mechanics 2

Question 1

describe the 2 min phases of heart beat

Answer 1

Diastole – Ventricular relaxation during which the ventricles fill with blood.
o Split into FOUR sub-phases.

Systole – Ventricular contraction when the blood is pumped into the arteries.
o Split into TWO sub-phases.

Question 2

End Diastolic Volume (EDV) =

Answer 2

The volume of the ventricle at the end of ventricular filling ~130ml. This is made up of:
o The ESV = ~60ml.
o The amount added in atrial diastole (filling without contraction into the ventricle = ~40ml
o The amount added by atrial systole (contraction of atria, topping off ventricle volume = ~30ml.

Question 3

End Systolic Volume (ESV) =

Answer 3

The volume left in the ventricle at the end of contraction ~60ml.

Question 4

Stroke Volume (SV) =

Answer 4

Volume of blood ejected by ventricular contraction ~70ml. 𝑆𝑉=𝐸𝐷𝑉−𝐸𝑆𝑉 ~70𝑚𝑙=~130𝑚𝑙−~60𝑚𝑙

Question 5

Ejection Fraction (EF) =

Answer 5

The proportion of the end diastolic volume that is pumped out of the heart. It is normally 65% but in patients with heart failure, this can drop to 35%.

Question 6

ejection fraction equation

Answer 6

𝐸𝐹=𝑆𝑉/𝐸𝐷𝑉=~65% (𝑛𝑜𝑟𝑚𝑎𝑙𝑙𝑦)

Question 7

describe atrial systole

Answer 7

Anatomy
§ Blood has been flowing passively into the ventricles through open AV valves and now the atria contract which tops up the ventricular volume (giving the EDV). Pressure Changes
§ Atrial pressure shows a small increase due to the contraction – the ‘a’ wave.
§ There may also be a jugular pulse due to atria contraction pushing some blood back up the jugular vein. ECG Changes & Heart Sounds
§ P wave marks atrial systole (atrial depolarisation).
§ During this time, abnormal S4 heart sound can be heard – caused by valve incompetency (bad valve shutting). This can occur due to:
o Pulmonary Embolism.
o Congestive Heart Failure.
o Tricuspid Incompetence.

Question 8

describe isovolumic contraction

Answer 8

Anatomy
§ This is contraction of the ventricles with NO change in volume (only pressure builds up) i.e. both valves are shut.
§ Ventricles are contracting isometrically and so muscles fibres are not changing length but are generating force. Pressure Changes
§ The AV valve shuts as ventricular pressure exceeds atrial pressure. The ventricular pressure then approaches that of the aortic pressure (without exceeding aortic pressure, aortic valve will NOT open).
§ When ventricular pressure exceeds aortic pressure (the afterload) the aortic valve opens. ECG Changes & Heart Sounds
§ QRS complex marks the ventricular depolarisation.
§ The S1 is heard (“Lub” of the “Lub-Dub”) due to closure of atria-ventricular valves. 1st heart sound.

Question 9

describe rapid ejection

Answer 9

Anatomy
§ Aortic and Pulmonary valves open. Pressure Changes
§ As ventricles isotonically contract, the ventricular pressure rapidly rises and exceeds aortic pressure (the afterload) and so the semilunar valves open and ventricular volume decreases.
§ The ‘c’ wave is caused by the pushing of the tricuspid valve into the atrium causing a small pressure increase in the jugular vein – due to the ventricular contraction. ECG Changes & Heart Sounds
§ no heart sounds for this phase

Question 10

describe reduced ejection

Answer 10

Anatomy
§ Aortic and Pulmonary valves begin to close. Pressure Changes
§ As blood has left the ventricles, ventricular volume and pressure begin to decrease à semilunar valves begin to shut as pressure gradient causes backflow from the arteries.
§ T wave is due to ventricular re-polarisation.
marks the end of systole

Question 11

describe isovolumic relaxation

Answer 11

Anatomy
§ Aortic and Pulmonary valves have shut. Pressure Changes
§ Atria have filled with blood but due to the AV valves being shut, the atrial pressure rises.
§ The ‘v’ wave is due to blood pushing the tricuspid valve (this gives the second jugular pulse).
§ DICHROTIC notch – A small, sharp increase in aortic pressure due to rebound pressure against the aortic valve as the distended aortic wall relaxes. ECG Changes & Heart Sounds
§ The S2 sound is heard when the aortic and pulmonary valves shut.

Question 12

describe rapid ventricular filling

Answer 12

Anatomy
§ Atria-ventricular valves open, ventricles fill. Pressure Changes
§ Ventricular volume increases while atrial pressure falls.
§ This filling is PASSIVE and not isometric. ECG Changes & Heart Sounds
§ An abnormal S3 may be heard which signifies turbulent ventricular filling.
o Can be due to severe hypertension or mitral incompetence.
o Often referred to as ‘Ventricular Gallop’.

Question 13

describe reduced passive filling

Answer 13

Anatomy
§ Also called ‘Diastasis’. Pressure Changes
§ Ventricular volume increases more slowly.
The ventricles are able to fill considerably without the contraction of the atria

Question 14

how do the patterns of pressure in the right and left side of the heart compare?

Answer 14

The same pattern of pressure changes occurs in the right side of the heart BUT the right side of the heart displays lower pressures.

Question 15

Pressure volume loops

Answer 15

1. The EDV – The ventricles are full but haven’t generated any isotonic pressure.
2. Isovolumic contraction – The volume hasn’t changed but the isotonic contraction generates a large increase in pressure.
3. The afterload pressure is reached (aortic pressure) and then ventricle begins to expel blood into the aorta (pressure rise and fall). This ends at the ESV. 2à3 = SV!
4. Pressure falls due to Isovolumic relaxation.

Question 16

increase is preload

Answer 16

results in increase of stroke volume

Question 17

increases in afterload

Answer 17

results in decreased stroke volume

Increasing afterload decreases amount of shortening.
o I.E. I cannot lift a 2-ton weight so not much shortening will occur in my own muscles.
§ When afterload increases, more pressure is needed to open the aortic valve so point 2 moves in y-direction.
§ Point 1 remains the same as the EDV is the same.
§ Increase in afterload also means less shortening can occur so the stroke volume decreases.

Question 18

Cardiac Output = ?

Answer 18

Cardiac Output - 𝐶𝑎𝑟𝑑𝑖𝑎𝑐 𝑂𝑢𝑡𝑝𝑢𝑡 (𝐶𝑂)= 𝐻𝑒𝑎𝑟𝑡 𝑅𝑎𝑡𝑒 𝑥 𝑆𝑡𝑟𝑜𝑘𝑒 𝑉𝑜𝑙𝑢𝑚𝑒

Question 19

Stroke volume in this equation can be changed by changing the:

Answer 19

Stroke volume in this equation can be changed by changing the:
o Preload – volume of blood returning to the heart.
o Afterload – arterial pressure.
o Contractility – how forcefully the heart contracts (e.g. using adrenaline).

Question 20

define contractility
+ simple measure
+ increased by

Answer 20

Contractility = The strength of contraction of the heart.
o The simple measure is the ejection fraction (proportion of EDV pumped out of the heart).
o Can be increased by sympathetic stimulation – e.g. exercise.