabolizing and transporting enzymes, their physiologic role in cardiocirculatory regulation by affecting the properties of blood-borne sympathetic neurotransmitters is unclear. Accordingly, the present study evaluated the possibility that effects of pulmonary vasculature on systemic actions of catecholamines might be due to dilutional influences rather than to enzymatic activity. The experimental design was to compare left atrial (LA) and right atrial (RA) injections of norepinephrine (NEP) to ascertain a specific injection site effect, and upon documenting such a difference, to delineate whether the lesser RA injection effect could be accounted for by dilutional instead of enzymatic considerations. Thus, 0.2 µg/kg NEP was rapidly injected into RA or LA of 17 vagotomized open-chest intact canine preparations, and changes were observed in systemic blood pressure (BP), myocardial contractility (left ventricular dp/dt at 50 mm Hg pressure) and cutaneous vascular resistance (perfusion pressure of isolated hind-paw). TheLA bolus increased peak BP more (p < 0.01) than RA injection due to differential action (p < 0.05) on myocardial contractility, rather than by differential increase (p > 0.05) in peripheral resistance. However, when pulmonary vascular bed dilutional effects were obviated by steady state infusion (0.1 NEP µg/kg/min) into RA or LA, no

show abstract

“…In actual experiments, however, T g (n) is never quite identical to T f (n) because T g (n) and T f (n) are dependent upon curves and bends in the catheter geometry. 9 In summary, this section has presented the mathematics and necessary criteria for obtaining a time and frequency-domain representation of the forward-loop transfer function in the presence of a feedback signal. The conditions of the model were linearity and stationarity and with the added assumption of steady-state conditions, Fourier-series transformations were used.…”

Section: Effects Of the Sampling Systemmentioning

confidence: 99%

“…Transfer-Function Computation (5) (6) (7) (8) (9) where N = total number of coefficients used for forming curve. …”

Section: Fourier Seriesmentioning

confidence: 99%

A steady-state transfer function analysis of portions of the circulatory system using indicator dilution techniques

Coulam

Warner

Marshall

et al. 1967

Computers and Biomedical Research

View full text Add to dashboard Cite

A digital computer program has been developed whereby the distribution of dye-particle transit times across circulatory pathways can be found from recordings of upstream and downstream indicator-dilution curves. This distribution or transfer function is computed from Fourier-series representations of the upstream and downstream indicator curves and makes possible, for the first time, the calculation of transit-time distributions independent of the effects of recirculating dye. Since a discontinuity is introduced into the tails of the upstream and downstream curves at the end of sampling, the method requires an iterative approach in the termination of the upstream and downstream curves. The accuracy of the calculated distribution pattern is determined by comparison of the recorded downstream curve with the results of the convolution of the recorded upstream curve and computed transfer function. Effects of noise, bandwidth and sampling rate have been investigated through the use of analog computer models of the circulatory pathways. These studies show that the transfer-function description is limited by the bandwidth of the upstream (input) curve. Noise, or variations in magnitude and phase angle of input-and outputcurve frequencies, tends to introduce oscillations into the time-domain representation of the transfer function as does the use of too few frequencies. This means that in biological systems the upstream sampling site must be relatively close to the dye injection site if the input and output sampling sites are close together. Circulatory transfer functions have been obtained from dogs across their lower extremity, renal and systemic circulations before, during and following moderate exercise (walking on treadmill at two miles per hour for four minutes).

show abstract

The dispersion of indicator flowing through simplified models of the circulation and its relevance to velocity profile in blood vessels

Cited by 53 publications

References 8 publications

Discovery of the Role of Wall Shear in Atherosclerosis

Discovery of the Role of Wall Shear in Atherosclerosis

Physiological Evaluation of Pulmonary Dilutional and Enzymatic Activity on Blood-Borne Catecholamines in Cardiocirculatory Performance

A steady-state transfer function analysis of portions of the circulatory system using indicator dilution techniques

Contact Info

Product

Resources

About