Mechanics 2 Flashcards
What are the in vivo correlates of Frank Starling relationship?
force –> pressure
length –> volume
How are PV loops used clinically?
show contractility
give idea of filling pressure of ventricles
What does the cardiac cycle consist of?
diastole
2/3 ventricular relaxation - 4 subphases
systole
1/3 ventricular contraction - 2 subphases
What is isovolumetric ventricular contraction?
pressure builds up in ventricles in early systole until pressure exceeds pressure of afterload
increase tension, no change in volume
What is EDV?
volume of blood in ventricle at end of ventricular filling just before contraction
approx 130ml
ESV = 60ml, 40ml added in atrial diastole, 30ml added in atrial systole
What is ESV?
volume left in ventricle at end of contraction
approx 60ml
What is stroke volume?
volume of blood ejected by ventricular contraction
approx 70ml
SV = EDV - ESV
= 130-60
What is ejection fraction %?
proportion of EDV pumped out of heart
= SV/EDV x 100%
What is normal heart rate?
72bpm or 0.8s per beat of heart
What is cardiac output?
HR x SV
What is MAP?
DBP + 1/3PP
What is pulse pressure?
DBP - SBP
What affects stroke volume?
preload (venous return)
afterload (arterial pressure)
contractility (influenced by autonomic NS and adrenaline - sympathetic branch)
What is contractility?
strength of contraction of heart
measured by ejection fraction
increased by sympathetic stimulation (exercise)
What is the last stage of diastole?
Atrial systole
P wave
atrial depolarisation
initiated by pacemaker potential emanating from the SAN
Describe the process of atrial systole?
final phase of diastole
atria contract to fill the ventricles (EDV)
AV valves open
atrial pressure increases
Why are atria almost full before atrial systole?
passive filling of atria driven by pressure gradient
What happens as the atria contract?
jugular pulse as blood is pushes back up the jugular vein
What can be heard abnormally during atrial systole? What are the causes?
S4 heart sound - lub lub dub due to valve incompetency (bad shutting) 1. pulmonary embolism 2. congestive heart failure 3. tricuspid incompetence
Step 1 of systole?
isovolumic contraction
QRS is the start - ventricular depolarisation
AV valves shut
Describe isovolumic contraction?
GOAL: to reach pressure that exceeds arterial pressure
- contraction of ventricles with no change in volume
- no change in fibre length
- SI sound heart ‘lub’ which is the AV valve shutting
Step 2 of systole?
rapid ejection
start marked by opening of aortic/pulmonary valves
Describe rapid ejection?
ventricles contract isotonically
ventricular pressure rapidly rises to exceed aortic pressure (afterload) so SL valves open
ventricular volume decreases
no ECG or heart sounds
What is the a wave?
increase atrial pressure due to passive filling
What is the c wave?
pushing of tricuspid valve into atrium which increases pressure in the jugular vein due to ventricular contraction
Step 3 of systole?
Reduced ejection
Marks the end of systole
T wave - ventricular repolarisation (positive to negative potential)
Describe reduced ejection?
Aortic and pulmonary valves begin to close - pressure gradient causes backflow from arteries
Blood flow from ventricles decreases because blood has left ventricles so ventricular volume and pressure decrease more slowly
Stage 1 of diastole?
isovolumic relaxation
aortic and pulmonary valves close
S2 heard when valves close - ‘dub’
What is the dichrotic notch?
small sharp increase in aortic pressure due to rebound pressure against aortic valve as distended aortic wall relaxes
Describe isovolumic relaxation
atria are filled with blood
AV valve shuts
atrial pressure increases
What is the v wave?
second jugular pulse
blood pushes back on tricuspid valve
Stage 2 of diastole?
Rapid/passive ventricular filling
AV valves open
Describe rapid/passive ventricular filling
atrial pressure falls as ventricular volume increases passive during flat (isoelectric) ECG between cycles
What might be heart during rapid/passive ventricular filling?
abnormal S3
due to turbulent ventricular filling
= ventricular gallop lub dub dub
Caused by severe hypertension/mitral incompetence
Stage 3 of diastole?
Reduced ventricular filling
= diastasis
Describe reduced ventricular filling?
ventricular volume increases more slowly
aortic pressure gradually decreasing
What defines the preload?
how much ventricles fill
the stretch in turn defined contractility on-top of the heart own intrinsic control of contraction
Where is there shorter insulation?
L than R
Why must the ventricular septum depolarise first?
to allow heart to have an anchor to contract around and eject blood
What is normal systemic BP?
120/80
What is normal pulmonary BP?
25/5
What is pulmonary wedge pressure?
measure pressure in pulmonary artery (RHS) to measure the preload on the left as sides are linked by the pulmonary circuit
an increase in PAWP is indicative of LEFT heart failure
What does pulmonary circuit pressure do?
changes
Describe extrinsic heart stimulation
PNS at rest slows HR from SAN from 110 to 70 bpm
SNS increases HR by
- hormonal control (adrenaline from adrenal gland)
- neural control (noradrenaline released from nerves)