Lecture 7

# Lecture 7 - NPB113 Hemodynamics 7-1 Outline Relationship...

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1 January 24, 2010 NPB113 Hemodynamics 7-1 Outline Relationship between Pressure and Flow. What determines pressure in a vessel or a chamber? Capacitance, compliance properties of the vascular system. Affect of changes in length, viscosity, and radius on vascular resistance. Fahreus-Lindqvist Effect – Affect of Radius on Blood Viscosity Parameters that affect radius in the vascular system – relative effects on arterioles, and venules and small veins. Sympathetic neural affects Affect of local metabolites and metabolism. Local control through endothelial derived vasodilator and vasoconstrictor substances. (nitric oxide, endothelin, angiotensin, prostaglandins, and bradykinins) Laminar Flow versus Turbulent Flow

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2 January 24, 2010 NPB113 Hemodynamics 7-2 Relationship between Pressure & Flow General Relationships Q = P 1 – P 2 R Q = π (P 1 – P 2 )r 4 8 η l Poiseuille’s Law Q = Flow r = radius η = Viscosity of Fluid (ratio of Shear Stress:Shear Rate) l = length Resistance = 8 η l π r 4
3 January 24, 2010 NPB113 Hemodynamics 7-3 What Determines Pressure in a Vessel or Chamber? Pressure determined by 1. Capacitance & compliance of the vessel or chamber – its holding capacity 2. Volume contained within the capacitance. P = Volume Capacitance Problem . 10 ml volume change in two vessels. One is stiff with a small capacitance. The second vessel is a very compliant, large capacitance vessel. Compare the effect of this volume change on the change in pressure for the two vessels.

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4 January 24, 2010 NPB113 Hemodynamics 7-4 Compliance – Capacitance Properties of Vessels in the Vascular system & Pressure in These Vessels Arterial system – conduit system. Arterioles resistance vessels in vascular system. Capacitance, compliance small, 1/20 th that of venous system Capacitance – fixed, changes minimally. Therefore, pressure in arterial system determined primarily by volume. Volume determined by rate of flow into arterial system and rate of flow out of arterial system. Capillaries
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Lecture 7 - NPB113 Hemodynamics 7-1 Outline Relationship...

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