Respiratory Path III Dr Rotimi Adigun Hemodynamics, Vascular disturbances.
Chapter 5.9 Vascular Function Hemodynamics
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Transcript of Chapter 5.9 Vascular Function Hemodynamics
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Chapter 5.9: VASCULAR FUNCTION: HEMODYNAMICS
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The circulatory system uses four major physical principles:
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Flow is driven by a pressure difference.
The total mechanical energy is:
The total equivalent pressure is:
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Fig. 5.9.1 Difference between lateral and end pressure
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Fig. 5.9.2 The Bernoulli principle
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Compliance describes the relation between pressure and volume
The compliance of the veins is much greater than the compliance of the arteries.
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Ejection of blood into the arterial tree cause the arterial pressure pulse.
The pulse pressure depends on the stroke volume and arterial compliance.
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Fig. 5.9.3 Proximal arterial pressure pulse
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Fig. 5.9.4 Relation between pressure pulse and stroke volume
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Diastolic pressure plus one-third pulse pressure estimates mean arterial pressure.
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Fig. 5.9.5 Effect of decreased compliance on pressure pulse
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Fig. 5.9.6 Changes in the pressure pulse from proximal to distal arteries
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Fig. 5.9.7 Estimationof blood pressure bysphygmomanometry
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Fig. 5.9.8 Pressure profiles in the systemic and pulmonary circulation
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Poiseuille’s Law approximately describes flow in the vasculature.
Assumptions for Poiseuille Flow:
• the fluid is Newtonian (viscosity is independent of shear rate)
• flow is laminar
• no “slippage” at the walls
• tube is cylindrical with circular cross section, parallel walls
• the walls of the tube are rigid
• the tube is long compared to the entrance length
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Fig. 5.9.9 Entrance effects in establishing Poiseuille flow
Poiseuille flow has a parabolic velocity profile:
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The ratio of P to Q defines the vascular resistance:
This is analogous to Ohm’s Law:
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Resistances in series add:
Resistances in parallel add inversely: