7150 BCIT Course
What is stroke volume? correct answersthe amount of blood ejected by the
heart in any one contraction
How can the body increase CO? correct answersBy increasing SV or HR
What happens when HR increases? correct answersSV decreases to
compensate What 3 determinants influence SV? correct answersPreload
Afterload
Contractility
What is preload? correct answersvolume of blood in ventricles at end
of diastole What is preload determined by? correct answersvenous
return
this any factor affecting venous return will alter afterload
What conditions will affect venous return? correct answersVasodilation
which will decrease preload and a decrease in circulating volume
How does vasodilation cause preload to decrease? correct answerscauses an
increase in intravascular or "venous capacitance", which allows blood to pool
in the peripheral circulation = reduced venous return
Why is preload and contractility's relationship important? correct
answersDue to Starling's law
What is Starling's Law? correct answersStretching of heart muscle fibers
causes increased force of contraction (e.g., more blood going to heart ->
heart pumps harder)
In HF - this mechanism doesn't work (more blood coming in, but heart
doesn't pump harder)
Greater the stretch, greater the contraction
Therefore if you increase preload, you increase contractility
How does impaired contractility impact preload? correct answersCan also
increase preload bc the ventricle doesn't empty effectively during systole
then the volume in the ventricle at the beginning at diastolic is increased
What is compliance? correct answersMeasure of distensibility
, How is preload effected by ventricular compliance? correct answersless
distensible = less compliant
Decrease in ventricular compliance may occur as a result of scarring
associated with a MI
What is afterload? correct answersThe force, or the resistance, against
which the ventricles have to pump in order to eject blood
If high resistance is encountered, the ventricles must contract move
formally in order to maintain a normal SV, an action that increases workload
and O2 demand
What is the primary determinant of afterload? correct answersThe
diameter of the arteriole and arteries
Although valve diameter and blood viscosity also influence afterload
What will an increase in arterial vascular tone or vasoconstriction result
in? correct answersDecreased diameter and increased afterload
What are increases in afterload promoted by? correct
answersCirculating catecholamine (E&NE)
Hypotherm
ia Drugs
What are decreases in afterload promoted by? correct
answersHyperthermia Drugs
What is contractility? correct answersThe ability of the heart's myofibrils to
change their strength of contraction
How can contractility be decreased? correct answersInadequate O2 supply
to myocardial tissue, negative inotropic drugs (BB & CCBs) & some
electrolyte balances
What are mechanical cells? correct answersThe working cells of the heart,
making up the bulk of the cardiac musculature
Their job is contraction
They respond to electrical stimulus from electrical cells
What are the two factors of mechanical cells? correct
answersContractility (enables mechanical cells to shorten & return to
their original length) & extensibility (ability of muscle fibres to stretch)
What are electrical cells correct answersAKA
Pacemaker cells The specialized cells of the electrical
conduction system
What is stroke volume? correct answersthe amount of blood ejected by the
heart in any one contraction
How can the body increase CO? correct answersBy increasing SV or HR
What happens when HR increases? correct answersSV decreases to
compensate What 3 determinants influence SV? correct answersPreload
Afterload
Contractility
What is preload? correct answersvolume of blood in ventricles at end
of diastole What is preload determined by? correct answersvenous
return
this any factor affecting venous return will alter afterload
What conditions will affect venous return? correct answersVasodilation
which will decrease preload and a decrease in circulating volume
How does vasodilation cause preload to decrease? correct answerscauses an
increase in intravascular or "venous capacitance", which allows blood to pool
in the peripheral circulation = reduced venous return
Why is preload and contractility's relationship important? correct
answersDue to Starling's law
What is Starling's Law? correct answersStretching of heart muscle fibers
causes increased force of contraction (e.g., more blood going to heart ->
heart pumps harder)
In HF - this mechanism doesn't work (more blood coming in, but heart
doesn't pump harder)
Greater the stretch, greater the contraction
Therefore if you increase preload, you increase contractility
How does impaired contractility impact preload? correct answersCan also
increase preload bc the ventricle doesn't empty effectively during systole
then the volume in the ventricle at the beginning at diastolic is increased
What is compliance? correct answersMeasure of distensibility
, How is preload effected by ventricular compliance? correct answersless
distensible = less compliant
Decrease in ventricular compliance may occur as a result of scarring
associated with a MI
What is afterload? correct answersThe force, or the resistance, against
which the ventricles have to pump in order to eject blood
If high resistance is encountered, the ventricles must contract move
formally in order to maintain a normal SV, an action that increases workload
and O2 demand
What is the primary determinant of afterload? correct answersThe
diameter of the arteriole and arteries
Although valve diameter and blood viscosity also influence afterload
What will an increase in arterial vascular tone or vasoconstriction result
in? correct answersDecreased diameter and increased afterload
What are increases in afterload promoted by? correct
answersCirculating catecholamine (E&NE)
Hypotherm
ia Drugs
What are decreases in afterload promoted by? correct
answersHyperthermia Drugs
What is contractility? correct answersThe ability of the heart's myofibrils to
change their strength of contraction
How can contractility be decreased? correct answersInadequate O2 supply
to myocardial tissue, negative inotropic drugs (BB & CCBs) & some
electrolyte balances
What are mechanical cells? correct answersThe working cells of the heart,
making up the bulk of the cardiac musculature
Their job is contraction
They respond to electrical stimulus from electrical cells
What are the two factors of mechanical cells? correct
answersContractility (enables mechanical cells to shorten & return to
their original length) & extensibility (ability of muscle fibres to stretch)
What are electrical cells correct answersAKA
Pacemaker cells The specialized cells of the electrical
conduction system
