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Lecture 11 - Cardio Intro
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Path of Blood Through the Heart
- deoxygenated blood from the systemic circulation enters the Right Atrium through the Superior Vena Cava & the Inferior Vena Cava
- once in the Right Atrium, blood flows through the Tricuspid Valve into the Right Ventricle
- from the Right Ventricle blood is pumped through the Pulmonary Semilunar Valve, enters the pulmonary artery & is taken to the lungs
- oxygenated blood from the lungs flows through the pulmonary vein into the Left Atrium
- it's then pumped through the Mitral Valve into the Left Ventricle
- from the Left Ventricle it's pumped through the Aortic Semilunar Valve to the aorta & enters the systemic circulation
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Tricuspid Valve
- separates the Right Atrium & the Right Ventricle
- prevents back-flow of blood back into the Right Atrium
- opens during diastole so blood can empty from the Right Atrium into the Right Ventricle
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Pulmonary Semilunar Valve
- lies between the Right Ventricle & the pulmonary artery
- opens in ventricular systole when the pressure in the Right Ventricle rises above the pressure in the pulmonary artery
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Mitral Valve
- separates the Left Atrium & the Left Ventricle
- opens during diastole
- open during diastole
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Aortic Semilunar Valve
- separates the Left Ventricle & the aorta
- opens in ventricular systole when the pressure in the Left Ventricle rises above the pressure in the aorta
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Stenosis
- when the tissues forming the valve leaflets become stiffer, narrowing the valve opening & reducing the amount of blood that can flow through it
- main cause: arteriosclerosis
- result: the body may not receive adequate blood flow
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Organization of Cardiac Muscle
- cardiac muscle layers are oriented differently in comparison to each other
- innermost layer = longitudinal
- middle layer = circular
- 2 outside layers = oblique
- important so that the atria & ventricles can pump all blood they come in contact with into where they need to go
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How does the pressure in the Left Ventricle compare to the pressure in the Right Ventricle?
- L: 120/0 mm Hg
- R: 25/0 mm Hg
- the left ventricle needs to pump blood throughout the entire systemic circulation which the right ventricle need only pump it through the pulmonary system
- even though the SAME amount of blood is pumped through systemic & pulmonary systems, the pressure generated is difficult due to the fact that the L ventricle experiences more RESISTANCE to flow than the R
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Cardiac Output (CO)
- the TOTAL volume of blood flow through the systemic or pulmonary circulation
- units = mL/min
- CO = heart rate X stroke volume
- typically 5L/min
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What are the two parameters that determine cardiac output?
- 1. heart rate
- 2. stroke volume: volume of blood ejected from a ventricle (~70 cc)
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Flow (Q)
- volume/time; cm3 of blood per minute
- a snapshot of blood moving
- is kept in one direction by the presence of valves, between atria & ventricles (tricuspid & mitral) & between ventricles & pulmonary artery or aorta (pulmonic & aortic valves)
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Velocity (V)
- distance blood moves/time; cm/min
- V (cm/min) = flow (Q) (cm3/min) / X-Sectional Area (cm2)
- how far a RBC moves per some time frame (can measure using doppler principle)
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Will a certain volume of blood move faster through a vessel with a large cross sectional area or a small cross sectional area?
- a certain volume of blood flow will have a HIGHER velocity going through a vessel with a small cross sectional area than it will going through a vessel with a large cross sectional area

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How is cardiac output minus coronary flow measured?
- using an ultrasonic doppler flow meter
- it's placed over the ascending aorta & measures both its cross sectional area & the velocity of flow through the vessel
- Q (cm3/min) = V (cm/min) * A (cm2)
- Q = VA
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How does the velocity of blood change through the vascular system?
- the flow always stays constant - it's determined by cardiac output, however blood velocity changes
- the aorta is branching into smaller vessels & the overall cross sectional area is INCREASING (capillary x-sectional A = > 40,000 cm2)
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Blood Velocity
- fastest
- Aorta = Arteries
- Vena Cava (~same as arterioles)
- Arterioles (large variation)
- Veins
- Venules
- Capillaries
- slowest

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Why is blood velocity slowest in the capillaries?
- because that's where exchange of nutrients, O2, & CO2 is happening - blood wants to move SLOWLY here to allow for thorough exchange to occur
- the entire point of the cardiovascular system is to get blood to the capillaries
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Relationship Between Pressure & Flow
- QR = P1 - P2
- (Flow)(Resistance) = Mean Pressure
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Mean Arterial Pressure (MAP)
- (SYSP - DIASP)/3 + DIASP
- 1/3(S - D) + D
- an average blood pressure in an individual; the average arterial pressure during a single cardiac cycle
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Poiseuille’s Law
- defines the effects of fluid viscosity, tube radius, & length on the relationship between pressure drop & flow
- Q = ΔPπr4/8ηL
- ΔP = Q * { 8ηL/πr4 } {} = resistance
- ΔP = QR, Q = ΔP/R
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In Poiseuille’s Law why is the blood vessel radius raised to the 4th power?
- because blood vessel walls can stretch - their radius can change
- has a profound effect on resistance
- constricting & dilating BVs is one of the main ways vessels direct blood flow throughout the body
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η (Eta)
- difficulty of blood to flow over other blood (viscosity)
- stays the same unless a person becomes very sick
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Lecture 12 - Mechanical Events of the Cardiac Cycle
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How are pressures in blood vessels & cardiac chambers measured?
via saline filled catheters of 2 basic types attached to electronic pressure transducers
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How are volumes of cardiac chambers measured?
- using echo-cardiographic imaging techniques or calculated from flow measurements
- echocardiography looks at chamber volume & how much blood they hold
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Cardiac Catheterization
- used to study the mechanical events of the cardiac cycle
- inserted into artery or vein & passed into chambers of the heart
- attached to electronic pressure transducers to measure pressure
- blood can be withdrawn through the catheters to obtain blood gas measurements
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Swan-Ganz catheter
- used to catheterize the chambers & vessels of the right side of the heart
- measure pressures in the right side of the heart, pulmonary arteries, veins, & left atrium
- can be inserted into a (neck) vein & pushed forward to a position where the tip is at the junction of the vena cava & the right atrium
- here the catheter is swept along w/ venous return into the right atrium
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What pressure can be measured when Swan-Ganz catheter is carried into a small pulmonary artery & then “wedges” there?
- the “pulmonary wedge pressure”
- this is a good indicator of left atrial pressure, which otherwise can't be measured by a catheter
- records the back pressure pushing against the catheter coming from the L atrium

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Left Heart Catheterization
- measures aortic pressure & L ventricular pressure
- the catheter must be inserted into a peripheral artery (femoral) & advanced against the direction of arterial blood flow
- it approaches the left ventricle is from the aorta
- used to get left ventricular pressure (NOT arterial)
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How can mitral stenosis be assessed?
by examining the pressure gradient between the “pulmonary wedge” pressure & the ventricular pressure during diastole (when the mitral valve is open)
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Both ventricular & atrial ________ happen simultaneously, while there is a slight time difference between atrial _______ & ventricular _______.
- ventricular & atrial DIASTOLE happen simultaneously
- there is a time difference between atrial systole, which happens first, followed by ventricular systole
- atrial contraction is complete before the ventricle begins to contract
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http://library.med.utah.edu/kw/pharm/1Atrial_Systole.html
good website*
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Atrial Systole
- when both L & R atria CONTRACT to push blood through mitral & tricuspid valves → this is the "topping off" of ventricles
- mitral & tricuspid valves are open facing ventricles nearly completely full of blood
- atrial systole is the final part of diastole (filling)
- causes an increase in endiastolic (ventricle) pressure
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Describe the behavior of the mitral & tricuspid valve during Atrial Systole:
- in the beginning it's open & has been since rapid ventricular filling during ventricular diastole
- at the end the mitral valve CLOSES
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"a" wave
occurs when the atrium contracts, increasing atrial pressure, during atrial systole
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Atrial Fibrillation
- NO atrial systole - ventricle don't get "topped off" but because the ventricle is mostly full, enough blood is pumped out to the systemic circulation
- causes a ~5-10% reduction in normal cardiac output
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Ventricular Systole
- both semilunar valves are open (aortic & pulmonary)
- the mitral & tricuspid valves are closed
- both ventricles CONTRACT to push blood through the semilunar valves
- includes Isovolumetric contraction, Rapid ejection, & Reduced Ejection
- (mitral valve closure tells you it starts, aortic valve closure tells you its over)
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S1
- signifies the beginning of Systo1e
- corresponds to closing of mitral (& tricuspid) valve
- noise made is actually caused by the eversion of the mitral valve slightly back into the left atria due to the large force generated by the L ventricle contracting
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What does the QRS complex seen on an EKG indicate?
it triggers the start of ventricular contraction (systole)
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Isovolumetric Contraction
- the ventricles contract, causing ventricular pressure to rise sharply, but there is no overall volume change b/c atrioventricular valves have just been shut (after atrial systole) & semilunar valves have not yet opened
- the 1st, short lived part of ventricular systole
- the beginning corresponds to the R peak seen on an EKG
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Describe the behavior of the aortic & pulmonary valve during Isovolumetric contraction (aka the beginning of ventricular systole):
- both are closed at the start
- both open at the end of isovolumetric contraction
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Rapid Ejection
- the semilunar (aortic & pulmonary) valves open at the beginning of this phase of ventricular systole
- ventricles continue contracting, the pressure in the ventricles exceeds pressure in the aorta & pulmonary arteries
- the semilunar valves open & blood exits the ventricles → causing the volume in the ventricles to decrease rapidly
- as more blood enters the arteries, pressure there builds until the flow of blood reaches a peak
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"c" wave
- a small wave created by right ventricular contraction which pushes the tricuspid valve into the atrium & increases atrial pressure
- is normally simultaneous with the carotid pulse
- visible right between isovolumetric contraction & rapid ejection
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Reduced Ejection
- after the peak in ventricular & arterial pressures, blood flow out of the ventricles decreases & ventricular volume slowly decreases
- when the pressure in the ventricles falls below the pressure in the arteries, blood in the arteries begins to flow back toward the ventricles & causes the aortic & pulmonary valves to close, marking the end of ventricular systole
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Ventricular Diastole
- mitral (bicuspid) valve open - into left ventricle
- tricuspid valve open - into right ventricle
- the ventricles fill during diastole (atrial pressure > ventricle pressure)
- includes Isovolumetric relaxation, Rapid ventricular filling, Reduced ventricular filling, & Atrial systole
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S2
- the beginning of ventricular diastole
- corresponds to closing of pulmonary & aortic valve
- is normally split b/c the aortic valve closes slightly before the pulmonary valve
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Isovolumetric relaxation
- the beginning of diastole during which the atrioventricular valves are still closed
- throughout this & the previous two phases (rapid & reduced ejection) the atrium in diastole was filling w/ blood on top of the closed AV valves, causing atrial pressure to rise gradually
- the pressure in the ventricles continues to fall
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During which phase is ventricular volume lowest/at a MINIMUM?
- in isovolumetric relaxation during ventricular diastole
- at this point the ventricles are ready to be filled again w/ blood
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"v" wave
a slow rise in atrial pressure due to the back flow of blood after it hits the closed AV valves
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Rapid Ventricular Filling
the AV valves open & blood that has accumulated in the atria flows rapidly into the ventricles causing a swift increase in ventricular volume
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Reduced Ventricular Filling
- ventricular volume increases more slowly now
- the ventricles continue to fill with blood until they are nearly full
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End Diastolic Volume (EDV)
- the volume of blood in the right & left ventricle at end diastole (when it's been almost completely filled)
- ~50% of it is ejected into the systemic or pulmonary circulation w/ each beat
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End Systolic Volume (ESV)
- the volume of blood in a ventricle at the end of systole (contraction) or the beginning of diastole (filling)
- is the lowest volume of blood in the ventricle at any point in the cardiac cycle - NEVER 0
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EDV - ESV = ?
- stroke volume
- amount of blood pumped in each cardiac cycle
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Systolic Murmur
- mitral valve insufficiency (regurgitation, prolapse)
- aortic stenosis
- the direction of blood flow is out of the chamber
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Diastolic Murmur
- mitral stenosis: softer murmur
- aortic insufficiency (regurgitation): more pronounced
- is softer b/c pressure behind them is lower
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