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41 Cards in this Set
- Front
- Back
Pressure
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the force applied or distributed over a surface as force per unit area
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Pressure equation
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P= F/A
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2 Sources of Force
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1. force of gravity
2. Energy within atom or molecule (kinetic molecular theory) |
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Units of force
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Newton
N = kg m/s squared |
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1 mmHg = ? cm water
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1mmHg = 1.36 cm water
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Absolute pressure
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Gauge pressure + Atmospheric pressure
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Gauge pressure
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what the gauge states
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Flow
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the quantity of a fluid (gas or liquid) passing a point in unit time
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PRESSURE represents what type of energy
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Potential or stored energy
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FLOW represents what type of energy
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Kinetic energy (energy of motion)
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Flow equation
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F = Q/T
Q = quantity (mass or volume) T = time |
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Laminar Flow
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- occurs in smooth tubes
- occurs at low flow rates - Flow is greatest at the center & approaches zero at the walls - there must be a pressure gradient across the ends of the tube - linear relationship between Pressure and Flow - increase polarity increases viscosity |
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In Laminar Flow there is a linear relationship between:
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Linear relationship between Pressure and Flow
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In Laminar Flow what is the key factor
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Viscosity
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Viscosity
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- a measure of a liquid's resistance to flow
- the greater the viscosity, the greater the interaction between adjacent fluid layers so there is decreased flow |
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Poiseuille's Equation relationships
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Flow is directly proportional to Pressure
Flow is inversely proportional to Viscosity and Length of tube |
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According to Poiseuille's Equation if radius doubles what happens to flow?
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If radius doubles than Flow Increases by 16 times
- (diameter is radius doubled) |
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The greatest role in determining the rate of flow thru a vessel
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radius or diameter of the blood vessel plays the most important role in determining the rate of flow
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2/3 of systemic vascular resistance is due to what?
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is due to blood flow in the smallest arterioles ranging diameter from 4-25 micrometers
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OHM's Law (Equation)
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Q = (P1-P2)/R
R = (P1-P2)/Q |
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What does OHM's Law allow us to do?
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it allows us to calculate SVR and C.O.
- use this law to describe blood flow through a vessel |
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Turbulent Flow
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- molecules travel in nonparallel paths leading to eddy currents
- occurs at points of constriction causing increased fluid velocity - Non-linear between Flow and Pressure - Pressure is approximately proportional to the square root of the flow rate - Occurs with increased or variable Velocity - Density is the important property - greater resistance than for laminar flow at the same flow rate |
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In Turbulent Flow what is the important property
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Density is the important property in Turbulent flow
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Reynold's Number
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Determines if the flow is laminar or turbulent
- relates ratio of density of a gas to its viscosity |
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Reynold's Number Equation
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Re = 2rvd/n
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Critical Flow rate
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Change from Laminar to Turbulent flow
- depends on velocity of gas which... - depends on volume flow and diameter of tube |
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Critical Flow is defined by what?
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Defined by the gas and temperature
- with warming of anesthetic gases as they enter the airway, the critical flow rises due to the decreased density from increased temperature |
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Examples of Laminar Flow
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- Quiet breathing
- Blood flow except at bifurcations |
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Examples of Turbulent Flow
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- Coughing, speaking, deep breathing
- Increased secretions - Carotid stenosis |
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Heliox
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clinical use of density and viscosity to decrease resistance to flow
- used in acute, sever airway obstruction: subglottic edema, foreign bodies, tracheal tumors - Only Helium has a lower density to viscosity ratio |
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Bernoulli's Law
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when liquids flow through a tube, a pressure is exerted against the sides of the tube. The faster the flow rate, the less side pressure is generated. If the pathway is varried in cross-sectional area, forward velocity is FASTEST and side pressure is LEAST at the point of greatest constriction
- rational behind Venturi's Priniciple |
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Venturi's Principle
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pressure is lowest at area of constriction d/t fast flow in the middle and when there's a pressure decrease than air can be entrained from outside
- how nebs and venturi masks work |
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Jet Ventilation
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used in upper airway lesions in OR.
- inhalation is by pressing toggle and expiration is passive. - measure ventilation by O2 sat and chest rise |
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Tension
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a tangential force in Newtons/meters acting on a length of the wall.
- caused by the smooth muscle and elastic tissue - balance between tension and the fluid pressure inside the tube to prevent it from collapsing or distending |
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Law of Laplace for a tube or cylinder
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P = Tension/Radius
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Law of Laplace for a sphere
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P = 2 Tension/Radius
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transmural pressure (hydrostatic pressure)
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pressure that distends the tube
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Explanation of Law of Laplace
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- explains how aorta can sustain high pressures and how capillary with much smaller radius can also sustain pressure of 100mmHg
- Tiny, thin-walled capillaries can withstand surprisingly large pressures because of their tiny radius - aorta has elastin, collagen, and smooth muscle where as capillaries only have elastin and collagen |
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What happens to the wall tension required to sustain a developing aortic aneurysm when the radius increases from 2cm to 3cm
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Tension Increases with Increased Radius to be able to withstand pressure
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Law of Laplace regarding Aneurysms
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Wall tension is proportional to vessel radius for cylindrical vessels. Approaching a spherical shape gives less tension than the same radius cylinder, but continued expansion produces wall tension exceeding that of the original cylinder
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Law of Laplace regarding blood pressure measurements
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- as the distended heart fails the radius increases and the pressure falls unless the muscle contracts proportionally more forcefully
- as distended heart fails the radius increases |