Basics of cardiovascular system

The right atrium receives blood through superior vena cava and inferior vena cava

Every valve in the heart has 3 cusps except the mitral valve which has 2 cusps

The pulmonary artery carries deoxygenated blood whereas pulmonary vein carries oxygenated blood

What is cardiac output?

Cardiac output is the amount of blood the heart pumps in 1 minute

It is expressed in liters/minute

CO = HR × SV

Cardiac output is the product of heart rate( number of times the heart beats per minute) and stroke volume ( volume of blood ejected from the left ventricle per beat)

Cardiac index

Cardiac index = Cardiac output/Body surface area

The unit of measurement is litres per minute per square metre (L/min/m2)

Cardiac index is useful to compare cardiac function between individuals of different sizes

Blood pressure

BP = CO × TPR

CO = Cardiac output

TPR = Total peripheral resistance

Vasoconstriction increases the peripheral resistance which in turn increases the blood pressure

Vasodilatation decreases the peripheral resistance which decreases the blood pressure

EDV = End diastolic volume

It is the volume of blood present in the heart at the end of diastole

SV = Stroke volume

It is the volume of blood ejected during systole

ESV = End systolic volume

It the volume of blood present in the heart at the end of systole. That means this volume of blood was not ejected during systole 

SV = EDV - ESV

Ejection fraction = SV / EDV

Ejection fraction is the amount of blood left ventricle pumps out each time it contracts. Ejection fraction is expressed as a percentage

What will be the effect of increased afterload on stroke volume?

Because of increased afterload it will be harder for the left ventricle to pump blood

This leads to -

Decreased stroke volume

Decreased cardiac output

Increased end systolic volume

What is the effect of ionotropy on stroke volume?

Because of increased force of contraction -

Stroke volume increases

Cardiac output increases

Decreased end systolic volume

What is the effect of increased heart rate on cardiac output?

Tachycardia (increased heart rate) increases cardiac output

However, extreme tachycardias decreases cardiac output. This happens because due to extremely high heart rate, there is not enough time for the heart to fill properly. This, in turn, leads to low cardiac output