Cardiac cycle and cardiac output

[1ST ORDER] What is the cardiac cycle?

The repeating sequence of electrical, pressure, volume, and mechanical events during one heartbeat

[1ST ORDER] What are the two major phases of the cardiac cycle?

Ventricular systole and ventricular diastole

[1ST ORDER] What does systole mean unless otherwise specified?

Ventricular contraction and associated ejection events

[1ST ORDER] What does diastole mean unless otherwise specified?

Ventricular relaxation and filling

[1ST ORDER] What are the two major components of ventricular systole?

Isovolumetric contraction and ventricular ejection

[1ST ORDER] What are the two major components of ventricular diastole?

Isovolumetric relaxation and ventricular filling

[1ST ORDER] What determines the direction of blood flow through cardiac valves?

The pressure gradient across each valve

[1ST ORDER] When does a valve open?

When upstream pressure exceeds downstream pressure sufficiently to move the valve open

[1ST ORDER] What is end-diastolic volume (EDV)?

The volume of blood in a ventricle at the end of ventricular filling

[1ST ORDER] What is end-systolic volume (ESV)?

The volume of blood remaining in a ventricle after ventricular ejection

[1ST ORDER] What is stroke volume (SV)?

The volume of blood ejected by a ventricle in one heartbeat

[HIGH-YIELD][1ST ORDER] What is the equation for stroke volume?

SV = EDV − ESV

[HIGH-YIELD][1ST ORDER] What is ejection fraction (EF)?

The fraction of end-diastolic ventricular volume ejected during systole

[HIGH-YIELD][1ST ORDER] What is the equation for ejection fraction?

EF = SV/EDV × 100%

[2ND ORDER] If EDV increases and ESV remains unchanged, what happens to stroke volume?

Stroke volume increases because SV = EDV − ESV

[2ND ORDER] If ESV increases while EDV remains constant, what happens to stroke volume?

Stroke volume decreases

[CALCULATION][2ND ORDER] EDV is 120 mL and ESV is 50 mL. Calculate stroke volume.

120 − 50 = 70 mL/beat

[CALCULATION][2ND ORDER] EDV is 120 mL and ESV is 50 mL. Calculate EF.

70/120 × 100 ≈ 58%

[CALCULATION][3RD ORDER] EDV is 150 mL and ESV is 90 mL. Calculate SV and EF.

SV = 60 mL

EF = 60/150 × 100 = 40%

[CALCULATION][3RD ORDER] A patient has an EF of 40% and EDV of 150 mL. What is ESV?

SV = 60 mL

ESV = 150 − 60 = 90 mL

[DRAW/MAP] Map the four major ventricular phases in order.

Ventricular filling → isovolumetric contraction → ventricular ejection → isovolumetric relaxation → repeat

[1ST ORDER] What is a Wiggers diagram?

A graph integrating cardiac pressures, ventricular volume, ECG events, and heart sounds across the cardiac cycle

[1ST ORDER] What variables are compared in the lecture's Wiggers diagram?

Left atrial, left ventricular, and aortic pressures

LV volume

ECG

and heart sounds

[2ND ORDER] Why is the Wiggers diagram useful?

It connects electrical activation, valve movement, pressure changes, volume changes, and heart sounds in time

[1ST ORDER] What happens during ventricular filling?

Blood moves from the atrium into the ventricle through an open AV valve

[1ST ORDER] Which valves are open during left ventricular filling?

The mitral valve is open and the aortic valve is closed

[1ST ORDER] What occurs during atrial systole?

Atrial contraction adds blood to the ventricle near the end of ventricular filling

[2ND ORDER] What ECG event precedes atrial contraction?

The P wave

[2ND ORDER] What ECG event precedes ventricular contraction?

The QRS complex

[2ND ORDER] What ECG event represents ventricular repolarization?

The T wave

[1ST ORDER] What is isovolumetric contraction?

Ventricular pressure rises while ventricular volume remains constant because all valves are closed

[HIGH-YIELD][2ND ORDER] Why does ventricular volume remain constant during isovolumetric contraction?

Both AV and semilunar valves are closed, so no blood enters or leaves

[2ND ORDER] What initiates closure of the mitral valve?

Left ventricular pressure rises above left atrial pressure

[2ND ORDER] What ends isovolumetric contraction?

Left ventricular pressure exceeds aortic pressure, opening the aortic valve

[1ST ORDER] What occurs during ventricular ejection?

Blood leaves the ventricle through an open semilunar valve, decreasing ventricular volume

[2ND ORDER] Which valves are open during left ventricular ejection?

Aortic valve open

mitral valve closed

[1ST ORDER] What is isovolumetric relaxation?

Ventricular pressure falls while volume remains constant because all valves are closed

[2ND ORDER] What initiates isovolumetric relaxation?

Closure of the semilunar valve as ventricular pressure falls below arterial pressure

[2ND ORDER] What ends isovolumetric relaxation?

Ventricular pressure falls below atrial pressure, opening the AV valve

[HIGH-YIELD][2ND ORDER] During which cardiac phases are all four valves closed?

Isovolumetric contraction and isovolumetric relaxation

[3RD ORDER] LV pressure is rising rapidly but volume is unchanged. Identify the phase.

Isovolumetric contraction

[3RD ORDER] LV pressure is falling rapidly but volume is unchanged. Identify the phase.

Isovolumetric relaxation

[3RD ORDER] LV volume decreases while aortic pressure rises. Which phase is occurring?

Ventricular ejection

[3RD ORDER] LV volume increases while the aortic valve is closed. Which phase is occurring?

Ventricular filling

[DRAW/MAP] Trace the mitral and aortic valves through one LV cycle.

Filling: mitral open/aortic closed → isovolumetric contraction: both closed → ejection: mitral closed/aortic open → isovolumetric relaxation: both closed

[1ST ORDER] What is a pressure-volume (PV) loop?

A graph of ventricular pressure versus ventricular volume throughout one cardiac cycle

[1ST ORDER] What is on the x-axis of a ventricular PV loop?

Ventricular volume

[1ST ORDER] What is on the y-axis of a ventricular PV loop?

Ventricular pressure

[2ND ORDER] What does the width of a PV loop represent?

Stroke volume

[2ND ORDER] What does the rightmost point of the PV loop represent?

End-diastolic volume

[2ND ORDER] What does the leftmost point of the PV loop represent?

End-systolic volume

[2ND ORDER] Why are the vertical sides of a PV loop called isovolumetric phases?

Pressure changes without a corresponding change in ventricular volume

[DRAW/MAP] Trace the LV pressure-volume loop.

Bottom right EDV → vertical rise during isovolumetric contraction → move left during ejection → vertical fall during isovolumetric relaxation → move right during filling

[3RD ORDER] A PV loop becomes wider because EDV rises while ESV remains constant. What changed?

Stroke volume increased

[3RD ORDER] A PV loop becomes narrower because ESV rises while EDV is unchanged. What happened?

Stroke volume decreased

[1ST ORDER] What produces the first heart sound (S1)?

Closure of the atrioventricular valves at the beginning of ventricular systole

[1ST ORDER] Which valves contribute to S1?

Mitral and tricuspid valves

[1ST ORDER] What produces the second heart sound (S2)?

Closure of the semilunar valves at the end of ventricular ejection

[1ST ORDER] Which valves contribute to S2?

Aortic and pulmonic valves

[2ND ORDER] Which sound marks the beginning of isovolumetric contraction?

S1

[2ND ORDER] Which sound marks the beginning of isovolumetric relaxation?

S2

[1ST ORDER] What is the aortic component of S2 called?

A2

[1ST ORDER] What is the pulmonic component of S2 called?

P2

[2ND ORDER] Why can S2 split during inspiration?

Increased right ventricular filling can prolong RV ejection and delay pulmonic valve closure

[2ND ORDER] What is the physiological effect of inspiration on normal S2 splitting?

Inspiration increases separation between A2 and P2

[1ST ORDER] What is an S3 heart sound?

An early-diastolic sound occurring during rapid ventricular filling

[1ST ORDER] What is another name for S3?

Protodiastolic gallop

[2ND ORDER] When does S3 occur relative to S2?

Shortly after S2 during early rapid ventricular filling

[2ND ORDER] When can S3 be a normal finding?

In some young individuals

[HIGH-YIELD][2ND ORDER] What can an S3 suggest in an older patient with dyspnea and edema?

Volume overload and ventricular dysfunction, including heart failure

[1ST ORDER] What is an S4 heart sound?

A late-diastolic sound associated with atrial contraction against a stiff ventricle

[2ND ORDER] When does S4 occur relative to S1?

Immediately before S1 during late diastole

[2ND ORDER] Why can decreased ventricular compliance produce S4?

Atrial contraction forces blood into a stiff, poorly compliant ventricle

[HIGH-YIELD][2ND ORDER] What distinguishes the timing of S3 from S4?

S3 occurs early in diastole after S2

S4 occurs late in diastole before S1

[3RD ORDER] An older patient with orthopnea has an extra sound immediately after S2. Identify the sound.

S3, associated with rapid ventricular filling and possible heart failure

[3RD ORDER] A patient with a stiff ventricle has an extra sound immediately before S1. Identify it.

S4, caused by atrial contraction against reduced ventricular compliance

[4TH ORDER] Why would loss of coordinated atrial contraction prevent a typical S4?

S4 depends on atrial contraction forcing blood into a stiff ventricle

[DRAW/MAP] Map the timing of S1–S4.

Late diastole: S4 may occur with atrial contraction → S1 closes AV valves → systole/ejection → S2 closes semilunar valves → early filling may produce S3

[1ST ORDER] What is the jugular venous pulse (JVP)?

Visible venous pressure fluctuations reflecting changes in right atrial pressure

[1ST ORDER] What produces the JVP a wave?

Right atrial contraction

[1ST ORDER] What produces the JVP c wave?

Bulging of the closed tricuspid valve into the right atrium during early ventricular systole

[1ST ORDER] What produces the JVP v wave?

Right atrial filling while the tricuspid valve is closed

[2ND ORDER] Which JVP wave corresponds most closely to atrial systole?

The a wave

[2ND ORDER] Which JVP wave occurs during early ventricular systole?

The c wave

[2ND ORDER] Which JVP wave reflects right atrial filling against a closed tricuspid valve?

The v wave

[DRAW/MAP] Map the three major JVP waves.

a wave → right atrial contraction

c wave → tricuspid valve bulges during early RV systole

v wave → right atrium fills while tricuspid valve remains closed

[2ND ORDER] What does elevated JVP suggest about right atrial pressure?

Right atrial pressure is elevated

[3RD ORDER] A patient has peripheral edema and elevated JVP. Which side of the heart may be failing?

The right side, causing systemic venous congestion

[2ND ORDER] How does inspiration affect venous return to the thorax?

Lower intrathoracic pressure helps draw venous blood toward the heart

[2ND ORDER] How does the skeletal muscle pump enhance venous return?

Contracting muscles compress veins, while one-way valves direct blood toward the heart

[3RD ORDER] Why does walking reduce lower-extremity venous pooling compared with standing motionless?

Skeletal muscle contraction compresses veins and promotes forward venous return