Regulation of Cardiac Function 1 Flashcards
What are the steps of the cardiac cycle?
- Diastole (passive filling)
- Atrial systole
- Ventricular systole (isovolumetric contraction)
- Systole (ejection)
- Diastole (isovolumetric relaxation)
What occurs during diastole (passive filling)?
Blood flows into heart from vena cava and pulmonary veins
AV valves open; semilunar valves closed
Consistent pressure increase in atria and ventricles
What occurs during atrial systole?
Last of blood ejected from atria into ventricles
Small increase in pressure in both atria and ventricles
What occurs during ventricular systole (isovolumetric contraction)?
No flow as all valves closed
Pressure increases sharply in ventricles with no change in volume
What occurs during systole?
Ejection of blood
Ventricular pressure > outflow vessel pressure so semilunar valves open
What occurs just before and during diastole (isovolumetric relaxation)?
Ejection slows as ventricular contraction loses force
When ventricular pressure falls below pressure of outflow vessels, semilunar valves close
Rapid decrease in ventricular pressure without changing volume
What aids ventricular filling?
Elastic recoil of ventricle walls
What is the dicrotic notch?
Aortic pressure trace dips when aortic valve closes due to brief backflow of blood against valve
What percentage of ventricular filling is accounted for by atrial systole?
<20%
Why does the atrial pressure increase slightly during systole?
Ventricular contraction causes flexible AV valve to bulge into atrium
What does an electrocardiogram do?
Measures electrical activity of heart
What are the waves shown on a typical electrocardiogram caused by?
P - atrial depolarisation
QRS complex - ventricular depolarisation
T - ventricular repolarisation
Approximately how much time passes between P and R on an ECG?
120ms
Approximately how much time passes during the QRS complex on an ECG?
80ms
Approximately how much time passes between Q and T on an ECG?
300ms
What does a phonocardiogram do?
Measures heart sounds
What causes the S1 on a phonocardiogram?
AV valves closing (initiation of ventricular systole)
What kind of sound does the closing of the AV valves create?
Low frequency ‘lub’
What causes the S2 on a phonocardiogram?
Semilunar valves closing
What kind of sound does the closing of the semilunar valves create?
High frequency, short ‘dup’
What causes the S3 on a phonocardiogram?
Opening of AV valves and rapid refilling
What causes the S4 on a phonocardiogram?
Atrial systole (due to blood flow in) when end diastolic pressure is raised
What happens to the heart sounds when end diastolic pressure is raised?
S4 is heard
S3 and S4 give rise to a galloping rhythm
What causes heart murmurs?
Turbulent blood flow
What causes turbulent flow in the heart?
Increased blood velocity
Exercise
What can increase blood velocity in the heart?
Stenosis
What kind of murmur does mitral stenosis cause?
Diastolic murmur as ventricle fills
What kind of murmur does aortic stenosis cause?
Systolic murmur
What murmur does mitral valve incompetence cause?
Systolic murmur (“lush” from blood flowing into left atrium during contraction)
What murmur does aortic valve incompetence cause?
Early diastolic murmur with softening and prolongation of S2 (blood flows into heart from aorta)
How can pulsing veins in the neck show valve incompetence?
Reclining patient sat upright - if pulsing stops then pulse was in jugular vein
Incompetence of tricuspid valve
What can cause valve incompetence?
Endocarditis
What is endocarditis?
Rare life-threatening inflammation of lining of heart muscles/valves
What can cause endocarditis?
Bacterial infection during dental procedures
Severe gum disease
What influences stroke volume?
Energy of ventricular contraction
Resistance to outflow from left ventricle/TPR
What affects the energy of ventricular contraction?
Preload/filling pressure of right heart which in turn influences diastolic stretch
Sympathetic innervation
What was the Otto Frank experiment?
Frog hearts connected to a fluid reservoir at varying heights to see effect of filling pressure on contractile force
How does filling pressure affect contractile force (relationship)?
Increased filling pressure increases contractile force (and ventricular pressure)
What is the Frank-Starling law?
Energy of heart contraction increases as a function of diastolic distention/stretching
Why does increased filling pressure increase contractile force?
Increased stretch/distention
Increased initial muscle fibre length
Increased cross-bridging
Increased tension
What is the optimal length of a sarcomere to maximise contractile force?
1.75-2.25um
Why would overstretching a sarcomere result in no/less tension formed?
Little/no overlap of actin and myosin
So little/no cross-bridging
Why does heart failure decrease contractile force?
Enlargement of cardiac myocytes and ventricles
Inappropriate alignment of actin and myosin
How does sympathetic stimulation affect the EDP/stroke volume graph and why?
Upward shift
Stimulation affects contractility not EDP/volume entering
How will increasing the stroke volume of the left heart affect the stroke volume of the right heart?
Increase as it’s a closed/loop system
