Flashcards in Physics Quiz #4 Deck (59):
Both liquids and gases are fluids?
What are the forces associated with fluids(3)?
What is friction?
-the resistance to flow from the surface interaction
-it is proportional to viscosity
What is viscosity?
The inherent property of a fluid that resists flow
What is the result of pressure forces in a fluid established by differences in pressure from one point to another, which creates a pressure gradient?
-all flow moves from higher pressure, or resistance to lower
What is Laminar flow?
a type of flow which all molecules of a fluid travel in a parallel path within the tube
Which molecules in laminar flow encounter the least adhesive force of the walls of the tube?
molecules in the center of the tube
Molecules in the center of the tube move at a velocity twice that of the mean flow?
True laminar flow predominates in the smallest airways(terminal bronchioles)?
What is transitional flow?
a mixture of laminar flow along the walls of the tube with turbulent flow in the center
What is turbulent flow?
described as chaotic with irregular eddies throughout
Which law is described: In straight circular tubes, the radius will have the most dramatic effect on flow = constancy X Radius to the 4th power(r^4) X pressure gradient
According to Poiseuille's law, doubling the radius will result in_____-fold increase in flow; tripling of the radius increases the flow by_____-fold?
Resistance is inversely proportional to r^4(the greater the radius, the smaller the resistance).
When the radius of a tube is tripled, how much will the resistance decrease?
Resistance is directly proportional to fluid viscosity(the greater the blood viscosity, the greater the resistance).
Resistance is directly proportional to tube length(the longer the tube, the greater the resistance).
How are flow and resistance related?
-flow through a tube is inversely proportional to resistance
-if resistance doubles, flow is halved
-if resistance is halved, flow is doubled
Whose law is described: When considering flow through a tube, the gradient in hydrostatic pressure(inflow pressure minus outflow pressure) equal flow times resistance.
Whose law is described: MAP-CVP = CO x SVR or SVR = (MAP-CVP)/CO x 80
What happens to flow and what happens to resistance when the radius of the tube increases? When radius of the tube decreases?
-When the radius of a tube increases, resistance to flow decreases and flow increases
-When the radius of a tube decreases, resistance to flow increases and flow decreases
Is flow through 16 gauge IV catheter greater or lesser than through a 20 gauge catheter?
-the greater the radius, the more flow
What happens to fluid flow if viscosity is increased?
Patients with polycythemia have ___ blood flow due to ___ viscosity of blood. Patients with anemia have ___ blood viscosity, hence ___ flows through tissues.
Polycythemia = decreased, greater
Anemia = decreased, greater
How will flow be affected when length of a tube increases? If the length of tube is decreased by 50%? If the length of a tube is doubled?
-flow will decrease
-flow will double
-flow will be decreased by half
If the radius of a tube decreases to 1/3 of its original size, flow will decrease to 1/81 of its original value?
Which of the following will decrease peak inspiratory pressure? 1. change ETT from 8.0 to 6.0 or 2. change ETT from 6.0 to 8.0?
changing ETT from a 6.0 to a 8.0 will decrease the PIP, PIP is greater when inflow resistance is higher and vice versa
These interventions are a direct manipulation of whose law: To improve flow when delivering a unit of PRBC's a large-diameter IV catheter is recommend, a pressure bag may be placed on the unit of PRBCs to increase the driving pressure(pressure gradient) and the PRBCs may be diluted with normal saline to lower viscosity.
Which factor will have the most dramatic improvement on flow: increasing the pressure, thinning the liquid(less viscous), shortening the tube, or increasing the diameter of the IV catheter?
increasing the diameter of the catheter
Identify 3 conditions that can change laminar to turbulent flow during anesthetic administration.
1. Gases changing direction(bend in tube of more than 20 degrees)
2. increased velocity
3. rough walled(corrugated) tubes
This is used to predict when flow through a cylindrical tube changes from laminar to turbulent.
Reynold's number states that resistance to flow increases when flow becomes turbulent.
What is the formula for Reynold's number(Re)?
Re=(fluid velocity x fluid density x tube diameter)/fluid viscosity
When Reynold's number exceeds 1500-2000, flow changes from laminar to turbulent
When flow is turbulent, density(p), not viscosity(n), determines flow.
Identify the Reynold's number at which laminar flow changes to turbulent flow.
> 2000, flow changes from laminar to turbulent
When density is large, Re is ___?
When viscosity is large, Re is ___?
Viscosity is a determinant of gas flow when flow is laminar?
-flow is inversely proportional to viscosity(the greater the viscosity, the lower the flow) when flow is laminar(non-turbulent).
What property of a gas determines gas flow rate through a variable orifice flow meter at low flow rates?
-flow through a variable orifice flow meter is laminar when flow is low, so flow is inversely proportional to viscosity
What property of gas determines gas flow rate through a variable orifice flow meter a high flow rates?
-With high flows, flow through a variable orifice flow meter is turbulent and flow rate is inversely proportional to gas density.
Delivery of which mixture to status asthmatics patients who are refractory to standard treatments, will help in reestablishing laminar flow through airway: delivery of He/O2 mixtures, or delivery of N2O/O2 mixtures?
Helium, which has a significantly lower density than nitrogen, improves flow by restoring laminar flow through the significantly narrowed airways of a severe asthma attach.
Describe Orifice Flow.
- a type of turbulent flow
-occurs at severe constrictions, such as a nearly closed larynx, trachea, or kinked ETT
-can occur when the diameter of tube is greater than the tube length.
What is Bernoulli's Principle?
-describes the effect of fluids(liquids and gases) flow through a tube containing a constriction
-as flow passes through the narrowing in a tube, the velocity of that flow increases
What is the Venturi effect?
-as with a funnel, the velocity of the fluid increases as the cross sectional area decreases, with the static pressure correspondingly decreasing
-by placing the orifice at the narrowed region of flow, air is allowed to be entrained and to enter the flow
-air may be entrained into a flow of liquid, or a liquid may be entrained into a flow of gas
Venturi extended whose work? What observations did Venturi make?
-Venturi extended Bernoulli's work on the relationship between the velocity of flow of a fluid and the lateral pressure exerted on the wall of a tube.
-the lateral pressure exerted by a fluid(gas or liquid) going through a tube of varying diameter is lowest at the narrowest part, where velocity is greatest
What is LaPlace's Law?
-describes the relationship of wall tension(T) to pressure(P) and radius(r) in cylinders(blood vessels, left cardiac ventricle) and spheres(alveoli with and without surfactant)
-the internal force generated by a structure
-a linear force
-a force directed along a straight line(formulas to calculate tension vary between cylinders and spheres)
What is LaPlace's law and cylindrical calculation for Tension?
As a cylinder expands(the radius increases), the tension(force) in the wall of the structure increases
Tension(T) = Pressure(P) x radius(r)
Is an aortic aneurysm more likely to rupture than a normal segment of aorta?
yes, because the radius is larger, it increases the tension in the wall to the "breaking point"
What vessel can withstand a pressure of 100 mmHg better; a capillary or a vein?
-it has a tiny radius compared to a vein
-the tension in the wall of the capillary is extraordinarily smaller than that of a vein
The law of LaPlace states that the tension in the left ventricular wall of the heart is increased when filling is increased?
-the greater the filling, the greater the tension
-since the left ventricular wall has a substantial thickness, the law of LaPlace is modified to account for wall thickness(h)
What is LaPlace's calculation for spherically-shaped structures, such as alveoli?
-in spheres, wall tension is increased twice as much, with increasing radius compared to cylinders
P x r = 2T or T= (P x r)/2
When do you need more pressure to blow up a ballon?
when the ballon is small
For alveoli that are deficient of normal surfactant(as well as for a plastic ballon), wall tension is content and independent of radius?
-because tension in the wall is independent of size, the pressure inside the surfactant-deficient alveoli will change with size
Pressure is greater in the larger alveoli than the smaller alveoli?
-according to LaPlace, if two alveoli have the same surface tension, the smaller sphere will have higher pressure
Smaller alveoli empty into larger alveoli causing atelectasis in patients with ARDS and premature neonates who are deficient of surfactant?
For alveoli with surfactant(the normal situation), tension increases with increases in radius?
-because alveolar will tension increases in proportion to increases in radius, the pressure within the alveolus does not change