3 - Cardiovascular mechanics 2 Flashcards
What are the 2 main phases of a heart beat? How long do they last?
DIASTOLE
Lasts 2/3 of each beat
Ventricular relaxation
4 phases
SYSTOLE
Lasts 1/3 of each beat
Ventricular contraction
3 phases
What are the 3 phases of systole?
Isovolumetric contraction
Rapid ejection
Slow ejection
What are the 4 phases of diastole?
Isovolumetric relaxation
Rapid passive filling
Slow(reduced) passive filling
Atrial systole
What is end diastolic volume?
The amount of blood in the ventricle at the end of diastole, just before contraction begins.
What is end systolic volume?
The amount of blood in the ventricle just after contraction has finished and blood has been ejected, but before it starts refilling with blood.
What is stroke volume and how is it calculated?
The volume of blood ejected from the heart.
Stroke volume = EDV - ESV
What is the value for a normal resting stroke volume?
72mL
What is ejection fraction and how is it calculated?
The amount of blood that left the heart in relation to the amount of blood that entered. Calculated as a %
Ejection fraction = SV/EDV x 100
What is the first step in the cardiac cycle?
Atrial systole.
Atria and ventricles are almost full from passive filling.
SAN causes atria to contract and ‘top up’ blood in ventricles.
P-wave on ECG.
S4 found here.
Outline step 2 in the cardiac cycle - isovolumetric contraction.
Volume stays the same, pressure builds up. ALL VALVES CLOSED. Ventricles begin to contract QRS complex on ECG. S1 - Lub: closing of AV valves.
Outline step 3 in the cardiac cycle - rapid ejection.
Ventricles contract and overcome pressure in aorta
Semilunar valves open
Blood leaves ventricles.
No sounds
Outline step 4 in the cardiac cycle - reduced ejection.
Blood leaves ventricles at a slower rate.
Aortic and pulmonary valves begin to close as pressure in ventricles decreases.
Marks the end of systole.
Outline step 5 of the cardiac cycle - Isovolumetric relaxation
Volume of ventricles doesn’t change - all valves shut
S2 - closure of semilunar valves
Pressure in ventricles falls
Dichrotic notch - caused by rebound pressure against aortic valve as distended aortic wall relaxes.
Outline step 6 of the cardiac cycle - Rapid passive filling
Ventricles fill with blood passively.
Relaxation of cardiac tissue
Nothing on ECG.
S3 - if AV valves have hardened or don’t close properly.
Outline step 7 of the cardiac cycle - Reduced passive filling
Also called diastasis
Ventricle fills more slowly.
How does pressure differ on the left and right sides of the heart?
Pressure CHANGES are identical.
Pressures on the right side are lower.
Same volume of blood is pumped both sides.
What is the pulmonary capillary wedge pressure?
Used to assess back pressure in lungs.
Pump is inflated in the pulmonary artery.
LO: define and state normal pressure and volume values during cardiac cycle
Systemic: 120/80
Pulmonay: 25/5
Draw a pressure-volume loop
Check review 1 page
How does increased preload affect the PV loop?
Wider - ventricular volume increases so stroke volume increases
How does increased afterload affect the PV loop?
Taller- volume stays the same but pressure increases.
Narrower as less shortening occurs.
How is cardiac output measured?
Cardiac output = heart rate x stroke volume
What 3 things is stroke volume affected by?
Preload
Afterload
Contractility (the strength of contraction of the heart, affected by sympathetic stimulation)
How does contractility afftect PV loops?
Increase in contractility makes gradient steeper (lower volume can generate more pressure)
Decrease in contractility makes gradient shallower (More volume required to make same pressure)
