What is Preload
Preload is the muscle length prior to contractility
What is the preload of a cardiac muscle dependent on
ventricular filling (or end diastolic volume…EDV).
What is Contractility
the intrinsic force that the muscle can create at the given length
What is Afterload
the tension which must be developed in the wall of ventricles during systole to open the semilunar valves and eject blood to aorta/pulmonary artery
What is Cardiac Output
the volume of blood pumped by the heart per minute,
Equation for cardiac output
CO= SV x HR
What is Stroke Volume
the volume ejected from the ventricle on a single beat
What is End Diastolic Volume
the amount of blood collected in a ventricle during diastole
What is End Systolic Volume
the amount of blood remaining in a ventricle after contraction.
What is cardiac performance
It demonstrates the capacity of ventricles to pump blood and to maintain blood circulation throughout the body
What are the three conditions necessary for optimal cardiac performance
Normal structure and functions of the heart (C.O)
- Normal structure and function of tissue
surrounding heart - Adequate filling of the heart by blood (venous return)
Two factors that affect cardiac output
Changes in stroke volume or heart rate
Two factors that can control heart rate
autonomic nervous system
hormonal/humoral control
Examples of things that can control stroke volume
- preload, contractility, afterload, number and size of myocytes,
heart architecture, synchronisation of function of the atrias and
ventricles
Which four factors establish the volume of blood pumped with each heart beat.
Heart rate, contractility, preload and afterload
Which chamber pressure is preload related to
right atrial pressure
What are the indices for preload
EDV, EDP,
pulmonary capillary wedge pressure (PCWP)
and end diastolic wall stress.
What does the Frank Starling principle illustrates
This principle illustrates the relationship between cardiac output and left ventricular end diastolic volume
(or the relationship between stroke volume and right atrial pressure.)
Which one of the factors that determine the amt of blood pumped out the heart, if increased, incresing tension of the muscle
Preload
What is the Frank-Starling mechanism (or Starling’s Law of the heart
The contraction and therefore stroke volume in response to changes in venous return
Stretching of which heart chamber wall directly increases HR by 10 to 20%
right atrial wall
two things that can increase intracellular calcium concentration and ultimately increase contractility of the heart
Catecholamines and inotropic drugs (eg. digitalis)
Afterload for the left ventricle is determined by which vessel’s pressure
aortic pressure
Afterload for the right ventricle is determined by which vessel’s pressure
pulmonary artery pressure
True or False
If arterial pressure increases, afterload also increases
True
What does the Law of Laplace state
Pressure correlates directly with tension and wall thickness and correlates inversely with radius.
Two conditions that can increase left ventricular pressure (which would increase afterload)
systemic hypertension and aortic valve stenosis.
Two conditions that can increase left ventricular wall thickness
chronic hypertension or aortic valve stenosis as a compensatory mechanism to decrease wall stress
Two conditions that can increase left ventricular radius
valvular heart disease (especially aortic regurgitation) or cardiomyopathies causing systolic heart failure.
What are the indices for afterload
Aortic pressure, systolic wall tension, LV systolic pressure
What regulates the heart rate and what regulates the heart rhythm
The rate is controlled by the autonomic nervous system and the rhythm is controlled by the SA node
Where are the three baroreceptors
carotid sinus reflex
Bainbridge reflex
Aortic sinus reflex
Where do each of the baroreceptors maintain blood pressure
carotid sinus reflex - maintains BP in brain
Bainbridge reflex – maintains BP in heart
Aortic sinus reflex – maintains BP in aorta
What is the function of barorecptors
Maintain blood pressure
What initiates the Bainbridge reflex
increased blood in the atria
What does the Bainbridge reflex cause
stimulation of the SA node and increased sympathetic nervous system stimulation
What is tachycardia
Increased heart rate
What is bradycardia
Decreased heart rate
By how much percent can strong vagal stimulation decrease heart muscle contraction
20-30%
The vagal fibers are distributed mainly to which chambers of the heart
the atria and not much to the ventricles
Great decrease in heart rate combined with a slight decrease in heart contraction strength can decrease ventricular pumping by about how much percent
50%
What is the normal cardiac output value
~5 L/min
What is the normal stroke volume
70 ml/beat
How do you calculate stroke volume
EDV (preload) - ESV (afterload)
What is cardiac reserve
Cardiac reserve is the difference
between resting and maximal CO
How do you calculate ejection fraction
Stroke volume / EDV
How is the diastolic pressure curve determined
filling the heart with progressively greater volumes of blood and then measuring the diastolic pressure immediately before ventricular contraction occurs
How is systolic pressure determined
by recording the systolic pressure achieved during ventricular contraction at each volume of filling
Which volume is usually a little higher EDP or ESP
EDP
During isovoumetric contraction the pressure inside the ventricle increases to equal the pressure in the aorta, at a pressure value of
about 80 mm Hg
Which one is preload, EDV or ESV
EDV
What would change in a Pressure-Volume loop if preload was increased
SV- increase
EDV - increases
What would change in a Pressure-Volume loop if afterload was increased
SV- decreased
ESV- increases
ventricular pressure- increases
What would change in a Pressure-Volume loop if contractility was increased
SV- increases
ESV- decreases
ventricular pressure -increases
Which hormones increase heart rate
epinephrine and thyroxine (T4)
Which hormones regulate blood pressure
Renin
ADH
Aldosterone
What happens to the heart when there is Hypocalcemia
reduced ionic calcium depresses the heart. Heart stops during systole. (similar to the effect of high potassium)
What happens to the heart when there is hypercalcemia
dramatically increases heart irritability and leads to spastic contractions.
What happens to the heart when there is hypernaturemia
blocks heart contraction by inhibiting ionic calcium transport.
What happens to the heart when there is hyperkalemia
leads to heart block and cardiac arrest.
What happens to the heart when there is hyperthermia (fever)
increases heart rate, due to increase permeability of cardiac muscle membrane to ions that controls heart rate.
What happens to the heart when there is hypothermia
decreases heart rate
4 ways how hyperkalemia can decrease cardiac performance
partially depolarizes the cell membrane, causing the membrane potential to be less negative. which decreases the intensity of the action potential
Decreases the resting membrane potential in the cardiac muscle fibers
block conduction of the cardiac impulse from the atria to the ventricles through the A-V bundle.
causes the heart to become dilated and flaccid and slows the heart rate.
What are cardiac glycosides
Positive inotropic agents (eg. digitalis, quabain)
What is the mechanism by which positive inotropic agents act
inhibition of Na+-K+ ATPase