mechanics

Question 1

2 phases of cardiac cycle and relative durations

Answer 1

diastole (2/3) and systole (1/3)

Question 2

define diastole

Answer 2

ventricular relaxation when ventricles fill

Question 3

define systole

Answer 3

ventricular contraction when ventricles generate pressure and eject blood into arteries

Question 4

4 phases of diastole

Answer 4

isovolumetric relaxation, rapid passive filling, reduced passive filling, atrial systole

Question 5

3 phases of systole

Answer 5

isovolumetric contraction, rapid ejection, reduced ejection

Question 6

what happens in atrial systole

Answer 6

contraction of atria started off from action potentials from SAN causing depolarisation; atria almost full from passive filling by pressure gradient cause ventricles to top up with blood; atrioventricular valve open (Patr > Pvent), semilunar valves closed

Question 7

how is atrial systole denoted on ECG and in pressure-volume loop

Answer 7

P wave, D→A (filling)

Question 8

why might atrial systole cause a 4th heart sound

Answer 8

abnormal and occurs with congestive heart failure, pulmonary embolism or tricuspid incompetence

Question 9

what happens in isovolumetric contraction

Answer 9

contraction of ventricles with no fibre shorterning to increase pressure but not change volume (isometric) caused by depolarisation; both valves are closed as Patr < Pvent < Part

Question 10

how is start of isovolumetric contraction denoted on ECG and pressure-volume loop

Answer 10

QRS, A→B

Question 11

what makes the 1st heart sound ‘lub’ during isovolumetric contraction

Answer 11

closure of AV valves and associated vibrations

Question 12

what happens in rapid ejection

Answer 12

ventricles depolarised and contracting; pressure gradient outward now exists, so isotonic muscle contraction forces blood into arteries after overcoming afterload, decreasing ventricular volume and increasing ventricular pressure; atrioventricular valve closed (Patr < Pvent), and semilunar valve open (Part < Pvent); no heart sounds

Question 13

what happens in reduced ejection

Answer 13

ventricles repolarise as there is a decrease in ventrical pressure, which reduces gradient, closing semilunar valve (Part = Pvent)

Question 14

how are rapid and reduced ejection denoted on ECG and pressure-volume loop

Answer 14

rapid: ST segment; reduced: T wave; both are B→C

Question 15

what happens in isovolumetric relaxation and how is it denoted on pressure-volume loop

Answer 15

ventricles relax (reduce pressure) and fibre length is constant; both valves are closed as Pvent is lowest pressure; C→D

Question 16

what makes the 2nd heart sound ‘dub’ during isovolumetric relaxation

Answer 16

semi-lunar valves closing

Question 17

what happens in rapid passive filling and how is it denoted on a pressure-volume loop

Answer 17

occurs during isoelectric ECG between cardiac cycles; atrioventricular valves open (Patr > Pvent) to allow rapid filling of ventricles down gradient; D→A

Question 18

why might rapid passive filling cause a 3rd heart sound

Answer 18

usually abnormal and may signify turbulent ventricular filling (valves aren’t closing properly due to severe hypertension or mitral incompetence)

Question 19

what happens in reduced passive filling

Answer 19

isoelectric ECG period; most blood has entered ventricles, so gradient reduced and slower filling; longest phase; valves remain in same state; D→A

Question 20

what will the amount ventricles are filled define

Answer 20

preload, so stretch, so how forceful contraction will be

Question 21

extrinsic stimulation at rest: stimulation and effect on SA node rate

Answer 21

parasympathetic stimulation so decrease SA node rate

Question 22

extrinsic stimulation: stimulation and effect on SA node rate

Answer 22

sympathetic stimulation so increase SA node rate

Question 23

how does sympathetic stimulation increase SA node rate

Answer 23

hormonal (adrenaline) and neural (noradrenaline)

Question 24

when does the heart receive meaningful blood flow

Answer 24

during diastole, as during systole it blocks coronary supply

Question 25

effect of tumour causing adrenaline release on diastole time

Answer 25

decreases diastole time as myocardium becomes ischaemic; O2 demand is also higher as beating harder