Lec 14&15 Cardiac Cycle/Pumping Action of the Heart

What happens in S4?

It may be heard during atrial contraction or when atrial pressure is high or ventricle is stiff. E,g,. S4 may be heard if there's ventricular hypertrophy, which causes stiffening (rigid/hard to bend) of the ventricle.

Heart sounds

Lub-Dub (S1&S2) S1: closing of AV valves S2: closing of semilunar valves

Picture of the cardiac cycle

Need to know every detail

In order to increase contractility (ionotrophy), does there have to be an increase in EDV?

No, if you increase contractility, ESV decreases.

What's the role of papillary muscle of AV valves?

Papillary muscle of AV valves prevent cusps from protruding into atria as ventricles contract. Damage to chordae tendinae or papillary muscle results in backward flow of blood as ventricles contract and could be lethal. *Semilunar valves DO NOT have chordae tendinae or papillary muscle.

5. Ventricular filling

Passive filling of ventricle: blood flows into the atriums and also ventricles as the AV valves are open.

Cardiac output

The amount of blood pumped out of the left ventricle per minute. = Heart rate * stroke volume (*5000ml*)

Venous return

The amount of blood returned to the heart

1. Atrial contraction

The atriums contract and push blood into the ventricles. AV valve is open, and atrium pumps blood into ventricle.

What are the phases of cardiac cycle?

The cardiac cycle refers to the sequence of events (electrical and mechanical) occurring in the heart during a single beat. 1. Atrial contraction 2. Period of isovolumetric contraction 3. Period of ejection 4. Period of isovolumetric relaxation 5. Ventricular filling

Pulse pressure

The difference between the systolic and diastolic pressure (SBP-DBP)

Ejection fraction

The fraction of EDV that was pumped out of the left ventricle per contraction (60%). = (SV/EDV)*100

How are valves open and closed?

Valves open and close passively. 1. Forward pressure gradient opens valves. 2. Backward pressure gradient closes valves.

What happens in S3?

Vibrations during rapid phase of ventricular filling. It is thought to be caused by the oscillation of blood back and forth between the walls of the ventricles initiated by inrushing blood from atria (-> increased volume of blood within ventricle and maybe associated with ventricular dilation).

The mitral valve opens due to contraction and corresponding pressure rise of the atrium. T/F?

False. The AVs are already open during ventricular filling (passive). It is open until atrium contracting and pumping blood into the ventricules until the pressure rise in ventricles are high, closing the AVs.

4. Period of isovolumetric relaxation (volume doesn't change; pressure drops)

1. Ventricle begin to relax and pressure begins to drop within ventricle. 2. As pressure drops below arterial pressure, semilunar valve closes. 3. *This period of relaxation while both valves (AV and semilunar valves) are closed is the isovolumetric relaxation phase*. 4. Ventricle continues to relax and eventually the pressure drops below that of atrium and therefore the AV valve opens leading to the ventricular filling phase.

2. Period of isovolumetric contraction (volume doesn't change; pressure rises)

1. Ventricle begins to contract (increasing pressure) and once pressure in ventricle exceed that of atrium, the AV valve will close. 2. *This period of contraction while the AV valve and semilunar valve are closed is the isovolumetric contraction phase*. 3. Once the pressure in the ventricle exceeds that of the aorta (arterial pressure) then the semilunar valve will open-> Leading to the ejection phase.

What's the difference between preload and contractility?

An increase of either one will increase the strength of contraction; however they do it by different mechanisms. 1. Preload is dependent on stretch. 2. Contractility is dependent on Ca2+ concentration.

3. Period of ejection

As ventricular pressure rises above arterial pressure (aortic pressure), semilunar valve opens and blood is ejected out of ventricles.

Systole

Contraction phase of cardiac cycle

What is inotropic effect?

It affects contractility.

What is chronotropic effect?

It affects the heart rate.

Filling phase includes?

It includes ventricular filling (passive) and atrial contraction (active). We can survive without atrial contraction phase because most blood in ventricle is filled during ventricular filling.

How will an increase in afterload affect ESV?

It increase the ESV. The increase of afterload decreases stroke volume, causing an increase blood left behind.

How would aortic stenosis (narrowing the valve) affect afterload?

It increases the afterload. If you narrow that valves, the left ventricle has to produce a higher pressure to eject blood through that smaller valve.

What is Pressure-Rate product?

It is an indirect index of myocardial O2 consumption (how hard the ventricle is working). It is equal to HR*SBP (or HR*MAP).

Preload

It is the stretch stage of the heart before it contracts. The pressure stretching the chamber of the heart before it contracts. As the muscle stretches, the stretching induce length-dependent activation of the contractile apparatus leading to greater strength of contraction. *It is determined by EDV (+)*.

What is the function of the ventricles?

It is to pump blood through pulmonary circulation (right) and systemic circulation (left).

Diastole

Relaxation phase of cardiac cycle

What does it mean with the presence of S3 and/or S4?

S3/S4 may be indicative of an abnormality.

Contractility (Inotrophy)

The intrinsic ability of cardiac muscle to produce tension, independent of fiber (sarcomere) length. (The ability of the ventricles to contract *completely independent of stretch*, *Intracellular Ca2+ determines the force of contraction*. A change in the force of contraction at a constant end-diastolic fiber length reflects a change in contractility (anything that affects excitation-contraction, other than sarcomere/fiber length, affects contractility).

End systolic volume (ESV)

The left-behind blood in the ventricles after they were contracted. It is the volume of blood in the ventricle at the end of systole (*40ml*).

Systolic Blood Pressure (SBP)

The pressure in the systemic arteries (aorta) while the left ventricle is contracting and ejecting blood (*120mmHg*).

Diastolic Blood Pressure (DBP)

The pressure in the systemic arteries (aorta) while the left ventricle is relaxing and not ejecting blood (*80mmHg*)

Afterload

The pressure that the chamber of the heart has to overcome in order to eject blood. *Aortic pressure is an important determinant of the after load of the left ventricle while pulmonary pressure is an important determinant of the after load of the right ventricle*. 1. As aortic pressure increases, such as when a patient has systemic hypertension, the left ventricle has to produce higher pressure (more tension, work harder) in order to eject blood into the aorta against that higher pressure. 2. Therefore, it can be said that as aortic pressure increases, the after load of the left ventricle increases.

End diastolic Volume (EDV)

The volume of blood in the ventricle at the end of diastole (*110ml*). It is the amount of blood in the ventricle once it is filled just before it contracts (max volume). *Venous return is an important determinant of EDV*.

Stroke volume (SV)

The volume of blood pumped out of the ventricle per contraction (*70ml*) per beat or per stroke. = (EDV - ESV). *It is determined by preload (+), afterload (-), and contractility (+).

What is cardiac reserve?

The work that the heart is able to perform beyond that required of it under basal/resting conditions (300-400%)

What is the function of the Atria?

When AV valves are open, most blood returning to atria pass right through to the ventricles (60-90% of blood). 1. When atria do contract, they push more blood into ventricles (10-40%). 2. Atria function to enhance the amount of blood in ventricles, which enhances ventricular pumping. 3. *Heart can function without atrial contraction*.