mechanics Flashcards
phases of the cardiac cycle: recall electrical and mechanical events, valve movements, and points where this occurs on pressure-volume loops
2 phases of cardiac cycle and relative durations
diastole (2/3) and systole (1/3)
define diastole
ventricular relaxation when ventricles fill
define systole
ventricular contraction when ventricles generate pressure and eject blood into arteries
4 phases of diastole
isovolumetric relaxation, rapid passive filling, reduced passive filling, atrial systole
3 phases of systole
isovolumetric contraction, rapid ejection, reduced ejection
what happens in atrial systole
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
how is atrial systole denoted on ECG and in pressure-volume loop
P wave, D→A (filling)
why might atrial systole cause a 4th heart sound
abnormal and occurs with congestive heart failure, pulmonary embolism or tricuspid incompetence
what happens in isovolumetric contraction
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
how is start of isovolumetric contraction denoted on ECG and pressure-volume loop
QRS, A→B
what makes the 1st heart sound ‘lub’ during isovolumetric contraction
closure of AV valves and associated vibrations
what happens in rapid ejection
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
what happens in reduced ejection
ventricles repolarise as there is a decrease in ventrical pressure, which reduces gradient, closing semilunar valve (Part = Pvent)
how are rapid and reduced ejection denoted on ECG and pressure-volume loop
rapid: ST segment; reduced: T wave; both are B→C
what happens in isovolumetric relaxation and how is it denoted on pressure-volume loop
ventricles relax (reduce pressure) and fibre length is constant; both valves are closed as Pvent is lowest pressure; C→D
what makes the 2nd heart sound ‘dub’ during isovolumetric relaxation
semi-lunar valves closing
what happens in rapid passive filling and how is it denoted on a pressure-volume loop
occurs during isoelectric ECG between cardiac cycles; atrioventricular valves open (Patr > Pvent) to allow rapid filling of ventricles down gradient; D→A
why might rapid passive filling cause a 3rd heart sound
usually abnormal and may signify turbulent ventricular filling (valves aren’t closing properly due to severe hypertension or mitral incompetence)
what happens in reduced passive filling
isoelectric ECG period; most blood has entered ventricles, so gradient reduced and slower filling; longest phase; valves remain in same state; D→A
what will the amount ventricles are filled define
preload, so stretch, so how forceful contraction will be
extrinsic stimulation at rest: stimulation and effect on SA node rate
parasympathetic stimulation so decrease SA node rate
extrinsic stimulation: stimulation and effect on SA node rate
sympathetic stimulation so increase SA node rate
how does sympathetic stimulation increase SA node rate
hormonal (adrenaline) and neural (noradrenaline)
when does the heart receive meaningful blood flow
during diastole, as during systole it blocks coronary supply
effect of tumour causing adrenaline release on diastole time
decreases diastole time as myocardium becomes ischaemic; O2 demand is also higher as beating harder
