The values of series and parallel resistances in steady blood-flow

Weale, F.E.

doi:10.1002/bjs.1800510818

Cited by 18 publications

(9 citation statements)

References 14 publications

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“…But local vasodilatation also alters the degree of the stenosis (A,/A2) by increasing the unstenosed cross-sectional luminal area At, thus largely offsetting the expected increase in velocity of flow. resistance stream with 'rolling or mixed' flow characteristics, which is somewhere between laminar and turbulent flow [8][9][10].…”

Section: Discussionmentioning

confidence: 99%

Effects of Local Vasodilatation on Blood Flow through Arterial Stenosis

Kreuzer

Schenk

1973

Eur Surg Res

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The effect of 2 different locally administered vasodilators on blood flow over a ‘critical’ arterial stenosis was studied in the dog. Blood flow increase always occurred, but this increase was small. Local vasodilatation – besides decreasing peripheral resistance – was found to simultaneously increase the resistance of the stenosis itself, thus largely offsetting the flow increase expected from the decrease in peripheral resistance. The explanation for these findings seems to be the alteration in geometry and degree of the stenosis caused by vasodilatation, rendering the stenosis more ‘critical’.

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Section: Discussionmentioning

confidence: 99%

Effects of Local Vasodilatation on Blood Flow through Arterial Stenosis

Kreuzer

Schenk

1973

Eur Surg Res

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“…However, this seems unlikely to be involved in our present experiments since much of this corresponding nerve plexus around the sciatic artery would have been P. J. BUTLER AND D. R. JONES destroyed by application of the flow probe. Furthermore, since the sciatic artery is in series with the resistance at the periphery then the total resistance of the vascular bed will be given by the value of the greatest resistance under consideration and this is unlikely to be the sciatic artery (Vonruden, Blaisdell, Hall & Thomas, 1964;Weale, 1964). It may be that the function of the adrenergic supply to the major arteries is to increase the stiffness of these vessels during a dive so that the oscillatory work load of the left ventricle is decoupled from the greatly increased terminal impedance (Taylor, 1964).…”

Section: Cardiovascular Adjustments To Diving 475mentioning

confidence: 99%

The effect of variations in heart rate and regional distribution of blood flow on the normal pressor response to diving in ducks

Butler¹,

Jones²

1971

The Journal of Physiology

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SUMMARY1. During a 2 min period of submersion of normal ducks, sciatic artery blood flow fell to 10 + 1'5 % control and carotid artery blood flow was reduced to 71 + 7 % control. Mean arterial blood pressure (M.A.P.), however, was maintained at 83 + 3-5 % of control. The whole animal showed a constrictor response during submersion, with the sciatic vascular bed showing average constriction. Both resistance to flow and yield pressure increased in the sciatic bed but changed little in the carotid bed. After 1 min submersion Pa,°2 was 52+ 1 mm Hg.2. Upon emersion, as soon as ventilation commenced, the whole animal showed a dilator response. The carotid bed exhibited marked vasodilatation whereas the sciatic bed returned to its control level.3. After a-receptor blockade, ducks were submerged for 1 min. During this time M.A.P. fell to 64 + 5-6 0/ of control and heart rate was reduced to 49 + 8*3 % of control. Blood flow through the sciatic and carotid arteries also fell to values of 41 + 6-9 0/ of control and 91 + 13 % of control respectively. There was little change in either resistance to flow or yield pressure in the sciatic bed compared to normal ducks, and the carotid bed showed reductions in resistance to flow and yield pressure during submersion.Pa,02 after 1 min under water was 41 + 1-1 mm Hg.4. fl-receptor blockade had no effect on any of the measured variables during submersion. Upon surfacing, however, although the whole animal response was one of dilatation, the carotid bed was less dilated than in normal ducks at this time and the sciatic bed was more constricted. * Present address: Department of Zoology, University of British Columbia, Vancouver, B.C., Canada. P. J. BUTLER AND D. R. JONES 5. Injection of atropine not only abolished the bradycardia during submersion but also caused a rise in M.A.P. and sciatic blood flow during the period under water. After 1 min submersion Pa,02 was 30 + 1-2 mm Hg.6. It is concluded that stimulation of adrenergic a-receptors is responsible for the increase in resistance to flow through the sciatic artery and the maintenance of blood pressure during submersion in the normal animals. This selective constrictor activity and the resulting ischaemia is important in the maintenance of Pa,02 during submersion. Adrenergic fl-receptors (cardiac and/or peripheral) are involved, to a small extent, in the blood pressure and blood flow changes that occur when ventilation commences upon emersion.

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“…Equation [5] includes both a linear and a non-linear term representing the partition of energy loss between viscous and inertial processes. These fluid dynamic relations are only applicable if the fluid is incompressible and of constant viscosity, but for blood flow in arteries greater than 0.5 mm in diameter these conditions are likely t o b e valid'.…”

Section: A$ A: 151mentioning

confidence: 99%

“…These fluid dynamic relations are only applicable if the fluid is incompressible and of constant viscosity, but for blood flow in arteries greater than 0.5 mm in diameter these conditions are likely t o b e valid'. The relationship between the pressure drop and flow predicted by equation [5] is dependent on the magnitude of the empirical constants k, and k,. If the linear term is dominant then the stenosis may b e represented as a fixed resistance (RJ that is independent of the flow; if the non-linear term is dominant then the resistance is variable and will increase linearly with the flow (R,=S,Q).…”

Section: A$ A: 151mentioning

confidence: 99%

Effect of flow on the resistance of modelled femoral artery stenoses

Dodds

Bourne

Chant

1996

Journal of British Surgery

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An accurate model of the pressure-flow relationship of a stenosis is necessary for the correct interpretation of haemodynamic measurements. Modelled femoral artery stenoses were tested in vitro and the pressure drop: flow ratio (resistance) was most accurately represented by a fixed component (Rf) combined with a variable component (Rv) that increased linearly with flow (Q) such that Rv = SvQ. For stenoses of 68-94 per cent area, Rf increased from 3.2 to 77.7 milliperipheral resistance units (mPRU), while Sv increased from 0.009 to 0.578 mPRU ml-1 min and Rv was dominant for physiological flow rates. It was concluded that the approximation of a significant stenosis to a fixed resistance is incorrect.

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The values of series and parallel resistances in steady blood-flow

Cited by 18 publications

References 14 publications

Effects of Local Vasodilatation on Blood Flow through Arterial Stenosis

Effects of Local Vasodilatation on Blood Flow through Arterial Stenosis

The effect of variations in heart rate and regional distribution of blood flow on the normal pressor response to diving in ducks

Effect of flow on the resistance of modelled femoral artery stenoses

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