Hemodynamics Flashcards
What is hemodynamics
The study of blood flow. Fluid flows from a high energy state to a low energy state. From the left heart (120 mmHg)to the right heart. ( veins
Energy & Pressure
There must be a pressure difference for blood to flow. Energy is lost during flow due to friction (heat). Total fluid energy never changes though.. May just end up in a different shape or form.
Name the three types of flow (Q)
Plug
Laminar
Turbulent
Plug Flow
Aorta exiting the heart. Entrance to a large vessel. Flow is all traveling the same speed.
Laminar Flow
MOST COMMON. Friction causes RBCs adjacent to vessel walls to be slower than the flow in the center.. Fastest flow in the center of the vessel.
Turbulent Flow
“chaotic” flow. Flow is going all over the place. Occurs with large vessels and Hugh velocities, distal to an obstruction lesion or stricture and within a ‘kink’ or sharp turn within a vessel. Commonly from PLAQUE.
Reynold’s Number
Quantitate the degree of turbulence. Reynold’s number >2000usually results in turbulence
Bernoulli’s Law
You have the same amount of total energy, but it might be in a different form. As VELOCITY INCREASES–>PRESSURE DECREASES!
TriangleP= 4v squared.
Poiseuille’s Law
The amount of flow (Q) is dependent on:
The PRESSURE differential, the RADIUS of the vessel, the LENGTH of the vessel, the VISCOSITY of the blood. Radius is the most significant factor.
Poiseuille’s Law
Differential in Pressure:
The higher the pressure gradient, or difference, the more flow there is. If there is no difference then there is no flow!
Poiseuille’s Law
Length of vessel
The longer the vessel the greater the amount of energy loss due to friction. Shorter vessels have more flow at the end due to less energy loss.
Poiseuille’s Law
Viscosity
Units: kg/m-s or poise. One poise =1g/cm-s
Blood is thicker then water. Have has a higher viscosity, so it would have less flow than water, which is very thin. Thicker blood= slower flow.
Poiseuille’s Law
Radius
Volume of flow equals the fourth power of the radius. Even a small change in radius results in a significant change of flow. Decreasing the radius by half causes a 16 fold decrease in flow.
2(to the fourth power) = 16
Resistance
Occurs through friction. Most of the arterial resistance occurs at the level of the arterioles. Vessels IN-SERIES (lined up/connected) have more resistance then vessels IN-PARALLEL. Increase resistance by decreasing vessel radius, increasing vessel length, and increasing viscosity.
Poiseuille’s Law
Assumes:
Rigid pipe with no curves or bends, has constant viscosity & fluid has constant rate. Anything that increases friction decreases flow.
Q=VA–> increase velocity or increase are = increased flow
Friction
RBCs rubbing against the sides of the vessels causes heat. Anything that causes more contact with the vessel walls increases friction, and therefore heat, and therefore RESISTANCE.
Smallest area equals ______ pressure & ______ velocity
Lowest pressure & highest velocity
How a stenosis affects flow
Blood has to speed up to get through narrowed channel. There is a pressure drop within the stenosis due to the increased velocity. Distal to the turbulent area the diameter is the same as the pre-stenotic area. Then velocity slows down & the pressure increases. Distal to the point of narrowing = turbulence.
Flow Separation
Occurs at or distal to bifurcations and at areas of flow disturbances such as plaque, stenosis, etc. large angle btw the main flow & the vessel wall. SHEAR EFFECT.
Inertia loss
Dividing of vessels causes _____ _____.
Inertia loss. Slows the blood down until the capillaries, where it needs to be slow. Constant flow.
A __% reduction in area corresponds to a __% diameter reduction in the presence of circumferential stenosis.
75% area, 50% diameter.
2 or more stenotic lesions that occur in a series have a more significant (negative) impact downstream than 1 single lesion.
Phasicity
Multiphasic
Indicate higher resistance vessels. Resting leg
Shows a pulse … Straight line… Shows a pulse. Just systole flow.
Phasicity
Monophasic
Low resistance downstream. Always abnormal in (resting) lower extremity.
Distal arterioles dilate to increase oxygen to segment. Changed bed to low resistance.
Tardus Parvus
Signifies significant disease proximal to point of sampling. Delayed upstroke (acceleration) from proximal obstruction.
“you’ve already missed it”
Effects of Collaterals
Blood flow increases in branches to compensate for disease in main vessel. The net flow may be normal if collateral network extensive enough. Collaterals form over time in response to severe disease/obstruction.(not in acute)
Steady Flow
At the capillary level, there is n pulsatility. Steady flow through capillaries is essential for exchanging nutrients.
Hydrostatic Pressure
The amount of force measured in a vein. It is the effect of gravity on the blood. Changes with blood density, acceleration due to gravity, and distance (height) from the heart. The weight of the blood itself affects all the blood below it. The right atrium is the reference point where the hydrostatic pressure = 0. Superior to right atrium is a Negative pressure. Anything inferior to the right atrium is a Positive pressure.
When supine the HP = 0 b/c everything is level.
Transmural Pressure
Low transmural pressure when supine keeps the veins elliptical-shaped. When standing Transmural pressure increases. Vein looks more like a circle.
Flow goes from—>
High pressure to low pressure
According to Bernoulli…
Pressure & velocity are inversely related
What is the type of flow that has the slowest flow towards the edge of the vessel, progressively increasing in velocity towards the middle of the vessel?
Laminar
Poiseuille’s Law states:
Radius is the most significant factor in determining flow.
The law that states an object at rest will stay at rest is…
Principle of inertia
Blood makes it back to the heart because
Venous Valves
3 ways blood fights gravity to get to the heart:
Intrathoracic pressure changes
Venous valves
Calf-muscle pump
