Cardiac cycle Flashcards
What proportion of the heart beat does systole and diastole take up and how many phases comprise each?
Diastole-4 phases-Lasts 2/3 of each beat
Systole-3 phases-Lasts 1/3 of each beat
List the 7 phases of a heartbeat
Isovolumetric contraction
Rapid ejection
Slow ejection
Isovolumetric relaxation
Rapid passive filing
Slow passive filling
Atrial systole
How do you calculate ejection fraction?
Stroke volume/End diastolic volume
What heart sound will you hear with congestive heart failure, pulmonary embolism or tricuspid incompetence?
4th heart sound
What makes the 1st heart sound? (lub)
AV valves closing
What phase marks the end of systole?
Reduced ejection
What causes the t-wave on an ECG
Repolarisation of the ventricular muscle
What causes the QRS complex on an ECG
Ventricular muscle contraction
What causes the p-wave on an ECG
Atrial contraction
What occurs under isovolumetric contraction?
The ventricular muscles contract isometrically(muscle contracts but fibres stay the same length), applying pressure on the blood but not ejecting it
What is the pressure in the pulmonary circuit and how does the pressure pattern vary with the pattern on the left side of the heart?
25/5mmHg
-Identical pressure pattern, just lower on the right side
At what point on a pressure volume loop do the ventricles encounter afterload?
Right as the ventricles begin to contract in ejection(SL valves open
(Top right on this diagram)
What is ESPVR?
ESPVR: End systolic pressure-volume relationship
ESPVR is the maximal pressure that can be developed by the ventricle at any given volume
What is the relationship between increased preload causing increased stroke volume?
Frank-Starling relationship
How does increased preload affect stroke volume loops?
Stroke volume increases(FSR)
Loop widens to the right
How does increased afterload affect a stroke volume loop
Stroke volume decreases
Loop narrows to the right(Left edge moves right) and gets taller by proxy(ESPVR)
(Greater pressure required to open aortic valve)
What increases heart contractility and what is the mechanism?
Contractility: Strength of heart contraction
Sympathetic stimulation-Causes increased delivery of Ca2+ to myofilaments(Ionotropy)
What feature controls the ESPVR line in a PV loop?
Heart muscle contractility
How does noradrenaline/adrenaline affect heart muscle contractility?
Nor/adrenaline activates a g-protein coupled receptor, activating the protein kinase pathway which phosphorylates the
L-type Ca2+ channel,
SR Ca2+ release channel
SR Ca2+ ATPase
which increases delivery of Ca2+ to myofilaments and increases contractility
What causes the 2nd heart sound(dub)
Closure of the pulmonary/aortic valves
What is and what causes the dichrotic notch on an aorta pressure chart
Aortic valve closure - rebound pressure as distended aortic wall relaxes
What causes the 3rd heart sound?
May signify turbulent ventricular filling
Can be due to severe hypertension or mitral incompetence
When do the ventricles encounter preload?
When the ventricles start to be filled with blood by the atria
Give the ways a pressure volume loop changes during exercise
-The loop expands in width due to increased metabolic demand
-ESPVR line steepens due to sympathetic activation
-Loop gets taller, due to increased pressure(caused by contractility)
Why does afterload increase during exercise?
Increased arterial pressure means the ventricles have o generate higher pressures to open the semi-lunar valves
What is the longest phase of the cardiac cycle
Reduced passive filling
