Hemodynamics Flashcards Preview

Cardiology Exam 1 > Hemodynamics > Flashcards

Flashcards in Hemodynamics Deck (21):

Properties of Arteries (3)

* Large fluctuations in pressure (higher pulse pressure)

* Thickest walls to withstand high surface tension
* Tension = Pressure * Radius of Vessel

* Compliance of arteries DEC w/ age so inc pulse pressure for a given SV (more fluctuation)


Properties of Arterioles

Major resistance vessels; largest amount of smooth muscle for resistance SO BP drops substantially in arterioles


Properties of Capillaries

* Single layer of endothelial cells + basement membrane

* Velocity = Q/A so low velocity b/c huge area; good for exchange


Properties of Veins (3)

* Much lower pressure (around 0)
* Less pressure needed b/c lower resistance
* Means there must be local generation of pressure

* Thinner walls but larger diameter than arteries

* VERY compliant (blood pulling esp when standing b/c gravity)
* Compliance of veins INC w/ age
* However, venous compliance dec w/ higher pressures and volumes


Ohm's Law

Q= deltaP/R or deltaP= Q*R or R=deltaP/Q

So... flow inc if greater difference in pressure but dec if greater resistance

* DeltaP is change in pressure from one end of vessel to other
-For systemic circulation… deltaP = Paorta - Pright atrium = Paorta b/c Pright atrium almost 0 mmHg
-For pulmonary circulation… deltaP = MeanPulmPress - Pleft atrium



Total Peripheral Resistance

* one major factor is diameter of vessel (inc diameter = less R)

* 1/Rtotal = 1/R1 + 1/R2 + 1/R3 etc (if 1, 2, 3 parallel pathways)

* TPR is less than resistance in any one given vascular bed/pathway


Poiselle's Law

Q = pi*deltaP*r^4 / 8nl

* r- radius of vessel (so change by vasoconstriction/dilation causes huge change in flow); so flow through capillary depends on radius of arteriole right in front of it

* n- viscosity (higher if polycythemia and lower if anemic)

* l - length of vessel


Reynold's Number

Re = dvD/n

* d- density of fluid; D- diameter of tube; v-velocity; n - viscosity

* So larger vessels more likely to have turbulent flow (arteries)

* Re> 1000 leads to turbulent flow (concentric motion NOT forward motion; frictional resistance; vibrations heard as murmurs)

* Re < 1000 leads to laminar flow (fluid on inside moves faster b/c fluid on outside adheres to vessel wall - more prominent in small vessels)


Pulse Pressure & Compliance

* Pulse Pressure = Systolic - Diastolic

* Affected by compliance (tendency to resist recoil); greater compliance means greater storage of blood as potential energy so less fluctuation

C = deltaV/deltaP (more compliant means less change in pressure for given increase in volume of blood - b/c pool blood)


Mean Arterial Pressure

MAP = 2/3diastolicP + 1/3 systolicP

MAP = CO * TPR and CO = HR * SV so MAP = HR * SV * TPR

*If you inc resistance in some capillary beds/pathways… inc pressure in vessels prior to this increased resistance so inc pressure in other capillary beds/pathways


Surface Tension

Tension = Pr
* P- pressure against vessel wall
* r- radius of vessel

* So smaller vessel can withstand more pressure w/o breaking due to tension; aorta and other arteries have larger radius so need thicker wall to withstand greater surface tension


3 Mechanisms of Venous Return

1- Venous Valves
*If veins stretch (varicose veins) but valves do not stretch to same extent then valves do no adequately close)

2- Skeletal Muscle Pumping

3- Venomotor Tone
* vasoconstriction dec vein compliance/inc rigidity


Frank Starling Law of the Heart

* Heart will always pump out as much blood as is returned to heart

* Greater venous return —> myocardial cells stretched to optimal length or contraction —> greater force of contraction/greater stroke volume
* Tension of contraction inc
* Normally shorter than optimal length
* Stretch also inc sensitivity of troponin to Ca++


Orthostatic Hypotension Mechanism

* Postural change —> dec venous return —> dec CO —> dec MAP (lower BP)


5 Steps of Cardiac Cycle

1- Atria & ventricles in diastole - passive blood flow (80% vent blood)

2- Atria contract (last 20% vent blood)

3- Ventricles contract - forces tricuspid/mitral closed & aortic/pulmonic still closed - ISOVOLUMETRIC ventricular contraction

4- Ventricle ejection - now ventricular pressure high enough to open aortic/pulmonic valves to ventricular contraction —> ejection

5- Ventricles relax —> lower ventricle pressure —> causes retrograde flow back from artery into ventricles; causes aortic/pulmonic to snap shut & tricuspid/mitral still closed - ISOVOLUMETRIC ventricular relaxation ``



EDV - fullest ventricular volume; at end of atrial contraction

ESV- lowest ventricular volume; blood left in ventricle after ejection


Ejection Fraction



Terms to Describe Atrial Pressure Curve

* a wave - atrial contraction

* c wave - ventricular contraction - higher pressure caused by small back flow from ventricles when tricuspid closes & bulging of valve into atria when ventricle pressure inc

* x descent - aortic/pulmonic valve opens relieving pressure on tricuspid/mitral valve

* v wave - blood flow from veins to atrium during ventricular contraction (cannot leave atrium b/c tricuspid closed)

* y descent - tricuspid/mitral opens to relieve pressure


Which cells fire APs fastest? Which cells propogate APs fastest?

* Rate of AP initial firing: SA node cells > AV node cells >bundle/Purkinje

* Rate of AP conduction: Purkinje > atria inter-nodal > AV node (hence delay through AV node)


4 Steps in Electrical Conduction

1- Depolarization starts at the SA node (R atrium near superior vena cava)

2- Non-contractile conducting cells carry impulse from SA node —> AV node (floor of R atrium) via inter-nodal fibers WHILE slow wave of depolarization sweeps across atria —> atria contract

3- DELAY b/c SLOW conduction through AV node but eventually travels to bundle of His
* Ensures atria contract BEFORE ventricles

4- Pulse carried by bundle branches —> apex of ventricles along ventricular septum —> back up Purkinje fibers —> depolarization spreads up from apex —> ventricles contract
* Starting from apex/bottom ensures blood is squeezed out top of ventricles


4 Basic Heart Sounds

* First - tricuspid/mitral valves close (start of ventricular systole)

* Second - aortic/pulmonic (semilunar) valves close - start of ventricular diastole (retrograde flow closes valves)

* Third - turbulent flow into ventricle near beginning of filling (diastole)

* Fourth - additional turbulent flow into ventricle during atrial contraction (atrial systol