BSI: Pumping Action of the Heart

Refers to the sequence of events (electrical and mechanical) occurring in the heart during a single beat.

Systole: Contraction phase of cardiac cycle

Diastole: Relaxation phase of cardiac cycle

When AV valves are open, most blood returning to atria pass right through to the ventricles (75% of blood). In other words, there is no contraction needed; this is passive filling.

When atria do contract, they push more blood into ventricles (25%). This "tops off" the ventricles.

Atria function to enhance the amount of blood in ventricles, which enhances ventricular pumping.

The heart can function without atrial contraction.

The right ventricle functions to pump blood through pulmonary circulation.

The left ventricle functions to pump blood through systemic circulation.

No...there is always some blood volume in the ventricles.

• Valves open and close passively
• - Forward pressure gradient opens valves
• - Backward pressure gradient closes 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.

Only Atrioventricular (AV) Valves, which includes the tricuspid and bicuspid/mitral valves.

Semilunar valves DO NOT have chordae tendinae or papillary muscle.

• Atrial contraction
• Ventricles begin to contract—period of isovolumetric contraction
• - Pressure in ventricle begins to rise causing AV valve to close
• - Moments later, pressure rises further and causes semilunar valves to open

• Period of ejection
• As ventricular pressure rises above arterial pressure, blood is pushed out of ventricle as semilunar valves open

• Period of isovolumetric relaxation
• -Ventricles begin to relax; pressure begins to drop with ventricle
• - As pressure drops below arterial pressure, semilunar valves close
• - Ventricles continue to relax and eventually the pressure drops low enough that AV valves open again allowing ventricles to fill again

Ventricular filling

Systole: Contraction phase of cardiac cycle

Diastole: Relaxation phase of cardiac cycle

The volume of blood in the ventricle at the end of diastole (110 ml).

In other words, EDV is the volume in the ventricle right before the ventricle contracts.

This is considered the preload (the stretched condition of the heart at the end of diastole).

The volume of blood in the ventricle at the end of systole (40 ml).

In other words, ESV is the volume in the ventricle right after the ventricle contracts (which is the end of ventricle ejection or during isovolumetric relaxation).

Note that because the ESV has a volume of 40 ml, the ventricle is never empty.

The volume of blood pumped out of the left ventricle per contraction (70 ml).

Determined by preload, afterload, and contractility.

• Formula: SV = EDV - ESV
• SV = 110 ml - 40 ml
• SV = 70 ml

• 1) preload
• 2) afterload
• 3) contractility

The fraction of EDV that was pumped out of the left ventricle per contraction (60%).

• Formula: EF = (SV/EDV) x 100
• EF = [(SV = EDV- ESV)/EDV] x 100
• EF = [(SV = 110 - 40)/110] x 100
• EF = [70/110] x 100
• EF = 63.6%
• EF = round to ~60%

The amount of blood pumped out of the left ventricle per minute.

Cardiac output = heart rate x stroke volume (5000 ml).

• Formula: CO = HR x SV
• CO = HR x SV
• Given HR = 60 beats/min
• CO = HR x (EDV - ESV)
• CO = 60 x (110 ml - 40 ml)
• CO = 4,200 ml/min
• Note: CO is measured in ml per MINUTE...not per beat!

Cardiac output is one way to measure how efficient the heart is. High cardiac output is related to an increase in heart disease, heart failure and stroke. The harder the heart has to work when it is resting (i.e. not exercising), the less efficient it is.

The amount of blood returned to the right atrium.

Note: Venous Return is measured in ml per MINUTE...not per beat!

The pressure stretching the chamber of the heart.

The end diastolic volume is primary determinant of preload.

Frank-Starling Mechanism: as the muscle stretches, sarcomeres approach optimal length leading to greater strength of contraction.

End Diastolic Volume (EDV)

Because increased stretching optimizes the overlap of actin and myosin. Therefore, it creates a situation which increases or maximizes the number of cross bridges.

In other words, the more you increase the stretch of sarcomeres, the more you contract with greater force.

The pressure that the chamber of the heart has to overcome in order to eject blood.

• For the left ventricle:
• afterload = aortic pressure = diastolic pressure.

Diastolic pressure in a normal healthy individual is 80. For patients with high blood pressure, they may have to overcome measures of 100 or greater to overcome afterload.

Afterload will decrease stroke volume.

Afterload. The ventricle has to overcome the pressure of the aorta in order to eject blood because the valve has to open. This pressure is known as afterload.

The intrinsic property of cardiac muscle to produce tension.

A change in the force of contraction at a constant end-diastolic fiber length reflects a change in contractility.

The ability of a fiber to produce force at any given length in most cases has to do with the amount of intracellular Ca²⁺ present.

Therefore, most of the time, the primary determinant of contractility is the amount of intracellular Ca²⁺.

However, other things can affect contractility. For example, a structural problem could interfere with cross bridging and affect contractility.

• Affecting heart rate
• If you increase heart rate, you have a positive chronotropic effect.

Affecting contractility

If you increase or decrease contractility, you affect ionotropic effect.

Lub-dub

1st sound (Lub): closing of AV valves

2nd sound (Dub): closing of semilunar valves

Lub, the first sound, is sometimes called S1. Recall this sound is associated with the closing of AV valves.

Dub, the second sound, is sometimes called S2. Recall this sound is associated with closing of semilunar valves.

There is also an "S3" and "S4."

S3 is associated with ventricular filling. If S3 is heard, it may or may not signify an abnormality.

However, if you hear S4, there is almost always an abnormality with atrial contraction.

An Electrocardiogram, also known as "ECG" or an "EKG" measures the electrical activity of the heart.

• P wave
• Atrial depolarization

• QRS complex
• Ventricular depolarization

• T wave
• Ventricular repolarization

Atrial depolarization

Ventricular depolarization

Ventricular repolarization

Atrial repolarization is usually hidden in the QRS complex. Therefore, most of the time it is not visible on an EKG.

EDV: represented by the end of the first pink section. Recall that EDV is the volume of blood in the ventricle at the end of diastole (110 ml).

ESV: represented at the end of the purple section. Recall ESV is the volume of blood in the ventricle at the end of systole (40 ml).

SV: The difference between the EDV-ESV. Recall SV is the amount of blood pumped out of the left ventricle per contraction (70 ml).

Recall the Ejection fraction is the fraction of EDV that was pumped out of the left ventricle per contraction.

Therefore, to find the Ejection Fraction:

• Recall EF = (SV/EDV) x 100
• EF = [(SV = EDV- ESV)/EDV] x 100
• EF = [(SV = 110 - 40)/110] x 100
• EF = [70/110] x 100
• EF = 63.6%

• Recall SV = EDV- ESV = 110 - 40 = 70
• Recall CO = HR x SV = 85 x 70 = 5950 mL/min

Preload: the more you stretch the sarcomeres, the more you optimize the number of cross bridges, and therefore increase the force and strength and contraction.

Contractility: Recall Ca²⁺ binds to troponin to move tropomyosin out of the way and exposes myosin, therefore increased intracellular Ca²⁺ would increase the number of cross bridges and therefore increase the strength and force of contraction.