# pressure, flow, and tension

 .remove_background_ad { border: 1px solid #555555; padding: .75em; margin: .75em; background-color: #e7e7e7; } .rmbg_image { max-height: 80px; } What is pressure? force applied or distributed over a surface as force per unit area What is the formula for pressure? P=F/A What is a Newton? unit of force, N= kg m / s2 =units of accel / units of time What are sources of force? 1) gravity2)energy within an atom or molecule (kinetic molecular theory) Will a more dense substance exert more or less pressure? more How much more dense is Hg than water? 13.6 x more dense than water, so it exerts more force What is the SI unit of pressure? the Pascal How to pascals and newtons relate? 1 Pa = 1 N What are the different units of pressure and their conversions? 1 atm = 760 mmHg = 760 torr = 14.7 psi = 101 kPa 1 mmHg = ___ cm water. 1 mm Hg = 1.36 cm water Explain how a Bier block works. If the force is constant and the area increases, what will happen to the pressure? It will decrease. What is the toxic dose of lidocaine when NOT used with epi? 4 mg / kg When talking about pressure, force, and area with a syringe, what constitutes the "area"? Area is the cross sectional area of the syringe plunger If exerting the same amount of force, would a 5 cc or a 10 cc syringe exert more pressure? the 5 cc syringe What can occur if pressure points aren't padded and why? Ischemia to extremitiesIf pressure is greater than SBP (remember BP likely to be low during surgery), no blood flow What is the gravitational force? 9.81 N What is ischemic optic neuropathy? Pt prone during laminectomy (for example), pt can loose circulation to optic nerve and become blind. What is gauge pressure? Pressure on the gauge. What is absolute pressure? gauge pressure + atmospheric pressure What represents the kinetic energy of fluids? flow; kinetic energy is energy of motion Is pressure considered potential or kinetic energy? potential What is the total mechanical energy of a moving fluid? sum of kinetic energy (flow) + potential energy (pressure) What is the equation to calculate flow? F= Q/ t F= mean flowQ= quantity (mass or volume)t= time What is laminar flow? Occurs in smooth tubes, low flow rates, needs a pressure gradient to have flow In laminar flow where is flow greatest and where is it least? greatest in center of tubeleast at the walls What is the relationship btw pressure and flow in laminar flow? linear What is the key factor in laminar flow? viscosity (resistance to flow) What is turbulent flow? Nonparallel paths of travel, eddy currentsoccurs at points of constriction How are flow and pressure related in turbulent flow? flow is proportional to square root of the pressure What is a key factor in turbulent flow? density At the same flow rate where is resistance higher, laminar or turbulent flow? turbulent flow has greater resistance What is Reynold's Number? determines if flow is laminar or turbulent What is the formula for Re #? Re = 2rvd / n r= radiusv= velocityd= densityn= viscosity What does Re > 2000 mean? turbulent flow What does Re < 2000 mean? laminar flow What is critical flow? the change from laminar to turbulent flow; depends on velocity of gas which depends on volume of flow and tube diameter, depends on the gas, and on the T (as this can change density) Why are anesthetic gases likely to have laminar flow for longer? Anesthetic gases warmed as enter the airway, as T increases, density decreases, and critical flow increases (less likely for Re # to reach 2000 and for critical flow to occur) In what vessels would turbulent flow be likely to occur in? PA and aorta which benefit from pulsatile flow and high velocity blood flow Does turbulent flow usually occur in small vessels? No as the Reynold's Number is almost never high enough to cause turbulence What are clinical examples of laminar flow? quiet breathing, blood flow except at bifurcations What are clinical examples of turbulent flow? coughing, speaking, deep breathing, increased secretions, carotid stenosis (manifests as bruit) What is the formula for Poiseuille's equation? (Q) flow = Pi (P1-P2) r4 / 8 nl n= viscosityl= lengthr= radius What does the Hagan-Poiseuille's equation tell us? that changes in vessel size, airway, and IV catheter size can influence flow significantly Poiseuille's equation only applies to laminar flow, T or F? T! What happens to blood flow when radius doubles? Flow rate increases 16 fold! What is another name for flow rate? Conductance What is the driving force moving blood thru the vessel?  What opposes it? Pressure gradient Resistance What is Ohm's Law? R = change in P / Fresistance = change in P / flow What is a clinical application of Ohm's Law? Calculating CO or SVRCO = MAP-CVP / SVR What is a benefit of using Heliox? Uses density and viscosity to decrease resistance to flowWhen giving He mixed with O2, it decreases the pressure needed to deliver the O2 When might you use Heliox? subglottic edemaforeign bodiestracheal tumorasthma Why can Heliox effectively deliver O2 in cases of severe turbulent flow? It has a very low density / viscosity ratio What is Bernoulli's Law? applies to a neb or venturi mask; at the point of constriction, forward velocity is greatest and pressure is least, negative pressure is created, and this allows it to draw air or fluid in (RA is entrained) What is jet ventilation? Aimed into side channel of laryngoscope, provides high flow, RA is entrained; it is an example of Bernoulli's Principle What is tension?  What law defines it? a tangential force in N/ m acting on a length of a walltension is part of the structure of a blood vessel, is caused by smooth muscle and elastic tissueLaw of LaPlace What happens when there is an imbalance btw tension and fluid pressure inside tube? It becomes distended or collapses What is the equation for the Law of La Place for a cyllinder? P= T/ Rpressure = tension / radius What is the equation for the Law of La Place for a sphere? P= 2 T / RPressure = 2 tension / radius What force does tension oppose? It opposes the hydrostatic pressure inside the vessel How does tension change as shape changes from cylinder to sphere? What physiologic process resembles this? tension decreases due to law of laplace an enlarging aneurysm How does the Law of LaPlace apply to the heart? As distended heart fails, the radius increases and the pressure falls unless the muscle contracts more forcefully What law explains how both the aorta (very muscular vessel) and capillaries (only 1 layer of cells) can both withstand pressures high as 100 mm Hg? Law of LaPlace, smaller radii means less resistance .remove_background_ad { border: 1px solid #555555; padding: .75em; margin: .75em; background-color: #e7e7e7; } .rmbg_image { max-height: 80px; } Authorariadne9 ID215317 Card Setpressure, flow, and tension Descriptionlast quiz! Updated2013-04-23T17:57:45Z Show Answers