LECTURE 11 (Hemodynamics) Flashcards by Nerisse Rogador

What is the difference between Total pressure and Stagnation pressure?

Total pressure = the sum of the static, dynamic and hydrostatic pressure

Stagnation pressure = the sum of the static and dynamic pressures

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What does Velocity of flow depend on?

Flow rate (inversely proportional)
Radius (inversely proportional to radius to the power of 4)

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How do you calculate Velocity?

Velocity = Flow rate / Cross-sectional area

Explanation: velocity is greater when the radius is smaller

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What are the two components of the pressure exerted by moving fluid?

A dynamic, flowing component that represents the kinetic energy of the system
A lateral component that represents the hydrostatic pressure exerted on the walls of the system

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What happens in a system in which fluid is flowing?

Pressure falls over distance as energy is lost because of friction

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What is fluid characterised by?

A complex molecular structure that is considered as a continuous complex of excessively small particles

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What is a current curve?

Curve in fluid flow where the tangent, drawn at each point of it, has a direction of fluid particle velocity at this point called a current curve

[current curve’s location at any given time represents the distribution of fluid particles at this time]

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What is an Ideal fluid?

Fluid that is not characterised by viscosity and constriction

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When can a fluid be considered as “Ideal”?

When external forces exerting on the fluid are excessively greater than internal viscosity forces in fluids, the internal viscosity forces could be ignored in comparison with external forces and fluid can be considered as ideal

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Describe Real fluid molecules

Real fluid are characterised by internal friction (viscosity) while moving and interact with some force -> Individual fluid layers interact with each other by forces that are directed along tangent to surface -> called “INTERNAL FRICTION FORCES” while the event is called “INTERNAL FRICTION”

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What is a current tube?

A closed contour in fluid where current curve passes at each point and the system of curves limits some part of space

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What happens when fluid flow is stationary?

Current tube surface is not intersected by fluid flow particles and fluid flows like in a solid tube

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What is the Fluid jet stationary equation?

Sv = constant

[At any point, for any cross-section of a current tube, Sv product is constant value]

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When is Fluid flow considered stationary flow?

If velocity of any points of it is not changed with time

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What is Bernoulli’s equation?

As the speed of a moving fluid increases, the pressure within the fluid decreases

P+ ρgh+ ρv2/2 = constant

Equation when the fluid flows in a horizontal tube
P+ ρv2/2 = constant

P - hydrostatic/static pressure
ρv2/2 - dynamic pressure

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What is the main equation of hydrodynamics?

Bernoulli’s equation

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Sum of static and dynamic pressure is called a _________ ____________

Full pressure

Describe dynamic non-vicious fluid in a horizontal tube

Pressure is greater where velocity is less

What are the properties of viscosity?

Describes a fluid’s internal resistance to flow (measures fluid friction)
Viscosity forces between fluid layers are directed against motion
(after termination of influence of pressure forces, fluid velocity is gradually decreased and finally fluid stops moving)
All real fluid have some resistance to stress except for Ideal fluids/Inviscid fluids

The study of viscosity is known as ____________

Rheology

Viscosity coefficient fluid can be divided into which groups?

Newtonian fluids (water, melted metals and their salts low molecular organic compounds etc)
Non-Newtonian fluids (suspensions, emulsions, high molecular organic compounds)

Describe Laminar flow

Sliding without mixing with each other
Fluid particles move in parallel of tube walls
Do not remove from one layer to another
Fluid velocity is constant value at any point of fluid
Velocity of fluid layers adjacent to tube walls is MINIMAL, velocity in center is MAXIMUM

When is Flow laminar?

Only when fluid flow velocity (V) under all the other constant conditions is less than its critical value (Vc)

[When fluid flow velocity is GREATER than the critical value, it is TURBULENT FLOW]

Describe Turbulent flow

Fluid motion cannot be considered as a motion of sorted layers
The layers mix with each other
Fluid particle trajectories are not parallel tube walls
Certain point of fluid flow velocity is not constant -> changed chaotically, without any order

Flow character is significantly dependent on viscosity and density and is defined as ____________________

Reynold's number (R)

What is Reynold's number?

A number used in fluid mechanics to determine whether fluid flow is laminar or turbulent R= 2ρvr/ η r - tube radius v - main velocity of flow motion ρ - density R < 2000 is laminar flow R > 3000 is turbulent flow 2000 < R < 3000 is transitional

What is Reynold's number a criterion of?

Similarity of fluids flow Explanation: two different kinds of fluids have completely same character when their Reynold's numbers equal each other despite them having different values of viscosity, density flow velocity and tubes radiuses

Describe viscose fluid flow in a horizontal tube

If viscous fluid equally flows in a tube -> distribution of fluid particle velocities along the radius will be the same at any segment at points that are equally far from the center -> along central axis, flow velocity is GREATEST -> layer attached to tube surface is STATIC

What is Poiesuille's formula?

V = πR4ΔP/8lη - If tube length, radius and P1 and P2 are not changed, fluid volume that passes the tube in time unit is increased disproportionately of viscosity - Fluid stream intensity is increased with the increase in radius - Only works with laminar flow

What happens during heavy exercise?

The amount of blood pumped by the heart increases -> increases the average blood velocity -> critical values for Reynold's number will be reached even for the blood flow in the main arteries which will cause turbulences

What can Stoke's law calculate?

The resistance forces on red blood cells and other formed blood elements

What is Stoke's law?

The motion of a small spherical object in vicious fluid and the resistance forces which influences on their movement F= 6πrην η - dynamic fluid viscosity r - radius v - velocity INDICATIONS: - the greater the resistance force influencing the blood cell is, the greater its radius and movement velocity is - erythrocyte deformation degree is increased with increase in flow velocity

What is formation of erythrocytes aggregation carried out by?

- Formation of intercellular bridges between side amino acid residuals on the surface of aggregated cells - Creation of an osmotic gradient around erythrocytes

What does blood being a Non-Newtonian fluid mean?

Blood flow velocity in narrow capillaries is determined by the ability of erythrocytes deformability

What is the Fahrraeus-Lindqvis effect?

An effect where the viscosity of a fluid changes with the diameter of the tube it travels through

What does the Fahrraeus-Lindqvis cause?

- Distribution of various type of blood cells in blood vessels by size (speed is maximal in the center of the vessel) - Large blood vessels erythrocytes concentrate in central part of the vessel -> blood viscosity dependent on hematocrits is increased in the center of blood vessel and decreased at vessel walls

What is Vessels impedance to blood circulation largely dependent on?

- Vessel length - Diameter

What happens when stream flows through resistant tube?

Resistance absorbs energy -> work is performed against resistant forces -> decrease in pressure along with increase in vessel length

Describe blood vessels

Blood vessels have elastic walls which have the tendency to contract -> vessels may collapse due to wall tension CONTAINS - endothelium - elastic tissues - rebounds - smooth muscles - fibrous tissue

What is the difference between artery, vein and capillary?

- Artery = mainly consisting of elastic fiber - Vein = gelatinous fiber - Capillary = inner membrane

What is the Glycocalyx?

Surface of endothelia cells is lined with Glycocalyx which consists of glycoproteins, glycolipids, proteoglycans and proteins FUNCTION: Protection of vessels endothelial from collision of other forming elements of blood as well as from adhesion