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Important Measures of Flow
pressure, P, – force/area, usually given as mmHg or kPa
volume, V or q, given as liters or some fraction
particle velocity, v, given is m * s-1
Volume velocity, , given as liters/sec or minute
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Poiseuille’s Equation
Valid for established laminar flow.
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Work and Energy
Pressure is a measure of energy per volume
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Laminar and Turbulent Flow
In turbulent flow:
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Reynold’s Numbers and Turbulent Flow
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(a) high velocity,
(b) large diameter and
(c) low viscosity.
Factors that favor Turbulent flow
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Viscosity (η)
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Anomalous Viscosity
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Particle Velocity in Newtonian Solutions
If we consider tubes in series such that volume velocity is the same in each (steady-state) then:
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Pressures and Flow
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Blood Vessel Dimensions:Exchange vs. Transport Vessels
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Law of Laplace
Blood Vessel Wall Tension and Stress
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Tissue Composition of Blood Vessels
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"Blood vessels-en" by Kelvinsong - Own work. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Blood_vessels-en.svg#/media/File:Blood_vessels-en.svg
Blood Vessel Structure
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Capillaries
"2104 Three Major Capillary Types" by OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013.. Licensed under CC BY 3.0 via Commons - https://commons.wikimedia.org/wiki/File:2104_Three_Major_Capillary_Types.jpg#/media/File:2104_Three_Major_Capillary_Types.jpg
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Capacitance and dP/dT
This model is a bit unrealistic because it only considers compliance….
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Flow Relationships in Different Vessels
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Control of Microcirculation
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Control of the Peripheral CirculationCentral Control
Control at the arteriole and venule level -- vasomotion of smooth muscle components of vessels
Adrenergic
• α1: vasoconstriction in skin, GI, coronary, kidney and brain
• β2: vasodilation of small coronary & sk mus arteries
Cholinergic -- M3 muscarinic receptor on vascular endothelial cells causes synthesis of NO that leads to vasodilation of smooth muscle
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Local Control
Metabolites: H+, lactate, CO2 -- vasodilators
Adenosine, some prostaglandins are potent vasodilators
UTP and others are potent vasoconstrictors
Autoregulation -- changes in vasomotor tone in response to stretch induced by upstream/downstream changes in blood pressure
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Local Control in the Brain’sPericytes
Peppiatt et al., Nature 2006 v443 p 700
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Hydrostatic Filtration in Capillaries and the Formation of Interstitial Fluid/Lymph
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Filtration: The Starling Hypothesis
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Filtration in Capillaries
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"2108 Capillary Exchange" by OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013.. Licensed under CC BY 3.0 via Commons - https://commons.wikimedia.org/wiki/File:2108_Capillary_Exchange.jpg#/media/File:2108_Capillary_Exchange.jpg
Another View
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Large-scale Influences on Blood Flow
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Mean Arterial Pressure
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Mean Arterial Pressure and SV
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Total Peripheral Resistance
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End-Resistance and Pressure
Note greater filling with higher R.
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Changes in Capacitance
Remember -- low capacitance is high elastance
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Capacitance and ΔP/ΔT
1.
2.
So:
The rate at which pressure changes is directly proportional to the volume flow and inversely proportional to the vessel capacitance.
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Vessel Compliance and Age in Humans
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Resistance/Capacitance Considered Together When we consider compliance (capacitance) and resistance, the way we need to look at in arteries is different than how we looked at it in electrical circuits.
The crucial consideration is that arterial compliances have both and inflow and outflow.• Inflow is largely determined by stroke volume – resistance at this end is usually
constant.• Outflow is determined by resistance of the arterioles, which can change rapidly.
With a constant stroke volume, what is the effect of an increased peripheral resistance on dP/dt in the arteries? Of decreased capacitance?(Note that increased peripheral resistance and decreased capacitance often go together in vascular disease.)
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Hydraulic Filtration in the Arteries
What is the effect of reduced peripheral resistance on filtering?
Non-patent valve? Reduced capacitance?
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The Effect of Arterial Compliance on the Work of the Heart
(From pump to vessel)